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Abductor Biomechanics Clinically Impact the Total Hip Arthroplasty Dislocation Rate
Abductor biomechanics clinically impact the total hip arthroplasty dislocation rate Eduardo Garc´ıa-Rey MD, PhD, EBOT, Eduardo Garc´ıa-Cimbrelo MD, PhD PII: DOI: Reference:
S0883-5403(15)00853-0 doi: 10.1016/j.arth.2015.09.039 YARTH 54737
To appear in:
Journal of Arthroplasty
Received date: Revised date: Accepted date:
5 July 2015 14 September 2015 15 September 2015
Please cite this article as: Garc´ıa-Rey Eduardo, Garc´ıa-Cimbrelo Eduardo, Abductor biomechanics clinically impact the total hip arthroplasty dislocation rate, Journal of Arthroplasty (2015), doi: 10.1016/j.arth.2015.09.039
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ACCEPTED MANUSCRIPT Abductor biomechanics clinically impact the total hip arthroplasty dislocation rate
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A prospective long-term study
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Eduardo García-Rey, MD, PhD, EBOT
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Eduardo García-Cimbrelo, MD, PhD
Orthopaedics Department
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Hospital La Paz-Idi Paz
Corresponding Author:
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Eduardo García-Rey
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Madrid-Spain
Orthopaedics Department
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Hospital La Paz-Idi Paz PºCastellana 261
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28046 Madrid-Spain
Email:[email protected]. Phone: 0034917271690. FAX : 0034917277085
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A prospective long-term study
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Abductor biomechanics clinically impact the total hip arthroplasty dislocation rate
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ACCEPTED MANUSCRIPT Background: Factors related to the patient, to the implant and to the surgery have been associated to the rate of dislocation for total hip arthroplasty (THA). We ask if the position of
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the cup and the reconstruction of the abductor mechanism actually lower the THA dislocation
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rate.
Methods: We evaluated 1,318 patients (1,414 hips) undergoing cementless THA between 1992
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and 2012. All THAs had a 28 or a 32 mm femoral head size. Hip reconstruction was radiologically assessed evaluating cup position and the hip rotation center according to
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Ranawat. The reconstruction of the abductor mechanism was measured using two variables: the lever arm distance and the height of the greater trochanter. Results: There were 38 dislocations (2.7%). After controlling the relevant confounding
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variables, like demographic and implant data, multivariate regression analysis showed that the most important factors associated with dislocation were a greater distance to the anatomic hip
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rotation center and hips outside two safe windows for cup position (acetabular inclination and
trochanter) .
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version angles) and abductor mechanism (lever arm distance and height of the greater
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Conclusion: A proper reconstruction of the hip is essential to decrease the risk for dislocation after primary THA. The weakness of the abductor muscles of the hip may be one of the most important causes for dislocation. Keywords: total hip arthroplasty; dislocation; radiological; hip rotation center; abductor mechanism Introduction Despite the excellent outcome of primary total hip arthroplasty (THA), the occurrence of a dislocation affects the patients´ quality of life and health-related issues [1]. The risk is higher in the first postoperative year, and most are early dislocations since two-thirds usually remain
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ACCEPTED MANUSCRIPT stable after a closed reduction [2]. However, dislocation after THA has gained importance given the cumulative rate over time, which has increased the risk of late dislocations [3].
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Different factors like the characteristics of the patient (gender, body mass index, age or
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diagnosis), of the implant (femoral head size, femoral stem offset, bearing surface) or surgical technique (approach, cup position) have been related to dislocation after primary THA [1, 4, 5,
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6]. Soft-tissue imbalance is also a well known cause, however, there is a lack of clinical reports that assesses this problem. An abductor mechanism insufficiency can be observed when cup
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position is high, a low height of the greater trochanter or proximal femur bone loss [7]. Postoperative cup position is not always related to dislocation, suggesting muscular imbalance rather than malposition as cause [8, 9]. The low rate of this complication, and some
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intraoperative issues such as capsular laxity, soft-tissue tension, fascia lata involvement or possible osteophyte excision during surgery, add more difficulties when trying to analyze
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dislocation after THA.
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We hypothesized that radiographic assessment of the lever arm of the hip and the height of the greater trochanter after primary THA, in a large series of patients, might help to
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understand some problems of dislocation. We assessed different clinical issues related to patients, implant characteristics like femoral head size, bearing surface and femoral stem designs, and the quality of the postoperative hip reconstruction in an attempt to evaluate the most frequent factors for dislocation after primary THA. Materials and Methods In this retrospective cohort analysis of our prospective register, we assessed 1414 cementless primary THAs in 1318 patients operated in our Institution between 1992 and 2012. We evaluated all patients who underwent cementless THA with an end-arthritis of the hip. We excluded patients with a cemented THA, a femoral neck fracture, metastatic or tumoral disease and severe cognitive or neuromuscular diseases. 135 patients were lost to follow-up
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ACCEPTED MANUSCRIPT due to a follow-up of less than five years, and five died due to unrelated causes wtihout dislocation. During the same period a total of 1915 THAs were performed in our Department.
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Oral and written informed consent was always obtained from all patients and they were
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informed preoperatively that they might receive a cementless THA. The mean age of the patients was 60.1 years old and the physical activity level, according to Devane et al [10], was 4
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or 5 in 974 patients. The minimum follow-up of the patients was two years (range, 2-22). All procedures were performed by the same surgical team using a posterolateral approach
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with reconstruction of the external rotators [11] or by preserving the external rotator muscles [12]. The same postoperative protocol was used for all patients: after surgery, patients walked on crutches with toe-touch partial weight bearing for 3 weeks, after which they were allowed
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to walk using two crutches for the next 6 weeks. All patients were instructed to have an abduction pillow while in bed or sitting, and to avoid a hip flexion higher than 90º during the
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first month. Cefazolin (or vancomycin in allergic patients) was administered for antibiotic prophylaxis during the anesthetic induction and continued for 24 hours, with low-molecular-
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weight heparin to decrease the risk of thromboembolic disease in all patients according to the
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guidelines of our Institution. Different designs, cup/stem, with different bearing surfaces and femoral head sizes were compared: Duraloc/Profile (Depuy / Johnson&Johnson, Warsaw, IN, USA) with a 28 mm metal head-on-polyethylene (PE) liner; Allofit/Alloclassic (Centerpulse/Zimmer, Winterthur, Switzerland) with a 28 mm metal head-on-PE liner; Pinnacle or Duraloc/Summit (Depuy/Johnson&Johnson) with 28 mm metal head-on-PE liner; EP-Fit/SLPlus (Endoplus-Smith&Nephew, Rotkreuz, Switzerland) with either a 28 mm metal head-on-PE liner or an alumina-on-alumina coupling; Cerafit/Multicone (Ceraver Roissy, France) with a 28 or 32 mm alumina-on-alumina coupling; and Bihapro/Bimetric (Biomet, Warsaw, IN, USA) with a 32 mm metal head-on-PE liner making a total of six groups.
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ACCEPTED MANUSCRIPT Patients were followed at 6 weeks, 3, 6, and 12 months, and then annually after surgery. At every interval, we evaluated pain, function, and range of mobility according to the six-level
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scale described by Merle D’Aubigné and Postel [13]. We recorded the appearance of
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dislocation during the first year (early disocation), all further episodes (recurrent) and revision of the cup for this cause.
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Standard anteroposterior (AP) radiographs of the pelvis were made pre-operatively, immediately after the operation, at 6 weeks, at 3, 6, and 12 months, and annually thereafter
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following the same protocol. The patient was positioned supine, with his/her feet together. The x-ray tube was positioned over the symphysis pubis 1 m from and perpendicular to the table with a symmetric obturator foramen and visible lesser trochanter and iliac crest [14]. A
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single author made all measurements, which were repeated three times for each radiograph. Cup position was assessed according to the acetabular abduction angle, the height of the
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center of the hip (as measured from the centre of the femoral head to the interteardrop line), and the horizontal distance of the cup (measured from the center of the femoral head to the
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Köhler line) [15]. The reconstruction of the hip rotation center was evaluated according to the
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Ranawat triangle [16, 17]. The true acetabulum region was the area enclosed by a right triangle with a height and width equal to 20% of the height of the pelvis on the AP radiograph. The midpoint of the hypotenuse coincides with the approximate center of the femoral head (ACFH) and is the center of rotation of the hip. The ACFH was used as the reference point to measure distance to the center of the prosthetic femoral head (CPFH) (Fig. 1). This distance was recorded in the preoperative and postoperative radiographs to assess the reconstruction actually achieved. Cup anteversion was measured according to Widmer [18] using a trigonometric function: the relationship between the short axis of a projected ellipse and the total length of a projected cup cross-section along the short axis ratio and the cup inclination. The radiographic reconstruction of the abductor mechanism was also measured using two variables: 1) the lever arm as the distance from the CPFH to the line joining the lateral part of
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ACCEPTED MANUSCRIPT the greater trochanter to the anterosuperior iliac crest, and 2) the height of the greater trochanter as the distance between the line joining the two teardrops and the parallel line
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crossing the tip of the greater trochanter (Fig. 2). The intra-observer reliability for this method,
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using the mean of the three measurements, was 0.948 (intraclass correlation, 95% Confidence Interval (CI): 0.885-0.979). Inter-observer reliability was also assessed by using 74 post-
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operative radiographs that were evaluated by another observer using the same method. This inter-observer reliability was 0.979 (intraclass correlation 95% CI 0.726 to 0.995). Although
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these measurements were made using the sixth week post-operative radiograph, images with a low quality of the greater trochanter or anterosuperior iliac crest, or an un-true anteroposterior view were excluded and the 12th week post-operative radiograph for the hip was used. Of the 1414 hips analyzed, 89 were evaluated in the 12th postoperative week. Since
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different designs may produce different values regarding the abductor mechanism due to the characteristics of their femoral offset, these variables were calculated for each group in order
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Statistical Analysis
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to assess whether there was any difference.
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Qualitative data are expressed as counts and percentages and quantitative data by mean + standard deviation (SD) or range. Qualitative data for hips with and without dislocation were compared using the chi-square test or Fisher’s exact test, and quantitative data were also compared using Student’s t-test. Pearson’s chi-square test was used to compare the demographic qualitative data of patients between groups. We analyzed the possible influence of different factors: first, clinical factors related to the patient (age, gender, weight, and diagnosis); those related to the implant (cup and femoral head size, bearing surface, group/design); and those related to the surgical technique (radiological postoperative cup position and reconstruction of the abductor mechanism using the variables mentioned above). We recorded dislocated hips that fell inside or outside a window for cup position similar to the
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ACCEPTED MANUSCRIPT Lewinnek zone [4]. Limits for the window were an acetabular abduction angle from 35º to 50º and a cup version angle from 5º to 25º. We also recorded hips that fell inside or outside a
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second window for the reconstruction of the abductor mechanism according to the height of
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the greater trochanter; limits for both variables were chosen according to the mean values + SD for non-dislocated hips. The test of Homogeneity of Variances, ANOVA, was used to assess
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possible differences in the mean values for these two variables with a subset for alpha=0.05. Univariate and multivariate Cox regression models were used to assess risk factors for
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dislocation. Kaplan-Meier survivorship analysis, with 95% Confidence Intervals (CI), was used to estimate the cumulative probability of not having a dislocation for hips inside or outside either window and for patients. The differences in survival with and without dislocation were assessed using the log-rank test to compare the Kaplan-Meier curves. Statistical analysis was
Results
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significance was p < 0.05.
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performed using SAS® software (Version 9.3; SAS Institute Inc, Cary, NC, USA). The level of
Most patients had a satisfactory result with a mean postoperative clinical outcome at the
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latest follow-up of 5.8 points for pain, 5.7 for function and 5.7 for mobility for the whole series. Thirty-eight patients had a dislocation, a rate of 2.7%; 27 were stable after non-operative treatment and 11 required revision (0.8%) (Table 1). Dislocation was more frequent in older patients (p=0.011) (Table 2). The rate of dislocation also depended on implant characteristics and the postoperative reconstruction of the hip (Tables 3 and 4). The mean lever arm distances for the Cerafit/Multicone and the Bihapro/Bimetric groups (p<0.001) were greater than the other groups, and the mean height of the greater trochanter was smaller for the EP-Fit/SL-Plus and the Allofit/Alloclassic groups (p<0.001, test of Homogeinity of Variances. ANOVA, subset for alpha=0.05) (Table 5). After controlling the possible confounding variables, none of the patient-related factors analyzed was associated with a higher risk for dislocation (Table 6).
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ACCEPTED MANUSCRIPT Although 32 hips (4.5%) with a 28 mm femoral head size and 6 hips (0.9%) with a 32 mm femoral head size had dislocations, as well as 9 alumina-on-alumina hips (1.2%) and 29 metal-
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on PE hips (4.1%), with the number of hips available, the multivariate analysis did not show an
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increased risk associated to femoral head size or bearing surface. The rate of dislocation was 0.9% for the Ceraver group, 1.1% for the Bimetric group, 3.3% for the Duraloc/Profile group,
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5.3% for the Allofit/Alloclassic group, 5% for the EP-Fit/SL-Plus group and 4.6% for the Summit group, and statistical analysis showed that the Ceraver and Bimetric groups had a lower rate of
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dislocation (p<0.001), however, after controlling the possible confounding variables, we could not find a higher risk for dislocation (p=0.058).
We found that cups with a greater acetabular abduction angle on the postoperative
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radiograph and a greater distance to the approximate center of the hip had a higher risk for dislocation (p=0.006, p=0.018, respectively). Hips with a greater distance of the lever arm had
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a lower risk for dislocation (p<0.001). More hips outside the safe radiological position window had dislocations than those inside the window (Fig. 3). The survival rate for dislocation at 20
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years was 98.48% (95% CI 94.9 – 100) for hips inside this window and 93.9% (95% CI 89 – 98.9)
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for cups outside the window (p<0.001, Log Rank test) (Fig. 4). According to the mean values and their SD for the lever arm hip distance and the height of the greater trochanter, the limits for the safe zone of the radiological abductor mechanism were 56 to 64 mm for the first and -2 to 5 mm for the latter. The number of hips outside these windows was higher among dislocated hips, showing a survival rate for dislocations at 20 years of 98.33% (95% CI 94.7 – 100) for hips inside this window and 94.6% (95% CI 89.6 – 99.6) for cups outside the window (p<0.001, Log Rank test) (Fig. 5 and Fig. 6). We also found that hips outside either of these two windows had a higher risk for dislocation (p<0.001, p=0.004, respectively, Table 7). Discussion
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ACCEPTED MANUSCRIPT Dislocation is not frequent after primary THA, but it does affect clinical outcome, patient satisfaction and revision rates [1, 2, 6, 19]. Since new bearing surfaces, contemporary
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cementless implants and improvement in cementing techniques are decreasing the rates of
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revision for aseptic loosening, dislocation is gaining importance [3, 20]. Causes are difficult to analyze due to the low incidence of dislocation, so a large number of cases are needed for a
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solid statistical evaluation. To date, although an abductor mechanism insufficiency has been related to dislocation [3, 7-9], there is a lack of clinical reports that evaluate this problem. We
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have tried to assess the possible influence on dislocation of the lever arm hip distance and the height of the greater trochanter, as part of the assessment for hip biomechanics regarding the abductor mechanism, in order to ascertain whether an accurate surgical reconstruction of the
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hip could actually lower the risk for dislocation.
Contrary to previous reports, neither demographic nor clinical factors related to the patients
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were associated to a higher risk for dislocation. Dislocation was more frequent in older patients, pelvic stiffness and decreased abductor muscle strength being some of the possible
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reasons for this finding [19, 21], however, after controlling the possible confounding factors,
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regression analysis did not show a higher risk for dislocation in older patients. In our study, the exclusion of cemented THAs, more frequently used in old patients, and the absence of significant pathologies like cognitive dysfunction, neuromuscular diseases or femoral neck fractures may have influenced results [6]. On the other hand, the similar characteristics of the patients, with a relatively young age and high physical activity, may have allowed us to better analyze the abductor mechanism of the hip. A posterolateral approach, using short external repair or preserving posterior structures was used in all surgeries, and the dislocation rate was similar to other reports [11, 12]. Callanan et al. also observed that this approach may be one of the best to obtain a proper position of the cup [22].
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ACCEPTED MANUSCRIPT Charnley low-friction arthroplasty, one of the most studied implants, had different rates for dislocation, from 1% to 9%, an incidence that increases through the years and is difficult to
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solve when recurrent [19, 23]. Recently, Kumar et al. found that a contemporary cemented
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THA, with a 22.225 mm diameter femoral head operated through a posterior approach with a capsule repair, was associated with a low rate of dislocation [24]. They do not support the idea
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of using large-diameter heads since data from Registries and wear problems are being reported. We only used and analyzed conventional cementless THAs with 28 or 32 mm femoral
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heads with alumina-on-alumina or metal-on-PE bearings. The rate of dislocation was higher for implants with 28 mm femoral heads and metal-on-PE hips; however, regression analysis could not detect a higher risk of dislocation with this femoral head size and bearing surface. Hernigou et al. also observed that alumina-on-alumina decreased the risk for late dislocation, a
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finding that we can not confirm although the characteristics of the material are the same; however, the differences in the follow-up regarding other brands like the Duraloc/Profile
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group may have affected our findings [25, 26]. This influence may be particularly important for
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late dislocation since a thin pseudocapsule is observed in metal-on-polyethylene hips and a
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thicker capsule has been reported after placement of alumina-on-alumina hips [27]. Although cup position is usually associated to dislocation, the whole reconstruction of the hip may be more important. Anteversion on its own did not increase dislocation risk, however, an anteversion of 15º -25º combination with an acetabular abduction angle of 35º-50º did increase risk. A window with a safe zone for the cup position was evaluated in a way similar to that in Lewinnek et al [4], although we accepted wider limits for the acetabular inclination as discussed below. However, cup position is not the only cause for dislocation: Pierchon et al observed, in a Computed Tomography (CT) study, that cup position is not always related to dislocation and argued that muscular imbalance may be more important [8]. Biedermann et al, in an Ein Bild Röentgen Analyses software (EBRA) study, also observed that a proper cup position is desirable, however, they suggested that this is a multifactorial issue and they did
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ACCEPTED MANUSCRIPT not investigate other factors like femoral anteversion or soft-tissue tension [9]. Recently, Esposito et al suggested that a truly “safe zone” based upon acetabular position alone does
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not exist; their frequency over a six month period, using a posterolateral approach, of
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dislocation was 2.1% (147 of 7040 patients). They did not include extra-large femoral heads or metal-on-metal hips; they matched 142 dislocated and 142 non-dislocated patients in order to
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assess the acetabular abduction and the cup anteversion angles, measured by EBRA, and did not find differences regarding a “safe zone” for dislocation, they also emphasized the notion
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that hip dislocation is multivariate in etiology [28]. Similar findings have also been made by Grammatopoulos et al, who although reporting that acetabular orientation affected the clinical outcome, suggested that the range of the safe zone may be wider than the Lewinnek zone
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when influencing clinical and dislocation rate parameters [29]. Although this study only used plain radiographs on the AP view, as previously mentioned, an
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attempt was made to evaluate the abductor mechanism in order to add new variables for the radiological reconstruction of the hip. First, the lever arm was evaluated. McGrory et al. used a
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similar method in order to assess this issue although they emphasize femoral offset rather
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than the lever arm [30]. Traina et al. also used a similar method to the one used here, but we have tried to evaluate a large number of cases and calculate the reliability of the method [31]. We are aware that studying the abductor mechanism is challenging when evaluating pelvic radiographs on AP view and many variables affecting this issue are practically unevaluable, such as capsular laxity or osteophytes, however, the findings observed in our study suggest that the variables assessed here emphasize the importance of hip biomechanics rather than other previously reported clinical factors. They can also serve as new variables that might help to assess this complex problem. First, we observed that hips with a greater mean value for the lever arm distance showed a lower risk for dislocation, thus, this effect was even greater when it was combined with the height of the greater trochanter as shown in the multivariate analysis. Eftekhar observed that a soft-tissue imbalance may be one of the most important
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ACCEPTED MANUSCRIPT causes for dislocation, regardless of the idoneity of the cup position, a finding also reported by others [7, 24, 32]. We also observed that the lever arm distance and the height of the greater
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trochanter differed among the different designs, which may also affect the differences
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observed in the rates of dislocation. As well, hips with a greater distance to the hip rotation center had a higher risk for dislocation. Recently, Terrier et al, in a finite element model based
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on preoperative CT scans in fifteen patients, quantified the effect of cup medialization on moment arms and tested whether the increase in the moment arm of the gluteus minimus and
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medius was correlated to acetabular and femoral offset, trochanteric height and femoral antetorsion [33]. They confirmed this increase and found a variability in the patients´ anatomy, and laxity, and an inverse correlation with femoral antetorsion, concluding cup medialization
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might be considered in active patients with little femoral antetorsion. The first limitation of this study, as previously mentioned, is the number of cases. Although it is
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relatively common in most previous reports, the low incidence of dislocation makes it very difficult to analyze the possible causes and may have affected some findings, particularly with
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respect to demographic data. Secondly, we are aware that the lack of a proper lateral view in
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the hip radiographs might complicate analysis of cup anteversion, however, Nomura et al. recently reported the method described by Widmer, used here, as the most appropriate to evaluate this variable on the AP view [34]. Third, we did not analyze CT images [8], and femoral anteversion has not been analyzed as discussed above [9, 33, 35]. Fourth, although intra- and inter-observer errors for the radiological measurements were calculated, the absence of a biomechanical assessment does not allow us to correlate the method used here. Cumulative risk has been studied using different follow-ups for different implants and this may have affected the results. To date, although all surgeries were done by the same surgical team, we are aware that the clinical experience and evolution of the surgeons over time, a twenty years period, may also have influenced these findings. These findings may also influence the rates of dislocation since they affect hip biomechanics and have not been evaluated here.
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ACCEPTED MANUSCRIPT The possible causes for dislocation are still difficult to determine, therefore possible solutions for recurrent or late dislocations are also difficult to find since many treatments are being tried
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to improve the outcome of this complication. Revision of acetabular and femoral components
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for evident malposition may be a relatively easy answer, however, different options for muscular imbalance, like constrained or dual mobility cups and trochanter advancements, are
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still under debate. The findings reported here may indicate that a more accurate reconstruction of the hip, including cup position and abductor mechanism, with an adequate
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surgical technique, is probably one of the most important factors to influence the dislocation rate. A proper selection of the implants, which are well-studied and do not increase other types of new or old complications, must be made in order to maintain the excellent results of
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THA over time. References
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J Bone Joint Surg [Br] 1981;63-B:214-8 3. Berry DJ, von Knoch M, Schleck CD, Harmsen WS. The cumulative long-term risk of dislocation after primary Charnley total hip arhtroplasty. J Bone Joint Surg [Am] 2004;86-A:9-14 4. Lewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR. Dislocations after total hipreplacement arthroplasties. J Bone Joint Surg [Am] 1978;60-A:217-20 5. Berry DJ, Von Knoch M, Schleck CD, Harmsen WS. Effect of femoral head diameter and operative approach on risk of dislocation after total hip arthroplasty. J Bone Joint Surg [Am] 2005;87:2456-63.
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ACCEPTED MANUSCRIPT 6. Hailer NP, Weiss RJ, Stark A, Kärrholm J. The risk of revision due to dislocation after total hip arthroplasty depends on surgical approach, femoral head size, sex, and
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ACCEPTED MANUSCRIPT 15. Johnston RC, Fitzgerald RH, Harris WH, Poss R, Müller ME, Sledge CB. Clinical and radiographic evaluation of total hip arthroplasty: a standard system of terminology for
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operations. Acta Orthop 2010;81:34-41. 21. De Thomasson E, Guingand O, Terracher R, Mazel C. Role of sagittal spinal curvature in
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early dislocation after revision total hip arthroplasty: prospective analysis of 49 revision procedures. Rev Chir Orthop Reparatrice Appar Mot 2004;90:226-31 22. Callanan MC, Jarrett B, Bragdon CR, Zurakowski D, Rubash HE, Freiberg AA, Malchau H. Risk factors for cup malpositioning. Quality improvement through a joint registry as a tertiary hospital. Clin Orthop Relat Res 2011;469: 319-329 23. García-Cimbrelo E, Munuera L. Dislocation in low-friction arthroplasty. J Arhtroplasty 1992;7:149-55 24. Kumar V, Sharma S, James J, Hodgkinson, Hemmady MV. Total hip replacement through a posterior approach using a 22-mm diameter femoral head. Bone Joint J 2014;96-B:1202-6
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ACCEPTED MANUSCRIPT 25. Hernigou P, Homma Y, Pidet O, Guissou I, Hernigou J. Ceramic-on ceramic bearing decreases the cumulative ong-term risk of dislocation. Clin Orthop Relat Res 2013;
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28. Esposito CI, Gladnik BP, Lee Y, Lyman S, Wright TM, Maynam DJ, Padgett DE. Cup
2015;30:109-113
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position alone does not predict risk of dislocatiob after hip arthroplasty. J Arthroplasty
29. Grammatopoulos G, Thomas GE, Pandit H, Beard DJ, Gill HS, Murray DW. The effect of
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orientation of the acetabular component on outcome following total hip arthroplasty
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with small diameter hard-on-soft bearings. Bone Joint J. 2015;97-B(2):164-72. 30. McGrory BJ, Morrey BF, Cahalan TD, An KN, Cabanela ME. Effect of femoral offset on
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range of motion and abductor muscle strength after total hip arthroplasty J Bone Joint Surg [Br] 1995;77-B:865-9 31. Traina F, De Fine M, Biondi F, Tassinari E, Galvani A, Toni A The influence of centre of rotation on implant survival using a modular stem hip prosthesis. Int Orthop 2009;33:1513-8 32. Dorr LD, Wolff AW, Chandler R, Conaty JP. Classification and treatment of dislocations of total hip arthroplasty. Clin Orthop Relat Res 1983; 173: 151-8 33. Terrier A, Florencio FL, Rüdinger HA. Benefit of cup medialization in total hip arthroplasty is associated with femoral anatomy. Clin Orthop Relat Res 2014;472:31593165
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ACCEPTED MANUSCRIPT 34. Nomura T, Naito M, Nakamura Y, Ida T, Kuroda D, Kobayashi T, Sakamoto T, Seo H. An analysis of the best method for evaluating anteversion of the acetabular component
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after total hip arthroplasty on plain radiographs. Bone Joint J 2014; 96-B:597-603.
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35. Weber M, Lechler P, von Kunow F, Völlner F, Keshmiri A, Hapfelmeier A, Grifka J, Renkawitz T. The validity of a novel radiological method for
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measuring femoral stem version on anteroposterior radiographs of the hip after
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total hip arthroplasty. Bone Joint J. 2015;97-B:306-11
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ACCEPTED MANUSCRIPT Acknowlwdgements
The authors gratefully thank Rosario Madero, MS, for her statistical analysis and review
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of the manuscript
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ACCEPTED MANUSCRIPT Figure Legends
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Fig 1. Cup position assessment on the anteroposterior radiograph. AAA: Acetabular abduction angle; K –K´: Köhler line; CPFH: Center prosthetic femoral head; TAR: True acetabulum region;
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AFHC: Approximate femoral head center
Fig. 2. Measurement of the radiographic reconstruction of the abductor mechanism: The lever
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arm as the distance (D), from the femoral head to the line joining the lateral part of the greater trochanter to the anterosuperior iliac crest; and 2) the height of the greater trochanter as the distance (H), between the line joining the two teardrops and the parallel line crossing the tip of
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the greater trochanter.
Fig. 3. Hips inside and outside the window for radiological cup position (acetabular abduction,
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range 35 - 50º, and cup anteversion angles, range 15º - 25º).
position.
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Fig. 4. Probability of not having dislocation for hips inside or outside the windows for cup
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Fig. 5. Hips inside and outside the window for abductor mechanism reconstruction (lever arm distance, range 56 - 64 mm, and height of the greater trochanter, range -2 - 5 mm). Fig. 6. Probability of not having dislocation for hips inside or outside the window for abductor mechanism reconstruction
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ACCEPTED MANUSCRIPT Table 1. Data on patients with revision surgery due to dislocation
Fe mal e 64
60
3
Primary Dural osteoart oc/ hritis Profil 5 e 4
2
70
4
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Fe mal e 69
72
Mal e 73
4
65
77
4
Primary Dural osteoart oc/ hritis Sum 5 mit 2
4
Primary Dural osteoart oc/ hritis Sum 5 mit 4
4
Primary Dural osteoart oc/ hritis Sum 5 mit 2
2 8
5
Avascul ar
2 8
6
Mal e 28
2 8
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Mal e 56
Primary Dural osteoart oc/ hritis Profil 5 e 6
PT
3
5
2 8
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Fe mal e 65
2 8
74
7 Mal e 44 108
CrC o/P 4 1 4 1 E 7 0 2 5 7
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2
Congeni Dural tal Hip oc/ Disease Profil 5 e 0
1
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Ca Sex Age Wei Acti Diagnosi Desig C F Bear A C V H C L H Disloc Revi (ye ght vity u H ing I A D D R A G ation sion se s n p S Surf surg ars) (kg) leve H D T l Si ery ace z (mo [10] e nths)
EPfit/
5 8
2 8
2 8
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CrC o/P E
CrC o/P E
CrC o/P E
CrC o/P E
CrC o/P E
4 2 3 5 6 0 0 6
4 1 2 3 5 0 0 5 6
Late
150
Late
124
Late
110
Recur rent
94
Recur rent
73
Recur rent
39
5 Recur 6 -3 rent
108
5 6
5 6
5 6
6 1 2 1 5 5 8 5 5 -4 4
4 3 1 5 5 5 5 5
4 1 3 2 2 4 5 0 3
4 2 3 1 Al5 0 5 7 1 on-
5 2
5 6
1
1
1
3
0
4
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77
74
5
5
Avascul Ceraf ar it/ necrosis Multi 5 cone 2
4
Avascul Ceraf ar it/ necrosis Multi 5 cone 2
11
67
2 8
Alon2 Al 5 5 7 5 6 5
Recur rent
22
Recur rent
3
Recur rent
3
Recur rent
85
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2 8
3 2
AlonAl 4 1 3 1 2 5 5 2 3
3 2
AlonAl 6 1 3 3 0 4 5 0 5
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Fe mal e 61
4 8
Postrau Ceraf it/ matic Multi 4 cone 8
10 Mal e 37
SLPlus
CrC o/P 5 3 3 2 E 0 0 0 0 2
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3
9 Mal e 52
EPfit/
Al
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68
Develop mental arthritis
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Fe mal e 74
SLPlus
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8
necrosis
5 8 -1
5 6
5 8
5 8
0
0
1 4
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Cr-Co: Chrome-Cobalt; PE:Polyethylene; Al: Alumina, FHS: Femoral Head size in mm; AI: Acetabular Inclination or Acetabular abduction angle in degrees; CA: Cup Anteversion in degrees; VD: Vertical distance in mm; HD: Horizontal distance in mm; CRH: Center of rotation of the hip or distance from the approximate center of the femoral head to the center of the prosthetic femoral head in mm; LAD: Lever arm distance in mm; HGT: Height of the greater trochanter in mm.
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ACCEPTED MANUSCRIPT Table 2. Preoperative patient data and dislocation Total
Age in years (mean, +SD)
59.9 +15.1
65.4 +13.5
Weight in kilograms (mean,
73.4 +14.1
72.1 +14.6
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+SD) Gender
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Yes
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No
60.13 +14.2
0.011 a
73.36 +14.4
0.497 a
0.116 b
718 (97.9%)
15 (2.1%)
733
Female
658 (96.6%)
23 (3.4%)
681
8
2
10
97
2
99
271
9
280
594
19
613
355
6
361
Primary Osteoarthritis
773 (97.2%)
22 (2.8%)
795
Avascular Necrosis
203 (98.1%)
4 (1.9%)
207
Congenital Hip Disease
149 (98.1%)
3 (1.9%)
152
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Male
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Activity Level [10]
Level 3 Level 4
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Level 2
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Level 1
Level 5
p values
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Dislocation
Etiology
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0.563 b
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2 (1.9%)
107
Postraumatic
74 (98.7%)
1 (1.3%)
75
Developmental Disease
58 (98.3%)
1 (1.7%)
59
17
0
b
Pearson chi-square test Fisher´s exact test
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Mann-Whitney
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a
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Other
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Rheumatologic Disorders
24
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52.3 (38-64)
52.5 (46-62)
Metal-on-Polyethylene
682 (95.9%)
Femoral head size
p values
52.4 (38-64)
0.865 a
9 (1.3%)
703
29 (4.1%)
711
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694 (98.7%)
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Bearing surface Alumina-on-alumina
Total
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Yes
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Cup Size in mm (mean, range)
No
28 mm
676 (95.5%)
32 (4.5%)
708
32 mm
698 (99.1%)
6 (0.8%)
704
118 (9.6.7%)
4 (3.3%)
122
108 (94.7%)
6 (5.3%)
114
206 (95.4%)
12 (4.6%)
218
172 (95%)
9 (5%)
181
678 (99.1%)
6 (0.9%)
684
94 (98.9%)
1 (1.1%)
95
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Cup/Femoral Stem
Allofit/Alloclassic
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Duraloc/Profile
EP-Fit/SL-Plus
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Pinnacle or Duraloc/Summit
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Cerafit/Multicone Bihapro/Bimetric
a
Mann-Whitney
b
Pearson chi-square test Fisher´s exact test
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0.002 b
0.001 b
0.001 b
ACCEPTED MANUSCRIPT Table 4. Postoperative radiographic data and dislocation p
Dislocation
Acetabular Abduction Angle in degrees (mean,
45.6 +6.1
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+SD)
Yes
Total
48.8 +10.9
45.7
0.003 a
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No
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values
16.3 + 6.7
16.8 + 9.1
16.3
0.720 a
Horizontal Distance in mm (mean, +SD)
33.5 + 6.1
32.9 + 8.7
33.5
0.630 a
Vertical Distance in mm (mean, +SD)
22.1 + 7.2
19.6 + 6.3
22.1
0.032 a
3.1 + 4.6
5.4 + 9.5
3.2
0.005 a
58.7 + 3.1
55.6 + 3.5
58.6
<0.001
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Cup Anteversion in degrees (mean, +SD)
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Hip rotation center distance in mm [16](mean,
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+SD)
Lever arm distance in mm (mean, +SD)
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a
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Height greater trochanter in mm (mean, +SD)
0.9 + 4.3
-1.13 + 4.9
0.83
1035
16 (1.5%)
1051
0.002 a
Cup position window * Inside
(98.5%) Outside
0.001 b
340 (93.9%)
22 (6.1%)
362
1004
17 (1.7%)
1021
Abductor mechanism window ** Inside
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(98.3%) Outside
370 (94.7%)
21 (5.3%)
391
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* According to the acetabular abduction angle (35º - 50º) and anteversion (15º- 25º)
Mann-Whitney
b
Pearson chi-square test Fisher´s exact test
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a
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** According to the height of the greater trochanter (-2 - 5 mm) and lever arm (56 - 64 mm)
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ACCEPTED MANUSCRIPT Table 5. Radiographic lever arm hip distance and height of the greater trochanter in mm
Height Greater Trochanter
Multicone/ Cerafit
59.3 + 2.0
1.46 + 3.5
Duraloc/Summit EP-Fit /SlPlus Duraloc / Profile
57.0 + 3.9 58.3 + 2.1 57.9 + 4.7
Allofit / Alloclassic Bihapro / Bimetric
58.2 + 3.0 59.3 + 5.1
Total p values
58.6 + 3.1 <0.001 a
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Lever arm distance
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Design
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for different designs used in this series (mean + SD)
test of Homogeneity of Variances, ANOVA
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1.51 + 5.4 -1.68 + 3.6 1.02 + 1.4 -0.47 + 6.0 0.79 + 5.2 0.83 + 4.3 <0.001 a
ACCEPTED MANUSCRIPT Table 6.Uni- and multi-variate Cox regression analysis and risk factors for dislocation.
0.011
Gender
0.116
Male Female Weight
0.497
Etiology
0.563 Other
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Rheumatoid Arthritis Cup Size
0.865
AC
32 mm
CE
Femoral Head Size
1.008 - 1066
1.0
reference
1.684
0.879 - 3.228
0.990
0.962 - 1.019
1.0
reference
1.841
0.442 - 7.664
0.636
0.153 - 2.652
1.008
0.915 - 1.112
HR
95% CI
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0.001
28 mm
Bearing Surface
p value
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Severe Congenital Hip Disease
95% CI **
0.102
1.026
0.995 1.057
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Age
HR*
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p value
Multivariate
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Univariate
0.555 1.0
reference
1.0
reference
5.141
2.149 12.299
1.672
0.304 9.204
0.002
0.061
Alumina-on-Alumina
1.0
reference
1.0
reference
Metal-on-Polyethylene
3.174
1.502 - 6.709
2.238
0.964 5.195
Design
<0.001
0.058
Cerafit/Multicone, Bihapro/Bimetric
1.0
reference
1.0
reference
Other
4.794
2.09 - 10.982
7.016
0.935 52.648
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1.054
1.018 - 1.091
Horizontal Distance
0.630
0.987
0.937 - 1.040
Vertical Distance
0.032
0.948
0.903 - 0.995
Cup Anteversion
0.720
0.991
0.944 - 1.041
Rotation Hip Center Distance
0.005
1.038
1.012 - 1.066
Lever arm Distance
<0.001
0.917
0.889 - 0.945
Height Greater Trochanter
0.002
0.913
0.006
1.053
1.015 1.093
0.121
0.964
0.921 1.010
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Acetabular Abduction Angle
1.043
1.007 1.081
<0.001
0.925
0.889 0.963
0.091
0.948
0.890 1.009
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0.018
0.861 - 0.968
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PT
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*HR: Hazard Ratio; ** CI: Confidence Interval
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ACCEPTED MANUSCRIPT Table 7. Uni- and multi-variate Cox regression analysis and risk factors for dislocation including
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hips inside and outside windows for cup position and abductor reconstruction.
Univariate HR*
abduction angle, range, 35º-50º and cup anteversion, range, 5º - 25º)
<0.001
1.0
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Inside
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value Cup position Window (acetabular
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Outside
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Abductor Reconstruction Window
95% CI**
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p
Multivariate p
HR
95% CI
1.0
reference
value <0.001
reference
4.111 2.158 -
3.418 1.784 -
7.831 <0.001
6.549 0.004
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(lever arm distance, range, 56 - 64 mm and height of the greater trochanter, range, -2 - 5 mm) Inside
1.0
reference
Outside
3.446 1.817 6.538
*HR: Hazard Ratio; ** CI: Confidence Interval
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1.0
reference
2.613 1.357 5.032
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Figure 1
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Figure 2
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PT
Figure 3
35
ED
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CE
PT
Figure 4
36
ED
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CE
PT
Figure 5
37
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Figure 6
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S0883-5403(15)00853-0 doi: 10.1016/j.arth.2015.09.039 YARTH 54737
To appear in:
Journal of Arthroplasty
Received date: Revised date: Accepted date:
5 July 2015 14 September 2015 15 September 2015
Please cite this article as: Garc´ıa-Rey Eduardo, Garc´ıa-Cimbrelo Eduardo, Abductor biomechanics clinically impact the total hip arthroplasty dislocation rate, Journal of Arthroplasty (2015), doi: 10.1016/j.arth.2015.09.039
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Abductor biomechanics clinically impact the total hip arthroplasty dislocation rate
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A prospective long-term study
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Eduardo García-Rey, MD, PhD, EBOT
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Eduardo García-Cimbrelo, MD, PhD
Orthopaedics Department
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Hospital La Paz-Idi Paz
Corresponding Author:
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Eduardo García-Rey
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Madrid-Spain
Orthopaedics Department
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Hospital La Paz-Idi Paz PºCastellana 261
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28046 Madrid-Spain
Email:[email protected]. Phone: 0034917271690. FAX : 0034917277085
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A prospective long-term study
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Abductor biomechanics clinically impact the total hip arthroplasty dislocation rate
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ACCEPTED MANUSCRIPT Background: Factors related to the patient, to the implant and to the surgery have been associated to the rate of dislocation for total hip arthroplasty (THA). We ask if the position of
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the cup and the reconstruction of the abductor mechanism actually lower the THA dislocation
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rate.
Methods: We evaluated 1,318 patients (1,414 hips) undergoing cementless THA between 1992
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and 2012. All THAs had a 28 or a 32 mm femoral head size. Hip reconstruction was radiologically assessed evaluating cup position and the hip rotation center according to
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Ranawat. The reconstruction of the abductor mechanism was measured using two variables: the lever arm distance and the height of the greater trochanter. Results: There were 38 dislocations (2.7%). After controlling the relevant confounding
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variables, like demographic and implant data, multivariate regression analysis showed that the most important factors associated with dislocation were a greater distance to the anatomic hip
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rotation center and hips outside two safe windows for cup position (acetabular inclination and
trochanter) .
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version angles) and abductor mechanism (lever arm distance and height of the greater
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Conclusion: A proper reconstruction of the hip is essential to decrease the risk for dislocation after primary THA. The weakness of the abductor muscles of the hip may be one of the most important causes for dislocation. Keywords: total hip arthroplasty; dislocation; radiological; hip rotation center; abductor mechanism Introduction Despite the excellent outcome of primary total hip arthroplasty (THA), the occurrence of a dislocation affects the patients´ quality of life and health-related issues [1]. The risk is higher in the first postoperative year, and most are early dislocations since two-thirds usually remain
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ACCEPTED MANUSCRIPT stable after a closed reduction [2]. However, dislocation after THA has gained importance given the cumulative rate over time, which has increased the risk of late dislocations [3].
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Different factors like the characteristics of the patient (gender, body mass index, age or
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diagnosis), of the implant (femoral head size, femoral stem offset, bearing surface) or surgical technique (approach, cup position) have been related to dislocation after primary THA [1, 4, 5,
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6]. Soft-tissue imbalance is also a well known cause, however, there is a lack of clinical reports that assesses this problem. An abductor mechanism insufficiency can be observed when cup
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position is high, a low height of the greater trochanter or proximal femur bone loss [7]. Postoperative cup position is not always related to dislocation, suggesting muscular imbalance rather than malposition as cause [8, 9]. The low rate of this complication, and some
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intraoperative issues such as capsular laxity, soft-tissue tension, fascia lata involvement or possible osteophyte excision during surgery, add more difficulties when trying to analyze
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dislocation after THA.
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We hypothesized that radiographic assessment of the lever arm of the hip and the height of the greater trochanter after primary THA, in a large series of patients, might help to
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understand some problems of dislocation. We assessed different clinical issues related to patients, implant characteristics like femoral head size, bearing surface and femoral stem designs, and the quality of the postoperative hip reconstruction in an attempt to evaluate the most frequent factors for dislocation after primary THA. Materials and Methods In this retrospective cohort analysis of our prospective register, we assessed 1414 cementless primary THAs in 1318 patients operated in our Institution between 1992 and 2012. We evaluated all patients who underwent cementless THA with an end-arthritis of the hip. We excluded patients with a cemented THA, a femoral neck fracture, metastatic or tumoral disease and severe cognitive or neuromuscular diseases. 135 patients were lost to follow-up
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ACCEPTED MANUSCRIPT due to a follow-up of less than five years, and five died due to unrelated causes wtihout dislocation. During the same period a total of 1915 THAs were performed in our Department.
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Oral and written informed consent was always obtained from all patients and they were
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informed preoperatively that they might receive a cementless THA. The mean age of the patients was 60.1 years old and the physical activity level, according to Devane et al [10], was 4
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or 5 in 974 patients. The minimum follow-up of the patients was two years (range, 2-22). All procedures were performed by the same surgical team using a posterolateral approach
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with reconstruction of the external rotators [11] or by preserving the external rotator muscles [12]. The same postoperative protocol was used for all patients: after surgery, patients walked on crutches with toe-touch partial weight bearing for 3 weeks, after which they were allowed
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to walk using two crutches for the next 6 weeks. All patients were instructed to have an abduction pillow while in bed or sitting, and to avoid a hip flexion higher than 90º during the
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first month. Cefazolin (or vancomycin in allergic patients) was administered for antibiotic prophylaxis during the anesthetic induction and continued for 24 hours, with low-molecular-
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weight heparin to decrease the risk of thromboembolic disease in all patients according to the
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guidelines of our Institution. Different designs, cup/stem, with different bearing surfaces and femoral head sizes were compared: Duraloc/Profile (Depuy / Johnson&Johnson, Warsaw, IN, USA) with a 28 mm metal head-on-polyethylene (PE) liner; Allofit/Alloclassic (Centerpulse/Zimmer, Winterthur, Switzerland) with a 28 mm metal head-on-PE liner; Pinnacle or Duraloc/Summit (Depuy/Johnson&Johnson) with 28 mm metal head-on-PE liner; EP-Fit/SLPlus (Endoplus-Smith&Nephew, Rotkreuz, Switzerland) with either a 28 mm metal head-on-PE liner or an alumina-on-alumina coupling; Cerafit/Multicone (Ceraver Roissy, France) with a 28 or 32 mm alumina-on-alumina coupling; and Bihapro/Bimetric (Biomet, Warsaw, IN, USA) with a 32 mm metal head-on-PE liner making a total of six groups.
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ACCEPTED MANUSCRIPT Patients were followed at 6 weeks, 3, 6, and 12 months, and then annually after surgery. At every interval, we evaluated pain, function, and range of mobility according to the six-level
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scale described by Merle D’Aubigné and Postel [13]. We recorded the appearance of
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dislocation during the first year (early disocation), all further episodes (recurrent) and revision of the cup for this cause.
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Standard anteroposterior (AP) radiographs of the pelvis were made pre-operatively, immediately after the operation, at 6 weeks, at 3, 6, and 12 months, and annually thereafter
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following the same protocol. The patient was positioned supine, with his/her feet together. The x-ray tube was positioned over the symphysis pubis 1 m from and perpendicular to the table with a symmetric obturator foramen and visible lesser trochanter and iliac crest [14]. A
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single author made all measurements, which were repeated three times for each radiograph. Cup position was assessed according to the acetabular abduction angle, the height of the
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center of the hip (as measured from the centre of the femoral head to the interteardrop line), and the horizontal distance of the cup (measured from the center of the femoral head to the
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Köhler line) [15]. The reconstruction of the hip rotation center was evaluated according to the
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Ranawat triangle [16, 17]. The true acetabulum region was the area enclosed by a right triangle with a height and width equal to 20% of the height of the pelvis on the AP radiograph. The midpoint of the hypotenuse coincides with the approximate center of the femoral head (ACFH) and is the center of rotation of the hip. The ACFH was used as the reference point to measure distance to the center of the prosthetic femoral head (CPFH) (Fig. 1). This distance was recorded in the preoperative and postoperative radiographs to assess the reconstruction actually achieved. Cup anteversion was measured according to Widmer [18] using a trigonometric function: the relationship between the short axis of a projected ellipse and the total length of a projected cup cross-section along the short axis ratio and the cup inclination. The radiographic reconstruction of the abductor mechanism was also measured using two variables: 1) the lever arm as the distance from the CPFH to the line joining the lateral part of
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ACCEPTED MANUSCRIPT the greater trochanter to the anterosuperior iliac crest, and 2) the height of the greater trochanter as the distance between the line joining the two teardrops and the parallel line
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crossing the tip of the greater trochanter (Fig. 2). The intra-observer reliability for this method,
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using the mean of the three measurements, was 0.948 (intraclass correlation, 95% Confidence Interval (CI): 0.885-0.979). Inter-observer reliability was also assessed by using 74 post-
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operative radiographs that were evaluated by another observer using the same method. This inter-observer reliability was 0.979 (intraclass correlation 95% CI 0.726 to 0.995). Although
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these measurements were made using the sixth week post-operative radiograph, images with a low quality of the greater trochanter or anterosuperior iliac crest, or an un-true anteroposterior view were excluded and the 12th week post-operative radiograph for the hip was used. Of the 1414 hips analyzed, 89 were evaluated in the 12th postoperative week. Since
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different designs may produce different values regarding the abductor mechanism due to the characteristics of their femoral offset, these variables were calculated for each group in order
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Statistical Analysis
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to assess whether there was any difference.
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Qualitative data are expressed as counts and percentages and quantitative data by mean + standard deviation (SD) or range. Qualitative data for hips with and without dislocation were compared using the chi-square test or Fisher’s exact test, and quantitative data were also compared using Student’s t-test. Pearson’s chi-square test was used to compare the demographic qualitative data of patients between groups. We analyzed the possible influence of different factors: first, clinical factors related to the patient (age, gender, weight, and diagnosis); those related to the implant (cup and femoral head size, bearing surface, group/design); and those related to the surgical technique (radiological postoperative cup position and reconstruction of the abductor mechanism using the variables mentioned above). We recorded dislocated hips that fell inside or outside a window for cup position similar to the
7
ACCEPTED MANUSCRIPT Lewinnek zone [4]. Limits for the window were an acetabular abduction angle from 35º to 50º and a cup version angle from 5º to 25º. We also recorded hips that fell inside or outside a
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second window for the reconstruction of the abductor mechanism according to the height of
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the greater trochanter; limits for both variables were chosen according to the mean values + SD for non-dislocated hips. The test of Homogeneity of Variances, ANOVA, was used to assess
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possible differences in the mean values for these two variables with a subset for alpha=0.05. Univariate and multivariate Cox regression models were used to assess risk factors for
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dislocation. Kaplan-Meier survivorship analysis, with 95% Confidence Intervals (CI), was used to estimate the cumulative probability of not having a dislocation for hips inside or outside either window and for patients. The differences in survival with and without dislocation were assessed using the log-rank test to compare the Kaplan-Meier curves. Statistical analysis was
Results
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significance was p < 0.05.
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performed using SAS® software (Version 9.3; SAS Institute Inc, Cary, NC, USA). The level of
Most patients had a satisfactory result with a mean postoperative clinical outcome at the
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latest follow-up of 5.8 points for pain, 5.7 for function and 5.7 for mobility for the whole series. Thirty-eight patients had a dislocation, a rate of 2.7%; 27 were stable after non-operative treatment and 11 required revision (0.8%) (Table 1). Dislocation was more frequent in older patients (p=0.011) (Table 2). The rate of dislocation also depended on implant characteristics and the postoperative reconstruction of the hip (Tables 3 and 4). The mean lever arm distances for the Cerafit/Multicone and the Bihapro/Bimetric groups (p<0.001) were greater than the other groups, and the mean height of the greater trochanter was smaller for the EP-Fit/SL-Plus and the Allofit/Alloclassic groups (p<0.001, test of Homogeinity of Variances. ANOVA, subset for alpha=0.05) (Table 5). After controlling the possible confounding variables, none of the patient-related factors analyzed was associated with a higher risk for dislocation (Table 6).
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ACCEPTED MANUSCRIPT Although 32 hips (4.5%) with a 28 mm femoral head size and 6 hips (0.9%) with a 32 mm femoral head size had dislocations, as well as 9 alumina-on-alumina hips (1.2%) and 29 metal-
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on PE hips (4.1%), with the number of hips available, the multivariate analysis did not show an
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increased risk associated to femoral head size or bearing surface. The rate of dislocation was 0.9% for the Ceraver group, 1.1% for the Bimetric group, 3.3% for the Duraloc/Profile group,
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5.3% for the Allofit/Alloclassic group, 5% for the EP-Fit/SL-Plus group and 4.6% for the Summit group, and statistical analysis showed that the Ceraver and Bimetric groups had a lower rate of
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dislocation (p<0.001), however, after controlling the possible confounding variables, we could not find a higher risk for dislocation (p=0.058).
We found that cups with a greater acetabular abduction angle on the postoperative
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radiograph and a greater distance to the approximate center of the hip had a higher risk for dislocation (p=0.006, p=0.018, respectively). Hips with a greater distance of the lever arm had
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a lower risk for dislocation (p<0.001). More hips outside the safe radiological position window had dislocations than those inside the window (Fig. 3). The survival rate for dislocation at 20
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years was 98.48% (95% CI 94.9 – 100) for hips inside this window and 93.9% (95% CI 89 – 98.9)
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for cups outside the window (p<0.001, Log Rank test) (Fig. 4). According to the mean values and their SD for the lever arm hip distance and the height of the greater trochanter, the limits for the safe zone of the radiological abductor mechanism were 56 to 64 mm for the first and -2 to 5 mm for the latter. The number of hips outside these windows was higher among dislocated hips, showing a survival rate for dislocations at 20 years of 98.33% (95% CI 94.7 – 100) for hips inside this window and 94.6% (95% CI 89.6 – 99.6) for cups outside the window (p<0.001, Log Rank test) (Fig. 5 and Fig. 6). We also found that hips outside either of these two windows had a higher risk for dislocation (p<0.001, p=0.004, respectively, Table 7). Discussion
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ACCEPTED MANUSCRIPT Dislocation is not frequent after primary THA, but it does affect clinical outcome, patient satisfaction and revision rates [1, 2, 6, 19]. Since new bearing surfaces, contemporary
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cementless implants and improvement in cementing techniques are decreasing the rates of
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revision for aseptic loosening, dislocation is gaining importance [3, 20]. Causes are difficult to analyze due to the low incidence of dislocation, so a large number of cases are needed for a
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solid statistical evaluation. To date, although an abductor mechanism insufficiency has been related to dislocation [3, 7-9], there is a lack of clinical reports that evaluate this problem. We
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have tried to assess the possible influence on dislocation of the lever arm hip distance and the height of the greater trochanter, as part of the assessment for hip biomechanics regarding the abductor mechanism, in order to ascertain whether an accurate surgical reconstruction of the
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hip could actually lower the risk for dislocation.
Contrary to previous reports, neither demographic nor clinical factors related to the patients
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were associated to a higher risk for dislocation. Dislocation was more frequent in older patients, pelvic stiffness and decreased abductor muscle strength being some of the possible
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reasons for this finding [19, 21], however, after controlling the possible confounding factors,
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regression analysis did not show a higher risk for dislocation in older patients. In our study, the exclusion of cemented THAs, more frequently used in old patients, and the absence of significant pathologies like cognitive dysfunction, neuromuscular diseases or femoral neck fractures may have influenced results [6]. On the other hand, the similar characteristics of the patients, with a relatively young age and high physical activity, may have allowed us to better analyze the abductor mechanism of the hip. A posterolateral approach, using short external repair or preserving posterior structures was used in all surgeries, and the dislocation rate was similar to other reports [11, 12]. Callanan et al. also observed that this approach may be one of the best to obtain a proper position of the cup [22].
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ACCEPTED MANUSCRIPT Charnley low-friction arthroplasty, one of the most studied implants, had different rates for dislocation, from 1% to 9%, an incidence that increases through the years and is difficult to
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solve when recurrent [19, 23]. Recently, Kumar et al. found that a contemporary cemented
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THA, with a 22.225 mm diameter femoral head operated through a posterior approach with a capsule repair, was associated with a low rate of dislocation [24]. They do not support the idea
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of using large-diameter heads since data from Registries and wear problems are being reported. We only used and analyzed conventional cementless THAs with 28 or 32 mm femoral
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heads with alumina-on-alumina or metal-on-PE bearings. The rate of dislocation was higher for implants with 28 mm femoral heads and metal-on-PE hips; however, regression analysis could not detect a higher risk of dislocation with this femoral head size and bearing surface. Hernigou et al. also observed that alumina-on-alumina decreased the risk for late dislocation, a
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finding that we can not confirm although the characteristics of the material are the same; however, the differences in the follow-up regarding other brands like the Duraloc/Profile
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group may have affected our findings [25, 26]. This influence may be particularly important for
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late dislocation since a thin pseudocapsule is observed in metal-on-polyethylene hips and a
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thicker capsule has been reported after placement of alumina-on-alumina hips [27]. Although cup position is usually associated to dislocation, the whole reconstruction of the hip may be more important. Anteversion on its own did not increase dislocation risk, however, an anteversion of 15º -25º combination with an acetabular abduction angle of 35º-50º did increase risk. A window with a safe zone for the cup position was evaluated in a way similar to that in Lewinnek et al [4], although we accepted wider limits for the acetabular inclination as discussed below. However, cup position is not the only cause for dislocation: Pierchon et al observed, in a Computed Tomography (CT) study, that cup position is not always related to dislocation and argued that muscular imbalance may be more important [8]. Biedermann et al, in an Ein Bild Röentgen Analyses software (EBRA) study, also observed that a proper cup position is desirable, however, they suggested that this is a multifactorial issue and they did
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ACCEPTED MANUSCRIPT not investigate other factors like femoral anteversion or soft-tissue tension [9]. Recently, Esposito et al suggested that a truly “safe zone” based upon acetabular position alone does
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not exist; their frequency over a six month period, using a posterolateral approach, of
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dislocation was 2.1% (147 of 7040 patients). They did not include extra-large femoral heads or metal-on-metal hips; they matched 142 dislocated and 142 non-dislocated patients in order to
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assess the acetabular abduction and the cup anteversion angles, measured by EBRA, and did not find differences regarding a “safe zone” for dislocation, they also emphasized the notion
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that hip dislocation is multivariate in etiology [28]. Similar findings have also been made by Grammatopoulos et al, who although reporting that acetabular orientation affected the clinical outcome, suggested that the range of the safe zone may be wider than the Lewinnek zone
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when influencing clinical and dislocation rate parameters [29]. Although this study only used plain radiographs on the AP view, as previously mentioned, an
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attempt was made to evaluate the abductor mechanism in order to add new variables for the radiological reconstruction of the hip. First, the lever arm was evaluated. McGrory et al. used a
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similar method in order to assess this issue although they emphasize femoral offset rather
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than the lever arm [30]. Traina et al. also used a similar method to the one used here, but we have tried to evaluate a large number of cases and calculate the reliability of the method [31]. We are aware that studying the abductor mechanism is challenging when evaluating pelvic radiographs on AP view and many variables affecting this issue are practically unevaluable, such as capsular laxity or osteophytes, however, the findings observed in our study suggest that the variables assessed here emphasize the importance of hip biomechanics rather than other previously reported clinical factors. They can also serve as new variables that might help to assess this complex problem. First, we observed that hips with a greater mean value for the lever arm distance showed a lower risk for dislocation, thus, this effect was even greater when it was combined with the height of the greater trochanter as shown in the multivariate analysis. Eftekhar observed that a soft-tissue imbalance may be one of the most important
12
ACCEPTED MANUSCRIPT causes for dislocation, regardless of the idoneity of the cup position, a finding also reported by others [7, 24, 32]. We also observed that the lever arm distance and the height of the greater
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trochanter differed among the different designs, which may also affect the differences
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observed in the rates of dislocation. As well, hips with a greater distance to the hip rotation center had a higher risk for dislocation. Recently, Terrier et al, in a finite element model based
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on preoperative CT scans in fifteen patients, quantified the effect of cup medialization on moment arms and tested whether the increase in the moment arm of the gluteus minimus and
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medius was correlated to acetabular and femoral offset, trochanteric height and femoral antetorsion [33]. They confirmed this increase and found a variability in the patients´ anatomy, and laxity, and an inverse correlation with femoral antetorsion, concluding cup medialization
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might be considered in active patients with little femoral antetorsion. The first limitation of this study, as previously mentioned, is the number of cases. Although it is
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relatively common in most previous reports, the low incidence of dislocation makes it very difficult to analyze the possible causes and may have affected some findings, particularly with
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respect to demographic data. Secondly, we are aware that the lack of a proper lateral view in
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the hip radiographs might complicate analysis of cup anteversion, however, Nomura et al. recently reported the method described by Widmer, used here, as the most appropriate to evaluate this variable on the AP view [34]. Third, we did not analyze CT images [8], and femoral anteversion has not been analyzed as discussed above [9, 33, 35]. Fourth, although intra- and inter-observer errors for the radiological measurements were calculated, the absence of a biomechanical assessment does not allow us to correlate the method used here. Cumulative risk has been studied using different follow-ups for different implants and this may have affected the results. To date, although all surgeries were done by the same surgical team, we are aware that the clinical experience and evolution of the surgeons over time, a twenty years period, may also have influenced these findings. These findings may also influence the rates of dislocation since they affect hip biomechanics and have not been evaluated here.
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ACCEPTED MANUSCRIPT The possible causes for dislocation are still difficult to determine, therefore possible solutions for recurrent or late dislocations are also difficult to find since many treatments are being tried
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to improve the outcome of this complication. Revision of acetabular and femoral components
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for evident malposition may be a relatively easy answer, however, different options for muscular imbalance, like constrained or dual mobility cups and trochanter advancements, are
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still under debate. The findings reported here may indicate that a more accurate reconstruction of the hip, including cup position and abductor mechanism, with an adequate
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surgical technique, is probably one of the most important factors to influence the dislocation rate. A proper selection of the implants, which are well-studied and do not increase other types of new or old complications, must be made in order to maintain the excellent results of
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THA over time. References
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1. Morrey BF. Difficult complications after hip joint replacement. Dislocation. Clin Orthop
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Relat Res 1997;179-87.
2. Ali Khan MA, Brakenbury PH, Reynolds IS. Dislocation following total hip replacement.
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J Bone Joint Surg [Br] 1981;63-B:214-8 3. Berry DJ, von Knoch M, Schleck CD, Harmsen WS. The cumulative long-term risk of dislocation after primary Charnley total hip arhtroplasty. J Bone Joint Surg [Am] 2004;86-A:9-14 4. Lewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR. Dislocations after total hipreplacement arthroplasties. J Bone Joint Surg [Am] 1978;60-A:217-20 5. Berry DJ, Von Knoch M, Schleck CD, Harmsen WS. Effect of femoral head diameter and operative approach on risk of dislocation after total hip arthroplasty. J Bone Joint Surg [Am] 2005;87:2456-63.
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ACCEPTED MANUSCRIPT 6. Hailer NP, Weiss RJ, Stark A, Kärrholm J. The risk of revision due to dislocation after total hip arthroplasty depends on surgical approach, femoral head size, sex, and
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primary diagnosis. An analysis if 78,098 operations in the Swedish Hip Arthroplasty
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Register. Acta Orthop 2012; 83:442-8
7. Eftekhar NS. Dislocation and instability complicationg low friction arthroplasty of the
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hip joint Clin Orthop Relat Res 1976;121:120-5
8. Pierchon F, Pasquier G, Cotton A, Fontaine C, Clarisse J, Duquennoy A. Causes of
Surg [Br] 1994; 76:45-8.
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dislocation of total hip arthroplasty. CT study of component alignment. J Bone Joint
9. Biedermann R, Tonin A, Krismer M, Rachbauer F, Eibl G, Stöckl B. Reducing the risk of dislocation after total hip arthroplasty : the effect of orientation of the acetabular
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component. J Bone Joint Surg [Br] 2005;87-B:762-9 10. Devane PA, Horne JG, Martin K, Coldham G, Krause B. Three-dimensional polyethylene
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wear of a press-fit titanium prosthesis. Factors influencing generation of polyethylene
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debris. J Arthroplasty 1997;12:256-66. 11. Weeden SH, Paprosky WG, Bowling JW. The early dislocation rate in primary total hip
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arthroplasty following the posterior approach with posterior soft-tissue repair. J Arthroplasty 2003;18:709-13. 12. Kim YS, Kwon SY, Sun DH, Han SK, Maloney WJ. Modified posterior approach to total hip arthroplasty to enhance joint stability. Clin Orthop Relat Res 2008; 466: 294-9. 13. Merle D’Aubigné R, Postel M. Functional results of hip arthroplasty with acrylic prosthesis. J Bone Joint Surg [Am] 1954; 36:451-75. 14. Manning DW, Chiang PP, Martell JM, Galante JO, Harris WH. In vivo comparative wear study of traditional and highly-cross linked polyethylene in total hip arthroplasty. J Arthroplasty 2005;20:880-6.
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ACCEPTED MANUSCRIPT 15. Johnston RC, Fitzgerald RH, Harris WH, Poss R, Müller ME, Sledge CB. Clinical and radiographic evaluation of total hip arthroplasty: a standard system of terminology for
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reporting results. J Bone Joint Surg [Am] 1990;72-A:161-168
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16. Ranawat CS, Dorr LD, Inglis AE. Total hip arthroplasty in protrusio acetabuli of rheumatoid arthritis. J Bone Joint Surg [Am] 1980;62:1059-1065.
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17. García-Cimbrelo E, Díaz-Martín A, Madero R, Munuera L. Loosening of the cup after low-friction arthroplasty in patients with acetabular protrusion. The importance of the
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position of the cup. J Bone Joint Surg [Br] 2000; 82:108-15 18. Widmer KH. A simplified method to determine acetabular cup anteversion from plain radiographs. J Arthroplasty 2004;19:387-90.
19. Bozic KJ, Kurtz SM, Lau E, Ong K, Vail TP, Berry DJ. The epidemiology of revision total
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hip arthroplasty in the United States. J Bone Joint Surgery [Am] 2009;91-A:128-33 20. Hailer NP, Garellick G, Kärrlholm J. Uncemented and cemented primary total hip
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arthroplasty in the Swedish Hip Arthroplasty Register: evaluation of 170,413
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operations. Acta Orthop 2010;81:34-41. 21. De Thomasson E, Guingand O, Terracher R, Mazel C. Role of sagittal spinal curvature in
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early dislocation after revision total hip arthroplasty: prospective analysis of 49 revision procedures. Rev Chir Orthop Reparatrice Appar Mot 2004;90:226-31 22. Callanan MC, Jarrett B, Bragdon CR, Zurakowski D, Rubash HE, Freiberg AA, Malchau H. Risk factors for cup malpositioning. Quality improvement through a joint registry as a tertiary hospital. Clin Orthop Relat Res 2011;469: 319-329 23. García-Cimbrelo E, Munuera L. Dislocation in low-friction arthroplasty. J Arhtroplasty 1992;7:149-55 24. Kumar V, Sharma S, James J, Hodgkinson, Hemmady MV. Total hip replacement through a posterior approach using a 22-mm diameter femoral head. Bone Joint J 2014;96-B:1202-6
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ACCEPTED MANUSCRIPT 25. Hernigou P, Homma Y, Pidet O, Guissou I, Hernigou J. Ceramic-on ceramic bearing decreases the cumulative ong-term risk of dislocation. Clin Orthop Relat Res 2013;
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471:3875-82
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26. García Rey E, García Cimbrelo E, Cordero Ampuero J. Outcome of a hemispherical porous-coated acetabular component with a proximally hydroxyapatite-coated
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anatomic femoral component: a 12- to 15- year follow-up study. J Bone Joint Surg Br 2009;91: 327-32
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27. Coventry MB. Late disocation in patients with Charnley total hip arthroplasty. J Bone Joint Surg [Am] 1985; 67-A:832-41
28. Esposito CI, Gladnik BP, Lee Y, Lyman S, Wright TM, Maynam DJ, Padgett DE. Cup
2015;30:109-113
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position alone does not predict risk of dislocatiob after hip arthroplasty. J Arthroplasty
29. Grammatopoulos G, Thomas GE, Pandit H, Beard DJ, Gill HS, Murray DW. The effect of
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orientation of the acetabular component on outcome following total hip arthroplasty
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with small diameter hard-on-soft bearings. Bone Joint J. 2015;97-B(2):164-72. 30. McGrory BJ, Morrey BF, Cahalan TD, An KN, Cabanela ME. Effect of femoral offset on
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range of motion and abductor muscle strength after total hip arthroplasty J Bone Joint Surg [Br] 1995;77-B:865-9 31. Traina F, De Fine M, Biondi F, Tassinari E, Galvani A, Toni A The influence of centre of rotation on implant survival using a modular stem hip prosthesis. Int Orthop 2009;33:1513-8 32. Dorr LD, Wolff AW, Chandler R, Conaty JP. Classification and treatment of dislocations of total hip arthroplasty. Clin Orthop Relat Res 1983; 173: 151-8 33. Terrier A, Florencio FL, Rüdinger HA. Benefit of cup medialization in total hip arthroplasty is associated with femoral anatomy. Clin Orthop Relat Res 2014;472:31593165
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ACCEPTED MANUSCRIPT 34. Nomura T, Naito M, Nakamura Y, Ida T, Kuroda D, Kobayashi T, Sakamoto T, Seo H. An analysis of the best method for evaluating anteversion of the acetabular component
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after total hip arthroplasty on plain radiographs. Bone Joint J 2014; 96-B:597-603.
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35. Weber M, Lechler P, von Kunow F, Völlner F, Keshmiri A, Hapfelmeier A, Grifka J, Renkawitz T. The validity of a novel radiological method for
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measuring femoral stem version on anteroposterior radiographs of the hip after
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total hip arthroplasty. Bone Joint J. 2015;97-B:306-11
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ACCEPTED MANUSCRIPT Acknowlwdgements
The authors gratefully thank Rosario Madero, MS, for her statistical analysis and review
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of the manuscript
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ACCEPTED MANUSCRIPT Figure Legends
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Fig 1. Cup position assessment on the anteroposterior radiograph. AAA: Acetabular abduction angle; K –K´: Köhler line; CPFH: Center prosthetic femoral head; TAR: True acetabulum region;
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AFHC: Approximate femoral head center
Fig. 2. Measurement of the radiographic reconstruction of the abductor mechanism: The lever
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arm as the distance (D), from the femoral head to the line joining the lateral part of the greater trochanter to the anterosuperior iliac crest; and 2) the height of the greater trochanter as the distance (H), between the line joining the two teardrops and the parallel line crossing the tip of
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the greater trochanter.
Fig. 3. Hips inside and outside the window for radiological cup position (acetabular abduction,
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range 35 - 50º, and cup anteversion angles, range 15º - 25º).
position.
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Fig. 4. Probability of not having dislocation for hips inside or outside the windows for cup
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Fig. 5. Hips inside and outside the window for abductor mechanism reconstruction (lever arm distance, range 56 - 64 mm, and height of the greater trochanter, range -2 - 5 mm). Fig. 6. Probability of not having dislocation for hips inside or outside the window for abductor mechanism reconstruction
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ACCEPTED MANUSCRIPT Table 1. Data on patients with revision surgery due to dislocation
Fe mal e 64
60
3
Primary Dural osteoart oc/ hritis Profil 5 e 4
2
70
4
AC
Fe mal e 69
72
Mal e 73
4
65
77
4
Primary Dural osteoart oc/ hritis Sum 5 mit 2
4
Primary Dural osteoart oc/ hritis Sum 5 mit 4
4
Primary Dural osteoart oc/ hritis Sum 5 mit 2
2 8
5
Avascul ar
2 8
6
Mal e 28
2 8
CE
Mal e 56
Primary Dural osteoart oc/ hritis Profil 5 e 6
PT
3
5
2 8
ED
Fe mal e 65
2 8
74
7 Mal e 44 108
CrC o/P 4 1 4 1 E 7 0 2 5 7
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2
Congeni Dural tal Hip oc/ Disease Profil 5 e 0
1
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Ca Sex Age Wei Acti Diagnosi Desig C F Bear A C V H C L H Disloc Revi (ye ght vity u H ing I A D D R A G ation sion se s n p S Surf surg ars) (kg) leve H D T l Si ery ace z (mo [10] e nths)
EPfit/
5 8
2 8
2 8
21
CrC o/P E
CrC o/P E
CrC o/P E
CrC o/P E
CrC o/P E
4 2 3 5 6 0 0 6
4 1 2 3 5 0 0 5 6
Late
150
Late
124
Late
110
Recur rent
94
Recur rent
73
Recur rent
39
5 Recur 6 -3 rent
108
5 6
5 6
5 6
6 1 2 1 5 5 8 5 5 -4 4
4 3 1 5 5 5 5 5
4 1 3 2 2 4 5 0 3
4 2 3 1 Al5 0 5 7 1 on-
5 2
5 6
1
1
1
3
0
4
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77
74
5
5
Avascul Ceraf ar it/ necrosis Multi 5 cone 2
4
Avascul Ceraf ar it/ necrosis Multi 5 cone 2
11
67
2 8
Alon2 Al 5 5 7 5 6 5
Recur rent
22
Recur rent
3
Recur rent
3
Recur rent
85
T
2 8
3 2
AlonAl 4 1 3 1 2 5 5 2 3
3 2
AlonAl 6 1 3 3 0 4 5 0 5
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Fe mal e 61
4 8
Postrau Ceraf it/ matic Multi 4 cone 8
10 Mal e 37
SLPlus
CrC o/P 5 3 3 2 E 0 0 0 0 2
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3
9 Mal e 52
EPfit/
Al
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68
Develop mental arthritis
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Fe mal e 74
SLPlus
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8
necrosis
5 8 -1
5 6
5 8
5 8
0
0
1 4
AC
CE
Cr-Co: Chrome-Cobalt; PE:Polyethylene; Al: Alumina, FHS: Femoral Head size in mm; AI: Acetabular Inclination or Acetabular abduction angle in degrees; CA: Cup Anteversion in degrees; VD: Vertical distance in mm; HD: Horizontal distance in mm; CRH: Center of rotation of the hip or distance from the approximate center of the femoral head to the center of the prosthetic femoral head in mm; LAD: Lever arm distance in mm; HGT: Height of the greater trochanter in mm.
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ACCEPTED MANUSCRIPT Table 2. Preoperative patient data and dislocation Total
Age in years (mean, +SD)
59.9 +15.1
65.4 +13.5
Weight in kilograms (mean,
73.4 +14.1
72.1 +14.6
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+SD) Gender
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Yes
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No
60.13 +14.2
0.011 a
73.36 +14.4
0.497 a
0.116 b
718 (97.9%)
15 (2.1%)
733
Female
658 (96.6%)
23 (3.4%)
681
8
2
10
97
2
99
271
9
280
594
19
613
355
6
361
Primary Osteoarthritis
773 (97.2%)
22 (2.8%)
795
Avascular Necrosis
203 (98.1%)
4 (1.9%)
207
Congenital Hip Disease
149 (98.1%)
3 (1.9%)
152
ED
Male
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Activity Level [10]
Level 3 Level 4
AC
Level 2
CE
Level 1
Level 5
p values
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Dislocation
Etiology
23
0.563 b
ACCEPTED MANUSCRIPT 105 (98.1%)
2 (1.9%)
107
Postraumatic
74 (98.7%)
1 (1.3%)
75
Developmental Disease
58 (98.3%)
1 (1.7%)
59
17
0
b
Pearson chi-square test Fisher´s exact test
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Mann-Whitney
AC
CE
PT
ED
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a
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Other
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Rheumatologic Disorders
24
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ACCEPTED MANUSCRIPT Table 3. Implant data for the series and dislocation Dislocation
52.3 (38-64)
52.5 (46-62)
Metal-on-Polyethylene
682 (95.9%)
Femoral head size
p values
52.4 (38-64)
0.865 a
9 (1.3%)
703
29 (4.1%)
711
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694 (98.7%)
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Bearing surface Alumina-on-alumina
Total
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Yes
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Cup Size in mm (mean, range)
No
28 mm
676 (95.5%)
32 (4.5%)
708
32 mm
698 (99.1%)
6 (0.8%)
704
118 (9.6.7%)
4 (3.3%)
122
108 (94.7%)
6 (5.3%)
114
206 (95.4%)
12 (4.6%)
218
172 (95%)
9 (5%)
181
678 (99.1%)
6 (0.9%)
684
94 (98.9%)
1 (1.1%)
95
ED
Cup/Femoral Stem
Allofit/Alloclassic
PT
Duraloc/Profile
EP-Fit/SL-Plus
CE
Pinnacle or Duraloc/Summit
AC
Cerafit/Multicone Bihapro/Bimetric
a
Mann-Whitney
b
Pearson chi-square test Fisher´s exact test
25
0.002 b
0.001 b
0.001 b
ACCEPTED MANUSCRIPT Table 4. Postoperative radiographic data and dislocation p
Dislocation
Acetabular Abduction Angle in degrees (mean,
45.6 +6.1
SC
+SD)
Yes
Total
48.8 +10.9
45.7
0.003 a
RI P
No
T
values
16.3 + 6.7
16.8 + 9.1
16.3
0.720 a
Horizontal Distance in mm (mean, +SD)
33.5 + 6.1
32.9 + 8.7
33.5
0.630 a
Vertical Distance in mm (mean, +SD)
22.1 + 7.2
19.6 + 6.3
22.1
0.032 a
3.1 + 4.6
5.4 + 9.5
3.2
0.005 a
58.7 + 3.1
55.6 + 3.5
58.6
<0.001
MA NU
Cup Anteversion in degrees (mean, +SD)
ED
Hip rotation center distance in mm [16](mean,
PT
+SD)
Lever arm distance in mm (mean, +SD)
CE
a
AC
Height greater trochanter in mm (mean, +SD)
0.9 + 4.3
-1.13 + 4.9
0.83
1035
16 (1.5%)
1051
0.002 a
Cup position window * Inside
(98.5%) Outside
0.001 b
340 (93.9%)
22 (6.1%)
362
1004
17 (1.7%)
1021
Abductor mechanism window ** Inside
26
ACCEPTED MANUSCRIPT 0.001 b
(98.3%) Outside
370 (94.7%)
21 (5.3%)
391
RI P
T
* According to the acetabular abduction angle (35º - 50º) and anteversion (15º- 25º)
Mann-Whitney
b
Pearson chi-square test Fisher´s exact test
AC
CE
PT
ED
MA NU
a
SC
** According to the height of the greater trochanter (-2 - 5 mm) and lever arm (56 - 64 mm)
27
ACCEPTED MANUSCRIPT Table 5. Radiographic lever arm hip distance and height of the greater trochanter in mm
Height Greater Trochanter
Multicone/ Cerafit
59.3 + 2.0
1.46 + 3.5
Duraloc/Summit EP-Fit /SlPlus Duraloc / Profile
57.0 + 3.9 58.3 + 2.1 57.9 + 4.7
Allofit / Alloclassic Bihapro / Bimetric
58.2 + 3.0 59.3 + 5.1
Total p values
58.6 + 3.1 <0.001 a
SC
ED PT CE AC a
RI P
Lever arm distance
MA NU
Design
T
for different designs used in this series (mean + SD)
test of Homogeneity of Variances, ANOVA
28
1.51 + 5.4 -1.68 + 3.6 1.02 + 1.4 -0.47 + 6.0 0.79 + 5.2 0.83 + 4.3 <0.001 a
ACCEPTED MANUSCRIPT Table 6.Uni- and multi-variate Cox regression analysis and risk factors for dislocation.
0.011
Gender
0.116
Male Female Weight
0.497
Etiology
0.563 Other
PT
Rheumatoid Arthritis Cup Size
0.865
AC
32 mm
CE
Femoral Head Size
1.008 - 1066
1.0
reference
1.684
0.879 - 3.228
0.990
0.962 - 1.019
1.0
reference
1.841
0.442 - 7.664
0.636
0.153 - 2.652
1.008
0.915 - 1.112
HR
95% CI
T 1.037
0.001
28 mm
Bearing Surface
p value
ED
Severe Congenital Hip Disease
95% CI **
0.102
1.026
0.995 1.057
SC
Age
HR*
MA NU
p value
Multivariate
RI P
Univariate
0.555 1.0
reference
1.0
reference
5.141
2.149 12.299
1.672
0.304 9.204
0.002
0.061
Alumina-on-Alumina
1.0
reference
1.0
reference
Metal-on-Polyethylene
3.174
1.502 - 6.709
2.238
0.964 5.195
Design
<0.001
0.058
Cerafit/Multicone, Bihapro/Bimetric
1.0
reference
1.0
reference
Other
4.794
2.09 - 10.982
7.016
0.935 52.648
29
ACCEPTED MANUSCRIPT 0.003
1.054
1.018 - 1.091
Horizontal Distance
0.630
0.987
0.937 - 1.040
Vertical Distance
0.032
0.948
0.903 - 0.995
Cup Anteversion
0.720
0.991
0.944 - 1.041
Rotation Hip Center Distance
0.005
1.038
1.012 - 1.066
Lever arm Distance
<0.001
0.917
0.889 - 0.945
Height Greater Trochanter
0.002
0.913
0.006
1.053
1.015 1.093
0.121
0.964
0.921 1.010
RI P
T
Acetabular Abduction Angle
1.043
1.007 1.081
<0.001
0.925
0.889 0.963
0.091
0.948
0.890 1.009
MA NU
SC
0.018
0.861 - 0.968
AC
CE
PT
ED
*HR: Hazard Ratio; ** CI: Confidence Interval
30
ACCEPTED MANUSCRIPT Table 7. Uni- and multi-variate Cox regression analysis and risk factors for dislocation including
RI P
T
hips inside and outside windows for cup position and abductor reconstruction.
Univariate HR*
abduction angle, range, 35º-50º and cup anteversion, range, 5º - 25º)
<0.001
1.0
ED
Inside
MA NU
value Cup position Window (acetabular
PT
Outside
CE
Abductor Reconstruction Window
95% CI**
SC
p
Multivariate p
HR
95% CI
1.0
reference
value <0.001
reference
4.111 2.158 -
3.418 1.784 -
7.831 <0.001
6.549 0.004
AC
(lever arm distance, range, 56 - 64 mm and height of the greater trochanter, range, -2 - 5 mm) Inside
1.0
reference
Outside
3.446 1.817 6.538
*HR: Hazard Ratio; ** CI: Confidence Interval
31
1.0
reference
2.613 1.357 5.032
ED
MA NU
SC
RI P
T
ACCEPTED MANUSCRIPT
AC
CE
PT
Figure 1
33
ED
MA NU
SC
RI P
T
ACCEPTED MANUSCRIPT
AC
CE
PT
Figure 2
34
ED
MA NU
SC
RI P
T
ACCEPTED MANUSCRIPT
AC
CE
PT
Figure 3
35
ED
MA NU
SC
RI P
T
ACCEPTED MANUSCRIPT
AC
CE
PT
Figure 4
36
ED
MA NU
SC
RI P
T
ACCEPTED MANUSCRIPT
AC
CE
PT
Figure 5
37
ED
MA NU
SC
RI P
T
ACCEPTED MANUSCRIPT
AC
CE
PT
Figure 6
38