- Email: [email protected]
Effect of Femoral Offset on Pain and Function After Total Hip Arthroplasty
The Journal of Arthroplasty Vol. 27 No. 10 2012
Effect of Femoral Offset on Pain and Function After Total Hip Arthroplasty Kevin A. Cassidy, MD, Manish S. Noticewala, MD, William Macaulay, MD, Jonathan H. Lee, MD, and Jeffrey A. Geller, MD
Abstract: The effects of altering patients’ femoral offset (FO) during total hip arthroplasty on postoperative pain and function have not been well described. This study compared clinical outcomes as assessed by the Short Form 12 Health Survey and Western Ontario and McMaster University Osteoarthritis Index between patients who had their FOs restored to varying degrees (compared to the contralateral normal hip [CL]). We retrospectively measured postoperative FOs on standard anteroposterior pelvis radiographs and compared to the CL. Patients were categorized into one of 3 groups: decreased offset (b − 5 mm compared to CL), normal offset (between − 5 and + 5 mm), and increased offset (N + 5 mm). The decreased offset group exhibited Western Ontario and McMaster University Osteoarthritis Index Physical Function scores that were less than those of the normal offset and increased offset groups (72.03, 82.23, and 79.51, respectively [P = .019]). In conclusion, reducing a patients’ native FO led to inferior functional outcome scores. Keywords: femoral offset, post-operative pain, post-operative function, total hip arthroplasty, native offset. © 2012 Elsevier Inc. All rights reserved.
Total hip arthroplasty (THA) has become a very effective way of surgically treating arthritic conditions of the hip. As metallurgy has become more advanced, surgeons have had increasing options of changing the modularity of the prosthetic designs to optimize leg length and femoral offset (FO) to best match the contralateral side [1]. Several methods have been described to measure the femoral offset on a standard anteroposterior (AP) pelvis radiograph, including measuring the perpendicular distance from the teardrop through the femoral head center of rotation to the axis of the femur, termed the hip offset by Dastane [2]. However, most authors measure the hip offset as the perpendicular distance from the femoral head center of rotation to the axis of the femur (Fig.). Femoral offset is increased when the stem is placed in varus, decreased when the stem is in valgus, increased by placing the neck more medial on the stem (an “extended offset” stem), and increased with a longer femoral neck. Because several factors, such as femoral anteversion and external rotation, affect the
From the Center for Hip and Knee Replacement (CHKR), New YorkPresbyterian Hospital at Columbia University, New York, New York. Submitted October 8, 2011; accepted May 3, 2012. The Conflict of Interest statement associated with this article can be found at http://dx.doi.org/10.1016/j.arth.2012.05.001. Reprint requests: Jeffrey A. Geller, MD, Department of Orthopedic Surgery, 622 West 168th Street, PH 1147, New York, NY 10032. © 2012 Elsevier Inc. All rights reserved. 0883-5403/2710-0021$36.00/0 http://dx.doi.org/10.1016/j.arth.2012.05.001
accurate measurement of offset on plain radiographs, several authors have advocated the use of computed tomography scans to more accurately measure offset [3-6]. Sariali reports that computed tomography evaluation found a mean FO of 42.2 mm, which is 2.2 mm greater than previous reports based on plain films and more accurately measures FO when compared to cadaveric measurements [6,7]. As the modularity of implants has increased, thus allowing surgeons a greater variety of offset choices, several studies have analyzed the correlation of offset with abductor strength, range of motion, and wear rate. Many studies have shown that increasing FO has been correlated with increasing abductor strength [8-12]. Along with abductor strength, range of motion is also optimized with increased offset [14]. Although some studies have shown that increased offset affects only range of motion in abduction, others have shown increased offset correlated with increased range of motion in flexion and internal rotation as well by delaying the affect of osseous impingement of the greater trochanter on the anterior acetabulum [12,15]. These range of motion studies have been confirmed by computer models as well [16,17]. The advantages with an increased offset are not limited to strength and range of motion. Sakalkale et al performed staged bilateral hip arthroplasties in 17 patients with the only difference between the 2 implants being the use of an extended offset stem on one side and a standard offset stem on the other side. Increasing the offset resulted in a 50%
1863
1864 The Journal of Arthroplasty Vol. 27 No. 10 December 2012 decrease in both linear and volumetric wear rate [18]. This trend has been shown to hold true in a study by Little et al, although their results were not statistically significant because the study was underpowered [19]. Although much has been written regarding the effect of FO on strength and range of motion, there are little data on pain and function and its relationship to FO. Several studies have retrospectively looked at patients who have reported lateral trochanteric pain after THA and tried to identify causative factors; offset was not found to correlate with trochanteric pain [20,21]. Incavo et al retrospectively looked at all patients who underwent THA with a high offset femoral stem and found that 15% of these patients had either trochanteric or gluteal pain at a follow-up of 2 to 5 years [22]. However, this study did not have a control group to which these results could be compared. Therefore, our objective was to determine the effect of varying FO (compared to the normal contralateral side) had on pain and function at minimum 1-year postoperative follow-up after THA. We hypothesized that patients with decreased FO compared to the opposite side would have decreased function scores secondary to decreased abduction strength. We also hypothesized that increasing the FO compared to the contralateral side would not result in increasing pain scores based on the preliminary data from the aforementioned studies [20,21].
Methods
Fig. A, The femoral offset in the native hip is measured as a line from the center of the femoral head to a line representing the anatomic femoral axis (AB). The FO in THA is measured as a line from the center of the replaced head to the femoral axis (DE). The hip offset is measured as a line from the teardrop through the center of the femoral head to the anatomic femoral axis (CE). Femoral offset was measured in this study. B, Placing the stem in valgus decreases femoral offset. C, Placing the stem in varus increases femoral offset.
After obtaining approval from our institutional review board, 249 patients were evaluated from our institution's THA registry as being eligible to participate in this investigation. Patients were excluded from the study if they did not complete a 1-year follow-up questionnaire, if postoperative radiographs were not available for analysis, if postoperative radiographs were available but deemed subpar for analysis, or if the patient had a contralateral hip fusion which made contralateral offset impossible to measure. Before their surgery, patients completed the 12-item Short-Form Health Survey (SF-12) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaires. Both questionnaires were mailed to patients’ homes 4 weeks before surgery dates and were considered valid for inclusion in this study only if postmark dates on return envelopes were before surgery dates. The SF-12 form is a validated health status questionnaire concerning physical function and mental health [23]. A Physical Component score and a Mental Component score are derived from this questionnaire. The WOMAC survey is another validated questionnaire that consists of 3 domains: joint-specific pain (5 items), stiffness (2 items), and physical function (17 items) [24]. Each item is scored using a 5-point Likert scale, and each domain score is transformed to range from 0 to 100. A higher score on SF-12 or WOMAC reflects a better
Effect of Femoral Offset on Pain and Function After Total Hip Arthroplasty Cassidy et al
condition (0–100, worst to best). Postoperatively, patients were urged to follow-up with surgeons at 4 weeks, 3 months, 1 year, and annually thereafter. At each follow-up visit, patients completed SF-12 and WOMAC questionnaires. Only patients with 1-year postoperative questionnaire data were included. Data collection and maintenance were performed using Patient Analysis and Tracking System (PATS 4.0) software (Axis Clinical Software, Portland, OR). All surgeries were performed by one of the 2 senior authors (WM, JAG). All hips were templated preoperatively with a conventional low AP radiograph which was used to determine both length and offset. Each surgery was performed via the posterolateral approach. Computer navigation was not performed during any of the surgeries. All measurements of the operated and contralateral offset were performed by one investigator (KAC) who was blinded to the SF-12 and WOMAC scores before the offsets were measured. All radiographs were conventional low AP pelvis films with the femurs internally rotated 15° to account for the 15° anteversion of the femur. All measurements were performed on Centricity Enterprise Web, GE Medical Systems Information Technologies. Femoral offset was measured with a perpendicular line from the center of the femoral head on both the replaced hip and the contralateral side to a line representing the anatomic axis of the femur. Image magnification was accounted for by first measuring the size of the replaced femoral head, since this value was known from the operative report, and calculating the magnification ratio, which averaged to 1.22. After all measurements were made, patients were grouped into one of 3 categories: decreased femoral offset, in which the calculated offset of the operated side was less than − 5 mm when compared to the opposite side; normal offset, in which the calculated offset of the operated side was between − 5 mm and 5 mm when compared to the opposite side; and increased offset, in which the calculated offset of the operated side was greater than 5 mm when compared to the opposite side. Statistical Analysis The minimal clinically important difference for the WOMAC scale has been suggested to range from 7.4 to 15 units [25-28]. To have an 80% chance of detecting a significant difference (at the 2-sided 5% level), a 10-point difference in mean WOMAC subscales, with a standard deviation of 18 units, a minimum of 160 patients with normal femoral offset, 31 patients with decreased offset, and 34 patients with increased femoral offset were required. Age, SF-12 Mental Component, SF-12 Physical Component, WOMAC Pain, WOMAC Stiffness, and WOMAC Physical Function scores were treated as continuous variables. When comparing continuous variables, normality was assessed with the Kolmogorov-
1865
Smirnov test and/or graphical analysis. If assumptions of normal distribution were satisfied, an analysis of variance test was performed followed by post hoc 2-tailed t tests, adjusting for variance appropriately. If data did not meet assumptions of normality, a Kruskal-Wallis test was performed followed by post-hoc Wilcoxon rank sum tests. When comparing categorical variables (sex, diagnosis, implant femoral head size, and type of offset stem), a χ 2 test was performed. For all tests, P b .05 was considered significant. When evaluating postoperative scores, we defined the minimal clinically important difference for the SF-12 Form as 3 units and for the WOMAC index as 10 units as suggested by others [25-29]. All statistical analyses were performed using R version 2.11.1 (The R Foundation for Statistical Computing).
Results Two hundred sixty-three patients had completed preoperative WOMAC and SF-12 questionnaires before undergoing a THA for end-stage hip arthritis and were eligible for the study. They had completed the same questionnaires at the 1-year follow-up visits, but 14 of these patients did not have adequate postoperative radiographs for the accurate measurement of FO and therefore, were excluded from the study, leaving a total of 249 patients. Of the patients meeting radiographic inclusion criteria, 31 were found to have an offset of less than 5 mm compared to the opposite side, 163 had a “normal” offset between − 5 mm and + 5 mm compared to the opposite side, and 55 had an increased offset. The average FO postoperatively was 42.1 mm compared to the contralateral side of 41.2 mm.
Table 1a. Baseline Characteristics Among FO Groups Variable Age Sex Male Female Diagnosis Osteoarthritis Inflammatory arthritis Developmental dysplasia of hip Avascular necrosis Posttraumatic arthritis Type of stem Standard offset Extended offset Reduced offset
dFO (n = 31)
nFO (n = 163)
iFO (n = 55)
63 ± 13
62 ± 13
63 ± 12
45.2 54.8
44.2 55.8
41.8 58.2
61.3 3.2 6.5
75.5 3.1 3.6
58.2 1.8 14.5
16.1 12.9
16.6 1.2
23.6 1.8
77.4 22.6 0
60.7 37.4 1.8
72.7 23.6 3.6
P-Value .78 .92
.01
.164
dFO, less than −5 mm compared to contralateral hip; nFO, between −5 and 5 mm compared to contralateral hip; iFO, greater than 5 mm compared to contralateral hip.
1866 The Journal of Arthroplasty Vol. 27 No. 10 December 2012 Table 1b. Relationship Between Head Size Among FO Head Size
dFO
nFO
iFO
b28 mm 28-32 mm N32 mm
4 19 8
15 111 37
6 39 10
Test: χ2 with Monte Carlo Simulation for correction of small cell counts. P = .8641.
Table 1a shows the average ages for the decreased, normal, and increased offset groups were 63, 62, and 63, respectively (P = .78). There were no significant differences among sex between the 3 groups with the percentage of men being 45.2%, 44.2%, and 41.8% (P = .92). There was a significant difference in diagnosis among the three groups, with osteoarthritis comprising 61.3% of patients in the decreased offset, 75.5% in the normal offset, and 58.2% in the increased offset groups (P = .01). Further analysis of the diagnoses shows a higher preponderance of posttraumatic arthritis comprising 12.9% of the decreased offset group as compared to 1.2% in the normal offset and 1.8% in the increased offset. Likewise, a larger percentage of patients with hip dysplasia were in the increased offset group (14.5%) compared with 6.5% in the decreased offset and 3.6% in the normal offset. Inflammatory arthritis comprised 3.2% of patients in the decreased FO, 3.1% in normal FO, and 1.8% in increased FO. Avascular necrosis of the femoral head represented 16.1% of the decreased FO, 16.6% of the normal FO, and 23.6% of the increased FO diagnoses. The type of stem used (standard offset, extended offset, and reduced offset) was not found to be significantly different but trended toward more extended offset stems used in the normal offset group (P = .164). The percentages of standard offset stems used in the decreased, normal, and increased FO groups were 77.4%, 60.7%, and 72.7%, while the percentages of extended offset stems used in each group was 22.6%, 37.4%, and 23.6%, respectively. Reduced offset stems were less commonly used, representing 0%, 1.8%, and 3.6%, respectively. Head size, demonstrated in Table 1b, was analyzed with χ 2 test with Monte Carlo Simulation for correction of small cell counts. Head size was defined as small (b28 mm), medium (28-32 mm) and large (N32
mm). No significant difference was found between head size and offset (P = .86). Table 2 shows that preoperative SF-12 Physical Component scores were similar among the 3 groups, with the decreased FO, normal FO, and increased FO group averages being 27.82, 29.71, and 29.86 (P = .758). Likewise, preoperative SF-12 Mental Component scores were similar among the three groups, with the averages being 46.99, 50.63, and 50.77, respectively (P = .22). The preoperative WOMAC Pain scores were found to be significantly different, with their averages being 29.68, 43.39, and 43.63, respectively (P = .0048). However, the preoperative WOMAC Stiffness and Physical Function scores were not found to be significantly different. The preoperative WOMAC Stiffness score averages were 41.53, 44.56, and 47.73, respectively (P = .4456); the preoperative WOMAC Physical Function score averages were 38.97, 46.6, and 48.02 (P = .1106). Table 3 summarizes postoperative SF-12 and WOMAC outcome scores. There was no statistically significant difference among the three groups in terms of postoperative SF-12 Physical Component scores, with averages being 43.3, 46.99, and 44.39 (P = .2161) among the decreased FO, normal FO, and increased FO groups, respectively. Likewise, there was no difference in postoperative SF-12 Mental Component scores, with averages being 52.11, 54.14, and 54.5 (P = .382). In terms of WOMAC scores, the averages for the postoperative WOMAC Pain scores were 86.5, 91.69, and 92.87, respectively (P = .4163), and the averages of the WOMAC Stiffness scores were 69.35, 75.39, and 68.29, respectively (P = .1419). However, there was a statistically significant difference in terms of postoperative WOMAC Physical Function scores, with averages being 72.03, 83.23, and 79.51 (P = .0192).
Discussion Many studies have investigated the relationship of femoral offset with strength and range of motion [8-17]. In general, maximizing offset during THA to match that of the normal, contralateral side, has been shown to improve abductor strength by increasing the lever arm and decreasing joint reactive forces. This technique is beneficial in helping to reduce the incidence of Trendelenberg gait after THA. Likewise, range of motion is also improved with maximizing offset by decreasing bony impingement of the greater trochanter on the
Table 2. Preoperative SF-12 and WOMAC Clinical Scores Variable
dFO (n = 31)
nFO (n = 163)
iFO (n = 55)
P-Value
SF-12 Physical Component SF-12 Mental Component WOMAC Pain WOMAC Stiffness WOMAC Physical Function
27.82 ± 46.99 ± 29.68 ± 41.53 ± 38.97 ±
29.71 ± 7.86 50.63 ± 11.27 43.39 ± 24.53 44.56 ± 26.09 46.6 ± 21.15
29.86 ± 8.84 50.77 ± 10.68 43.63 ± 20.56 47.73 ± 23.58 48.02 ± 18.99
.758 .22 .0048 .4456 .1106
6.04 11.04 17.98 28.21 18.29
Effect of Femoral Offset on Pain and Function After Total Hip Arthroplasty Cassidy et al
1867
Table 3. Postoperative SF-12 and WOMAC Clinical Scores Variable
dFO (n = 31)
nFO (n = 163)
iFO (n = 55)
P-Value
SF-12 Physical Component SF-12 Mental Component WOMAC Pain WOMAC Stiffness WOMAC Physical Function
43.3 ± 11.45 52.11 ± 9.22 86.5 ± 22.02 69.35 ± 26.19 72.03 ± 24.67
46.99 ± 9.73 54.14 ± 8.38 91.69 ± 14.77 75.39 ± 23.14 83.23 ± 18.64
44.39 ± 11.37 54.5 ± 7.86 92.87 ± 12.87 68.29 ± 26.34 79.51 ± 20.40
.2161 .382 .4163 .1419 .0192
acetabulum during internal rotation, external rotation, flexion, and abduction. Although increased FO has been shown to be beneficial in terms of strength, range of motion, and wear rate, very few studies have investigated FO and its relationship to postoperative pain and function. Incavo et al reported a 15% incidence of lateral trochanteric and gluteal pain in patients whom he had implanted a high offset femoral stem but did not have a control group for comparison [22]. Another study investigated patients with lateral trochanteric pain after THA and found that surgical approach (lateral vs posterior) was significantly associated with lateral trochanteric pain. However, offset was not significantly associated with pain [20]. Although increased offset maximizes strength, range of motion, and attenuates polyethylene wear rate, it is not understood the cost, such as increased lateral trochanteric pain from increasing tension on the lateral tissues, with which increased femoral offset comes. Among the three groups in this study, there was no statistical difference in age, sex, or femoral head size. There was no statistical difference in type of stem used (P = .164) with a trend toward more patients in the normal FO group having an extended offset stem (37.4% extended offset vs 22.6% in the decreased offset group and 23.6% in the increased offset group). This result shows use of the extended offset stem more often than not helped to recreate normal anatomy as opposed to increasing the offset compared to the contralateral side. Furthermore, most patients who received a reduced offset stem were in the increased offset group (3.6% versus 1.8% in the normal offset and 0% in the decreased offset). This finding demonstrates that this stem is being appropriately used in patients that already have an increased offset to help normalize the FO to match the contralateral, non-diseased side. No patients in the decreased offset group received a reduced offset stem which shows that this factor did not contribute to patients having a reduced postoperative FO. A problem that arises from these data, however, is that 22.6% of the patients in the decreased offset group still had a decreased offset despite the use of an extended offset stem. In all cases, we chose an appropriately offset stem based on preoperative templating. If no stem fully re-established offset, we used a stem that came as close as possible, including stems with modular/exchangeable necks. After trialing our components, we would not do anything to augment our offset if we felt the implant was
stable through a full range of motion. If we felt the stability was compromised, we would use an extended offset liner to further augment the offset; however this situation was not encountered in this group of patients. In general, when components are trialed and we feel that stability could be improved, we prefer to increase the offset as opposed to alter the length so as to not create a leg length discrepancy. Although type of offset stem used was not significantly different among the groups, preoperative diagnosis was (P = .01). A diagnosis of osteoarthritis was much more likely in the normal offset group (75.5%) as compared to the decreased (61.3%) and increased (58.2%) offset groups. On the other hand, a diagnosis of hip dysplasia was much more likely to occur in the increased offset group (14.5%) as oppose to the reduced offset (6.5%) and normal offset (3.6%) groups. This result is likely due to dysplastic hips having a decreased FO preoperatively, leading to the increased propensity for the necks to be in valgus as well as anteverted [30]. Replacing these hips using standard offset necks would greatly increase the FO compared to the preoperative FO. However, these hips had a higher propensity to have a reduced offset stem used to counteract this trend. Likewise, the diagnosis of posttraumatic arthritis was carried in 12.9% of the decreased offset group as opposed to 1.2% and 1.8% in the normal and increased offset group, respectively. This diagnosis may also be an independent risk factor worsening function scores though it was not analyzed in this study. Preoperatively, there was no difference between the three groups in terms of SF-12 Physical Component, SF-12 Mental Component, WOMAC Stiffness, and WOMAC Physical Function scores. However, preoperative WOMAC Pain scores were found to be significantly different with the decreased offset group (29.68) having more pain than the normal offset (43.39) and increased offset (43.63) groups. This may be because there were a higher percentage of patients who had posttraumatic arthritis (12.9%) as opposed to the other groups, where normal offset and increased offset groups had 1.2% and 1.8% respectively. Posttraumatic diagnoses stemmed from previous acetabular fractures, femoral neck fractures, and slipped capital femoral epiphysis. It is possible that these diagnoses lead to a lower pain score preoperatively. Postoperatively, at one-year follow-up, there was no difference between the three groups in terms of SF-12
1868 The Journal of Arthroplasty Vol. 27 No. 10 December 2012 Physical Component, SF-12 Mental Component, WOMAC Pain, and WOMAC Stiffness scores. These results confirm our hypothesis that an increased femoral offset does not correlate with increased pain which echoes the results shown from previous smaller studies [20,21]. Although there was no difference in postoperative pain scores, there was a significant difference in postoperative WOMAC Physical Function scores (P = .0192). Further analysis showed that this difference was due to the decreased scores in the decreased offset group; there was no statistical difference when directly comparing the increased offset and normal offset groups. The decrease in function is likely secondary to decreased abduction strength and decreased range of motion which is associated with decreased offset. However, these variables were not measured in this study and are only postulated as the reasons leading to the decreased functional scores. This study has shown that increasing femoral offset does not correlate with increased pain while preserving function. On the contrary, patients left with decreased femoral offset had decreased function, which is consistent with prior studies. Several newer implant designs have allowed for modularity of the neck to further optimize offset and anteversion. However, more longterm studies are needed to determine the longevity of these implants [31-33]. The increasing use of modular necks in THA has underscored the increasing importance of obtaining the correct FO in optimizing outcome. This study has several strengths. All calculations of FO were done digitally to allow for correction of magnification and also to most accurately measure FO from the center of the femoral head to the axis of the femur. Only two fellowship-trained hip surgeons were involved in the surgeries which limited variability in surgical technique. However, this may also be viewed as a weakness in the lack of variability. Another weakness is that there were multiple diagnoses included in this study, which may have acted as a confounding variable, especially when measuring preoperative WOMAC pain scores, with a higher percentage of decreased offset patients carrying a diagnosis of posttraumatic arthritis. However, the fact that we had multiple diagnoses included in this study helped us to identify which patients were more prone to have decreased offset (posttraumatic) vs. increased offset (dysplastic hips). This finding allows for better preoperative planning, in which a surgeon may be more likely to put an extended offset stem in a patient with posttraumatic arthritis and a reduced offset stem in a dysplastic hip. In conclusion, the goal of performing a THA is to not only to relieve pain and improve function but also to accurately reconstruct FO and leg length. Not fully reconstructing FO leads to decreased function at oneyear follow-up. On the contrary, having an increased femoral offset does not affect either postoperative pain
or function. This statement should be viewed cautiously, as the objective of any reconstruction is to normalize FO and leg length. However, an increased offset did not show a statistically significant decrease in functional outcomes in our investigation.
References 1. Bourne RB, Rorabeck CH. Soft tissue balancing: the hip. J Arthroplasty 2002;17:17. 2. Dastane M, Dorr LD, Tarwala R, et al. Hip offset in total hip arthroplasty: quantitative measurement with navigation. Clin Orthop Relat Res 2011;469:429. 3. Lecerf G, Fessy MH, Philippot R, et al. Femoral offset: anatomical concept, definition, assessment, implications for preoperative templating and hip arthroplasty. Orthop Traumatol Surg Res 2009;95:210. 4. Kjellberg M, Englund E, Sayed-Noor AS. A new radiographic method of measuring femoral offset. The Sundsvall method. Hip Int 2009;19:377. 5. Pasquier G, Ducharne G, Ali ES, et al. Total hip arthroplasty offset measurement: is C T scan the most accurate option? Orthop Traumatol Surg Res 2010;96:367. 6. Sariali E, Mouttet A, Pasquier G, et al. Three-dimensional hip anatomy in osteoarthritis. Analysis of the femoral offset. J Arthroplasty 2009;24:990. 7. Noble PC, Alexander JW, Lindahl LJ, et al. The anatomic basis of femoral component design. Clin Orthop Relat Res 1988;148. 8. Husby VS, Bjorgen S, Hoff J, et al. Unilateral vs. bilateral total hip arthroplasty—the influence of medial femoral head offset and effects on strength and aerobic endurance capacity. Hip Int 2010;20:204. 9. Yamaguchi T, Naito M, Asayama I, et al. Total hip arthroplasty: the relationship between posterolateral reconstruction, abductor muscle strength, and femoral offset. J Orthop Surg (Hong Kong) 2004;12:164. 10. Asayama I, Chamnongkich S, Simpson KJ, et al. Reconstructed hip joint position and abductor muscle strength after total hip arthroplasty. J Arthroplasty 2005;20:414. 11. Kiyama T, Naito M, Shinoda T, et al. Hip abductor strengths after total hip arthroplasty via the lateral and posterolateral approaches. J Arthroplasty 2010;25:76. 12. McGrory BJ, Morrey BF, Cahalan TD, et al. Effect of femoral offset on range of motion and abductor muscle strength after total hip arthroplasty. J Bone Joint Surg Br 1995;77:865. 13. Preininger B, Schmorl K, von Roth P, et al. A formula to predict patients' gluteus medius muscle volume from hip joint geometry. Man Ther 2011. 14. Malik A, Maheshwari A, Dorr LD. Impingement with total hip replacement. J Bone Joint Surg Am 2007;89:1832. 15. Matsushita A, Nakashima Y, Jingushi S, et al. Effects of the femoral offset and the head size on the safe range of motion in total hip arthroplasty. J Arthroplasty 2009;24: 646. 16. Patel AB, Wagle RR, Usrey MM, et al. Guidelines for implant placement to minimize impingement during activities of daily living after total hip arthroplasty. J Arthroplasty 2010;25:1275 e1.
Effect of Femoral Offset on Pain and Function After Total Hip Arthroplasty Cassidy et al 17. Kurtz WB, Ecker TM, Reichmann WM, et al. Factors affecting bony impingement in hip arthroplasty. J Arthroplasty 2010;25:624–34 e1-2. 18. Sakalkale DP, Sharkey PF, Eng K, et al. Effect of femoral component offset on polyethylene wear in total hip arthroplasty. Clin Orthop Relat Res 2001;125. 19. Little NJ, Busch CA, Gallagher JA, et al. Acetabular polyethylene wear and acetabular inclination and femoral offset. Clin Orthop Relat Res 2009;467:2895. 20. Iorio R, Healy WL, Warren PD, et al. Lateral trochanteric pain following primary total hip arthroplasty. J Arthroplasty 2006;21:233. 21. Sayed-Noor AS, Sjoden GO. Greater trochanteric pain after total hip arthroplasty: the incidence, clinical outcome and associated factors. Hip Int 2006;16:202. 22. Incavo SJ, Havener T, Benson E, et al. Efforts to improve cementless femoral stems in THR: 2- to 5-year follow-up of a high-offset femoral stem with distal stem modification (Secur-Fit Plus). J Arthroplasty 2004;19:61. 23. Ware Jr JE, Kosinski M, Keller SD. A 12-item short-form health survey: Construction of scales and preliminary tests of reliability and validity. Med Care 1996;34:220. 24. Bellamy N, Buchanan WW, Goldsmith CH, et al. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. J Rheumatol 1988;15: 1833. 25. Bellamy N, Kean WF, Buchanan WW, et al. Double blind randomized controlled trial of sodium meclofenamate (Meclomen) and diclofenac sodium (Voltaren): post
26.
27.
28.
29.
30.
31.
32.
33.
1869
validation reapplication of the WOMAC Osteoarthritis Index. J Rheumatol 1992;19:153. Quintana JM, Escobar A, Bilbao A, et al. Responsiveness and clinically important differences for the WOMAC and SF-36 after hip joint replacement. Osteoarthritis Cartilage 2005;13:1076. Mahomed NN, Davis AM, Hawker G, et al. Inpatient compared with home-based rehabilitation following primary unilateral total hip or knee replacement: a randomized controlled trial. J Bone Joint Surg Am 2008;90:1673. Ehrich EW, Davies GM, Watson DJ, et al. Minimal perceptible clinical improvement with the Western Ontario and McMaster Universities osteoarthritis index questionnaire and global assessments in patients with osteoarthritis. J Rheumatol 2000;27:2635. Shulman LM, Gruber-Baldini AL, Anderson KE, et al. The clinically important difference on the unified Parkinson's disease rating scale. Arch Neurol 2010;67:64. Tokuhara Y, Kadoya Y, Kim M, et al. Anterior knee pain after total hip arthroplasty in developmental dysplasia. J Arthroplasty 2010. Omlor GW, Ullrich H, Krahmer K, et al. A stature-specific concept for uncemented, primary total hip arthroplasty. Acta Orthop 2010;81:126. Sakai T, Sugano N, Nishii T, et al. Optimizing femoral anteversion and offset after total hip arthroplasty, using a modular femoral neck system: an experimental study. J Orthop Sci 2000;5:489. Traina F, De Fine M, Biondi F, et al. The influence of the centre of rotation on implant survival using a modular stem hip prosthesis. Int Orthop 2009;33:1513.
Effect of Femoral Offset on Pain and Function After Total Hip Arthroplasty Kevin A. Cassidy, MD, Manish S. Noticewala, MD, William Macaulay, MD, Jonathan H. Lee, MD, and Jeffrey A. Geller, MD
Abstract: The effects of altering patients’ femoral offset (FO) during total hip arthroplasty on postoperative pain and function have not been well described. This study compared clinical outcomes as assessed by the Short Form 12 Health Survey and Western Ontario and McMaster University Osteoarthritis Index between patients who had their FOs restored to varying degrees (compared to the contralateral normal hip [CL]). We retrospectively measured postoperative FOs on standard anteroposterior pelvis radiographs and compared to the CL. Patients were categorized into one of 3 groups: decreased offset (b − 5 mm compared to CL), normal offset (between − 5 and + 5 mm), and increased offset (N + 5 mm). The decreased offset group exhibited Western Ontario and McMaster University Osteoarthritis Index Physical Function scores that were less than those of the normal offset and increased offset groups (72.03, 82.23, and 79.51, respectively [P = .019]). In conclusion, reducing a patients’ native FO led to inferior functional outcome scores. Keywords: femoral offset, post-operative pain, post-operative function, total hip arthroplasty, native offset. © 2012 Elsevier Inc. All rights reserved.
Total hip arthroplasty (THA) has become a very effective way of surgically treating arthritic conditions of the hip. As metallurgy has become more advanced, surgeons have had increasing options of changing the modularity of the prosthetic designs to optimize leg length and femoral offset (FO) to best match the contralateral side [1]. Several methods have been described to measure the femoral offset on a standard anteroposterior (AP) pelvis radiograph, including measuring the perpendicular distance from the teardrop through the femoral head center of rotation to the axis of the femur, termed the hip offset by Dastane [2]. However, most authors measure the hip offset as the perpendicular distance from the femoral head center of rotation to the axis of the femur (Fig.). Femoral offset is increased when the stem is placed in varus, decreased when the stem is in valgus, increased by placing the neck more medial on the stem (an “extended offset” stem), and increased with a longer femoral neck. Because several factors, such as femoral anteversion and external rotation, affect the
From the Center for Hip and Knee Replacement (CHKR), New YorkPresbyterian Hospital at Columbia University, New York, New York. Submitted October 8, 2011; accepted May 3, 2012. The Conflict of Interest statement associated with this article can be found at http://dx.doi.org/10.1016/j.arth.2012.05.001. Reprint requests: Jeffrey A. Geller, MD, Department of Orthopedic Surgery, 622 West 168th Street, PH 1147, New York, NY 10032. © 2012 Elsevier Inc. All rights reserved. 0883-5403/2710-0021$36.00/0 http://dx.doi.org/10.1016/j.arth.2012.05.001
accurate measurement of offset on plain radiographs, several authors have advocated the use of computed tomography scans to more accurately measure offset [3-6]. Sariali reports that computed tomography evaluation found a mean FO of 42.2 mm, which is 2.2 mm greater than previous reports based on plain films and more accurately measures FO when compared to cadaveric measurements [6,7]. As the modularity of implants has increased, thus allowing surgeons a greater variety of offset choices, several studies have analyzed the correlation of offset with abductor strength, range of motion, and wear rate. Many studies have shown that increasing FO has been correlated with increasing abductor strength [8-12]. Along with abductor strength, range of motion is also optimized with increased offset [14]. Although some studies have shown that increased offset affects only range of motion in abduction, others have shown increased offset correlated with increased range of motion in flexion and internal rotation as well by delaying the affect of osseous impingement of the greater trochanter on the anterior acetabulum [12,15]. These range of motion studies have been confirmed by computer models as well [16,17]. The advantages with an increased offset are not limited to strength and range of motion. Sakalkale et al performed staged bilateral hip arthroplasties in 17 patients with the only difference between the 2 implants being the use of an extended offset stem on one side and a standard offset stem on the other side. Increasing the offset resulted in a 50%
1863
1864 The Journal of Arthroplasty Vol. 27 No. 10 December 2012 decrease in both linear and volumetric wear rate [18]. This trend has been shown to hold true in a study by Little et al, although their results were not statistically significant because the study was underpowered [19]. Although much has been written regarding the effect of FO on strength and range of motion, there are little data on pain and function and its relationship to FO. Several studies have retrospectively looked at patients who have reported lateral trochanteric pain after THA and tried to identify causative factors; offset was not found to correlate with trochanteric pain [20,21]. Incavo et al retrospectively looked at all patients who underwent THA with a high offset femoral stem and found that 15% of these patients had either trochanteric or gluteal pain at a follow-up of 2 to 5 years [22]. However, this study did not have a control group to which these results could be compared. Therefore, our objective was to determine the effect of varying FO (compared to the normal contralateral side) had on pain and function at minimum 1-year postoperative follow-up after THA. We hypothesized that patients with decreased FO compared to the opposite side would have decreased function scores secondary to decreased abduction strength. We also hypothesized that increasing the FO compared to the contralateral side would not result in increasing pain scores based on the preliminary data from the aforementioned studies [20,21].
Methods
Fig. A, The femoral offset in the native hip is measured as a line from the center of the femoral head to a line representing the anatomic femoral axis (AB). The FO in THA is measured as a line from the center of the replaced head to the femoral axis (DE). The hip offset is measured as a line from the teardrop through the center of the femoral head to the anatomic femoral axis (CE). Femoral offset was measured in this study. B, Placing the stem in valgus decreases femoral offset. C, Placing the stem in varus increases femoral offset.
After obtaining approval from our institutional review board, 249 patients were evaluated from our institution's THA registry as being eligible to participate in this investigation. Patients were excluded from the study if they did not complete a 1-year follow-up questionnaire, if postoperative radiographs were not available for analysis, if postoperative radiographs were available but deemed subpar for analysis, or if the patient had a contralateral hip fusion which made contralateral offset impossible to measure. Before their surgery, patients completed the 12-item Short-Form Health Survey (SF-12) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaires. Both questionnaires were mailed to patients’ homes 4 weeks before surgery dates and were considered valid for inclusion in this study only if postmark dates on return envelopes were before surgery dates. The SF-12 form is a validated health status questionnaire concerning physical function and mental health [23]. A Physical Component score and a Mental Component score are derived from this questionnaire. The WOMAC survey is another validated questionnaire that consists of 3 domains: joint-specific pain (5 items), stiffness (2 items), and physical function (17 items) [24]. Each item is scored using a 5-point Likert scale, and each domain score is transformed to range from 0 to 100. A higher score on SF-12 or WOMAC reflects a better
Effect of Femoral Offset on Pain and Function After Total Hip Arthroplasty Cassidy et al
condition (0–100, worst to best). Postoperatively, patients were urged to follow-up with surgeons at 4 weeks, 3 months, 1 year, and annually thereafter. At each follow-up visit, patients completed SF-12 and WOMAC questionnaires. Only patients with 1-year postoperative questionnaire data were included. Data collection and maintenance were performed using Patient Analysis and Tracking System (PATS 4.0) software (Axis Clinical Software, Portland, OR). All surgeries were performed by one of the 2 senior authors (WM, JAG). All hips were templated preoperatively with a conventional low AP radiograph which was used to determine both length and offset. Each surgery was performed via the posterolateral approach. Computer navigation was not performed during any of the surgeries. All measurements of the operated and contralateral offset were performed by one investigator (KAC) who was blinded to the SF-12 and WOMAC scores before the offsets were measured. All radiographs were conventional low AP pelvis films with the femurs internally rotated 15° to account for the 15° anteversion of the femur. All measurements were performed on Centricity Enterprise Web, GE Medical Systems Information Technologies. Femoral offset was measured with a perpendicular line from the center of the femoral head on both the replaced hip and the contralateral side to a line representing the anatomic axis of the femur. Image magnification was accounted for by first measuring the size of the replaced femoral head, since this value was known from the operative report, and calculating the magnification ratio, which averaged to 1.22. After all measurements were made, patients were grouped into one of 3 categories: decreased femoral offset, in which the calculated offset of the operated side was less than − 5 mm when compared to the opposite side; normal offset, in which the calculated offset of the operated side was between − 5 mm and 5 mm when compared to the opposite side; and increased offset, in which the calculated offset of the operated side was greater than 5 mm when compared to the opposite side. Statistical Analysis The minimal clinically important difference for the WOMAC scale has been suggested to range from 7.4 to 15 units [25-28]. To have an 80% chance of detecting a significant difference (at the 2-sided 5% level), a 10-point difference in mean WOMAC subscales, with a standard deviation of 18 units, a minimum of 160 patients with normal femoral offset, 31 patients with decreased offset, and 34 patients with increased femoral offset were required. Age, SF-12 Mental Component, SF-12 Physical Component, WOMAC Pain, WOMAC Stiffness, and WOMAC Physical Function scores were treated as continuous variables. When comparing continuous variables, normality was assessed with the Kolmogorov-
1865
Smirnov test and/or graphical analysis. If assumptions of normal distribution were satisfied, an analysis of variance test was performed followed by post hoc 2-tailed t tests, adjusting for variance appropriately. If data did not meet assumptions of normality, a Kruskal-Wallis test was performed followed by post-hoc Wilcoxon rank sum tests. When comparing categorical variables (sex, diagnosis, implant femoral head size, and type of offset stem), a χ 2 test was performed. For all tests, P b .05 was considered significant. When evaluating postoperative scores, we defined the minimal clinically important difference for the SF-12 Form as 3 units and for the WOMAC index as 10 units as suggested by others [25-29]. All statistical analyses were performed using R version 2.11.1 (The R Foundation for Statistical Computing).
Results Two hundred sixty-three patients had completed preoperative WOMAC and SF-12 questionnaires before undergoing a THA for end-stage hip arthritis and were eligible for the study. They had completed the same questionnaires at the 1-year follow-up visits, but 14 of these patients did not have adequate postoperative radiographs for the accurate measurement of FO and therefore, were excluded from the study, leaving a total of 249 patients. Of the patients meeting radiographic inclusion criteria, 31 were found to have an offset of less than 5 mm compared to the opposite side, 163 had a “normal” offset between − 5 mm and + 5 mm compared to the opposite side, and 55 had an increased offset. The average FO postoperatively was 42.1 mm compared to the contralateral side of 41.2 mm.
Table 1a. Baseline Characteristics Among FO Groups Variable Age Sex Male Female Diagnosis Osteoarthritis Inflammatory arthritis Developmental dysplasia of hip Avascular necrosis Posttraumatic arthritis Type of stem Standard offset Extended offset Reduced offset
dFO (n = 31)
nFO (n = 163)
iFO (n = 55)
63 ± 13
62 ± 13
63 ± 12
45.2 54.8
44.2 55.8
41.8 58.2
61.3 3.2 6.5
75.5 3.1 3.6
58.2 1.8 14.5
16.1 12.9
16.6 1.2
23.6 1.8
77.4 22.6 0
60.7 37.4 1.8
72.7 23.6 3.6
P-Value .78 .92
.01
.164
dFO, less than −5 mm compared to contralateral hip; nFO, between −5 and 5 mm compared to contralateral hip; iFO, greater than 5 mm compared to contralateral hip.
1866 The Journal of Arthroplasty Vol. 27 No. 10 December 2012 Table 1b. Relationship Between Head Size Among FO Head Size
dFO
nFO
iFO
b28 mm 28-32 mm N32 mm
4 19 8
15 111 37
6 39 10
Test: χ2 with Monte Carlo Simulation for correction of small cell counts. P = .8641.
Table 1a shows the average ages for the decreased, normal, and increased offset groups were 63, 62, and 63, respectively (P = .78). There were no significant differences among sex between the 3 groups with the percentage of men being 45.2%, 44.2%, and 41.8% (P = .92). There was a significant difference in diagnosis among the three groups, with osteoarthritis comprising 61.3% of patients in the decreased offset, 75.5% in the normal offset, and 58.2% in the increased offset groups (P = .01). Further analysis of the diagnoses shows a higher preponderance of posttraumatic arthritis comprising 12.9% of the decreased offset group as compared to 1.2% in the normal offset and 1.8% in the increased offset. Likewise, a larger percentage of patients with hip dysplasia were in the increased offset group (14.5%) compared with 6.5% in the decreased offset and 3.6% in the normal offset. Inflammatory arthritis comprised 3.2% of patients in the decreased FO, 3.1% in normal FO, and 1.8% in increased FO. Avascular necrosis of the femoral head represented 16.1% of the decreased FO, 16.6% of the normal FO, and 23.6% of the increased FO diagnoses. The type of stem used (standard offset, extended offset, and reduced offset) was not found to be significantly different but trended toward more extended offset stems used in the normal offset group (P = .164). The percentages of standard offset stems used in the decreased, normal, and increased FO groups were 77.4%, 60.7%, and 72.7%, while the percentages of extended offset stems used in each group was 22.6%, 37.4%, and 23.6%, respectively. Reduced offset stems were less commonly used, representing 0%, 1.8%, and 3.6%, respectively. Head size, demonstrated in Table 1b, was analyzed with χ 2 test with Monte Carlo Simulation for correction of small cell counts. Head size was defined as small (b28 mm), medium (28-32 mm) and large (N32
mm). No significant difference was found between head size and offset (P = .86). Table 2 shows that preoperative SF-12 Physical Component scores were similar among the 3 groups, with the decreased FO, normal FO, and increased FO group averages being 27.82, 29.71, and 29.86 (P = .758). Likewise, preoperative SF-12 Mental Component scores were similar among the three groups, with the averages being 46.99, 50.63, and 50.77, respectively (P = .22). The preoperative WOMAC Pain scores were found to be significantly different, with their averages being 29.68, 43.39, and 43.63, respectively (P = .0048). However, the preoperative WOMAC Stiffness and Physical Function scores were not found to be significantly different. The preoperative WOMAC Stiffness score averages were 41.53, 44.56, and 47.73, respectively (P = .4456); the preoperative WOMAC Physical Function score averages were 38.97, 46.6, and 48.02 (P = .1106). Table 3 summarizes postoperative SF-12 and WOMAC outcome scores. There was no statistically significant difference among the three groups in terms of postoperative SF-12 Physical Component scores, with averages being 43.3, 46.99, and 44.39 (P = .2161) among the decreased FO, normal FO, and increased FO groups, respectively. Likewise, there was no difference in postoperative SF-12 Mental Component scores, with averages being 52.11, 54.14, and 54.5 (P = .382). In terms of WOMAC scores, the averages for the postoperative WOMAC Pain scores were 86.5, 91.69, and 92.87, respectively (P = .4163), and the averages of the WOMAC Stiffness scores were 69.35, 75.39, and 68.29, respectively (P = .1419). However, there was a statistically significant difference in terms of postoperative WOMAC Physical Function scores, with averages being 72.03, 83.23, and 79.51 (P = .0192).
Discussion Many studies have investigated the relationship of femoral offset with strength and range of motion [8-17]. In general, maximizing offset during THA to match that of the normal, contralateral side, has been shown to improve abductor strength by increasing the lever arm and decreasing joint reactive forces. This technique is beneficial in helping to reduce the incidence of Trendelenberg gait after THA. Likewise, range of motion is also improved with maximizing offset by decreasing bony impingement of the greater trochanter on the
Table 2. Preoperative SF-12 and WOMAC Clinical Scores Variable
dFO (n = 31)
nFO (n = 163)
iFO (n = 55)
P-Value
SF-12 Physical Component SF-12 Mental Component WOMAC Pain WOMAC Stiffness WOMAC Physical Function
27.82 ± 46.99 ± 29.68 ± 41.53 ± 38.97 ±
29.71 ± 7.86 50.63 ± 11.27 43.39 ± 24.53 44.56 ± 26.09 46.6 ± 21.15
29.86 ± 8.84 50.77 ± 10.68 43.63 ± 20.56 47.73 ± 23.58 48.02 ± 18.99
.758 .22 .0048 .4456 .1106
6.04 11.04 17.98 28.21 18.29
Effect of Femoral Offset on Pain and Function After Total Hip Arthroplasty Cassidy et al
1867
Table 3. Postoperative SF-12 and WOMAC Clinical Scores Variable
dFO (n = 31)
nFO (n = 163)
iFO (n = 55)
P-Value
SF-12 Physical Component SF-12 Mental Component WOMAC Pain WOMAC Stiffness WOMAC Physical Function
43.3 ± 11.45 52.11 ± 9.22 86.5 ± 22.02 69.35 ± 26.19 72.03 ± 24.67
46.99 ± 9.73 54.14 ± 8.38 91.69 ± 14.77 75.39 ± 23.14 83.23 ± 18.64
44.39 ± 11.37 54.5 ± 7.86 92.87 ± 12.87 68.29 ± 26.34 79.51 ± 20.40
.2161 .382 .4163 .1419 .0192
acetabulum during internal rotation, external rotation, flexion, and abduction. Although increased FO has been shown to be beneficial in terms of strength, range of motion, and wear rate, very few studies have investigated FO and its relationship to postoperative pain and function. Incavo et al reported a 15% incidence of lateral trochanteric and gluteal pain in patients whom he had implanted a high offset femoral stem but did not have a control group for comparison [22]. Another study investigated patients with lateral trochanteric pain after THA and found that surgical approach (lateral vs posterior) was significantly associated with lateral trochanteric pain. However, offset was not significantly associated with pain [20]. Although increased offset maximizes strength, range of motion, and attenuates polyethylene wear rate, it is not understood the cost, such as increased lateral trochanteric pain from increasing tension on the lateral tissues, with which increased femoral offset comes. Among the three groups in this study, there was no statistical difference in age, sex, or femoral head size. There was no statistical difference in type of stem used (P = .164) with a trend toward more patients in the normal FO group having an extended offset stem (37.4% extended offset vs 22.6% in the decreased offset group and 23.6% in the increased offset group). This result shows use of the extended offset stem more often than not helped to recreate normal anatomy as opposed to increasing the offset compared to the contralateral side. Furthermore, most patients who received a reduced offset stem were in the increased offset group (3.6% versus 1.8% in the normal offset and 0% in the decreased offset). This finding demonstrates that this stem is being appropriately used in patients that already have an increased offset to help normalize the FO to match the contralateral, non-diseased side. No patients in the decreased offset group received a reduced offset stem which shows that this factor did not contribute to patients having a reduced postoperative FO. A problem that arises from these data, however, is that 22.6% of the patients in the decreased offset group still had a decreased offset despite the use of an extended offset stem. In all cases, we chose an appropriately offset stem based on preoperative templating. If no stem fully re-established offset, we used a stem that came as close as possible, including stems with modular/exchangeable necks. After trialing our components, we would not do anything to augment our offset if we felt the implant was
stable through a full range of motion. If we felt the stability was compromised, we would use an extended offset liner to further augment the offset; however this situation was not encountered in this group of patients. In general, when components are trialed and we feel that stability could be improved, we prefer to increase the offset as opposed to alter the length so as to not create a leg length discrepancy. Although type of offset stem used was not significantly different among the groups, preoperative diagnosis was (P = .01). A diagnosis of osteoarthritis was much more likely in the normal offset group (75.5%) as compared to the decreased (61.3%) and increased (58.2%) offset groups. On the other hand, a diagnosis of hip dysplasia was much more likely to occur in the increased offset group (14.5%) as oppose to the reduced offset (6.5%) and normal offset (3.6%) groups. This result is likely due to dysplastic hips having a decreased FO preoperatively, leading to the increased propensity for the necks to be in valgus as well as anteverted [30]. Replacing these hips using standard offset necks would greatly increase the FO compared to the preoperative FO. However, these hips had a higher propensity to have a reduced offset stem used to counteract this trend. Likewise, the diagnosis of posttraumatic arthritis was carried in 12.9% of the decreased offset group as opposed to 1.2% and 1.8% in the normal and increased offset group, respectively. This diagnosis may also be an independent risk factor worsening function scores though it was not analyzed in this study. Preoperatively, there was no difference between the three groups in terms of SF-12 Physical Component, SF-12 Mental Component, WOMAC Stiffness, and WOMAC Physical Function scores. However, preoperative WOMAC Pain scores were found to be significantly different with the decreased offset group (29.68) having more pain than the normal offset (43.39) and increased offset (43.63) groups. This may be because there were a higher percentage of patients who had posttraumatic arthritis (12.9%) as opposed to the other groups, where normal offset and increased offset groups had 1.2% and 1.8% respectively. Posttraumatic diagnoses stemmed from previous acetabular fractures, femoral neck fractures, and slipped capital femoral epiphysis. It is possible that these diagnoses lead to a lower pain score preoperatively. Postoperatively, at one-year follow-up, there was no difference between the three groups in terms of SF-12
1868 The Journal of Arthroplasty Vol. 27 No. 10 December 2012 Physical Component, SF-12 Mental Component, WOMAC Pain, and WOMAC Stiffness scores. These results confirm our hypothesis that an increased femoral offset does not correlate with increased pain which echoes the results shown from previous smaller studies [20,21]. Although there was no difference in postoperative pain scores, there was a significant difference in postoperative WOMAC Physical Function scores (P = .0192). Further analysis showed that this difference was due to the decreased scores in the decreased offset group; there was no statistical difference when directly comparing the increased offset and normal offset groups. The decrease in function is likely secondary to decreased abduction strength and decreased range of motion which is associated with decreased offset. However, these variables were not measured in this study and are only postulated as the reasons leading to the decreased functional scores. This study has shown that increasing femoral offset does not correlate with increased pain while preserving function. On the contrary, patients left with decreased femoral offset had decreased function, which is consistent with prior studies. Several newer implant designs have allowed for modularity of the neck to further optimize offset and anteversion. However, more longterm studies are needed to determine the longevity of these implants [31-33]. The increasing use of modular necks in THA has underscored the increasing importance of obtaining the correct FO in optimizing outcome. This study has several strengths. All calculations of FO were done digitally to allow for correction of magnification and also to most accurately measure FO from the center of the femoral head to the axis of the femur. Only two fellowship-trained hip surgeons were involved in the surgeries which limited variability in surgical technique. However, this may also be viewed as a weakness in the lack of variability. Another weakness is that there were multiple diagnoses included in this study, which may have acted as a confounding variable, especially when measuring preoperative WOMAC pain scores, with a higher percentage of decreased offset patients carrying a diagnosis of posttraumatic arthritis. However, the fact that we had multiple diagnoses included in this study helped us to identify which patients were more prone to have decreased offset (posttraumatic) vs. increased offset (dysplastic hips). This finding allows for better preoperative planning, in which a surgeon may be more likely to put an extended offset stem in a patient with posttraumatic arthritis and a reduced offset stem in a dysplastic hip. In conclusion, the goal of performing a THA is to not only to relieve pain and improve function but also to accurately reconstruct FO and leg length. Not fully reconstructing FO leads to decreased function at oneyear follow-up. On the contrary, having an increased femoral offset does not affect either postoperative pain
or function. This statement should be viewed cautiously, as the objective of any reconstruction is to normalize FO and leg length. However, an increased offset did not show a statistically significant decrease in functional outcomes in our investigation.
References 1. Bourne RB, Rorabeck CH. Soft tissue balancing: the hip. J Arthroplasty 2002;17:17. 2. Dastane M, Dorr LD, Tarwala R, et al. Hip offset in total hip arthroplasty: quantitative measurement with navigation. Clin Orthop Relat Res 2011;469:429. 3. Lecerf G, Fessy MH, Philippot R, et al. Femoral offset: anatomical concept, definition, assessment, implications for preoperative templating and hip arthroplasty. Orthop Traumatol Surg Res 2009;95:210. 4. Kjellberg M, Englund E, Sayed-Noor AS. A new radiographic method of measuring femoral offset. The Sundsvall method. Hip Int 2009;19:377. 5. Pasquier G, Ducharne G, Ali ES, et al. Total hip arthroplasty offset measurement: is C T scan the most accurate option? Orthop Traumatol Surg Res 2010;96:367. 6. Sariali E, Mouttet A, Pasquier G, et al. Three-dimensional hip anatomy in osteoarthritis. Analysis of the femoral offset. J Arthroplasty 2009;24:990. 7. Noble PC, Alexander JW, Lindahl LJ, et al. The anatomic basis of femoral component design. Clin Orthop Relat Res 1988;148. 8. Husby VS, Bjorgen S, Hoff J, et al. Unilateral vs. bilateral total hip arthroplasty—the influence of medial femoral head offset and effects on strength and aerobic endurance capacity. Hip Int 2010;20:204. 9. Yamaguchi T, Naito M, Asayama I, et al. Total hip arthroplasty: the relationship between posterolateral reconstruction, abductor muscle strength, and femoral offset. J Orthop Surg (Hong Kong) 2004;12:164. 10. Asayama I, Chamnongkich S, Simpson KJ, et al. Reconstructed hip joint position and abductor muscle strength after total hip arthroplasty. J Arthroplasty 2005;20:414. 11. Kiyama T, Naito M, Shinoda T, et al. Hip abductor strengths after total hip arthroplasty via the lateral and posterolateral approaches. J Arthroplasty 2010;25:76. 12. McGrory BJ, Morrey BF, Cahalan TD, et al. Effect of femoral offset on range of motion and abductor muscle strength after total hip arthroplasty. J Bone Joint Surg Br 1995;77:865. 13. Preininger B, Schmorl K, von Roth P, et al. A formula to predict patients' gluteus medius muscle volume from hip joint geometry. Man Ther 2011. 14. Malik A, Maheshwari A, Dorr LD. Impingement with total hip replacement. J Bone Joint Surg Am 2007;89:1832. 15. Matsushita A, Nakashima Y, Jingushi S, et al. Effects of the femoral offset and the head size on the safe range of motion in total hip arthroplasty. J Arthroplasty 2009;24: 646. 16. Patel AB, Wagle RR, Usrey MM, et al. Guidelines for implant placement to minimize impingement during activities of daily living after total hip arthroplasty. J Arthroplasty 2010;25:1275 e1.
Effect of Femoral Offset on Pain and Function After Total Hip Arthroplasty Cassidy et al 17. Kurtz WB, Ecker TM, Reichmann WM, et al. Factors affecting bony impingement in hip arthroplasty. J Arthroplasty 2010;25:624–34 e1-2. 18. Sakalkale DP, Sharkey PF, Eng K, et al. Effect of femoral component offset on polyethylene wear in total hip arthroplasty. Clin Orthop Relat Res 2001;125. 19. Little NJ, Busch CA, Gallagher JA, et al. Acetabular polyethylene wear and acetabular inclination and femoral offset. Clin Orthop Relat Res 2009;467:2895. 20. Iorio R, Healy WL, Warren PD, et al. Lateral trochanteric pain following primary total hip arthroplasty. J Arthroplasty 2006;21:233. 21. Sayed-Noor AS, Sjoden GO. Greater trochanteric pain after total hip arthroplasty: the incidence, clinical outcome and associated factors. Hip Int 2006;16:202. 22. Incavo SJ, Havener T, Benson E, et al. Efforts to improve cementless femoral stems in THR: 2- to 5-year follow-up of a high-offset femoral stem with distal stem modification (Secur-Fit Plus). J Arthroplasty 2004;19:61. 23. Ware Jr JE, Kosinski M, Keller SD. A 12-item short-form health survey: Construction of scales and preliminary tests of reliability and validity. Med Care 1996;34:220. 24. Bellamy N, Buchanan WW, Goldsmith CH, et al. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. J Rheumatol 1988;15: 1833. 25. Bellamy N, Kean WF, Buchanan WW, et al. Double blind randomized controlled trial of sodium meclofenamate (Meclomen) and diclofenac sodium (Voltaren): post
26.
27.
28.
29.
30.
31.
32.
33.
1869
validation reapplication of the WOMAC Osteoarthritis Index. J Rheumatol 1992;19:153. Quintana JM, Escobar A, Bilbao A, et al. Responsiveness and clinically important differences for the WOMAC and SF-36 after hip joint replacement. Osteoarthritis Cartilage 2005;13:1076. Mahomed NN, Davis AM, Hawker G, et al. Inpatient compared with home-based rehabilitation following primary unilateral total hip or knee replacement: a randomized controlled trial. J Bone Joint Surg Am 2008;90:1673. Ehrich EW, Davies GM, Watson DJ, et al. Minimal perceptible clinical improvement with the Western Ontario and McMaster Universities osteoarthritis index questionnaire and global assessments in patients with osteoarthritis. J Rheumatol 2000;27:2635. Shulman LM, Gruber-Baldini AL, Anderson KE, et al. The clinically important difference on the unified Parkinson's disease rating scale. Arch Neurol 2010;67:64. Tokuhara Y, Kadoya Y, Kim M, et al. Anterior knee pain after total hip arthroplasty in developmental dysplasia. J Arthroplasty 2010. Omlor GW, Ullrich H, Krahmer K, et al. A stature-specific concept for uncemented, primary total hip arthroplasty. Acta Orthop 2010;81:126. Sakai T, Sugano N, Nishii T, et al. Optimizing femoral anteversion and offset after total hip arthroplasty, using a modular femoral neck system: an experimental study. J Orthop Sci 2000;5:489. Traina F, De Fine M, Biondi F, et al. The influence of the centre of rotation on implant survival using a modular stem hip prosthesis. Int Orthop 2009;33:1513.