- Email: [email protected]
Dislocation After Total Hip Arthroplasty Among Patients With Developmental Dysplasia of the Hip
The Journal of Arthroplasty Vol. 27 No. 5 2012
Dislocation After Total Hip Arthroplasty Among Patients With Developmental Dysplasia of the Hip Liao Wang, MD,*z Robert T. Trousdale, MD,y Songtao Ai, MD,* Kai-Nan An, PhD,z Kerong Dai, MD,* and Bernard F. Morrey, MDy
Abstract: The precise relationship between developmental dysplasia of the hip and dislocation among patients after total hip arthroplasty has not been well clarified. A total of 820 patients with developmental dysplasia of the hip who underwent total hip arthroplasty from January 2000 to December 2009 were categorized according to Crowe classification, and postoperative dislocation rates were analyzed among subgroups. The overall dislocation rate was 2.93%. No statistically significant differences in dislocation rates were observed between these with and without subtrochanteric osteotomy. Femoral head size was the only factor with significant difference between the dislocated and stable groups, especially when femoral head diameter increased from 28 to 32 mm. Of all dislocations, 69.6% were anterior dislocation, and the degree of cup anteversion and combined anteversion of anterior dislocators was higher than that of the posterior dislocators (P = .0082 and P = .001). Keywords: dislocation, cup anteversion, combined anteversion, developmental dysplasia of the hip, total hip arthroplasty. © 2012 Elsevier Inc. All rights reserved.
Patients with developmental dysplasia of the hip (DDH) have a wide spectrum of deformities, ranging from a hip that is mildly dysplastic to one that is severely dysplastic or dislocated. It has been divided into 4 subgroups by Crowe based on the migration magnitude of femoral head relative to interteardrop line [1]. When a total hip arthroplasty (THA) is performed in a DDH patient, it is commonly believed that the more severe the deformity, the greater the technical difficulty is during surgery [2,3]. Minoda et al [4] reported a higher risk of positioning a cup outside the safe range in patients with Crowe IV DDH. However, they could neither find a significant relationship between the risk of dislocation
From the *Department of Orthopaedics, Shanghai Ninth People's Hospital, Shanghai Key Laboratory of Orthopaedic Implant, Shanghai Jiao Tong University School of Medicine and Engineering Research Center of Digital Medicine, Ministry of Education, Shanghai, PR China; yDepartment of Orthopedic Surgery, Mayo Clinic,, Rochester, Minnesota; and zBiomechanics Laboratory, Mayo Clinic, Rochester, Minnesota. Submitted October 14, 2010; accepted August 26, 2011. The Conflict of Interest statement associated with this article can be found at doi:10.1016/j.arth.2011.08.021. One or more of the authors (RTT) receives royalties from DePuy, Wright Medical, and the Orthopedic Department. Reprint requests: Robert T. Trousdale, MD, Department of Orthopedic Surgery, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905. © 2012 Elsevier Inc. All rights reserved. 0883-5403/2705-0017$36.00/0 doi:10.1016/j.arth.2011.08.021
and the cup orientation nor give detailed description about relevant dislocation rates among subgroups [4,5]. The precise effect of the severity of the preoperative deformity on the postoperative dislocation among DDH patients has not been clarified yet. To our knowledge, there is no large sample follow-up study to date focusing on the dislocation rate among DDH patients after THA and, more importantly, the dislocation rate according to the severity of the hip dysplasia. In this follow-up study, we tried to clarify the following questions: Is a higher Crowe classification indicative of a higher dislocation rate? What are the predisposing factors of postoperative dislocation among DDH patients? Among the dislocated cases, is there any special pattern?
Materials and Methods Patient Selection The study protocol was approved by the local institutional review board, and informed consent was obtained from all patients. A retrospective review of our institutional total joint registry identified 886 hips with a diagnosis of osteoarthritis secondary to DDH that were treated with THA using cementless cup from January 2000 to December 2009 [6]. All the preoperative anteroposterior (AP) pelvic radiographs were reviewed to subgroup the patients according to Crowe classification [1]. We were unable to determine the Crowe classification among 62 patients as a result of unavailable preoperative
764
Dislocation After THA Among Patients With DDH Wang et al
radiographs, and these patients were excluded. Four patients with a minimal invasive approach were also excluded because this approach was rarely used among our target patients. Among these excluded, there were no dislocations. These exclusions left us with 820 DDH patients. Surgical Technique In our institute, to avoid the malpositioning of implant, the patient was carefully positioned on the operating table, the trunk was aligned with the leg, and the position of the shoulder was marked with a clip on the surgical drape. The identity of the degree of anteversion was predicated on the images as well as the intraoperative finding. Orientation of the cup should be at 15° of anteversion. A cup holder inserted the cup at 15° referable to the shoulder landmark. If at this position there was inadequate anterior wall coverage and excessive posterior wall coverage, this revealed an excessive amount of acetabular anteversion. For the stem, the neck was assessed referable to the flexion plane of the knee. We matched the anteversion of both cup and stem. Because the stem was more difficult to adjust, we therefore did not secure the cup until the femoral stem preparation was complete. Excessive inherent anteversion was reduced at the femur by resecting greater amounts of the femoral neck. We anteverted the cup component less if the femoral component had more anteversion.
765
Follow-Up Routine Patients were routinely evaluated in person, by telephone, or by a questionnaire at 3 months, 6 months, 1 year, 2 years, and 5 years after the index surgery. The average follow-up of these patients was 3 years, with a minimum follow-up of 6 months. At each time point, the patients were asked specifically whether a dislocation had occurred. A dislocation in our study was defined as a dislocated hip requiring a reduction by a physician. Patients with subluxation were not included in our study. Clinical and Radiographic Evaluation Among these 820 patients, 94 received a cemented stem, which version can be controlled. The rest of the patients were implanted with uncemented stem, with 106 patients being implanted with S-ROM stem (Depuy, Warsaw, Ind). None of these patients who received S-ROM stem had a postoperative dislocation. They were divided into stable (n = 796) and dislocated groups (n = 24) depending on whether a postoperative dislocation occurred. Related risk factors were recorded, and their distributions were compared between the stable and dislocated groups to determine their effects on postoperative dislocation among DDH patients, including demographic factors, Crowe classification, surgical approach, diameter of femoral head, and the difference between cup and femoral head diameter, and others. (Table 1). For these who experienced a postoperative dislocation, the direction of dislocation was
Table 1. The Distribution of Risk Factors Between Dislocated and Stable Groups Parameters Age at operation (y) Sex Male Female Side Left Right Crowe classification Crowe I, II, and III Crowe IV Operative approach Anterior Posterior Lateral Femoral head size (mm) 22 28 ≥32 Cup size–head size (mm) ≥34 b34 Previous hip osteotomy Yes No Periacetabular osteotomy Yes No
Overall (n = 820)
Stable Cases (n = 796)
Dislocated Cases (n = 24)
49.79 ± 13.08 (12-86 )
49.75 ± 13.13 (12-86)
51.13 ± 11.71 (35-75)
209 (25.5%) 611 (74.5%)
203 (97.05%) 593 (97.13%)
6 (2.95%) 18 (2.87%)
396 (48.29%) 424 (51.71%)
385 (97.22%) 411 (96.93%)
11 (2.78%) 13 (3.07%)
774 (94.39%) 46 (5.61%)
752 (97.16%) 44 (95.65%)
22 (2.84%) 2 (4.35%)
236 (28.78%) 536 (65.37%) 48 (5.85%)
231 (97.88%) 520 (93.75%) 45 (97.01%)
5 (2.12%) 16 (6.25%) 3 (2.99%)
35 (4.32%) 355 (43.29%) 430 (52.44%)
33 (94.29%) 338 (95.21%) 425 (98.84%)
2 (5.71%) 17 (4.79%) 5 (1.16%)
15 (1.83%) 805 (98.17%)
14 (93.33%) 782 (97.14%)
1 (6.67%) 23 (2.86%)
179 (21.83%) 641 (78.17%)
177 (98.88%) 619 (96.57%)
2 (1.12%) 22 (3.43%)
12 (1.46%) 808 (98.54%)
12 (100%) 784 (97.03%)
0 (0%) 24 (2.97%)
P .61 1.00
.84
.395
.30
.0067
.36
.98
1.00
766 The Journal of Arthroplasty Vol. 27 No. 5 May 2012 identified by reviewing clinical records or confirmed by reviewing cross-table lateral radiographs. A standardized radiographic protocol was applied for the dislocated patients, including the following measurements performed on preoperative AP pelvic radiograph, postoperative AP pelvic radiograph, and crosstable lateral radiograph. The radiographic measurement was done by an orthopedic research fellow (LW), who was not involved in the operations. The ischial spine sign and crossover sign were observed on preoperative AP pelvic radiograph to roughly assess the orientation of bony acetabulum (anteverted or retroverted). The postoperative AP pelvic radiographs with a symmetrical pelvic posture were selected for radiographic evaluation. The reference landmarks were marked on these symmetrical AP pelvic radiographs, including anatomical axis of the femur (F, F'), transtrochanter lines (T and T'), transischial line (H1), transteardrop line (H2), and its perpendicular line (I, I'), and others. Lines I and I' were the vertical lines running through the crossing point of teardrop and Kohler line. Points O and C were the centers of rotation (COR) of the reconstructed hip and the contralateral hip. OA and CA' were the horizontal distance of COR. OB and CB' were the vertical distance of COR. OD and CD' were the femoral offset. Hip offset was represented by the combination of femoral offset and the horizontal distance of COR. Hip length referred to the vertical distance between transteardrop line and line running through less trochanter (Fig. 1). The marked radiographs were rotated using adobe Photoshop cs3 extended version 10.0.1(Adobe Systems Inc, San Jose, Calif) making transteardrop line parallel with
the horizontal line. The rotated AP pelvic radiographs were loaded into EBRA cup software [7] (Ein-BildRoentgen-Analyse, release 2007; Department of Geometry, University of Innsbruck, Innsbruck, Austria). EBRA allows the measurement of radiographic cup anteversion and inclination with an accuracy of 2° [8]; helps in determining the COR; and measures vertical and horizontal distance of COR, femoral offset, hip offset, and hip length [9,10]. For comparison, above radiographic parameters were measured on both the reconstructed and contralateral hips, if the contralateral hip was approximately normal. Radiographic measurement was considered abnormal if there was more than 10 mm difference between the reconstructed and contralateral hips. Cross-table lateral radiographs were reviewed to assess the stem anteversion [11] (Fig. 2), then, the combined anteversion could be calculated. Treatment When a dislocation was encountered, closed or open reduction was generally performed, and this would be followed by postreduction abduction bracing for 6 weeks. Should the hip remain stable, no further surgery would be performed. For those who developed recurrent dislocations, a revision surgery would then be contemplated and performed. Statistical Analysis Statistical analyses were performed using JMP 8.0 software (SAS Institute, Inc, Cary, NC). Quantitative variables were described by mean ± SD or frequency (percentage %). Two-sample t test, Fisher exact test, and Pearson χ 2 test were used to investigate the relationship
Fig. 1. A representative radiograph showed how the parameters were measured.
Dislocation After THA Among Patients With DDH Wang et al
767
Fig. 2. Stem anteversion was defined as the angle formed by the bottom of the radiographic plate representing the posterior plane of the condyles and the axis of the stem neck realizing leg rotation affects measurements.
between the postoperative dislocation and related risk factors. Two-sample t test was used to investigate the statistical difference between the anterior and posterior dislocators regarding cup anteversion, cup inclination, stem anteversion, and combined anteversion. Paired t test was used to compare the radiographic parameters between the reconstructed and contralateral hips. Any P value less than .05 was considered statistically significant.
Results One or more dislocations occurred in 24 (2.93%) of the 820 DDH hips. The dislocation rates among Crowe I, II, III, and IV groups were 3.04%, 2.52%, 1.59%, and 4.35%, respectively. Initially, we assumed that a higher Crowe classification might be the indicative of a higher dislocation rate. However, as a result of low incidence of dislocations among subgroups, Pearson χ 2 test was unable to be applied. Thus, we combined these without subtrochanteric osteotomy (Crowe I, II, and III) and compared them with those with subtrochanteric osteotomy (Crowe IV) using Fisher exact test. With such a big sample size and detailed grouping, we still could not find a statistically significant difference regarding dislocation rates between the 2 groups. Among all the risk factors, the diameter of femoral head was the only one with a statistically significant difference between the stable and dislocated groups (P = .0067). The dislocation rates were 5.71%, 4.79%, and 1.16% in patients with a femoral head diameter of 22, 28, and 32 mm above, respectively. Further stratifying our data, we found no significant difference regarding hip dislocation rate between these using 22-mm femoral head and those using 28 mm (P = .52). However, compared with patients with a 28-mm femoral head, patients with a 32-mm and above femoral head had a significantly lower dislocation rate (P = .002). Besides, we could not find any significant difference of dislocation rate between the 2 groups regarding other clinical risk factors (Table 1).
Of these dislocators, 69.6% dislocated anteriorly, and the rest of the patients dislocated posteriorly. By reviewing preoperative pelvis radiographs, 23 of 24 patients had a negative ischial spine sign, and 17 patients has a negative crossover sign. One of the patients had a questionable positive ischial spine sign, whereas the pelvis showed obvious rotation on the radiograph. On the other hand, the crossover sign was also difficult to be determined in this patient. The crossover sign in the other 6 patients was also difficult to be determined because of severe osteophyte presenting around acetabulum. The radiographic measurements of cup orientation were able to be performed in 23 dislocated patients, except the one without any available postoperative radiograph. Radiographic cup anteversion and combined anteversion of anterior dislocators were statistically higher compared with that of those posterior dislocators (Table 2). On a case-by-case basis, 10 patients, whose combined anteversion were higher than 45°, dislocated anteriorly. Actually, all the patients in our study, whose combined anteversion were bigger than 42°, dislocated anteriorly, and for those 4 patients, whose combined anteversion were less than 30°, dislocated posteriorly. Stem anteversion and radiographic cup inclination showed no significant difference between patients with an anterior dislocation and these with a posterior dislocation (Table 2). Eighteen patients have a nearly normal hip on the contralateral side. Compared with the contralateral hip joint, CORs of the reconstructed hips were medialized with a mean horizontal displacement of 4.3 mm and were superiorized with a mean vertical displacement of 3.52 mm. The femoral offset among the reconstructed hips was elongated with a mean magnitude of 5.59 mm. Overall, there was no significant difference between the reconstructed and contralateral hips regarding hip offset and hip length. None of these patients has more than 10 mm difference between the reconstructed and contralateral hips (Table 3).
768 The Journal of Arthroplasty Vol. 27 No. 5 May 2012 Table 2. Component Orientation in Anteriorly and Posteriorly Dislocated Groups Component Orientation, Mean ± SD (95% CI)
Anterior Dislocation (n = 16)
Posterior Dislocation (n = 7)
Cup anteversion Cup inclination Stem anteversion Combined anteversion
30.07 ± 44.13 ± 16.06 ± 46.14 ±
16.00 ± 43.45 ± 15.74 ± 31.75 ±
6.07 (25.93-34.22) 7.05 (40.37-47.88) 5.49 (13.14-18.99) 8.18 (41.78-50.50)
Most of the dislocated cases were treated in our hospital (20/24). The treatments and outcomes of the other 4 patients were also recorded based on the information from questionnaire. Overall, 62.5% of dislocated cases regained stability with open (n = 2) or close reduction (n = 15) combined with abduction brace for 6 weeks. All patients with recurrent dislocations regained stability after revision surgery (7/24).
Discussion Total hip arthroplasty in the treatment of patients with DDH is known to be more technically demanding [1,12]. Dislocation rate in DDH patients has been suspected to be higher because of limited bone stock and malformation of the acetabulum [13]. However, previous studies showed controversial results regarding the dislocation rates among DDH patients [14-18]. Developmental dysplasia of the hip, as a developmental disease, includes a wide spectrum of deformity. Thus, we performed this study with a large sample size and detailed grouping to further clarify the relationship between DDH subgroups and related dislocation rates and to describe and explain the special dislocation pattern. In this study, we did not find a statistically significant difference in dislocation rates between patients with and without subtrochanteric osteotomy. However, we did note that anterior dislocation was the most common pattern among DDH patients after THA. The safe zone of combined anteversion confirmed in our study for DDH patients was 30° to 45°. Another important finding was that larger head size tended to provide better stability among DDH patients, especially when the femoral head increased from 28 to 32 mm. Our study has a few limitations. First, although from 1 institution, the operations were in fact performed by many surgeons, which might brought some confusion in data analysis. Second, there were only 24 dislocations in our study, which might be a potential reason for not Table 3. Radiographic Comparison Between Reconstructed and Contralateral Hips Paired Differences 95% CI
Reconstructed vs Contralateral Hips (n = 18)
Mean (mm)
SD
Lower
Upper
P
Horizontal offset of COR Vertical offset of COR Femoral offset Hip offset Hip length
−4.30 3.52 5.59 1.29 3.15
4.17 4.87 4.00 6.37 7.27
−6.38 1.10 3.60 −1.88 −.47
−2.23 5.94 7.59 4.46 6.77
.000 .007 .000 .403 .084
CI indicates confidence interval.
11.43 (9.73-22.28) 6.26 (37.66-49.24) 10.40 (6.12-25.37) 7.33 (24.97-38.52)
P .0082 .4105 .941 .001
detecting statistical difference among subgroups. Although the dislocation after THA in DDH patients is an uncommon event, these 24 patients were identified from 820 DDH patients. Thus, we believe that the dislocation rate reported in current study should be representative enough to show the general situation of postoperative dislocation among DDH patients. Third, the stem anteversion was measured on a cross-table lateral radiograph, which could roughly assess the stem anteversion. Impingement is an important biomechanical factor leading to instability of prosthetic hip, which is influenced by component orientation, and other reconstructive parameters [19,20]. Di schino et al [21] identified DDH as a risk factor for anterior dislocation after THA, because of an excessive acetabular and femoral anteversion. In this study, we also observed that a dysplastic hip predisposed to inadvertent malpositioning of cup and femoral components in excessive anteversion because of specific malformation of DDH patients, hence accounting for the higher anterior dislocation rate in our series (69.6%). On a case-by-case basis, we noted that all these (n = 10) with a combined anteversion bigger than 45° dislocated anteriorly, whereas all those (n = 4) with a combined anteversion less than 30° dislocated posteriorly. We believe that it is critical that a surgeon should be aware of the femoral anteversion so that the correct cup anteversion can be performed to make sure that the combined anteversion is within the safe zone (30°-45°) among DDH patients. Regarding other reconstruction parameters, the COR of the reconstructed hips were more medial and superior; however, the ipsilateral femoral offsets were also significantly elongated to compensate the shift of COR (Table 3). Overall, there was no significant difference regarding bilateral hip offset and hip length. Both component and osseous impingements could be avoided among our patients (Table 3). Thus, we believe that imperfect cup and stem anteversion should be the main source of impingement with modern surgical technique. However, besides implant orientation, for the best chance to avoid impingement, the correct reconstruction of hip offset and length also needs to be done. A larger femoral head was reported to be associated with a lower long-term cumulative risk of dislocation in the general population [22]. The present study confirmed that a bigger femoral head significantly decreases postoperative dislocation rate among DDH patients (Table 1), especially when the femoral head increased from 28 to 32 mm (P = .002). Among DDH patients, the dysplastic
Dislocation After THA Among Patients With DDH Wang et al
acetabulum tends to provide insufficient coverage to the cup [12,23]. Surgeons therefore tend to decrease the cup diameter to increase the cup coverage, which might decrease the femoral head diameter at certain situation. With limited knowledge about the minimum 3-dimensional surface cup coverage required for longterm fixation [24], it is difficult to choose the optimal cup size. Further study is needed to provide us with this information. When a smaller head size is needed, it is important that the surgeon pay critical attention to what they can do to avoid impingement, including combined anteversion, hip length, and offset mentioned above. A previous study reported that a difference of cuphead diameter bigger than 34 mm significantly increased the dislocation rate [25]. However, we could not find a significantly difference between the 2 groups in our study (P = .36) (Table 1). Although the number of patients with a cup-head difference bigger than 34 mm was not big (n = 15), it still met the need for the statistical analysis. Based on our data, the current study was unable to show a statistically significant effect of cuphead difference on hip dislocation among DDH patients. We considered that our special target population might be a confusion factor leading to this difference.
Acknowledgments The authors also gratefully acknowledge the support of the Innovation Program of Shanghai Municipal Education Commission, the Science and Technology Commission of Shanghai Municipality (09441900101), the Shanghai Science and Technology Development Fund (09dz2200400), the Program for Key Disciplines of Shanghai Municipal Education Commission (J50206), China Scholarship Council, and Mayo foundation. Special thanks go to Stephen Cha and Xin Wang for their help with statistics, and Karen Fasbender for her assistance in preparing the manuscript.
References 1. Crowe JF, Mani VJ, Ranawat CS. Total hip replacement in congenital dislocation and dysplasia of the hip. J Bone Joint Surg Am 1979;61:15. 2. Hartofilakidis G, Karachalios T. Total hip arthroplasty for congenital hip disease. J Bone Joint Surg Am 2004;86:242. 3. Masonis JL, Patel JV, Miu A, et al. Subtrochanteric shortening and derotational osteotomy in primary total hip arthroplasty for patients with severe hip dysplasia— 5-year follow-up. J Arthroplasty 2003;18:68. 4. Minoda Y, Kadowaki T, Kim M. Acetabular component orientation in 834 total hip arthroplasties using a manual technique. Clin Orthop Relat Res 2006;445:186. 5. Lewinnek GE, Lewis JL, Tarr R, et al. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am 1978;60:217. 6. Berry DJ, Kessler M, Morrey BF. Maintaining a hip registry for 25 years: Mayo clinic experience. Clin Orthop Relat Res 1997;344:61.
769
7. Krismer M, Bauer R, Tschupik J, et al. EBRA—a method to measure migration of acetabular components. J Biomech 1995;28:1225. 8. Biedermann R, Tonin A, Krismer M, et al. Reducing the risk of dislocation after total hip arthroplasty—the effect of orientation of the acetabular component. J Bone Joint Surg Br 2005;87:762. 9. Le Duff MJ, Wang CT, Wisk LE, et al. Benefits of thinshelled acetabular components for metal-on-metal hip resurfacing arthroplasty. J Orthop Res 2010;28:1665. 10. 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. 11. Abraham R, Malkani AL. Instability after total hip replacement. Semin Arthroplasty 2005;16:132. 12. Ai JW, Han YP. Application of Zweymüller system in total hip arthroplasty with Crowe-III and Crowe-IV developmental dysplasia hip. J Clin Rehab Tissue Eng Res 2008;12:8615. 13. Sanchez-Sotelo J, Berry DJ. Epidemiology of instability after total hip replacement. Orthop Clin North Am 2001;32:543. 14. Shen B, Yang J, Wang L, et al. Midterm results of hybrid total hip arthroplasty for treatment of osteoarthritis secondary to developmental dysplasia of the hip—Chinese experience. J Arthroplasty 2009;24:1157. 15. Krych AJ, Howard JL, Trousdale RT, et al. Total hip arthroplasty with shortening subtrochanteric osteotomy in Crowe type-IV developmental dysplasia. J Bone Joint Surg Am 2009;91:2213. 16. Mallory TH, Lombardi AV, Fada R, et al. Dislocation after total hip arthroplasty using the anterolateral abductor split approach. Clin Orthop Relat Res 1999;358:166. 17. Ito H, Hirayama T, Tanino H, et al. Tight fit technique in primary hybrid total hip arthroplasty for patients with hip dysplasia. J Arthroplasty 2007;22:57. 18. Masonis JL, Patel JV, Miu A, et al. Subtrochanteric shortening and derotational osteotomy in primary total hip arthroplasty for patients with severe hip dysplasia: 5-year follow-up. J Arthroplasty 2003;18:68. 19. Schmalzried TP. The importance of proper acetabular component positioning and the challenges to achieving it. Oper Tech Orthop 2009;19:132. 20. Malik A, Maheshwari A, Dorr LD. Impingement with total hip replacement. J Bone Joint Surg Am 2007;89:1832. 21. Di Schino M, Baudart F, Zilber S, et al. Anterior dislocation of a total hip replacement. Radiographic and CT-scan assessment. Behavior following conservative management. Orthop Traumatol Surg Res 2009;95:573. 22. Berry DJ, Von Knoch M, Schleck CD, et al. Effect of femoral head diameter and operative approach on risk of dislocation after primary total hip arthroplasty. J Bone Joint Surg Am 2008;87:2456. 23. Anderson MJ, Harris WH. Total hip arthroplasty with insertion of the acetabular component without cement in hips with total congenital dislocation or marked congenital dysplasia. J Bone Joint Surg Am 1999;81:347. 24. Sanchez-Sotelo J, Berry DJ, Trousdale RT, et al. Surgical treatment of developmental dysplasia of the hip in adults: II. Arthroplasty options. J Am Acad Orthop Surg 2002;10:334. 25. Kelley SS, Lachiewicz PF, Hickman JM, et al. Relationship of femoral head and acetabular size to the prevalence of dislocation. Clin Orthop Relat Res 1998;355:163.
Dislocation After Total Hip Arthroplasty Among Patients With Developmental Dysplasia of the Hip Liao Wang, MD,*z Robert T. Trousdale, MD,y Songtao Ai, MD,* Kai-Nan An, PhD,z Kerong Dai, MD,* and Bernard F. Morrey, MDy
Abstract: The precise relationship between developmental dysplasia of the hip and dislocation among patients after total hip arthroplasty has not been well clarified. A total of 820 patients with developmental dysplasia of the hip who underwent total hip arthroplasty from January 2000 to December 2009 were categorized according to Crowe classification, and postoperative dislocation rates were analyzed among subgroups. The overall dislocation rate was 2.93%. No statistically significant differences in dislocation rates were observed between these with and without subtrochanteric osteotomy. Femoral head size was the only factor with significant difference between the dislocated and stable groups, especially when femoral head diameter increased from 28 to 32 mm. Of all dislocations, 69.6% were anterior dislocation, and the degree of cup anteversion and combined anteversion of anterior dislocators was higher than that of the posterior dislocators (P = .0082 and P = .001). Keywords: dislocation, cup anteversion, combined anteversion, developmental dysplasia of the hip, total hip arthroplasty. © 2012 Elsevier Inc. All rights reserved.
Patients with developmental dysplasia of the hip (DDH) have a wide spectrum of deformities, ranging from a hip that is mildly dysplastic to one that is severely dysplastic or dislocated. It has been divided into 4 subgroups by Crowe based on the migration magnitude of femoral head relative to interteardrop line [1]. When a total hip arthroplasty (THA) is performed in a DDH patient, it is commonly believed that the more severe the deformity, the greater the technical difficulty is during surgery [2,3]. Minoda et al [4] reported a higher risk of positioning a cup outside the safe range in patients with Crowe IV DDH. However, they could neither find a significant relationship between the risk of dislocation
From the *Department of Orthopaedics, Shanghai Ninth People's Hospital, Shanghai Key Laboratory of Orthopaedic Implant, Shanghai Jiao Tong University School of Medicine and Engineering Research Center of Digital Medicine, Ministry of Education, Shanghai, PR China; yDepartment of Orthopedic Surgery, Mayo Clinic,, Rochester, Minnesota; and zBiomechanics Laboratory, Mayo Clinic, Rochester, Minnesota. Submitted October 14, 2010; accepted August 26, 2011. The Conflict of Interest statement associated with this article can be found at doi:10.1016/j.arth.2011.08.021. One or more of the authors (RTT) receives royalties from DePuy, Wright Medical, and the Orthopedic Department. Reprint requests: Robert T. Trousdale, MD, Department of Orthopedic Surgery, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905. © 2012 Elsevier Inc. All rights reserved. 0883-5403/2705-0017$36.00/0 doi:10.1016/j.arth.2011.08.021
and the cup orientation nor give detailed description about relevant dislocation rates among subgroups [4,5]. The precise effect of the severity of the preoperative deformity on the postoperative dislocation among DDH patients has not been clarified yet. To our knowledge, there is no large sample follow-up study to date focusing on the dislocation rate among DDH patients after THA and, more importantly, the dislocation rate according to the severity of the hip dysplasia. In this follow-up study, we tried to clarify the following questions: Is a higher Crowe classification indicative of a higher dislocation rate? What are the predisposing factors of postoperative dislocation among DDH patients? Among the dislocated cases, is there any special pattern?
Materials and Methods Patient Selection The study protocol was approved by the local institutional review board, and informed consent was obtained from all patients. A retrospective review of our institutional total joint registry identified 886 hips with a diagnosis of osteoarthritis secondary to DDH that were treated with THA using cementless cup from January 2000 to December 2009 [6]. All the preoperative anteroposterior (AP) pelvic radiographs were reviewed to subgroup the patients according to Crowe classification [1]. We were unable to determine the Crowe classification among 62 patients as a result of unavailable preoperative
764
Dislocation After THA Among Patients With DDH Wang et al
radiographs, and these patients were excluded. Four patients with a minimal invasive approach were also excluded because this approach was rarely used among our target patients. Among these excluded, there were no dislocations. These exclusions left us with 820 DDH patients. Surgical Technique In our institute, to avoid the malpositioning of implant, the patient was carefully positioned on the operating table, the trunk was aligned with the leg, and the position of the shoulder was marked with a clip on the surgical drape. The identity of the degree of anteversion was predicated on the images as well as the intraoperative finding. Orientation of the cup should be at 15° of anteversion. A cup holder inserted the cup at 15° referable to the shoulder landmark. If at this position there was inadequate anterior wall coverage and excessive posterior wall coverage, this revealed an excessive amount of acetabular anteversion. For the stem, the neck was assessed referable to the flexion plane of the knee. We matched the anteversion of both cup and stem. Because the stem was more difficult to adjust, we therefore did not secure the cup until the femoral stem preparation was complete. Excessive inherent anteversion was reduced at the femur by resecting greater amounts of the femoral neck. We anteverted the cup component less if the femoral component had more anteversion.
765
Follow-Up Routine Patients were routinely evaluated in person, by telephone, or by a questionnaire at 3 months, 6 months, 1 year, 2 years, and 5 years after the index surgery. The average follow-up of these patients was 3 years, with a minimum follow-up of 6 months. At each time point, the patients were asked specifically whether a dislocation had occurred. A dislocation in our study was defined as a dislocated hip requiring a reduction by a physician. Patients with subluxation were not included in our study. Clinical and Radiographic Evaluation Among these 820 patients, 94 received a cemented stem, which version can be controlled. The rest of the patients were implanted with uncemented stem, with 106 patients being implanted with S-ROM stem (Depuy, Warsaw, Ind). None of these patients who received S-ROM stem had a postoperative dislocation. They were divided into stable (n = 796) and dislocated groups (n = 24) depending on whether a postoperative dislocation occurred. Related risk factors were recorded, and their distributions were compared between the stable and dislocated groups to determine their effects on postoperative dislocation among DDH patients, including demographic factors, Crowe classification, surgical approach, diameter of femoral head, and the difference between cup and femoral head diameter, and others. (Table 1). For these who experienced a postoperative dislocation, the direction of dislocation was
Table 1. The Distribution of Risk Factors Between Dislocated and Stable Groups Parameters Age at operation (y) Sex Male Female Side Left Right Crowe classification Crowe I, II, and III Crowe IV Operative approach Anterior Posterior Lateral Femoral head size (mm) 22 28 ≥32 Cup size–head size (mm) ≥34 b34 Previous hip osteotomy Yes No Periacetabular osteotomy Yes No
Overall (n = 820)
Stable Cases (n = 796)
Dislocated Cases (n = 24)
49.79 ± 13.08 (12-86 )
49.75 ± 13.13 (12-86)
51.13 ± 11.71 (35-75)
209 (25.5%) 611 (74.5%)
203 (97.05%) 593 (97.13%)
6 (2.95%) 18 (2.87%)
396 (48.29%) 424 (51.71%)
385 (97.22%) 411 (96.93%)
11 (2.78%) 13 (3.07%)
774 (94.39%) 46 (5.61%)
752 (97.16%) 44 (95.65%)
22 (2.84%) 2 (4.35%)
236 (28.78%) 536 (65.37%) 48 (5.85%)
231 (97.88%) 520 (93.75%) 45 (97.01%)
5 (2.12%) 16 (6.25%) 3 (2.99%)
35 (4.32%) 355 (43.29%) 430 (52.44%)
33 (94.29%) 338 (95.21%) 425 (98.84%)
2 (5.71%) 17 (4.79%) 5 (1.16%)
15 (1.83%) 805 (98.17%)
14 (93.33%) 782 (97.14%)
1 (6.67%) 23 (2.86%)
179 (21.83%) 641 (78.17%)
177 (98.88%) 619 (96.57%)
2 (1.12%) 22 (3.43%)
12 (1.46%) 808 (98.54%)
12 (100%) 784 (97.03%)
0 (0%) 24 (2.97%)
P .61 1.00
.84
.395
.30
.0067
.36
.98
1.00
766 The Journal of Arthroplasty Vol. 27 No. 5 May 2012 identified by reviewing clinical records or confirmed by reviewing cross-table lateral radiographs. A standardized radiographic protocol was applied for the dislocated patients, including the following measurements performed on preoperative AP pelvic radiograph, postoperative AP pelvic radiograph, and crosstable lateral radiograph. The radiographic measurement was done by an orthopedic research fellow (LW), who was not involved in the operations. The ischial spine sign and crossover sign were observed on preoperative AP pelvic radiograph to roughly assess the orientation of bony acetabulum (anteverted or retroverted). The postoperative AP pelvic radiographs with a symmetrical pelvic posture were selected for radiographic evaluation. The reference landmarks were marked on these symmetrical AP pelvic radiographs, including anatomical axis of the femur (F, F'), transtrochanter lines (T and T'), transischial line (H1), transteardrop line (H2), and its perpendicular line (I, I'), and others. Lines I and I' were the vertical lines running through the crossing point of teardrop and Kohler line. Points O and C were the centers of rotation (COR) of the reconstructed hip and the contralateral hip. OA and CA' were the horizontal distance of COR. OB and CB' were the vertical distance of COR. OD and CD' were the femoral offset. Hip offset was represented by the combination of femoral offset and the horizontal distance of COR. Hip length referred to the vertical distance between transteardrop line and line running through less trochanter (Fig. 1). The marked radiographs were rotated using adobe Photoshop cs3 extended version 10.0.1(Adobe Systems Inc, San Jose, Calif) making transteardrop line parallel with
the horizontal line. The rotated AP pelvic radiographs were loaded into EBRA cup software [7] (Ein-BildRoentgen-Analyse, release 2007; Department of Geometry, University of Innsbruck, Innsbruck, Austria). EBRA allows the measurement of radiographic cup anteversion and inclination with an accuracy of 2° [8]; helps in determining the COR; and measures vertical and horizontal distance of COR, femoral offset, hip offset, and hip length [9,10]. For comparison, above radiographic parameters were measured on both the reconstructed and contralateral hips, if the contralateral hip was approximately normal. Radiographic measurement was considered abnormal if there was more than 10 mm difference between the reconstructed and contralateral hips. Cross-table lateral radiographs were reviewed to assess the stem anteversion [11] (Fig. 2), then, the combined anteversion could be calculated. Treatment When a dislocation was encountered, closed or open reduction was generally performed, and this would be followed by postreduction abduction bracing for 6 weeks. Should the hip remain stable, no further surgery would be performed. For those who developed recurrent dislocations, a revision surgery would then be contemplated and performed. Statistical Analysis Statistical analyses were performed using JMP 8.0 software (SAS Institute, Inc, Cary, NC). Quantitative variables were described by mean ± SD or frequency (percentage %). Two-sample t test, Fisher exact test, and Pearson χ 2 test were used to investigate the relationship
Fig. 1. A representative radiograph showed how the parameters were measured.
Dislocation After THA Among Patients With DDH Wang et al
767
Fig. 2. Stem anteversion was defined as the angle formed by the bottom of the radiographic plate representing the posterior plane of the condyles and the axis of the stem neck realizing leg rotation affects measurements.
between the postoperative dislocation and related risk factors. Two-sample t test was used to investigate the statistical difference between the anterior and posterior dislocators regarding cup anteversion, cup inclination, stem anteversion, and combined anteversion. Paired t test was used to compare the radiographic parameters between the reconstructed and contralateral hips. Any P value less than .05 was considered statistically significant.
Results One or more dislocations occurred in 24 (2.93%) of the 820 DDH hips. The dislocation rates among Crowe I, II, III, and IV groups were 3.04%, 2.52%, 1.59%, and 4.35%, respectively. Initially, we assumed that a higher Crowe classification might be the indicative of a higher dislocation rate. However, as a result of low incidence of dislocations among subgroups, Pearson χ 2 test was unable to be applied. Thus, we combined these without subtrochanteric osteotomy (Crowe I, II, and III) and compared them with those with subtrochanteric osteotomy (Crowe IV) using Fisher exact test. With such a big sample size and detailed grouping, we still could not find a statistically significant difference regarding dislocation rates between the 2 groups. Among all the risk factors, the diameter of femoral head was the only one with a statistically significant difference between the stable and dislocated groups (P = .0067). The dislocation rates were 5.71%, 4.79%, and 1.16% in patients with a femoral head diameter of 22, 28, and 32 mm above, respectively. Further stratifying our data, we found no significant difference regarding hip dislocation rate between these using 22-mm femoral head and those using 28 mm (P = .52). However, compared with patients with a 28-mm femoral head, patients with a 32-mm and above femoral head had a significantly lower dislocation rate (P = .002). Besides, we could not find any significant difference of dislocation rate between the 2 groups regarding other clinical risk factors (Table 1).
Of these dislocators, 69.6% dislocated anteriorly, and the rest of the patients dislocated posteriorly. By reviewing preoperative pelvis radiographs, 23 of 24 patients had a negative ischial spine sign, and 17 patients has a negative crossover sign. One of the patients had a questionable positive ischial spine sign, whereas the pelvis showed obvious rotation on the radiograph. On the other hand, the crossover sign was also difficult to be determined in this patient. The crossover sign in the other 6 patients was also difficult to be determined because of severe osteophyte presenting around acetabulum. The radiographic measurements of cup orientation were able to be performed in 23 dislocated patients, except the one without any available postoperative radiograph. Radiographic cup anteversion and combined anteversion of anterior dislocators were statistically higher compared with that of those posterior dislocators (Table 2). On a case-by-case basis, 10 patients, whose combined anteversion were higher than 45°, dislocated anteriorly. Actually, all the patients in our study, whose combined anteversion were bigger than 42°, dislocated anteriorly, and for those 4 patients, whose combined anteversion were less than 30°, dislocated posteriorly. Stem anteversion and radiographic cup inclination showed no significant difference between patients with an anterior dislocation and these with a posterior dislocation (Table 2). Eighteen patients have a nearly normal hip on the contralateral side. Compared with the contralateral hip joint, CORs of the reconstructed hips were medialized with a mean horizontal displacement of 4.3 mm and were superiorized with a mean vertical displacement of 3.52 mm. The femoral offset among the reconstructed hips was elongated with a mean magnitude of 5.59 mm. Overall, there was no significant difference between the reconstructed and contralateral hips regarding hip offset and hip length. None of these patients has more than 10 mm difference between the reconstructed and contralateral hips (Table 3).
768 The Journal of Arthroplasty Vol. 27 No. 5 May 2012 Table 2. Component Orientation in Anteriorly and Posteriorly Dislocated Groups Component Orientation, Mean ± SD (95% CI)
Anterior Dislocation (n = 16)
Posterior Dislocation (n = 7)
Cup anteversion Cup inclination Stem anteversion Combined anteversion
30.07 ± 44.13 ± 16.06 ± 46.14 ±
16.00 ± 43.45 ± 15.74 ± 31.75 ±
6.07 (25.93-34.22) 7.05 (40.37-47.88) 5.49 (13.14-18.99) 8.18 (41.78-50.50)
Most of the dislocated cases were treated in our hospital (20/24). The treatments and outcomes of the other 4 patients were also recorded based on the information from questionnaire. Overall, 62.5% of dislocated cases regained stability with open (n = 2) or close reduction (n = 15) combined with abduction brace for 6 weeks. All patients with recurrent dislocations regained stability after revision surgery (7/24).
Discussion Total hip arthroplasty in the treatment of patients with DDH is known to be more technically demanding [1,12]. Dislocation rate in DDH patients has been suspected to be higher because of limited bone stock and malformation of the acetabulum [13]. However, previous studies showed controversial results regarding the dislocation rates among DDH patients [14-18]. Developmental dysplasia of the hip, as a developmental disease, includes a wide spectrum of deformity. Thus, we performed this study with a large sample size and detailed grouping to further clarify the relationship between DDH subgroups and related dislocation rates and to describe and explain the special dislocation pattern. In this study, we did not find a statistically significant difference in dislocation rates between patients with and without subtrochanteric osteotomy. However, we did note that anterior dislocation was the most common pattern among DDH patients after THA. The safe zone of combined anteversion confirmed in our study for DDH patients was 30° to 45°. Another important finding was that larger head size tended to provide better stability among DDH patients, especially when the femoral head increased from 28 to 32 mm. Our study has a few limitations. First, although from 1 institution, the operations were in fact performed by many surgeons, which might brought some confusion in data analysis. Second, there were only 24 dislocations in our study, which might be a potential reason for not Table 3. Radiographic Comparison Between Reconstructed and Contralateral Hips Paired Differences 95% CI
Reconstructed vs Contralateral Hips (n = 18)
Mean (mm)
SD
Lower
Upper
P
Horizontal offset of COR Vertical offset of COR Femoral offset Hip offset Hip length
−4.30 3.52 5.59 1.29 3.15
4.17 4.87 4.00 6.37 7.27
−6.38 1.10 3.60 −1.88 −.47
−2.23 5.94 7.59 4.46 6.77
.000 .007 .000 .403 .084
CI indicates confidence interval.
11.43 (9.73-22.28) 6.26 (37.66-49.24) 10.40 (6.12-25.37) 7.33 (24.97-38.52)
P .0082 .4105 .941 .001
detecting statistical difference among subgroups. Although the dislocation after THA in DDH patients is an uncommon event, these 24 patients were identified from 820 DDH patients. Thus, we believe that the dislocation rate reported in current study should be representative enough to show the general situation of postoperative dislocation among DDH patients. Third, the stem anteversion was measured on a cross-table lateral radiograph, which could roughly assess the stem anteversion. Impingement is an important biomechanical factor leading to instability of prosthetic hip, which is influenced by component orientation, and other reconstructive parameters [19,20]. Di schino et al [21] identified DDH as a risk factor for anterior dislocation after THA, because of an excessive acetabular and femoral anteversion. In this study, we also observed that a dysplastic hip predisposed to inadvertent malpositioning of cup and femoral components in excessive anteversion because of specific malformation of DDH patients, hence accounting for the higher anterior dislocation rate in our series (69.6%). On a case-by-case basis, we noted that all these (n = 10) with a combined anteversion bigger than 45° dislocated anteriorly, whereas all those (n = 4) with a combined anteversion less than 30° dislocated posteriorly. We believe that it is critical that a surgeon should be aware of the femoral anteversion so that the correct cup anteversion can be performed to make sure that the combined anteversion is within the safe zone (30°-45°) among DDH patients. Regarding other reconstruction parameters, the COR of the reconstructed hips were more medial and superior; however, the ipsilateral femoral offsets were also significantly elongated to compensate the shift of COR (Table 3). Overall, there was no significant difference regarding bilateral hip offset and hip length. Both component and osseous impingements could be avoided among our patients (Table 3). Thus, we believe that imperfect cup and stem anteversion should be the main source of impingement with modern surgical technique. However, besides implant orientation, for the best chance to avoid impingement, the correct reconstruction of hip offset and length also needs to be done. A larger femoral head was reported to be associated with a lower long-term cumulative risk of dislocation in the general population [22]. The present study confirmed that a bigger femoral head significantly decreases postoperative dislocation rate among DDH patients (Table 1), especially when the femoral head increased from 28 to 32 mm (P = .002). Among DDH patients, the dysplastic
Dislocation After THA Among Patients With DDH Wang et al
acetabulum tends to provide insufficient coverage to the cup [12,23]. Surgeons therefore tend to decrease the cup diameter to increase the cup coverage, which might decrease the femoral head diameter at certain situation. With limited knowledge about the minimum 3-dimensional surface cup coverage required for longterm fixation [24], it is difficult to choose the optimal cup size. Further study is needed to provide us with this information. When a smaller head size is needed, it is important that the surgeon pay critical attention to what they can do to avoid impingement, including combined anteversion, hip length, and offset mentioned above. A previous study reported that a difference of cuphead diameter bigger than 34 mm significantly increased the dislocation rate [25]. However, we could not find a significantly difference between the 2 groups in our study (P = .36) (Table 1). Although the number of patients with a cup-head difference bigger than 34 mm was not big (n = 15), it still met the need for the statistical analysis. Based on our data, the current study was unable to show a statistically significant effect of cuphead difference on hip dislocation among DDH patients. We considered that our special target population might be a confusion factor leading to this difference.
Acknowledgments The authors also gratefully acknowledge the support of the Innovation Program of Shanghai Municipal Education Commission, the Science and Technology Commission of Shanghai Municipality (09441900101), the Shanghai Science and Technology Development Fund (09dz2200400), the Program for Key Disciplines of Shanghai Municipal Education Commission (J50206), China Scholarship Council, and Mayo foundation. Special thanks go to Stephen Cha and Xin Wang for their help with statistics, and Karen Fasbender for her assistance in preparing the manuscript.
References 1. Crowe JF, Mani VJ, Ranawat CS. Total hip replacement in congenital dislocation and dysplasia of the hip. J Bone Joint Surg Am 1979;61:15. 2. Hartofilakidis G, Karachalios T. Total hip arthroplasty for congenital hip disease. J Bone Joint Surg Am 2004;86:242. 3. Masonis JL, Patel JV, Miu A, et al. Subtrochanteric shortening and derotational osteotomy in primary total hip arthroplasty for patients with severe hip dysplasia— 5-year follow-up. J Arthroplasty 2003;18:68. 4. Minoda Y, Kadowaki T, Kim M. Acetabular component orientation in 834 total hip arthroplasties using a manual technique. Clin Orthop Relat Res 2006;445:186. 5. Lewinnek GE, Lewis JL, Tarr R, et al. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am 1978;60:217. 6. Berry DJ, Kessler M, Morrey BF. Maintaining a hip registry for 25 years: Mayo clinic experience. Clin Orthop Relat Res 1997;344:61.
769
7. Krismer M, Bauer R, Tschupik J, et al. EBRA—a method to measure migration of acetabular components. J Biomech 1995;28:1225. 8. Biedermann R, Tonin A, Krismer M, et al. Reducing the risk of dislocation after total hip arthroplasty—the effect of orientation of the acetabular component. J Bone Joint Surg Br 2005;87:762. 9. Le Duff MJ, Wang CT, Wisk LE, et al. Benefits of thinshelled acetabular components for metal-on-metal hip resurfacing arthroplasty. J Orthop Res 2010;28:1665. 10. 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. 11. Abraham R, Malkani AL. Instability after total hip replacement. Semin Arthroplasty 2005;16:132. 12. Ai JW, Han YP. Application of Zweymüller system in total hip arthroplasty with Crowe-III and Crowe-IV developmental dysplasia hip. J Clin Rehab Tissue Eng Res 2008;12:8615. 13. Sanchez-Sotelo J, Berry DJ. Epidemiology of instability after total hip replacement. Orthop Clin North Am 2001;32:543. 14. Shen B, Yang J, Wang L, et al. Midterm results of hybrid total hip arthroplasty for treatment of osteoarthritis secondary to developmental dysplasia of the hip—Chinese experience. J Arthroplasty 2009;24:1157. 15. Krych AJ, Howard JL, Trousdale RT, et al. Total hip arthroplasty with shortening subtrochanteric osteotomy in Crowe type-IV developmental dysplasia. J Bone Joint Surg Am 2009;91:2213. 16. Mallory TH, Lombardi AV, Fada R, et al. Dislocation after total hip arthroplasty using the anterolateral abductor split approach. Clin Orthop Relat Res 1999;358:166. 17. Ito H, Hirayama T, Tanino H, et al. Tight fit technique in primary hybrid total hip arthroplasty for patients with hip dysplasia. J Arthroplasty 2007;22:57. 18. Masonis JL, Patel JV, Miu A, et al. Subtrochanteric shortening and derotational osteotomy in primary total hip arthroplasty for patients with severe hip dysplasia: 5-year follow-up. J Arthroplasty 2003;18:68. 19. Schmalzried TP. The importance of proper acetabular component positioning and the challenges to achieving it. Oper Tech Orthop 2009;19:132. 20. Malik A, Maheshwari A, Dorr LD. Impingement with total hip replacement. J Bone Joint Surg Am 2007;89:1832. 21. Di Schino M, Baudart F, Zilber S, et al. Anterior dislocation of a total hip replacement. Radiographic and CT-scan assessment. Behavior following conservative management. Orthop Traumatol Surg Res 2009;95:573. 22. Berry DJ, Von Knoch M, Schleck CD, et al. Effect of femoral head diameter and operative approach on risk of dislocation after primary total hip arthroplasty. J Bone Joint Surg Am 2008;87:2456. 23. Anderson MJ, Harris WH. Total hip arthroplasty with insertion of the acetabular component without cement in hips with total congenital dislocation or marked congenital dysplasia. J Bone Joint Surg Am 1999;81:347. 24. Sanchez-Sotelo J, Berry DJ, Trousdale RT, et al. Surgical treatment of developmental dysplasia of the hip in adults: II. Arthroplasty options. J Am Acad Orthop Surg 2002;10:334. 25. Kelley SS, Lachiewicz PF, Hickman JM, et al. Relationship of femoral head and acetabular size to the prevalence of dislocation. Clin Orthop Relat Res 1998;355:163.