Recon

Effect of High Hip Center on Stress for Dysplastic Hip

Yong Nie, PhD; Fuxing Pei, MD; Zongming Li, PhD

Abstract

High hip center reconstruction has been advocated in treating deficient acetabulum. However, there is no consensus on the clinical outcome of this technique. In addition, it remains unclear to what extend this technique restores the normal hip biomechanics. The goal of this study was to investigate stress above the acetabular dome in response to a range of high hip center positioning for Crowe type I and II hip dysplasia. This study consisted of 2 main parts, radiologic and biomechanical. Pelvic radiographs of 18 patients were studied to determine the amount of displacement of the hip center in the superior direction compared with the normal side. Second, qualitative and quantitative changes in stress on cortical and trabecular bone in the region of the acetabular dome as a result of superior displacement of the hip center were analyzed with subject-specific finite element models. The results showed that the range of the hip center position in the superior direction for Crowe type I and II hip dysplasia was 0 to 15 mm above the contralateral femoral head center. When superior displacement of the hip center exceeded 5 mm above the anatomic hip center, cortical bone mass on the 2 thickest cross-sections above the acetabular dome decreased quickly and the stress value on posterolateral cortical bone was obviously lower than the normal level. This study showed that to restore the normal load above the acetabular dome, there is a limit of 5 mm above the anatomic hip center for high hip center acetabular reconstruction for Crowe type I and II hip dysplasia.

The authors are from the Department of Orthopedics (YN, FP), West China Hospital, Sichuan University, Chengdu, China; and the Department of Biomedical Engineering (ZL), Cleveland Clinic Lerner Research Institute, Cleveland, Ohio.

The authors have no relevant financial relationships to disclose.

The authors thank the School of Manufacturing Science and Engineering and the Biomechanics Institute of Sichuan University for supporting this study. Financial support was provided by the Special Research Project of Health Care Industry (No. 201302007), Ministry of Public Health, China.

Correspondence should be addressed to: Fuxing Pei, MD, Department of Orthopedics, West China Hospital, Sichuan University, No 37 Guo Xue Xiang, Chengdu, China 610041 ( peifuxing@vip.163.com).

Received: August 21, 2013
Accepted: December 20, 2013

Total hip arthroplasty (THA) is one of the most successful reconstructive surgeries and greatly improves patient quality of life. Although anatomic reconstruction of the acetabulum results in the best outcome, anatomic positioning of the cup during THA is often difficult to achieve as a result of hip dysplasia and bone deficiency.1,2The high hip center technique, which has been advocated as a compromise in treating deficient acetabulum, is defined as reconstruction of the hip at a high center located more than 35 mm from the inter-teardrop line or 15 mm higher than the approximate femoral head center.3,4 There is no consensus on the clinical outcome of this technique.

Previous studies reported biomechanical data unfavorable to high hip center placement. Doehring et al2,5 used an experimental study to assess the initial stability of implants with increasing positioning of an uncemented acetabular cup and showed that superior and lateral positioning of the hip center 25 mm above the femoral head center led to an increase in implant micromotion. Pagnano et al4reported unfavorable long-term clinical results with high hip center reconstruction in Crowe type II hip dysplasia. Cups that were more than 15 mm superior to the center of the femoral head without lateral displacement had an increased rate of loosening and revision. Similarly, Yoder et al6 concluded that the risk of loosening was 4 times greater if the hip center was raised 30 mm above the teardrop. Nevertheless, the high hip center technique in primary or revision arthroplasty for peri-acetabular bone deficiency has been proposed as a valuable alternative by many authors. Hendricks and Harris7 reported a low rate of implant aseptic loosening after a long-term follow-up study in which the high hip center technique was adopted for revision total hip arthroplasty in selected patients with severe acetabular bone loss. Christodoulou et al8 investigated the rate of polyethylene wear and long-term survivorship in patients with arthritis secondary to congenital hip disease when placing the acetabular cup at a high nonanatomic position and showed that the high hip center technique resulted in long-term survivorship of the implants.

Considering the variable clinical outcomes resulting from the high hip center technique, there is no standard high hip center technique to guide the process of acetabular reconstruction for a certain type of hip dysplasia. In addition, it remains unclear to what extent the high hip center technique restores normal hip biomechanics, particularly the loading profile above the acetabular dome.

Given the questions raised by these reports, the goal of this study was to investigate the range of high hip center positioning and its effect on stress distribution above the acetabular dome for Crowe type I or II hip dysplasia. The authors radiographically obtained the range of hip center position in the superior direction after placing the cup in a hip with dysplasia. The changes in stress distribution on cortical and trabecular bone as a result of superior displacement of the hip center were then described using finite element models. The authors quantified the variation of stress level above the acetabular dome with increasing superior displacement of the hip center.

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Josh Sandberg

Josh Sandberg is the President of Ortho Sales Partners and Partner for The De Angelis Group. He also serves as Co-Founder and Editor of OrthoSpineNews.

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