How Many Different Types of Femora are There in Primary Hip Osteoarthritis? An Active Shape Modeling Study C. Merle,1,2 W. Waldstein,1,2 J.S. Gregory,3 S.R. Goodyear,3 R.M. Aspden,3 P.R. Aldinger,4 D.W. Murray,2 H.S. Gill5 1

Department of Orthopaedic and Trauma Surgery, University Hospital Heidelberg, Schlierbacher Landstr. 200 A 69118, Heidelberg, Germany, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK, 3Musculoskeletal Research Programme, Division of Applied Medicine, University of Aberdeen, Aberdeen, UK, 4Department of Orthopaedic Surgery, Paulinenhilfe, Diakonieklinikum, Stuttgart, Germany, 5Department of Mechanical Engineering, University of Bath, Bath, UK 2

Received 7 August 2012; accepted 15 October 2013 Published online 19 November 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jor.22518

ABSTRACT: We assessed the variation in proximal femoral canal shape and its association with geometric and demographic parameters in primary hip OA. In a retrospective cohort study, the joint geometry of the proximal femur was evaluated on radiographs and corresponding CT scans of 345 consecutive patients with end-stage hip OA. Active shape modeling (ASM) was performed to assess the variation in endosteal shape of the proximal femur. To identify natural groupings of patients, hierarchical cluster analysis of the shape modes was used. ASM identified 10 independent shape modes accounting for >96% of the variation in proximal femoral canal shape within the dataset. Cluster analysis revealed 10 specific shape clusters. Significant differences in geometric and demographic parameters between the clusters were observed. ASM and subsequent cluster analysis have the potential to identify specific morphological patterns of the proximal femur despite the variability in proximal femoral anatomy. The study identified patterns of proximal femoral canal shape in hip OA that allow a comprehensive classification of variation in shape and its association with joint geometry. Our data may improve future stem designs that will optimize stem fit and simultaneously allow individual restoration of hip biomechanics. ß 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:413–422, 2014. Keywords: hip; anatomy; osteoarthritis; shape modeling; arthroplasty

In cementless total hip arthroplasty (THA), the optimal femoral component should allow both accurate endosteal stem fit and individual restoration of physiologic joint mechanics. This poses a challenge as the osseous anatomy of the proximal femur is highly variable1–3 and most stem designs are limited in their potential to adjust femoral offset, version, and limb length intraoperatively. Moreover, due to variability in the size and shape of the proximal femoral canal, surgeons may be forced to compromise between endosteal stem fit, critical to achieve stable fixation and proximal load transfer,4,5 and accurate restoration of joint center of rotation. Studies over the last three decades described the variation in femoral anatomy; however, most reported values were obtained from cadaveric specimens or individuals with non-arthritic hip joints,1,2,6 or from cohorts with limited patient numbers. Differences in femoral morphology between males and females were described,7,8 but only limited data exist on sex differences in patients with primary OA. Furthermore, it is unclear whether the shape of the proximal femoral canal is associated with geometric measures of the proximal femur, such as femoral offset, version, or neck-shaft angle. We hypothesized that distinct patterns of canal shape and joint geometry can be identified that allow a comprehensive classification of femoral morphology in primary hip OA. We aimed to investigate the variation in proximal femoral anatomy and to determine Grant sponsor: ENDO-Stiftung, Hamburg, Germany MRC New Investigator. Correspondence to: Christian Merle (T: þ49-6221-56-25000; F: þ49 6221 56 26347; E-mail: [email protected]) # 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

associations of proximal canal shape and joint geometry in a cohort of patients with primary hip OA.

MATERIALS AND METHODS Study Cohort For this retrospective cohort study, we reviewed a consecutive series of 597 patients who had undergone primary THA for end-stage OA with a custom-made cementless femoral component between June 2008 and December 2009.9 Each patient received standardized radiographs and a CT scan of the affected hip preoperatively, and all images were retrieved in generic DICOM format. To obtain normative values for variation in femoral shape and geometry, we excluded patients with a history of trauma, infection, rheumatic disease, developmental dysplasia of the hip, previous pelvic and/or femoral osteotomy, avascular necrosis of the femoral head, Legg–Calve´–Perthes disease, or symptomatic slipped capital femoral epiphysis. To identify patients with acetabular undercoverage, radiographic exclusion criteria were defined as a center-edge angle 42˚11 and an acetabular index

How many different types of femora are there in primary hip osteoarthritis? An active shape modeling study.

We assessed the variation in proximal femoral canal shape and its association with geometric and demographic parameters in primary hip OA. In a retros...
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