Does the optimal position of the acetabular fragment should be within the radiological normal range for all developmental dysplasia of the hip? A patient-specific finite element analysis.

Xuyi Wang,Hui Wang,Xiaodong Chen,Leisheng Jiang,De Li,Jianping Peng,Linlin Zhang

doi:10.1186/s13018-016-0445-3

Abstract

BackgroundThe success of Bernese periacetabular osteotomy depends significantly on how extent the acetabular fragment can be corrected to its optimal position. This study was undertaken to investigate whether correcting the acetabular fragment into the so-called radiological “normal” range is the best choice for all developmental dysplasia of the hip with different severities of dysplasia from the biomechanical view? If not, is there any correlation between the biomechanically optimal position of the acetabular fragment and the severity of dysplasia?MethodsFour finite element models with different severities of dysplasia were developed. The virtual periacetabular osteotomy was performed with the acetabular fragment rotated anterolaterally to incremental center-edge angles; then, the contact area and pressure and von Mises stress in the cartilage were calculated at different correction angles.ResultsThe optimal position of the acetabular fragment for patients 1, 2, and 3 was when the acetabular fragment rotated 17° laterally (with the lateral center-edge angle of 36° and anterior center-edge angle of 58°; both were slightly larger than the “normal” range), 25° laterally following further 5° anterior rotation (with the lateral center-edge angle of 31° and anterior center-edge angle of 51°; both were within the “normal” range), and 30° laterally following further 10° anterior rotation (with the lateral center-edge angle of 25° and anterior center-edge angle of 40°; both were less than the “normal” range), respectively.ConclusionsThe optimal corrective position of the acetabular fragment is severity dependent rather than within the radiological “normal” range for developmental dysplasia of the hip. We prudently proposed that the optimal correction center-edge angle of mild, moderate, and severe developmental dysplasia of the hip is slightly larger than the “normal” range, within the “normal” range, and less than the lower limit of the “normal” range, respectively.Electronic supplementary materialThe online version of this article (doi:10.1186/s13018-016-0445-3) contains supplementary material, which is available to authorized users.

Highlights

The success of Bernese periacetabular osteotomy depends significantly on how extent the acetabular fragment can be corrected to its optimal position
Throughout the postoperative follow-up, we found that hip pain did not improve significantly and the cartilage degeneration continued to deteriorate for some developmental dysplasia of the hip (DDH) patients, even though their acetabular angle had been corrected into the “normal” range
Theoretical biomechanics is based on a mathematical model for numerical analysis, such as finite element analysis (FEA), which can handle different complex geometries and can provide various noninvasive mechanical tests [12,13,14]

Summary

Introduction

The success of Bernese periacetabular osteotomy depends significantly on how extent the acetabular fragment can be corrected to its optimal position. This study was undertaken to investigate whether correcting the acetabular fragment into the so-called radiological “normal” range is the best choice for all developmental dysplasia of the hip with different severities of dysplasia from the biomechanical view? If not, is there any correlation between the biomechanically optimal position of the acetabular fragment and the severity of dysplasia?. Throughout the postoperative follow-up, we found that hip pain did not improve significantly and the cartilage degeneration continued to deteriorate for some DDH patients, even though their acetabular angle had been corrected into the “normal” range. The degree of correction for the acetabular fragment is not always directly proportional to the improvement of clinical symptoms, but this biomechanical mechanism has rarely been investigated. FEA is a time-consuming, expensive, and professional task, impossible to perform in every DDH patients preoperatively under present social and economic conditions

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