Effects of Curved Periacetabular Osteotomy on the Stress Fields of the Pubic Rami and Ischium: A Finite Element Model Analysis

Norio Imai,Tomoyuki Ito,Naoto Endo,Yoichiro Dohmae,Ken Suda,Dai Miyasaka

doi:10.4236/ojo.2013.34036

Abstract

Background: Postoperative pubic or ischial stress fracture may be a complication after curved periacetabular osteotomy (CPO). The discontinuity of the superior pubic rami is a risk factor for this complication. We investigated the stress field differences in standing and sitting positions after CPO. Methods: We used finite element analysis to assess the effects of inferior pubic rami and ischial fractures with or without discontinuity of superior pubic rami. We used the “union model”, obtained from a bony union at the osteotomy site of the superior pubic rami from 38-year-old woman who had undergone CPO for left hip dysplasia. We deleted the bony union region and created a discontinuity in the superior pubic rami equal to the non-union, creating the “discontinuity model”. We compared the stress field and stress value in the simulated standing and half weight-bearing positions on the operative side, one-legged standing position on the non-operative side, and the sitting position. Findings: In 4 cases, the inferior rami experienced the highest stress. Stress values in the discontinuity model were higher than those in the union model: 1.7 times in the case of one-legged standing on the operative side, 2.4 times in the case of half weight-bearing on the operative side, 3.8 times in the case of one-legged standing on the non-operative side, and 2.0 times in the sitting position, respectively. Interpretation: We recommend patients delay weight bearing on the operative side, avoid the sitting position as long as possible, and sit down slowly to prevent inferior pubic rami and ischial fractures after CPO.

Highlights

Acetabular osteotomies are useful for increasing the covering of the femoral head, and for medialization of the femoral head
Stress values in the discontinuity model were higher than those in the union model: 1.7 times in the case of one-legged standing on the operative side, 2.4 times in the case of half weight-bearing on the operative side, 3.8 times in the case of one-legged standing on the non-operative side, and 2.0 times in the sitting position, respectively
Our study model was originally obtained from a bony union at the osteotomy site of the superior pubic rami (Figure 1); this is defined as the “union model”

Summary

Introduction

Acetabular osteotomies are useful for increasing the covering of the femoral head, and for medialization of the femoral head. The method requires detachment of the gluteus medius muscle; the surgery is significantly invasive For this reason, curved periacetabular osteotomy (CPO) [4], considered less invasive than other acetabular osteotomies, was adopted as the treatment of first choice for hip dysplasia in young patients in our institution. Postoperative pubic or ischial stress fracture has been referred as a complication in some reports, and discontinuity of superior pubic rami [9,10] and narrowing of the inferior pubic rami [10,11] have been considered as risk factors. Interpretation: We recommend patients delay weight bearing on the operative side, avoid the sitting position as long as possible, and sit down slowly to prevent inferior pubic rami and ischial fractures after CPO

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