Effect of Postoperative Femoral Neck Shaft Angle on Femoral Head Sphericity Following Proximal Femoral Osteotomy in Legg-Calve-Perthes Disease

Abstract

Background: Herein, we aimed to examine the relationship between the postoperative neck shaft angle (NSA) and the Stulberg outcome at skeletal maturity in patients with Legg-Calvé-Perthes disease (LCPD) who underwent proximal femoral varus osteotomy (PFVO) and to determine the optimal angle of varization.

Methods: In this retrospective study, we analyzed the data of 90 patients aged older than 6 years at the time of diagnosis with LCPD who underwent PFVO at our institution between 1979 and 2014. Univariate and multivariate logistic regression analyses were used to examine the effects of variables on the sphericity of the femoral head at skeletal maturity, including the age at onset, sex, stage at operation, extent of epiphyseal involvement and epiphyseal collapse, presence of specific epiphyseal, metaphyseal, and acetabular changes, and postoperative NSA. The sphericity of the femoral head on the final plain follow-up radiographs of the hip joint at skeletal maturity was assessed using the Stulberg classification. Cases of spherical femoral head (Stulberg I or II) were rated as good, whereas those of ovoid or flat femoral head (Stulberg III, IV, or V) were rated as bad.

Results: The mean age at diagnosis was 7.93 (range, 6.0-12.33) years. The average follow-up period was 10.11 (range, 5.25-22.92) years. The pre and postoperative mean NSAs were 137.31±6.86 degrees (range, 115.7-158 degrees) and 115.7±9.83 degrees (range, 88.6-137.6 degrees), respectively. The age at diagnosis, lateral pillar classification, and postoperative NSA were found to be closely related to the sphericity of the femoral head at skeletal maturity. Patients with a postoperative NSA of <105 degree or more than 125 degree were less likely to have a spherical femoral head.

Conclusions: Our study showed that patients with a postoperative NSA between 105 and 125 degrees were more likely to have a spherical femoral head. When performing PFVO in patients with LCPD, reasonable varus angulation of PFVO should be taken into consideration for the success of the operation.

Level of evidence: Level III retrospective cohort study.