Medialization at the Site of Varus Derotational Osteotomy of the Proximal Femur May Reduce Instability Recurrence in Cerebral Palsy.

Abstract

Osseous reconstructive surgery for hip displacement in children with cerebral palsy (CP) consists of proximal femoral reorientation by varus derotational osteotomy (VDRO) combined with pelvic osteotomy when indicated. The rate of recurrent hip instability after the index surgery can be as high as 77%. We evaluated the association between femoral diaphyseal medialization at the VDRO site and recurrent instability. We hypothesized that medialization may modify the hip joint reaction force (HJRF), reducing the femoral remodeling that leads to recurrent coxa valga and instability. A retrospective evaluation of the clinical and radiographic records of 140 patients (280 hips) with CP, Gross Motor Function Classification System (GMFCS) Level IV or V, who had been treated with bilateral VDRO as the index surgery for hip displacement between 1998 and 2012 (mean follow-up, 11.3 years) was conducted. Radiographic measurement of medialization was performed using the medialization index (MeI) preoperatively, at 6 weeks and 12 months postoperatively, and at skeletal maturity. Recurrent instability was defined as the need for revision surgery before skeletal maturity or a final migration percentage (MP) of >40%.The influence of the MeI was determined by Poisson regression with multiple variances. The inter- and intra-observer reliability of the MeI, measured by 4 different observers, was assessed using the Cohen d test. Groups with and without relapse were comparable preoperatively regarding femoral and acetabular parameters. The baseline MP was higher in the relapse group (p < 0.001). The MeI at 6 weeks postoperatively was significantly lower in the relapse group (p = 0.004, relative risk [RR] = 0.07, 95% confidence interval [CI] = 0.01 to 0.42) than in the no-relapse group in multivariable analysis. The MeI showed good inter- and intra-observer reliability, with a Cohen d of <0.5. Patients with greater medialization had lower rates of recurrent hip instability at long-term follow-up. The MeI proved to be reliable as a radiographic measurement, and medialization did not increase mechanical instability. Therapeutic Level IV . See Instructions for Authors for a complete description of levels of evidence.