Sustained hip flexion contracture after femoral lengthening in patients with achondroplasia

BACKGROUND: Hip flexion contracture often occurs after femoral lengthening in patients with achondroplasia, but few studies have investigated its development in these patients. The purpose of this study was to analyze sustained hip flexion contracture in achondroplasia patients who underwent femoral lengthening and to identify contributing factors. METHODS: This study included 34 patients with achondroplasia who underwent femoral lengthening (mean age at operation, 11.1 years). Sustained hip flexion was defined as flexion contracture lasting > 6 months postoperatively despite physiotherapy. Demographic data, spinopelvic parameters (pelvic incidence, pelvic tilt, sacral slope, lumbar lordosis, and sagittal vertical axis), and quantitative assessments of femoral lengthening were investigated. The associations among these factors and the development of sustained hip flexion contracture were assessed. RESULTS: Sustained hip flexion contracture developed in 13 (38%) of 34 achondroplasia patients after femoral lengthening. Eight (62%) of these 13 patients concomitantly exhibited limitation of knee flexion. Excessive femoral lengthening (odds ratio [OR], 1.450; 95% confidence interval [CI], 1.064 to 1.975; p = 0.019) and forward sagittal vertical axis tilt (OR, 1.062; 95% CI, 1.001 to 1.127; p = 0.047) contributed to sustained hip flexion contracture. CONCLUSIONS: Sustained hip flexion contracture frequently occurs after femoral lengthening in achondroplasia patients. Both excessive femoral lengthening and preoperative forward SVA tilt may contribute to the development of sustained hip flexion contracture in these patients.