Reoperations After Soft Tissue Release for Spastic Hip Displacement: Which One Matters More-Migration Percentage, Acetabular Index, or Motor Function?

INTRODUCTION: Current treatments for hip displacement in cerebral palsy primarily rely on the migration percentage (MP). The literature highlights various factors contributing to treatment failure, though the significance of each remains debated. This study aimed to identify predictors of reoperation after soft tissue release (STR) for residual or recurrent hip displacement. METHODS: In this retrospective cohort study, 51 patients who underwent adductor, psoas, and hamstring releases for hip displacement with MP>30% were included. Reoperations within 5 years after STR were evaluated as the primary outcome. The χ2 tests, t tests, and binary logistic regression analyses were used to identify factors associated with reoperation, including age, motor function level, windswept deformity, worse-side MP, and acetabular index (AI). RESULTS: Twenty-three patients underwent reoperation at an average of 2.7 years after STR, whereas 28 patients had no reoperation within 5 years postoperatively. Patients with reoperations had significantly higher preoperative AI (29.5 vs. 25.0 degrees, P=0.002) and MP (49.1% vs. 41.4%, P=0.008) compared with those without reoperations. Receiver operating characteristic curve analysis identified cutoff values of 25 degrees for AI and 44% for MP to distinguish the 2 groups. Logistic regression analysis revealed AI as the only significant predictor of reoperation. Using the hips with AI<25 degrees and MP<44% as the reference, the odds ratios for reoperation were 5.4 for hips with AI>25 degrees and MP>44%, 3.6 for hips with AI>25 degrees and MP<44%, and nonsignificant for AI<25 degrees and MP>44%. CONCLUSIONS: Preoperative AI was a more reliable predictor of failure after STR than preoperative MP. This supports incorporating AI into preoperative decision-making, rather than relying solely on MP to guide the choice between STR and reconstructive surgery. LEVEL OF EVIDENCE: Level III-prognostic case-control study.