Reimers Migration Percentage in Cerebral Palsy Hip Displacement: A Literature-Based Rationale and Statistical...

Hip redislocation after reconstructive surgery remains a major challenge in children with cerebral palsy (CP), particularly those with severe motor impairment. The Reimers migration percentage (RMP) has long been used empirically to guide surgical decision-making, but the optimal cutoff for predicting redislocation has not been statistically validated.

This study aimed to determine the most accurate RMP threshold for predicting postoperative redislocation using statistical methods in a retrospective cohort of children with CP.

We retrospectively analyzed 116 hips from 95 children with CP (Gross Motor Function Classification System (GMFCS) Level IV-V) who underwent reconstructive hip surgery. Preoperative RMP was evaluated using receiver-operating characteristic (ROC) analysis, and the Youden index was applied to identify the optimal cutoff. Hierarchical, block-wise logistic regression analysis that incorporated relevant confounders and surgical variables was performed to assess redislocation.

To statistically determine the optimal RMP cutoff, we first observed that the median preoperative RMP was significantly higher in the Redislocation Group 72.5 (IQR 50-100) compared to the non-redislocation group 50 (IQR 42.25-70, p=0.002). ROC analysis yielded an area under the curve (AUC) of 0.66, with 70% identified as the optimal threshold. In the fully adjusted model, RMP ≥70% remained independently associated with redislocation (adjusted odds ratio (OR) = 3.59, 95% CI 1.45-8.85, p=0.006).

This study provides the first statistical validation of the empirically suggested 70% RMP cutoff for predicting redislocation after reconstructive hip surgery in CP. Although discrimination was modest, the threshold offers a practical tool for risk stratification. Clinically, RMP ≥70% should prompt closer postoperative surveillance and may support consideration of earlier or more extensive reconstructive strategies in high-risk patients.