Incidence and Risk Factors for Postoperative Hip Displacement Following Spinal Fusion in Nonambulant Patients With Spastic Neuromuscular Scoliosis.

Study Design: Retrospective multicenter cohort study.

Objective: To investigate the incidence and risk factors of postoperative hip displacement following spinal fusion in nonambulant patients with spastic neuromuscular scoliosis.

Summary Of Background Data: In patients with spastic neuromuscular disorders, spinal deformity, and hip displacement mutually influence each other; however, little is known about the clinical impact of spinal fusion on the incidence of hip displacement.

Methods: We retrospectively analyzed nonambulant patients with spastic neuromuscular disorders undergoing primary fusion with a minimum follow-up of 1 year. The primary outcome was new postoperative hip displacement. To identify potential risk factors for postoperative hip displacement, an association analysis was conducted.

Results: We identified 67 eligible patients (29 males and 38 females) with a mean age of 14.1 years and a mean follow-up period of 49.4 months. Overall, 11 cases of postoperative hip displacement (10 up hip, and 1 down hip) were identified in 11 patients (16.4%). Patients with hip displacement were significantly more skeletally immature at surgery, had a significantly larger preoperative curve magnitude (115.6 vs. 97.5 degrees), larger correction of the Cobb angle (71.0 vs. 56.8 degrees), larger preoperative pelvic obliquity (36.2 vs. 24.3 degrees), and included a significantly higher proportion of cases with pelvic fixation (P=0.03). Compared with patients with nondislocated stable up hip joints, 10 patients with new up hip displacement had a significantly higher preoperative migration percentage (MP) in the up hip (40.6 vs. 31.4, P=0.047). Receiver operating characteristic curve analysis revealed that the optimal cutoff value of the preoperative MP of the up hip for predicting postoperative displacement was 28.8 (sensitivity, 90.0%; specificity, 47.8%).

Conclusions: When performing spinal fusion in patients with spastic neuromuscular disorders, especially in those with identified potential risk factors, patients and their caregivers should be informed preoperatively about the possibility of subsequent hip displacement.

Level Of Evidence: Level III.