Summary: This study evaluates the failure of pelvic fixation in long instrumented posterior spinal fusions for neuromuscular scoliosis. We report that failure of traditional pelvic fixation is common and the amount of distal fixation affects the failure rate. Fixation in the pelvis failed in 30% of cases. However, no construct failed when sacroiliac screws (S2 screws) and bilateral pedicle screws at L5 and S1 was achieved.
Introduction: This study evaluates the failure of pelvic fixation in long instrumented posterior spinal fusions for scoliosis. This data reports that failure of traditional pelvic fixation is common and the amount of distal fixation affects the failure rate.
Methods: A retrospective review of consecutive cases of posterior‐only spinal instrumentation and fusion to the pelvis with iliac screws was performed. 43 patients (18 female, 25 male) with average age 14 years and an average of 16 levels fused (9‐19) met inclusion criteria. Diagnoses include cerebral palsy (22), Duchenne's muscular dystrophy (7), other neuromuscular (12), and spina bifida (2). Z‐test was used to compare rates of failure.
Results: The average preoperative primary Cobb angle was 81 (21‐144) degrees. The pelvic obliquity correction was 88%. All, but one, of the patients were non‐ambulatory. The fixation in the pelvis failed in 13/43 patients (30%). Failures include: screw head of iliac screw disengaged from screw shaft (5), iliac screw disengaged from rod (1), iliac connector disengaged from rod (3), iliac connector disengaged from iliac screw (2), and iliac screw loosened from bone (2). No failures occurred if there were at least 6 screws in L5, S1 and pelvis (0/17 patients). The failure rate with less than 6 screws in L5, S1 and pelvis was significantly higher at 50% (13/26 patients) (p=0.002). When using traditional iliac screws with connectors to rods, all constructs had < 6 screws in L5, S1 and pelvis. No failures occurred when sacral alar‐iliac screws were used. The mean time from surgery to failure was 18 months (1‐49 months).
Conclusion: Not placing bilateral pedicle screws at L5 and S1, in addition to 2 iliac screws, was associated with a 50% failure rate of pelvic fixation.
Significance: Even in a non‐ambulatory population, we recommend placement of 2 pedicle screws at L5, 2 pedicle screws at S1 and 2 iliac screws. This construct is technically most easily achieved when using sacral alar‐iliac screws instead of traditional iliac screws with offset connectors.
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