Predicting Failure of Iliac Fixation in Neuromuscular Spine Deformity

Study DesignRetrospective comparative cohort study.ObjectivesIdentify whether there are patient or surgical risk factors to predict the probability of failure of iliac screw fixation after correction of neuromuscular scoliosis.Summary of Background DataThere are high reported failure rates of pelvic fixation in long posterior spinal fusion (PSF) constructs to the sacrum for neuromuscular scoliosis.MethodsPatients aged 5 to 25 years, at a single institution, had PSF to the sacrum from 2001 to 2009 with pelvic fixation using iliac screws. Clinical data were retrospectively reviewed to identify patient and surgical variables related to surgery. Failure of iliac fixation was identified strictly as a broken screw, disengagement of the screw from the connector or the connector from the rod, or set plug failure. Lucency around the screws greater than 2 mm was recorded but not considered a failure. Variables were analyzed in a statistical model to identify predictors of failure.ResultsA total of 108 patients met inclusion criteria; 100 (38 female and 62 male) had appropriate radiographs and minimum 2-year follow-up (average, 5.5 years). Coronal deformity correction averaged 59%. Most patients (89%) had fill of 6 of 8 possible distal fixation points composed of L4, L5, S1, and ilium bilaterally. Iliac screw failure occurred in 27 patients (27%). The initial single predictor statistical model identified 2 possible predictors of failure (patient: spastic tone; and surgical: absence of distal crosslink). In the multivariable model, spastic tone remained a predictor of failure (p = .0103), whereas absence of distal crosslink bordered on significance (p = .0516).ConclusionsIliac screw fixation failure is common in patients with long PSF constructs for neuromuscular scoliosis. Spastic tone is a risk factor for failure of pelvic fixation. A distal crosslink may protect against pelvic fixation failure. Alternative techniques for pelvic fixation should be studied in an attempt to improve the failure rates of iliac screw pelvic fixation.