Mechanisms of curve progression following sublaminar (Luque) spinal instrumentation

Fifty-two patients with Luque instrumentation were reviewed for spinal deformities. Forty-two patients were reviewed during 1 year (longest 7.2 years) at follow-up. Two patients were included who lost correction within 1 year (both 8 months). Follow up averaged 2.9 years. Curve causes primarily were neuromuscular but included one was caused by idiopathic scoliosis, four by Scheuermann's disease, and 1 by post-laminectomy kyphosis. The Cobb angle progressed in 45% of patients postoperatively. Factors contributing to progression included progressive vertebral rotation or the crankshaft phenomenon (11), wire pull out (7), progressive pelvic obliquity (4), rod bending (3), pseudarthrosis (2), and rod migration (2). Factors correlating with progression were kyphosis, postoperative curve greater than 35 degrees, preoperative curve greater than 60 degrees, and not fusing to the pelvis in nonambulators. Crankshaft was common in patients Risser II or less but did not occur in more mature patients.