Late Proximal Pedicle Hook Migration Into Spinal Canal After Posterior Correction Surgery of Scoliosis Causing Neurologic Deficit: "Proximal Junctional Scoliosis"? Case Series and a Review of the Literature.

Methods: Case series. Objective: We describe 4 patients with proximal pedicle hook migration as a late complication (greater than 12 months postoperatively) of posterior correction surgery in adolescent idiopathic scoliosis. We studied failure mechanisms and propose strategies for revision surgery.

Background: Few published cases of hook migration into the spinal canal concern mainly intra-operative or early postoperative dislodgement. Re-operation rates for adolescent idiopathic scoliosis are 2% to 10%.

Methods: We retrospectively reviewed medical records and radiographic images in 4 patients with symptomatic pedicle hook migration into the spinal canal. We studied our scoliosis revision surgery rates over the past 10 years and reviewed the literature for instrumentation failure after scoliosis surgery.

Results: Our total re-operation rate between January 2002 and April 2012 was 7.0% (56 of 800 procedures), with a mean follow-up of 61 months (range, 6-129 months). Proximal hook migration presented in 1.0% (8 of 800 procedures), including 4 into the spinal canal. These 4 patients presented with pain symptoms 19-78 months after uneventful index posterior correction surgery. In all 4 patients, radiographic imaging showed proximal pedicle hook migration into the spinal canal without proximal sagittal alignment problems. In all patients, spinal fusion was observed on computed tomographic imaging and at revision surgery. Revision surgery consisted of at least hook removal. In all 4 patients, symptoms completely resolved over time.

Conclusions: Hooks can migrate and potentially cause neurologic impairment and pain long after index surgery, despite the presence of solid spinal fusion. We believe this is partly the result of the surgical technique we used and have since abandoned, and partly the proximal spine settling and fusion mass deformation over time, which we call "proximal junctional scoliosis." We recommend computed tomographic imaging in case of postoperative symptoms and removal of hooks in case of hook migration into the spinal canal.