Prevalence and Modes of Posterior Hardware Failure With a Staged Protocol for Circumferential Minimally Invasive Surgical Correction of Adult Spinal Deformity: A 13-Year Experience.

Background: One of the common complications of adult spinal deformity (ASD) correction is the failure to relieve pain. This may result from the failure of implanted hardware to provide adequate stabilization. While numerous studies exist, characterizing complications that can occur with minimally invasive correction of ASD and data regarding hardware failure in this setting are limited.

Objective: This article characterizes the rate and mode of posterior hardware failure in the setting of circumferential minimally invasive surgery (CMIS) for ASD correction.

Methods: Patients undergoing staged CMIS correction of ASD from January 2007 to September 2018 were identified. Patients with a minimum 2-year follow-up were included in the study.

Result: A total of 263 patients (168 women and 95 men) were included in the study. The mean age of patients was 64 years (21-85, SD 13.7), and the mean length of follow-up was 90 months (24-164, SD 40.2). An average of 6 levels (3-16, SD 3.15) was fused per patient.Eight patients had a mechanical hardware failure and required revision surgery (3.04%). No catastrophic failures were noted in our series. Hardware failures were characterized as follows: 2 patients with broken screws, 5 patients with loose screws, and 1 patient who had symptomatic T12-L1 and L5-S1 nonunion with bilateral distal rod fractures, iliac set screw loosening, and proximal T12 screw loosening. Following revision surgery, all of these patients had confirmed solid fusion on computed tomography (CT) scan at their latest follow-up visit.Interestingly, 3 other patients had loosening of the set screw on their iliac bolts. Five patients had rod fractures between L5 and S1 or below S1. All 8 of these patients were asymptomatic with confirmed fusion at L5-S1 on CT scans.

Conclusion: The prevalence of clinically significant hardware failure needing revision in our series was low at 3.04%. Symptomatic hardware prominence requiring revision was 2.3%. Specifically, rod fractures were not common (2.2%). Our study suggests that in the appropriately selected patient, CMIS to correct ASD without osteotomies may result in acceptable rates of hardware failure. Future studies should compare the results of CMIS deformity correction to a matched population of patients undergoing open deformity correction.

Clinical Relevance: This study suggests that in the appropriately selected patient, CMIS to correct ASD without osteotomies may result in acceptable rates of hardware failure.