Uncorrected sagittal plane imbalance predisposes to symptomatic instrumentation failure

BACKGROUND CONTEXT: Elucidation of the factors responsible for symptomatic failure of spinal instrumentation has been a keen interest for many investigators. PURPOSE: To quantitate the number of symptomatic instrumentation failures (SIFs) encountered during a 2-year period. The effect of sagittal plane imbalance (corrected or uncorrected) on the rate of SIF was evaluated. STUDY DESIGN: Retrospective evaluation of all patients requiring spinal instrumentation to determine which factors predispose toward instrumentation failure. PATIENT SAMPLE: All patients requiring spinal instrumentation over a 2-year period were retrospectively studied. OUTCOME MEASURES: Sagittal plane imbalance pre- and postoperatively was determined using Cobb angle analysis on plain X-rays. SIF was defined as screw back-out and/or breakage, pseudarthrosis, cage migration, or rod disconnection in patients with concordant symptoms. Asymptomatic patients did not demonstrate instrumentation failure on the routine postoperative X-rays. METHODS: Of the 355 patients who fit the criteria, 47 patients presented with either idiopathic or secondary sagittal plane deformity preoperatively. Additionally, long-segment fixation, smoking, age, and fixation across junctional segments were evaluated as risk factors for SIF. RESULTS: Of the 47 patients with sagittal plane deformity, 40 patients (85%) achieved correction demonstrated on postoperative radiographs whereas in 7 (15%), the sagittal plane imbalance was not corrected. Of these seven cases, five suffered instrumentation failure (failure rate 71.5%) versus no instrumentation failures (failure rate 0%) for the remaining 40 patients. SIF was demonstrated in 10 patients overall (failure rate of 2.8%). There was no correlation found between factors such as age, indications for surgery, or long-segment fixation, and instrumentation failure. CONCLUSIONS: Failure to correct sagittal plane deformity intraoperatively predisposes patients to SIF regardless of age, level of surgery, or indication of surgery. (C) 2008 Elsevier Inc. All rights reserved.