Computed tomography evaluation of superior-segment facet-joint violation after pedicle instrumentation of the lumbar spine with a midline surgical approach

Study Design. Retrospective study. Objectives. To determine the frequency of pedicle screw violation of superior nonfused facet joints adjacent to the most cephalad pedicle screws after a midline approach for lumbar fusion. Summary of Background Data. Facet-joint violations have been evaluated in patients undergoing lumbar pedicle screw instrumentation and fusion with a Wiltse muscle-splitting approach, but not via the more common midline approach. Methods. Between 1995 and 2003, 204 patients underwent this procedure. Computed tomography scans (within 1 year postsurgery) were evaluated independently for superior facet-joint violation. chi(2) tests were used to examine bivariate associations of superior level facet-joint violation, patient age, construct level, diagnosis, and revision status for significance (P <= 0.05). Results. Superior-level facet-joint violation occurred in 24% of patients and 15% of screws, twice as often on the left side (P = 0.0396) than on the right, more frequently in single than in multiple-level procedures (P < 0.0001), and most frequently with the most cephalad screws at L5 (48%). We found no significant associations between violation rates and other designated parameters. Conclusion. The left side, single-level fusion, and most cephalad pedicle screws at L5 are targets for interventions to reduce pedicle violations in this procedure.