Accuracy of computerized frameless stereotactic image-guided pedicle screw placement into previously fused lumbar spines.

STUDY DESIGN: A retrospective chart and radiographic review of 122 pedicle screws placed with computerized stereotactic image-guidance into posterolateral fusion masses.

OBJECTIVES: To determine the accuracy rate of computerized stereotactic image-guided pedicle screw placement in previously fused lumbar spines.

SUMMARY OF BACKGROUND DATA: Placement of pedicle screws into a previously fused lumbar spine is challenging. The normal anatomic landmarks used to determine the starting point and trajectory of the screws have either been removed or are obscured by the fusion mass. Computerized frameless stereotaxis provides precise intraoperative real time multiplanar image-guidance and may be valuable in this clinical situation.

METHODS: Computerized frameless stereotactic image-guidance was used to place pedicle screws into 78 consecutive patients with prior lumbar spine fusions. Postoperative computed tomography was available on 35 patients (231 screws). One hundred and twenty-two screws were placed into fusion masses. Pedicle cortical perforations were characterized by the direction (medial, inferior, lateral, or superior) and magnitude (in 2-mm increments) of perforation.

RESULTS: Five (4.1%) of the 122 pedicle screws placed into previously fused levels were found to have unintentional cortical violations. There were 1 superior (<2 mm), 1 medial (<2 mm), and 3 lateral perforations (<2, 4, and 6 mm). None of these perforations led to clinically apparent radicular pain or weakness. No pedicle screws required revision for malpositioning.

CONCLUSIONS: The accuracy rate of stereotactic image-guided pedicle screw placement into previously fused lumbar spine levels is 96%. Computerized stereotactic image-guidance may have particular application in situations in which posterior element anatomy is altered, such as in the presence of a prior fusion mass.