Computed Tomography Evaluation of Pedicle Screws Placed in the Pediatric Deformed Spine Over an 8-Year Period

Abstract

A retrospective review. To evaluate the incremental accuracy of pedicle screws used in spinal deformity via a free-hand technique at a single institution over an 8-year period. The in vivo accuracy of free-hand pedicle screws placed throughout the deformed spine as evaluated by computed tomography (CT) scanning is unknown over a long time period. A total of 1023 pedicle screws inserted from T1 to L4 in 60 patients (928 screws in 54 scoliosis patients and 95 screws in 6 kyphosis patients) over an 8-year period were investigated via postoperative CT scans. Patients were divided into 3 groups (group I = 1998-1999, group II = 2001-2002, and group III = 2005). All pedicle screws were inserted via the free-hand technique using anatomic landmarks, specific entry sites, neurophysiologic, and radiographic confirmation. Pedicle screw position on CT scan was graded as acceptable versus violated, defined as the screw axis being outside the pedicle wall. One hundred seven of 1023 pedicle screws (10.5%) demonstrated significant mediolateral pedicle wall violations (19 medial vs. 88 lateral, P = 0.001). groups I and III had significantly higher lateral wall violations than group II (P < 0.05) as did the kyphotic spines (vs. scoliotic spine, P < 0.05). There were significantly more screws placed in the periapical region over time (P < 0.0001), with left-sided lateral violations (T5-T8) increasing from group II to group III, while the number of medial violations significantly decreased with time (P < 0.0001). Pedicle screws placed on the right side showed a significant decrease in accuracy from group II to group III (P = 0.03). The average transverse angle of the acceptable screws was 15.3 degrees which was significantly different from the medial (23.0 degrees , P < 0.001) and lateral (10.6 degrees , P < 0.001) violations between group I and group II. No screws demonstrated neurologic, vascular, or visceral complications. Overall accuracy of acceptable screws using the free-hand pedicle screw placement technique in the deformed spine was 89.5%, without any neurologic, vascular, or visceral complications over an 8-year period. The rate of medial violations decreased with time, as the number of screws placed in the periapical region increased.