Accuracy and Efficacy of Thoracic Pedicle Screws in Curves Over 90 Degrees

· (a – Medtronic Sofamor Danek)

Introduction: Pedicle screw constructs, for treatment of thoracic scoliosis, have become increasingly more common. However, the debate continues as to the safety and efficacy of these constructs due to their perceived increased risk of neurologic injury and the increased cost of spinal instrumentation.

Purpose: 1) To evaluate the efficacy of pedicle screw only constructs to achieve sagittal and coronal correction for thoracic scoliosis ³ 90 degrees, and 2) to assess the accuracy of thoracic pedicle screw placement.

Methods: Since 1998, 19 pts with AIS, or adult progression of AIS, with a curve magnitude ³ 90° (22 curves) were treated with pedicle screw only constructs. Standing AP (or PA), lateral, and bending preoperative radiographs, and standing AP (or PA) standing radiographs were evaluated for curve magnitude, flexibility and postoperative correction to assess the efficacy of these constructs. Postoperative CT scans were also evaluated for screw accuracy using established 2 mm increments (intrapedicular, 0-2 mm breach, 2-4 mm breach, >4 mm breach). Preoperative plans were also reviewed to evaluate the ability to place a pedicle screw at each planned level in these large magnitude curves.

Results: 22 curves over 90° (ave. 101.1°, range 90-133°) in 19 patients (ave. age 21 yrs, range 11-62 yrs) with an average follow-up of 2.7 yrs (range 8 mos.- 4 yrs 6 mos.) were included in the study. Five patients underwent an anterior release in addition to the PSF. Average preop and postop curve magnitudes were as follows:

A total of 392 screws were used from T1-L5 in the 19 cases (20.1 screws/case, 12 levels/case). Screw accuracy (either intrapedicular or <2 mm breach) was 96.7% (321/332 screws) by postoperative CT scanning. Eight screws were considered to have a breach between 2-4 (2 medial, 6 lateral), and three> 4 mm (2 medial, 1 lateral). The two medial screws were the only screws that required removal (0.60%). Overall, 94% of planned screws (370/392 screws) were placed according to the preoperative plan. There were no incidences of screw or instrumentation failure. There was a temporary decrease in motor evoked potentials during curve correction in two cases; however, there were no identifiable neurologic complications.

Conclusions: Thoracic pedicle screw constructs can be safely used for large magnitude curves. Curve correction (67%) is powerful for these curves which are stiff and difficult to manage. Correction should be performed carefully with consideration given to convex compression while minimizing concave distraction for these hyper-rotatory or apparent hyperkyphotic cases and “at risk” spinal cords. Screw accuracy (96.7%) was excellent in this review. The authors have found that even in these large magnitude curves, screws can consistently be placed according to the preoperative plan.

· If noted, the author indicates something of value received. The codes are identified as: a-research or institutional support; b-miscellaneous funding; c-royalties; d-stock options.