Learning curve for placement of thoracic pedicle screws in the deformed spine.

OBJECTIVE: The placement of thoracic pedicle screws, particularly in the deformed spine, poses unique challenges, and a learning curve. We measured the in vivo accuracy of placement of thoracic pedicle screws by computed tomography in the deformed spine by a single surgeon over time.

METHODS: After obtaining institutional review board approval, we retrospectively selected the first 30 consecutive patients who had undergone a posterior spinal fusion using a pedicle screw construct for adolescent idiopathic scoliosis by a single surgeon. The average patient age was 14 years, and their preoperative thoracic Cobb angle was, on average, 62.6 degrees. Patients were divided into 3 groups: group A, patients 1 to 10; group B, patients 11 to 20; and group C, patients 21 to 30. Intraoperative evaluation of all pedicle screws included probing of the pedicle screw tract, neurophysiologic monitoring, and fluoroscopic confirmation. Postoperative computed tomographic scans were evaluated by 2 spine surgeons, and a consensus read was established, as previously described (Kim YJ, Lenke LG, Bridwell KH, Cho YS, Riew KD. Free hand pedicle screw placement in the thoracic spine: is it safe? Spine. 2004;29(3):333-342), as (1) "in," axis of pedicle screw within the confines of the pedicle; or (2) "out," axis of pedicle screw outside the confines of the pedicle.

RESULTS: A total of 553 thoracic pedicle screws were studied (group A, n = 181; group B, n = 189; group C, n = 183) with 64 graded as out (medial, 35; lateral, 29), for an overall breach rate of 11.6%. When the breach rates were stratified by the surgeon's evolving experience, there was a temporal decrease in the breach rate (group A, 15.5%; group B, 10.6%; group C, 8.7%; P < .05). This decreased breach rate was reflected in fewer medial breaches over time (group A, 9.4%; group B, 5.8%; group C, 3.8%; P < .05). Similar trends were observed for the concave periapical screws, although statistical significance was not attained (group A, 21.2%; group B, 16.2%; group C, 10.5%).

CONCLUSION: The overall accuracy of placement of thoracic pedicle screws in the deformed spine was 88.4%, with no neurologic or visceral complications. One patient from group A returned to the operating room on postoperative day 2 for removal of an asymptomatic left T7 thoracic pedicle screw abutting the aorta. As surgeon experience increased, there was an overall decreased breach rate, which was mainly reflected in fewer medial breaches.