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Consideration of Pedicle Screw Misplacement On a Per-Patient Basis: Can We Better Delineate Surgical Risk?

Saturday, October 20, 2012: 1:28 PM
Melrose (Hilton Riverside)
Vishal Sarwahi1, Terry Amaral1, Beverly Thornhill2, Preethi M. Kulkarni1, Jonathan J. Horn1 and Adam Wollowick1, (1)Orthopaedic Surgery, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, NY, (2)Radiology, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, NY

Purpose: Accuracy rate of pedicle screw (PS) placement varies from 85-95%. This demonstrates technical ability but does not represent the impact of misplacement on individual patients. This study quantifies the rate of screw misplacement on a per patient basis to highlight its effect on potential morbidity. 

Methods: A retrospective review of charts, x-rays and low dose CT scans of 106 pediatric patients who underwent spinal fusion with pedicle screws for spinal deformity was performed. Screws were divided into three categories. Type A: well placed or misplaced screw of no concern (in fat, muscle, costovertebral junction). Type B: screw of some concern (adjacent to aorta, viscera, or 2-4 mm medial breech). Type C: screw of major concern (impinging on aorta, viscera, medial displacement ≥ 4mm). 

Results: 2229 screws were placed in 106 patients. 1952 screws were placed accurately (87.6%) . 19% of patients had all screws placed accurately. In the remaining 81%, the mean number of misplaced screws was 3.25 per patient. Overall, there was a mean of 2.64 misplaced screws per patient. Type C screws (N=29) account for only 1.30% of total screw placements despite occurring in 17% of patients, and Type B screws (N=44) account for 1.97% of total screw placements despite occurring in 23% of patients. Overall, even with an 87.5% accuracy rate, 40% of patients had screws of concern (Types B or C). 

Conclusion: Although the overall screw misplacement rate is low, it does not reflect the potential impact on patient morbidity. When analyzed per patient, a higher number of patients had screws of some or major concern. With an increasing number of pedicle screws being placed in patients with spinal deformity, the number of patients with misplaced screws is likely to increase proportionally. The misplacement rate is relevant from a technical standpoint, but underestimates potential patient consequences. With 40% of patients having screw misplacement of some or major concern, better strategies need to be devised for evaluation of screw placement, including establishment of a national database of deformity surgery, use of intra-operative image guidance, and reevaluation of post-operative low-dose CT imaging.