Terminal position of a tibial intramedullary nail: a computed tomography (CT) based study.

ABSTRACT

PURPOSE: The purpose of this study is to characterize the distal anatomic end-point of a tibial intramedullary nail placed using modern surgical techniques. The goal is to improve reduction of distal tibia fractures. METHODS: An intramedullary nail was placed in 14 skeletally mature legs. This included 8 patients with mid-shaft tibial fractures and 6 intact cadaveric legs. Each nail was a titanium cannulated tibial nail, size 10- or 11-mm. The nails were placed using a suprapatellar or transpatellar approach with an ideal starting point. All legs received post-nail insertion CT scans and fluoroscopy. The main outcome measure was the terminal location of the nail just proximal to the distal tibial physeal scar, as seen on axial CT and fluoroscopic views of the ankle (mortise and lateral). The end-point was measured as the (1) ratio of medial-lateral tibial width (ML ratio) and (2) ratio of anterior-posterior tibial width (AP ratio). Two-tailed Welch's t tests were used to compare the actual, observed position of the nail to the hypothesized center-center position (H0 = ML and AP ratio of 0.5). RESULTS: All enrolled patients (n = 8) and cadaveric legs were included (n = 6). On axial CT, the average distance from the medial tibial cortex to the nail center as a ratio of medial-lateral tibial width was 0.63, 95% CI 0.60-0.67, p < 0.001 (Patient = 0.60, 95% CI 0.55-0.64, p = 0.001) (Cadaver = 0.68, 95% CI 0.64-0.73, p < 0.001). On fluoroscopic mortise views, the distance from the medial cortex to the nail center as ratio of medial-lateral tibial width was 0.64, 95% CI 0.60-0.67, p < 0.001 (Patient = 0.61, 95% CI 0.56-0.65, p < 0.001) (Cadaver = 0.67, 95% CI 0.63-0.72, p < 0.001). The AP ratio was not significantly different from 0.5 on either axial CT or fluoroscopic mortise views (p > 0.05). CONCLUSION: The distal end-point of a tibial intramedullary nail is lateral (ML plane) and center (AP plane) in both cadaveric legs and patients with midshaft tibia fractures. These results suggest that the treatment of distal tibia fractures with intramedullary nails may be improved by positioning the nail slightly lateral in the distal segment. LEVEL OF EVIDENCE Diagnostic level I.