What is the desired screw trajectory for fixation of noncontiguous posterior distal articular fractures associated with distal tibial shaft fractures?

Abstract

Posterior distal articular fractures (pDAFs) associated with tibial shaft fractures are often nondisplaced allowing for fixation with percutaneous screws. This study uses imaging of such injuries to determine trajectory for percutaneous screws such that the fixation is perpendicular to and engages the center of pDAFs. This retrospective review at a single academic level one trauma center included radiographic review of all patients with distal tibial shaft fractures and associated noncontiguous pDAFs between 2015 and 2020. The axial pDAF angle with reference to the trans-malleolar axis and sagittal pDAF angle with reference to the long axis of the tibial shaft were measured using computed tomography imaging. These measurements were used to determine the screw starting point and the trajectory angle in both axial and longitudinal axes that would ensure the screw crossed the fracture plane orthogonally and targeted the center of the posterior fracture fragment, defined for purposes of this study as the desired screw position. DAFs were overall identified in 74/145 cases (51.0%), 56/74 (75.6%) of which were pDAFs. With the far end of the screw positioned in the center of the posterior fragment, the mean axial screw angle for perpendicular fixation of pDAFs was 31° ± 4°, corresponding to a starting point at 76% ± 9% of the total width of the tibial plafond from the most lateral extent. The mean sagittal screw angle for perpendicular fixation of pDAFs was 80° ± 5°. Screw placement placed at these angles would be accurate within 1 SD of the desired screw position in only 29/56 (52%) fractures in the axial plane and 44/56 (78%) fractures in the sagittal plane. This study demonstrates that a standardized screw angle and starting point would place a screw in only 52% of fractures in the axial plane and 78% of fractures in the sagittal plane within 1 SD of the desired screw position. Results of this study suggest that computed tomography scans are useful for preoperative templating of screw trajectory for pDAFs associated with tibial shaft fractures as there is no single percutaneous trajectory that targets the screw in the ideal manner (orthogonal to the fracture plane and centered in the fragment) for every one of these fractures.