Dorsal subchondral arc line: A novel radiographic marker to avoid dorsal screw prominence during distal radius fixation with volar locking plates.

Abstract

The aim of this study was to evaluate a novel radiographic marker for measuring screw length during fixation of distal radius fractures with volar locking plates. The Dorsal Subchondral Arc Line (DSAL) is visualized on the lateral wrist view and screw length is determined using the intersection of a line along the longitudinal axis of the radius and the most dorsal extent of the subchondral arc. The hypothesis was that use of this marker would yield screws that did not penetrate the dorsal cortex and would provide similar fixation in the distal segment to bicortical screws. This was a study performed on 10 matched pairs of cadaveric forearms. Each specimen in a matched pair was randomized into two groups; one group received distal locking screws measured using the DSAL and the other group received distal locking screws that were fully bicortical. Specimens were all instrumented using volar locking plates and subsequently denuded of all soft tissue to determine presence of dorsal cortex penetration. Osteotomies were performed in order to simulate and extra-articular distal radius fracture with significant comminution (OTA 23-A3). All specimens were then tested under cyclical axial compression utilizing a servoelectric load frame and then loaded under axial compression to failure. All 10 matched pairs were included in final analysis. No distal screws in the DSAL group penetrated the dorsal cortex. All distal screws in the long group had bicortical purchase. No significant differences existed between the DSAL and bicortical groups in terms of stiffness (271 N/mm vs 297 N/mm, p = 0.65; respectively) or load to failure (1957 N vs 1929 N, p = 0.92; respectively). The results of this study suggest that utilizing the DSAL during fixation of distal radius fractures using volar locked plates provides a patient-specific radiographic marker to ensure ample fixation of the distal segment while minimizing the risk of dorsal screw prominence.