Distal Radius Volar Locking Plate Design and Associated Vulnerability of the Flexor Pollicis Longus

PurposeFlexor pollicis longus (FPL) tendon rupture is a well-documented complication related to the use of distal radius volar locking plates (VLPs). The final common pathway of flexor tendon rupture appears to involve implants prominent at the watershed line. We hypothesized that significant differences in VLP prominence exist between various plate designs.MethodsTen fresh frozen specimens were dissected to identify the path of the FPL in relationship to the distal radius at the watershed line. Five VLP designs were fixed to each specimen based on their anatomic fit, and slid distally until the distal edge of the plate reached the watershed line. The position of each fixed plate was evaluated by fluoroscopy. We used a 3-dimensional laser scanner to create computer models. The total surface area of plate prominence volar to the watershed line and the prominent area beneath the FPL were measured in the axial plane using computer software.ResultsAt the watershed line, the FPL was located at 54% of the maximal width of the radius, as measured from its volar-ulnar corner. There were no significant differences in the location of plate fixation on lateral view radiographs according to the classification of Soong et al. The mean total surface area of plate prominence was 36 mm2. The mean prominent area beneath the FPL was 10 mm2. Significant differences in plate prominence were noted for various designs.ConclusionsDespite optimal plate placement, various VLP designs were observed to have prominent profiles volar to the watershed line, to varying extents.Clinical relevanceThe results raise concerns regarding interference between all of the analyzed VLP designs and the FPL. This study may help guide both implant design considerations and assist the surgeon in better understanding implant morphology as it relates to iatrogenic flexor tendon injury.