Impact of Plate Design on Contact Force between the Flexor Tendons and Distal Radius Volar Plate

Objective: The purpose of this study is to determine whether the design of distal radius volar plates impact the amount of force exerted on the flexor digitorum profundus (FDP) and flexor pollicis longus (FPL) tendons when the plates are placed proximal and distal to the watershed line.

Methods: Three commercially available plates were applied to ten fresh, matched-pair upper extremity specimens. External cyclical loading was applied to the tendons, and the force generated between tendon and plate was measured. Linear mixed effect models were used to evaluate differences in log-transformed values of maximum and mean force by plate position, plate design and the interaction between position and design.

Results: The forces on the tendons differed significantly by position, as measured by Soong grade, but were not significantly different for plate design. For the FPL tendon, the average maximum force with a plate in Soong 2 was 4.50 [95% CI: 2.8, 7.3] times higher than when the plate was in a Soong 0 placement, and 4.63 [95% CI: 2.82, 7.61] times higher for the FDP tendon. While not statistically significant, lower observed force values with thinner plates when plates were placed distal to the watershed line suggest that that plate thickness could also be a critical plate characteristic for distally placed plates.

Conclusions: Despite differences in plate design, the main determinant of plate prominence and therefore flexor tendon injury potential is placement in relation to the watershed line. This study may help guide surgeon implant selection and volar plate design.