We used 7 fresh cadaveric upper extremities without wrist osteoarthritis or any deformity. External loads of 1.5 and 3.0 kgf were applied to the FPL tendon to simulate the pinch function of the thumb. A distal radius volar plate was applied to these cadaveric specimens in various positions relative to the watershed line. We measured contact pressure between the distal plate edge and the FPL tendon using a thin flexible pressure sensor and compared it among various positions of the volar plate for wrist extension angles of 0¡ã, 30¡ã, and 60¡ã and ulnar deviation angles of 0¡ã and 20¡ã.
Under the 30¡ã or 60¡ã wrist extension condition, contact pressure significantly increased when the distal plate edge was placed distal to the watershed line, compared with when it was placed proximal to or at the watershed line.
Our quantitative results support the theory that plates placed distal to the watershed line have the potential to impinge on the traversing FPL tendon, even when a radius fracture heals anatomically.
This study clarifies a mechanism of FPL tendon irritation after volar plate fixation for distal radius fractures.