Biomechanical analyses of the human flexor tendon adhesion models in the hand: A cadaveric study

Patients with longstanding trigger finger may develop flexion contracture at the proximal interphalangeal (PIP) joint that persists even after division of the A1 pulley. The purpose of this study was to explore the hypothesis that flexion deformity of the PIP joint in advanced trigger finger is caused by severe adhesion between the flexor digitorum superficialis (FDS) and the flexor digitorum profundus (FDP) tendons. Ten freshly frozen cadaveric hands were used in the experiments. After preparation of the extrinsic flexor, extrinsic extensor, and intrinsic muscle tendons, we applied weights to the flexor tendons and minimal tension to the extrinsic extensor and intrinsic muscle tendons. We then measured the initial flexion angles of the metacarpophalangeal (MCP) and PIP joints. Next, we measured the flexion angles of the MCP and PIP joints as increasing tension was applied to the extrinsic extensor and intrinsic muscle tendons, respectively. We repeated these experiments after constructing flexor tendon adhesion model. The initial flexion angles of the MCP and PIP joints were greater in the adhesion model, as were the average tensions required for full extension of these joints. Our results suggest that adhesion between two flexor tendons contributes to progression of flexion deformity in the PIP joint.