Bone-Prosthesis Junction for Active Tendon Implants: A Biomechanical Comparison of 2 Fixation Techniques.

PURPOSE: To study the biomechanical characteristics (percent stretch, stiffness, and ultimate load) of 2 distal fixation techniques for an active tendon implant used in the reconstruction of flexor tendons. METHODS: We evaluated percent stretch after cyclical loading and at failure, stiffness during load-to-failure, and peak load of 28 bone-prosthesis junctions using cadaveric canine middle phalanges to study 2 fixation techniques: metal cleat and screw versus polyester cords secured with a knot. RESULTS: The knot constructs displayed greater percent stretch during and following cyclical loading between 2 N and 50 N and at peak load. The screw construct showed greater stiffness from 50 N to 150 N during load-to-failure. Both fixation techniques failed at a mean peak load greater than 340 N. CONCLUSIONS: Both fixation techniques for active tendon implants withstood loads seen with passive and active motion in the immediate postoperative period. Knot constructs displayed significant stretch during cyclical and load-to-failure testing, which would need to be compensated for during surgery. The screw constructs showed greater stiffness than the constructs secured with the surgeon's knot, but failure created an intra-articular fracture. CLINICAL RELEVANCE: The results may aid the surgeon in choosing which fixation technique to use, during tensioning of cords, and in permitting active motion following surgery.