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.