Charles L. McDowell

Tendon healing: An experimental model in the dog

Based upon the studies of the healing process in dogs in which profundus tendons were severed partially by a method in which the cut surfaces remained in contact and the area of division was in an undamaged area of the sheath, it was shown that healing of the tendon took place without evidence of vascular contribution from the sheath. Vascular loop patterns, similar to those seen in synovial lining of joints or on either side of the growth plate of growing bone, were found on the surface of the tendons in the area of mesotenon reflection, the osseotendinous junctions, where the vinculum joined the tendon, and in various areas of the tendon sheath. No other vessels were found. A theory for nutrition of the tendon is proposed analagous to that postulated for maintenance of cartilage, first with the formation of synovial fluid by the vascular loop system and then a diffusion phase dependent upon the repetitive loading and unloading of the tissue to force the fluid into the system of canaliculi in the tendon.

Rehabilitation and surgical reconstruction of the upper limb in tetraplegia: An update☆

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Proximal Tendon-Prosthesis Junction for Active Tendon Implants of the Hand: A Biomechanical Comparison of 2 Techniques

PURPOSE To study the biomechanical characteristics (percent stretch, stiffness, and ultimate load) of 2 tendon-prosthesis techniques used to connect the proximal tendon stump to silicone active tendon implants used in reconstruction of flexor tendons. METHODS We evaluated percent stretch following cyclic loading and at failure, stiffness during load to failure, and ultimate load of 16 tendon-prosthesis junctions using cadaveric canine flexor digitorum profundus tendons to re-create 2 junction techniques: the tendon loop (TL) and the polyester weave (PW). RESULTS The TL junction showed greater percent stretch at a static load of 2 N, following 500 cycles of loading between 2 N and 50 N, and at peak load. The PW junction displayed greater stiffness from 50 to 150 N during load to failure. Both junctions failed at a mean ultimate load greater than 220 N. CONCLUSIONS The described proximal junction techniques for active tendon implants were strong enough to resist early active motion in the immediate postoperative period without significant elongation. The PW technique displayed greater stiffness and ultimate load compared with the TL. CLINICAL RELEVANCE Data on tendon-prosthesis characteristics of these 2 methods may aid the surgeon in choosing which junction technique to use, during surgical tensioning decisions, and in considering activity protocols after surgery. These data may also serve as a baseline for further investigations regarding active tendon implants.

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 surgeons 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.