Effects of increased loading and factors inhibiting tissue healing

Musculoskeletal tissues adapt to changes in repetitive loading and training. When the adaptive response fail to meet the increased demands imposed by a training or rehabilitative program, the exceeding loadings can damage the tissues, causing inflammation and repair. Aggressive rehabilitation programs early carried out after a tissue reconstruction put stress on the healing tissue. Repetitive exercise can increase the strength, size, matrix organization and possibly collagen content of tendons and ligament and their insertion into bone. The fine balance between reparative stimulus and damage requires the knowledge of the basis of healing process with biological properties of the tissues and biomechanical characteristics of the reconstructed structures. The effects of increased loading on different tissues during rehabilitation stages and the role of the primary fixation strength in surgical procedures were extensively studied (1-3). ACL Reconstruction Central-third bone-patellar tendon-bone and hamstring tendon autografts have been commonly used as substitutes for the ACL and they are fixed to the femur and the tibia using various kinds of fixation. Since 1990 postoperative rehabilitation after ACL reconstruction has been accelerated, so strength and stiffness of the femur-graft-tibia complex are required for such rehabilitation, especially during the immediate postoperative period. In 1995 Beynnon noted that the stress on the intact ACL range between 25N and 500N during squatting, leg extension and running; so 500N is considered the strength that a device should ensure for the initial biomechanical fixation. Our efforts were pointed on evaluation, using cyclic loading with final pull-out tests, of different coupled fixation devices (femoral and tibial together) commonly used for ACL reconstruction using doubled semitendinosus and gracilis tendons (DGST). For this study 5 different fixation methods were selected. We tested the complex with a cyclic loading of 1000 cycles between 10 and 150 N. This study shows that are now available some different fixation devices for femoral and tibial fixation of DGST for ACL reconstruction, differing for material, kind of fixation, surgical technique. Some among these devices shows good biomechanical properties, so they should be safely used for ACL reconstruction with an adequate post-op rehabilitation, but the best combination should also be in example of 2 different devices produced by different industries. So the surgeon could choice the best combination for each patients and the best technique in his own hands. Shoulder Rotator Cuff tears are a common cause of shoulder pain and dysfunction. The successful surgical reattachment of torn tendons to the humerus is the aim of reparable tears treatment. Recent studies have demonstrated the anchor suture repair technique to be significantly stronger than the bone tunnels technique. The initial ultimate tensile strength of the anchors was widely tested but resistance to cyclic loading provides a better simulation of the in vivo condition of fatigue of the “anchor-suture-tendon” complex. Three different bone anchors were tested: two absorbable anchors of 5.0 and 6.5 mm respectively (Bio-corkscrew, Arthrex-Naples-Florida) and a metallic anchor of 5.0 mm (Cork screw, Arthrex-Naples-Florida). Coupled with the anchors we tested two kind of suture: Ethibond (Ethicon Johnson&Johnson) and FiberWire (Arthrex-Naples-Florida). To simulate the postoperative conditions, a cyclic loading was performed, similar to previous studies. The tensile load was then increased until the failure of the anchor fixation system. The ultimate failure load, the stiffness and the site and the mode of failure were registered. Results of our study suggests: 1) The polyblend suture increases significantly the strength of fixation devices under cyclic load. 2) Bioabsorbable anchors coupled with FiberWire show ultimate failure load values similar to those of metallic anchor-FiberWire combination, with important differences in the failure mode, which seems suggest a safer use of absorbable devices in clinical applications, in order to avoid metallic anchor migration. 3) Future construction of stronger loop of absorbable anchors might increase the ultimate failure load of the Fiberwire-anchor complex. 4) There are not important differences in biomechanical evaluation between bioabsorbable anchors of the 2 different size tested in this study.