Temporal Healing of Achilles Tendons After Injury in Rodents Depends on Surgical Treatment and Activity.

INTRODUCTION: Achilles tendon ruptures affect 15 of 100,000 women and 55 of 100,000 men each year. Controversy continues to exist regarding optimal treatment and rehabilitation protocols. The objective of this study was to investigate the temporal effects of surgical repair and immobilization or activity on Achilles tendon healing and limb function after complete transection in rodents. METHODS: Injured tendons were repaired (n = 64) or left nonrepaired (n = 64). The animals in both cohorts were further randomized into groups immobilized in plantar flexion for 1, 3, or 6 weeks that later resumed cage and treadmill activity for 5, 3, or 0 weeks, respectively (n = 36 for each regimen), which were euthanized at 6 weeks after injury, or into groups immobilized for 1 week and then euthanized (n = 20). RESULTS: At 6 weeks after injury, the groups that had 1 week of immobilization and 5 weeks of activity had increased range of motion and decreased ankle joint toe stiffness compared with the groups that had 3 weeks of immobilization and 3 weeks of activity. The groups with 6 weeks of immobilization and no activity period had decreased tendon cross-sectional area but increased tendon echogenicity and collagen alignment. Surgical treatment dramatically decreased fatigue cycles to failure in repaired tendons from groups with 1 week of immobilization and 5 weeks of activity. Normalized comparisons between 1-week and 6-week postinjury data demonstrated that changes in tendon healing properties (area, alignment, and echogenicity) were maximized by 1 week of immobilization and 5 weeks of activity, compared with 6 weeks of immobilization and no activity period. DISCUSSION: This study builds on an earlier study of Achilles tendon fatigue mechanics and functional outcomes during early healing by examining the temporal effects of different immobilization and/or activity regimens after initial postinjury immobilization. CONCLUSION: This study demonstrates how the temporal postinjury healing response of rodent Achilles tendons depends on both surgical treatment and the timing of immobilization/activity timing. The different pattern of healing and qualities of repaired and nonrepaired tendons suggest that two very different healing processes may occur, depending on the chosen immobilization/activity regimen.

Effect of implant design on the cyclic loading properties of mini suture anchors in carpal bones.

Mini suture anchors are commonly used in hand surgery involving attachment of soft tissue to bone. There are few data on the biomechanical behavior of these implants under physiologic conditions. Commercially available mini anchors were inserted into the carpal bones of fresh-frozen cadaver wrists. Anchors were divided into threaded and pronged types according to design. The anchors were cyclically loaded. Pronged anchors (1.3 and 2.1 mm) failed at a range of 199 to 5,155 cycles. Threaded anchors (2.5 and 2.8 mm) consistently completed 40,000 cycles without failure. Before failure pronged anchors displaced on average 5.1 mm and threaded anchors displaced on average 0.01 mm. The pronged implants failed because of either prong fatigue or fracture; the threaded anchors remained structurally intact. The larger threaded suture anchors seem to have superior biomechanical properties than smaller pronged anchors.