Limited Scar Resection for Chronic Achilles Tendon Repair: Use of a Rat Model.

BACKGROUND: Achilles tendon rupture diagnosis is frequently missed, leading to the development of a chronic rupture that requires surgical intervention to remove scar tissue and return the elongated Achilles tendon to appropriate functional length. The limited scar resection (LSR) intervention strategy may provide an advantage over other techniques, as it is less invasive and nondestructive to other tissues, although there is little evidence comparing outcomes between intervention strategies. HYPOTHESIS: The LSR technique would be a viable treatment option for chronic Achilles tendon ruptures and would perform comparably with a more clinically accepted procedure, the gastrocnemius fascial turndown (GFT), in postintervention functional outcome measures and tendon mechanical and histological properties. STUDY DESIGN: Controlled laboratory study. METHODS: Chronic Achilles tendon ruptures were induced in the right hindlimb of Sprague-Dawley rats by Achilles tendon transection without repair, immobilization in dorsiflexion, and 5 weeks of cage activity. Animals were randomly divided between the intervention strategy groups (LSR and GFT), received 1 week of immobilization in plantarflexion, and were sacrificed at 3 or 6 weeks postintervention. In vivo functional outcome measures (gait kinetics, passive joint function, tendon vascular perfusion) were quantified during healing, and tendon mechanical and histological properties were assessed postsacrifice. RESULTS: When compared with the GFT, the LSR technique elicited a faster return to baseline in gait kinetics, although there were few differences between groups or with healing time in other functional outcome measures (passive joint function and vascular perfusion). Quasi-static mechanical properties were improved with healing in both surgical intervention groups, although only the LSR group showed an improvement in fatigue properties between 3 and 6 weeks postintervention. Histological properties were similar between intervention strategies, except for decreased cellularity in the LSR group at 6 weeks postintervention. CONCLUSION: The LSR technique is a viable surgical intervention strategy for a chronic Achilles tendon rupture in a rodent model, and it performs similarly, if not better, when directly compared with a more clinically accepted surgery, the GFT. CLINICAL RELEVANCE: This study supports the increased clinical use of the LSR technique for treating chronic Achilles tendon rupture cases.

Immersion in Raloxifene does not significantly improve bone toughness or screw pull-out strength in multiple in vitro models.

BACKGROUND: Failure of surgical fixation in orthopaedic fractures occurs at a significantly higher rate in osteoporotic patients due to weakened osteoporotic bone. A therapy to acutely improve the mechanical properties of bone during fracture repair would have profound clinical impact. A previous study has demonstrated an increase in mechanical properties of acellular cortical canine bone after immersion in raloxifene. The goal of this study was to determine if similar treatment yields the same results in cancellous fetal bovine bone and whether this translates into a difference in screw pull-out strength in human cadaveric tissue. METHODS: Cancellous bone from fetal bovine distal femora underwent quasi-static four-point bending tests after being immersed in either raloxifene (20 µM) or phosphate-buffered saline as a control for 7 days (n = 10). Separately, 5 matched pairs of human osteoporotic cadaveric humeral heads underwent the same procedure. Five 3.5 mm unicortical cancellous screws were then inserted at standard surgical fixation locations to a depth of 30 mm and quasi-static screw pull-out tests were performed. RESULTS: In the four-point bending tests, there were no significant differences between the raloxifene and control groups for any of the mechanical properties - including stiffness (p = 0.333) and toughness (p = 0.546). In the screw pull-out tests, the raloxifene soaked samples and control samples had pullout strengths of 122 ± 74.3 N and 89.5 ± 63.8 N, respectively. CONCLUSIONS: Results from this study indicate that cancellous fetal bovine samples did not demonstrate an increase in toughness with raloxifene treatment, which is in contrast to previously published data that studied canine cortical bone. In vivo experiments are likely required to determine whether raloxifene will improve implant fixation.