The Impact of Radiofrequency Shrinkage on the Mechanical and Histologic Properties of the Elongated Anterior Cruciate Ligament in a Sheep Model

Purpose: Shrinkage of the elongated anterior cruciate ligament (ACL) and its grafts with radiofrequency (RF) energy has become increasingly popular as an alternative to ACL reconstruction in the field of knee surgery. Although there have been a few clinical studies on the outcome and complications of RF shrinkage of the elongated ACL, there is a substantial lack of in vivo basic science studies to evaluate the mechanical and histologic changes of such treated tissue. Therefore, it was the aim of this study to simulate an ACL elongation in an animal model, treat this pathology with RF shrinkage, and analyze the mechanical and histologic changes at 6 months after initial treatment. Type of Study: Experimental in vivo animal study. Methods: A chronic elongation of the ACL was simulated in 16 mature female merino sheep. In group A, no treatment was applied; in group B, RF shrinkage was used. For biomechanical testing anteroposterior (AP) laxity was measured at time zero and 24 weeks. A load-to-failure test was also performed at 24 weeks. For histologic analysis, cell number and crimp pattern were measured by conventional histologic examination and the vascular status by immunohistochemical histologic examination. Results: The initial reduction of AP laxity after RF shrinkage could not be maintained at 24 weeks. A significant reduction in ultimate load was found at 24 weeks in the RF-treated group B compared with the untreated group A. At 24 weeks, an intensive process of tendon remodeling was ongoing in the RF-treated group that differed substantially from the untreated elongated ACLs and the intact ACL. Conclusions: The treatment of an elongated ACL with RF energy resulted in a significant impairment of its ultimate load and induced a process of intensive remodeling that was not completed at 24 weeks. Therefore, strong caution is warranted during the time of rehabilitation, considering the impaired ligamentous structure. Clinical Relevance: This study provides insights into the consequences of RF shrinkage of the ACL that will guide the clinician in the appropriate rehabilitation of patients and informs of possible complications associated with this procedure.