Histological Assessment of Mechanoreceptors in Achilles Allografts After Anterior Cruciate Ligament Reconstruction

Background: There is a lack of histological studies investigating the presence of mechanoreceptors in anterior cruciate ligament (ACL) allografts. Hypothesis: Mechanoreceptors would not grow in Achilles allografts after ACL reconstruction. Study Design: Case series study; Level of evidence, 4. Methods: Tissue samples were obtained from 11 patients who underwent ACL reconstruction using Achilles tendon allografts. They underwent biopsies during second-look arthroscopies. The mean period from ACL reconstruction to harvesting tissue was 26.63 months (range, 12-120 months). The control group consisted of 2 normal ACLs procured from 42- and 45-year-old men who underwent amputation above the knee due to trauma. Results: Ruffini corpuscles and free nerve endings were shown to be present in the specimens of the control group by processing hematoxylin-eosin stains and immunohistochemical stains with monoclonal antibodies against S-100. In the Achilles allografts, mechanoreceptors were not observed. However, fibroblasts, collagen fibers, and vessels that were not present in fresh-frozen Achilles allografts before surgery were observed. Conclusion: The results demonstrate that Achilles tendon allografts appeared similar to normal ligaments except for the lack of histological evidence of mechanoreceptors. In other words, there are no newly ingrown mechanoreceptors in ACL allografts.