Histological Evaluation of Regenerated Semitendinosus Tendon a Minimum of 6 Years After Harvest for Anterior Cruciate Ligament Reconstruction

BACKGROUND: Semitendinosus (ST) and/or gracilis (G) autografts are the most used grafts for anterior cruciate ligament (ACL) surgery. The tendons have been shown to be able to regenerate but with focal areas of scar tissue in the short term. There are no long-term histological studies of the regenerated tendons. HYPOTHESIS: In the long term, the regenerated ST tendon normalizes and has a similar histology as the contralateral nonharvested tendon. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: Eighteen patients (8 female, 10 male) who underwent ACL surgery using ipsilateral ST/G tendon autografts were included in this study. Percutaneous specimens were obtained from the regenerated ST tendon and the contralateral nonharvested ST tendon under ultrasonographic guidance at a median of 8.4 years (100.5 months; range, 77-129 months) after the harvest procedure. Specimens from the nonoperated side served as controls. The histology and presence of glycosaminoglycans (GAGs) were assessed using a light microscope and a semiquantitative grading system. RESULTS: Thirty-six biopsies were obtained (2 biopsies from each patient). In 5 biopsies, the amount of tissue was too small to analyze in the light microscope, and 1 patient had been operated on bilaterally and was therefore excluded. In total, 24 biopsies were included in the histological analysis. In overall terms, there were no significant differences between the regenerated and nonharvested ST tendon in terms of fiber structure, cellularity, vascularity, and level of GAGs a minimum 6 years after harvest of the ST tendon. However, 3 of the regenerated tendons displayed a loss of fiber structure. CONCLUSION: The ST tendon regenerates and may regain a histological appearance similar to that of the nonharvested contralateral tendon, as seen in this study a median of 8.4 years after harvesting. However, in some tendons, loss of fiber structure was found.