Radiographic and histologic analysis of the tibial tunnel after allograft anterior cruciate ligament reconstruction in goats

Background: Several problems have been reported with use of allogenic grafts in anterior cruciate ligament reconstruction, including local immune response to allograft tendon within the synovial fluid, delayed maturation and ligamentization, and progressive tibial tunnel enlargement. Hypothesis: There is a correlation between the use of allograft and tibial tunnel enlargement. Study Design: Controlled laboratory study. Methods: Twenty healthy adult female goats underwent allograft anterior cruciate ligament reconstruction and were followed with serial radiographs at 6-week intervals. Animals were randomly chosen for sacrifice between 18 and 36 weeks for histologic assessment. Results: Significant radiographic increases in tunnel size were noted within the first 6 weeks of healing and remained up to 36 weeks with no further remodeling noted. Histologic analysis showed progressive ligamentization of the allografts with tendon-to-tunnel wall biologic fixation with dense connective tissue. Remodeling and incorporation of the bone plug was seen in all cases. The allograft tendon underwent early fibrous attachment within the tunnel and remodeled toward ligament histologic structure. Remodeling and incorporation of the bone plug was seen by 18 weeks. Conclusion: Tibial tunnel enlargement, consistent with that seen in humans after allograft anterior cruciate ligament reconstruction, did not appear to affect the ultimate incorporation of the allograft on a histologic level.