Ultrastructural characteristics of chronically failed reconstructed anterior cruciate ligament

Abstract

Background: In the present study, we have examined the ultrastructure of chronically failed reconstructed anterior cruciate ligament (ACL). We aimed to investigate a faulty ligamentization process of a failed reconstructed anterior cruciate ligament. In other words, we want to study ultrastructural alterations a failed ACL graft undergoes. Methods: Two patients who underwent revision ACL reconstruction for nontraumatic failure without discontinuity of the graft were included in the study. The first patient was a 40-year-old male who had undergone ACL reconstruction of his right knee 21 years back using the bone-patellar tendon-bone autograft. The second patient was a 23-year-old male who had sustained an ACL tear with a medial collateral ligament injury treated by isolated ACL reconstruction 3 years back using hamstring tendon autograft. We collected punch biopsy specimens from the failed ligaments of both the patients during revision ACL reconstruction. These specimens were examined for the density of collagen fibrils within a fascicle (per 1.5 μm2), cellular metabolism, and fibril diameter (nm) by transmission electron microscopy. Results: Fibroblasts of both the ligaments showed features of increased metabolism, more so in the first patient. Compared to the second patient, the fascicles of the first specimen were more loosely arranged. Both ligaments had a unimodal distribution of collagen fibrils. The first patient had a mean fibril diameter of 45.2 (+/−8.5) nm and an average fibril density of 376.8 fibrils per 1.5 μm2. The second patient had an average fibril diameter of 64.1 nm (+/−7) and a mean fibril density of 152.9 fibrils/1.5 μm2. The difference in these parameters of the two patients was statistically significant (P < 0.001). Conclusion: Our study suggests that the absence of thicker collagen fibrils with unimodal distribution, the altered density of the collagen fibrils within a fascicle, and ovoid fibroblasts with increased metabolism may symbolize bad ligamentization changes.