Histomorphological changes in autologous anterior cruciate ligament graft failure show predominantly inflammatory reactions, fissure defects and osteonecrosis.

Purpose: The aim of this study was to identify morphological alterations that occur in graft failure following anterior cruciate ligament (ACL) reconstruction. It was hypothesised that multiple morphological regression phenomena are present at the time of revision surgery. Methods: In this prospective study, 43 consecutive patients undergoing revision surgery due to graft failure after autologous ACL reconstruction were analysed. Specimens were redrilled with a hollow reamer to obtain the entire drill channel and ACL remnants, which were examined histopathologically using haematoxylin and eosin (HE), Masson-Goldner, Elastika-Gieson and CD68+ stains to characterise ligamentous and osseous changes qualitatively and quantitatively under light microscopy. Results: A total of 76 bone blocks were obtained from 43 patients (mean age 29.67 ± 9.02 years; range 18-58). The cohort included 9 women (20.9%) and 34 men (79.1%). The mean time from graft failure to revision surgery was 53.4 months (range 0.23-84). Femoral fixation in the primary surgery used extracortical button fixation in 87.5% and the All-Press-Fit technique in 12.5%, while tibial fixation most commonly involved interference screws (86.4%). Spontaneous trauma was rare (2.5%), with inadequate trauma in 7.5%; 90% of failures followed adequate trauma. Histomorphologic analysis revealed various influential regression phenomena, predominantly central within the autograft. Findings included chronic histiocytic inflammation with associated capillary proliferation, fissure defects and osteonecrosis. Residual suture material emerged as a potential pathological factor contributing to severe regression and destructive changes. Occasionally, degenerative cysts, chondral metaplasia, myxoid degeneration, osteoporotic changes and ectopic ossifications were observed. Conclusion: Several histomorphological changes have been identified, each with the potential to contribute to graft failure following ACL reconstruction. The most prevalent were fissure defects, inflammatory reactions, osteonecrosis, capillary proliferation and foreign body reactions. Less common are myxoid degenerations, cystic alterations, ectopic ossifications, chondral metaplasia and osteoporotic changes. Their collective impact on graft stability and long-term clinical outcomes warrants further investigation. Level of Evidence: Level III, cohort study.