Anterior cruciate ligament (ACL) injuries are common, yet little is known about the relationship between time from injury to reconstruction and biological characteristics at the femoral insertion site. This study evaluated whether longer time from ACL injury to reconstruction was associated with differences in vascularity and bone microarchitecture at the femoral ACL footprint.

In this observational cohort study with cross-sectional histological assessment, 60 adult patients (22–53 years) undergoing primary ACL reconstruction and 10 reference patients (55–65 years) undergoing total knee arthroplasty (TKA) were enrolled. A 4.5-mm femoral bone core was harvested from the ACL femoral footprint or an anatomically corresponding site in the TKA reference cohort. Specimens underwent histological analysis and CD34 immunohistochemistry. The primary outcome was microvessel density (MVD; vessels/mm ² ). Secondary outcomes included CD34-positive cell cluster density and osteocyte lacunar density, quantified separately in three predefined regions (articular, median, and cranial). Analyses included correlation analyses, mixed-model ANOVA, and exploratory subgroup analyses according to age and time from injury to surgery.

Longer time from injury to surgery was associated with lower MVD and CD34-positive cluster density. Patients undergoing ACL reconstruction within 9 months of injury had higher mean articular-region MVD than those undergoing reconstruction after ≥9 months (2.96 ± 0.89 vs 0.40 ± 0.96 vessels/mm ² ; p = 0.014). Osteocyte lacunar density was also associated with time from injury to surgery. Exploratory age-stratified analyses suggested that the magnitude of some associations may vary according to age. Smoking was associated with lower vascular parameters, with smokers demonstrating lower mean vessel density than non-smokers (2.6 vs 3.4 vessels/mm²; p = 0.032).

Longer time from ACL injury to reconstruction, particularly intervals exceeding 9 months, was associated with lower vascular and bone microstructural parameters at the femoral insertion site. Exploratory subgroup analyses suggested potential age-related differences, while smoking was also associated with lower vascular parameters. These findings indicate that prolonged time from injury to surgery may be accompanied by differences in the local biological environment; however, the cross-sectional design precludes causal inference, and the relationship between these histological findings and postoperative graft performance remains uncertain.

III; cohort study with histological evaluation