State of the mineralized tissue comprising the femoral ACL enthesis in young women with an ACL failure

Abstract

Despite poor graft integration among some patients that undergo an ACL reconstruction, there has been little consideration of the bone quality into which the ACL femoral tunnel is drilled and the graft is placed. Bone mineral density of the knee decreases following ACL injury. However, trabecular and cortical architecture differences between injured and non-injured femoral ACL entheses have not been reported. We hypothesize that injured femoral ACL entheses will show significantly less cortical and trabecular mass compared to non-injured controls.Femoral ACL enthesis explants from 54 female patients (13 – 25 years) were collected during ACL reconstructive surgery. Control explants (n = 12) were collected from 7 donors (18 - 36 years). Injured (I) femoral explants differed from those of non-injured (NI) controls with significantly less (p ≤ 0.001) cortical volumetric bone mineral density (vBMD) (NI: 736.1 – 867.6 mg/cc; I: 451.2 – 891.9 mg/cc), relative bone volume (BV/TV) (NI: 0.674 – 0.867; I: 0.401 – 0.792) and porosity (Ct.Po) (NI: 0.133 – 0.326; I: 0.209 – 0.600). Injured explants showed significantly lesstrabecular vBMD (p = 0.013) but not trabecular BV/TV (p = 0.314), thickness (p = 0.412), or separation (p = 0.828). We found significantly less cortical bone within injured femoral entheses compared to non-injured controls.Lower cortical and trabecular bone mass within patient femoral ACL entheses may help explain poor ACL graft osseointegration outcomes in the young and may be a contributor to the osteolytic phenomenon that often occurs within the graft tunnel following ACL reconstruction.