title: Quantitative comparison of the microscopic anatomy of the human ACL femoral and tibial entheses.
abstract: The femoral enthesis of the human anterior cruciate ligament (ACL) is known to be more susceptible to injury than the tibial enthesis. To determine whether anatomic differences might help explain this difference, we quantified the microscopic appearance of both entheses in 15 unembalmed knee specimens using light microscopy, toluidine blue stain and image analysis. The amount of calcified fibrocartilage and uncalcified fibrocartilage, and the ligament entheseal attachment angle were then compared between the femoral and tibial entheses via linear mixed-effects models. The results showed marked differences in anatomy between the two entheses. The femoral enthesis exhibited a 3.9-fold more acute ligament attachment angle than the tibial enthesis (p<0.001), a 43% greater calcified fibrocartilage tissue area (p<0.001), and a 226% greater uncalcified fibrocartilage depth (p<0.001), with the latter differences being particularly pronounced in the central region. We conclude that the ACL femoral enthesis has more fibrocartilage and a more acute ligament attachment angle than the tibial enthesis, which provides insight into why it is more vulnerable to failure.
authors.affiliation: School of Kinesiology, University of Michigan, Ann Arbor, Michigan.|Biomechanics Research Laboratory, Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan.
authors.forename: Mélanie L
authors.initials: ML
authors.lastname: Beaulieu
authors.affiliation: School of Kinesiology, University of Michigan, Ann Arbor, Michigan.|Biomechanics Research Laboratory, Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan.
authors.forename: Grace E
authors.initials: GE
authors.lastname: Carey
authors.affiliation: Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, Michigan.
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Schlecht
authors.affiliation: Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, Michigan.|MedSport, University of Michigan, Ann Arbor, Michigan.
authors.forename: Edward M
authors.initials: EM
authors.lastname: Wojtys
authors.affiliation: School of Kinesiology, University of Michigan, Ann Arbor, Michigan.|Biomechanics Research Laboratory, Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan.
authors.forename: James A
authors.initials: JA
authors.lastname: Ashton-Miller
mesh_terms: D000328:Adult; D016118:Anterior Cruciate Ligament / Q000033:anatomy & histology* / Q000601:surgery*; D059549:Anterior Cruciate Ligament Reconstruction; D002114:Calcinosis; D002356:Cartilage / Q000473:pathology; D005260:Female; D005269:Femur / Q000033:anatomy & histology*; D051445:Fibrocartilage / Q000033:anatomy & histology / Q000473:pathology; D006801:Humans; D007718:Knee Injuries / Q000601:surgery; D008297:Male; D008853:Microscopy; D008875:Middle Aged; D013977:Tibia / Q000033:anatomy & histology*
keywords: anatomy; anterior cruciate ligament; enthesis; fibrocartilage; histology