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Comparative Anatomy of the Anterior Cruciate Ligament Insertions in Primates
Author(s) -
Ruth Aidan,
Raghanti Mary Ann,
Lovejoy C. Owen
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.902.21
Subject(s) - anatomy , enthesis , fibrocartilage , cadaver , anterior cruciate ligament , biology , ligament , tibia , gorilla , medicine , osteoarthritis , articular cartilage , paleontology , pathology , alternative medicine , tendon
Despite a robust body of clinical literature on human entheses, relatively little is known about their anatomy in other species. We sought to document the microstructure of the femoral and tibial insertions of the anterior cruciate ligament (ACL) in a number of mammals, with a particular focus on Primates . Species investigated included those using unguligrade (deer, sheep), digitigrade (lion, tiger), and plantigrade (gorilla, Diana monkey, human) postures. We also explored the relationships between fibrocartilage thickness at ligament insertion sites and body mass. We found that most anatomical landmarks of the human ACL insertion have homologues in other mammals, including the Lateral Intercondylar Ridge (LIR), the Lateral Intercondylar Posterior Ridge (LIPR), and the Medial Intercondylar Ridge of the Tibia. However, we found that these ridges are not limited termini as is often assumed. Rather, their entheses are expansive and exhibit fibers that extend from both anterior and posterior aspects of these ridges. Considerable variation exists at the lateral border of the tibial ACL insertion, most likely related to spatial distinction of three subdivisions of the ACL (“bundles”) in deer and other ungulates. While primates still display up to three ACL bundles, they adhere more closely to one another and lack distinct septa. Humans share this primate‐typical anatomy. We measured fibrocartilage thickness of the ACL enthesis on histological thin sections using the method of orthogonal intercepts. Results of a standard linear regression of fibrocartilage thickness and body size indicate that there is no relationship between the natural log of body size as reported in the literature and the natural log of fibrocartilage thickness for either the femoral (F = 1.505, p= 0.1) or tibial (F = 2.57, p = 0.09) insertion sites of the ACL. These data suggest the possibility that, despite the potential biomechanical advantage of substantial fibrocartilage thickness, there may be an upper limit dictated by the (in)ability of nutrients and other cellular signals to diffuse within its extracellular matrix.