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Differences in Anterior Cruciate Ligament Fiber Orientation Between Digitigrade and Palmigrade Animals
Author(s) -
Ruth Aidan Alifair,
Hieironymus Tobin,
Lovejoy C. Owen
Publication year - 2016
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.30.1_supplement.368.5
Subject(s) - anterior cruciate ligament , anatomy , biology , ultrastructure , ligament
In humans, the Anterior Cruciate Ligament (ACL) is divided into two main bundles; the Anteromedial (AM) and Posterolateral (PL). We sought to determine whether similar ACL divisions occur in animals with differing locomotion. We explored the gross detailed ACL anatomy in 22 mammalian species with both standard and quantitative polarized light microscopy. Traditional light microscopy with picrosirius red staining revealed that the ACL could not be divided into distinct bundles in most palmigrade mammals, including most primates. However, digitigrade animals (Tiger) and especially unguligrade mammals (deer) displayed distinct ultrastructure with demonstrable separation of at least two distinct bundles. Quantitative polarized light microscopy showed that in animals without such ultrastructural divisions, the ACL showed greater directional diversity. That is, the greater the separation between ACL sub‐bundles, the less variation occurred in fiber orientation. These results suggest that the ACL of palmigrade animals, which require a greater range of motion at the knee joint, in turn require more differentiation of fiber orientation and length than do digitigrade mammals, and thus display more “blended,” coalescent bundles.