title: Ultrastructure of the three anterior cruciate ligament bundles.
abstract: The anterior cruciate ligament (ACL) can be morphologically separated into not only two, but three bundles: the anteromedial-medial bundle (AM-MB), the anteromedial-lateral bundle (AM-LB), and the posterolateral bundle (PLB). Our hypothesis was that the three bundles differ in their microstructures. The purpose of this study was to clarify the microstructural differences among the three bundles. The normal ACLs of six fresh frozen cadavers were harvested. After the AM-MB, AM-LB, and PLB were identified, their fibril structures were analyzed using a transmission electron microscope. The fibril orientation, distribution pattern, and the mass average diameter of the fibrils (MAD) were compared among the AM-MBs, AM-LBs, and PLBs. The AM-MB and AM-LB fibrils were arranged mostly in the longitudinal direction, while the PLB fibrils were not aligned in a uniform direction. The fibril diameter distribution pattern of AM-MBs showed a bi-modal pattern due to the existence of small-diameter (30-40 nm) and large-diameter fibrils (70-80 nm), while that of the AM-LBs and PLBs had a unimodal pattern with one prominent high peak at a diameter of 50-60 nm. The mean MAD of the AM-MBs (83.2 - 11.2 nm) was significantly larger than that of the PLBs (66.8 - 7.7 nm), while it showed no significant difference compared to that of the AM-LBs (77.6 - 12.3 nm). The three ACL bundles have different ultrastructures. The AM-MB predominantly includes thick, uni-directionally oriented fibrils like tendons, while the PLB consists of thinner, multi-directionally oriented fibrils. The AM-LB shows an intermediate structure between the AM-MB and the PLB.
authors.affiliation: Department of Musculoskeletal Biomechanics and Surgical Development, Sapporo Medical University, Sapporo, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Suzuki
authors.affiliation: Department of Orthopaedic Surgery, Sapporo Medical University School of Medicine, Sapporo, Japan.
authors.forename: Hidenori
authors.initials: H
authors.lastname: Otsubo
authors.affiliation: Faculty of Agriculture, Shinshu University, Minami-minowa, Kami-ina, Nagano, Japan.
authors.forename: Takafumi
authors.initials: T
authors.lastname: Watanabe
authors.affiliation: Department of Orthopaedic Surgery, Sapporo Medical University School of Medicine, Sapporo, Japan.
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Kamiya
authors.affiliation: Department of Musculoskeletal Biomechanics and Surgical Development, Sapporo Medical University, Sapporo, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Nagoya
authors.affiliation: Department of Orthopaedic Surgery, Sapporo Medical University School of Medicine, Sapporo, Japan.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Yamashita
authors.affiliation: Sports Orthopaedic Center, Yukioka Hospital, Osaka, Japan.
authors.forename: Konsei
authors.initials: K
authors.lastname: Shino
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016118:Anterior Cruciate Ligament / Q000648:ultrastructure*; D002102:Cadaver; D003094:Collagen / Q000648:ultrastructure; D005260:Female; D006801:Humans; D008297:Male; D008854:Microscopy, Electron / Q000379:methods*; D010784:Photomicrography / Q000379:methods
chemical_list: D003094:Collagen
keywords: ACL; collagen fibril; mass average diameter; three bundles; ultrastructure