The anterolateral ligament in a Japanese population: Study on prevalence and morphology.

BACKGROUND: The anterolateral ligament of the knee (ALL) has been attracting research attention as the ligament related to the Segond fracture. In this study, we investigated the prevalence and morphological variation of the ALL and developed a classification for the ALL in Japanese people.

METHODS: A total of 94 knees of 54 room cadavers of Japanese people were examined (24 male, 30 female; age range 70-103 years; average age: 85.6 years). Knees with damaged ligaments, such as ACL rupture, and with bony abnormalities were excluded. The ALL-like structure was classified based on orientation and shape of the structures.

RESULTS: The fibrous structure independent from the knee joint capsule in the anterolateral part of the knee was present in 35 knees out of 94 knees (37.2%). This structure was classified into two types, based on thickness: type I is for the strong ligamentous structures of more than 1 mm in thickness; and type II is for weak aponeurotic structures of equal or less than 1 mm thickness. Here we regard the anterolateral ligament (ALL) as the type I and the type II is termed anterolateral ligamentous tissue (ALLT). Type I was seen in 19 of 35 knees (54.3%), and type II was seen in 16 of 35 knees (45.7%).

CONCLUSIONS: This study described the fibrous structure of the anterolateral portion of the knee, and classified the ligamentous structure into type I (ALL) and thin aponeurotic type II (ALLT). The prevalence of the ALL in Japanese people was approximately 20% and was significantly lower than in previous studies, which were reported values from 50% to 100%.