Common Origin Tendon of the Biceps Femoris and Semitendinosus Muscles, Functional and Clinical Relevance

The injury of Biceps Femoris long head (BFlh) and Semitendinosus (ST) is caused by over-stretch of the muscles at the back of the thigh. This condition encompasses almost one third of sports-related injuries and has severe consequences, such as pain and weakness of the muscles. This injury is related namely to quick and demanding activities, such as short distance sprinting in a limited time period. The Common Origin Tendon (COT) for these two muscles is affected in these injuries. This tendon is formed by the BFlh and ST muscles which together have a common origin in the ischial tuberosity. Given the lack of complete knowledge about the detailed structure of the COT, we dissected cadaveric limbs, describing their morphological characteristics, and discussing its functional and clinical implications.: Thirty-five human cadaveric lower limbs were dissected after fixation to analyze the morphology of the COT, focusing on their volume and muscular/tendinous proportion. We identified two subtypes of COT. The most frequent was the musculotendinous type, in which the origin of the BFlh was mainly tendinous, while the ST muscle was mainly muscular (91.4%). In the tendinous type both muscles had a tendinous origin (8.6%). In the musculotendinous type, the ST muscle ends with a microscopic connective tissue that extend into the ischial tuberosity. We conclude that there is a variability in the anatomical presentations of the COT, and we propose that this will correspond with biomechanical differences in the risks and the response to regional injuries. The connective tissue between the COT and the neighbouring structures could be a risk factor for adhesion tearing.