Among 71 osteoligamentous elbow joint specimens from Japanese subjects, 66% of the lateral ulnar collateral ligaments (LUCLs) were in an incomplete form, such as a fibrous intermuscular septum lying between the anconeus, supinator and extensors, and terminated on the annular ligament. The ‘typical’ complete ligament, extending from the lateral epicondyle and over the radial collateral ligament (RCL) to the crista spinatoris, appeared in only 20% of the elbows examined. This observation suggests that, in Japanese subjects, the LUCL is not usually a simple ligamentous static stabilizer, but acts as a dynamic stabilizer, together with its related muscles. In addition, when the elbow was flexed by more than 90°, the distance between the lateral epicondyle and the radial head became almost 1.5 mm larger than the distance from the epicondyle to the annular ligament. We therefore consider that, in the overflexed position, the radial head moves slightly distal while the length of the RCL remains almost constant. This morphometrical observation suggests that the annular ligament needs to be supported by the LUCL-muscle complex from the distal side, as well as by the RCL from the proximal side. This extended definition of the lateral collateral ligament complex and its associated muscular function is discussed.