The purpose of this study was to investigate the Bennett lesion using ultrasonography(US). We used US to investigate 42 shoulder joints of 21 baseball players (mean age,22.9 years old) who had a Bennett lesion. Aloka SSD 4000 ultrasonic device was used with a 10.0 MHz linear probe. We took long and short axis views of the posteroinferior glenoid and characterized the anatomical relationship between the Bennett lesion and the surrounding tissues. In all subjects, the posterior fiber of the triceps long head originated from about the 8o'clock position of the glenoid and the Bennett lesion was located very close to the origin of the triceps long head. There was a low echo area in the teres minor above the Bennett lesion which was attributed to inflammation or local edema. Bennett reported in 1941 that stress of the posterior capsule and the triceps long head resulted in the development of spur at the posterior and inferior glenoid edge, but the mechanism of this lesion remains controversial. In 2004, we studied 25 shoulder joints from 20 cadavers in order to clarify the anatomy of the posteroinferior glenoid and demonstrated that the Bennett lesion coincides with the origin of the triceps long head. The present study used US to confirm these previous results. We consider that the Bennett lesion is more closely associated with the triceps than with the posterior capsule.
