The present study uses three-dimensional computed tomography (3DCT) to analyze the location and size of the Bennett lesion in 9 right and 2 left shoulders of 11 baseball players (average age, 26.1 y; range, 16 to 32 y) with posterior shoulder pain during throwing. Bennett lesions were located from the 6:30 to the 8:30 position of the glenoid. The mean length of the lesions was 20.3 mm and the mean cranial, center and caudal widths were 4.3, 9.1 and 6.8 mm, respectively. The mean cranial, center and caudal distances from the edge of the glenoid were 2.0, 1.5 and 2.9 mm, respectively and the mean thickness of the lesions were 1.8, 6.5 and 4.2 mm, respectively. Our previous anatomical examination of the posteroinferior part of the glenoid revealed that the triceps long head originated from the 7:30 to the 9 o'clock position of the glenoid, its width was 2-3 cm, and the posterior capsule was attached to the glenoid rim with the labrum. These findings indicated that the Bennett lesion was located closer to the triceps long head than to the posterior capsule and supported our hypothesis that the Bennett lesion is an avulsion fracture of the triceps long head or of the traction spur of the triceps long head.
