Function of the rabbit supraspinatus muscle after large detachment of its tendon: 6-week, 3-month, and 6-month observation.

Thirty rabbits were anesthetized, and the supraspinatus tendon was detached from the greater tuberosity and the infraspinatus and subscapularis tendons. After 6 weeks (group A), 3 months (group B), and 6 months (group C), in vivo evaluation of twitch tension and fatigue index was done. Next, scapulas with muscles were examined with computed tomography. The most prominent decrease of twitch tension and fatigue index was noted during the first 6 weeks. The twitch tension and fatigue index after 2 and 4 minutes of the muscle operated on expressed as a percentage of the values developed by healthy contralateral nonoperated muscle were 58.2%, 34.5%, and 32.7% at the beginning of stimulation, 45.4%, 35.3%, and 26.7% after 2 minutes, and 42.5%, 32.6%, and 18.5% after 4 minutes of stimulation, respectively, in groups A, B, and C. Computed tomography examination showed fatty degeneration of the supraspinatus averaging 1.85 (group A), 2.28 (group B), and 2.43 (group C). Moderate infraspinatus fatty degeneration was noted in all groups. There was no significant fatty degeneration of subscapularis muscle.