Purpose of this study is to create an experimental model on rats for EMG evaluation of the supraspinatus muscle after traumatic rupture of its tendon.

The population of this study consisted of 5 male rats of 300–400g. Under general anaesthesia we proceeded with traumatic rupture of the supraspinatus tendon and exposure of the muscle. The electrode of a stimulator was placed under suprascapular nerve and the supraspinatus tendon was sutured on a transducer for digital record of the produced signal. Initially we found the resting length and the electric intensity for higher muscle contracture. The parameters that were evaluated after single contracture (single twitch) were strength, time to peak, half relaxation time. Furthermore, it was evaluated the strength of tetanic contractures at 10,20,40,80,100 Hz (Stimulation for 350msec each time).Finally it was evaluated the muscle fatigue with stimulation at 40Hz for 250msec and total duration of 3 minutes. Fatigue index was calculated according to the decrease of titanic muscle contracture (Initial value-Final Value/Initial Value x 100)

Our results are presented in mean ± sd. The single twitch was 8.2(5.1),the time to peak 0.034(0.02) msec, the half relaxation time 0.028(0.008)msec. The strength of titanic muscle contractures was 5.7msec at 10Hz and 17.7 at 100Hz. Finally the fatigue index was calculated at 48.4.

We believe that EMG evaluation of the supraspinatus muscle in rats will help us understanding the pathology of muscle atrophy after rotator cuff tears and possibly the functional restoration after cuff repair.