UNLABELLED The goal of this study was to assess the effects of the vertical section of the subscapularis muscle (internal rotation and muscular degeneration) during Latarjet procedure. MATERIAL AND METHODS From October 1st, 1990, to June 30th, 1991, 40 patients were operated according to Latarjet for chronic anterior shoulder instability. A vertical section of the subscapular muscle was performed. Except for one female patient, all of them practiced sports. Preoperative delay between first dislocation and surgery averaged 59 months. Postoperative rehabilitation was aimed at external rotation, recovery began 48 hours after surgery, without specific indications as far as internal rotation was concerned. Sports activity was resumed 90 days after surgery. 38 were reviewed after 4 years. Clinical review was made according to Constant's score and by measuring strength, and amplitude of internal rotation. Radiological assessment of the shoulders was made with standard x-rays and CT. RESULTS For global results, we noted absence of recurrence, a weighted Constant score of 88 per cent, 87 per cent of patients satisfied or very satisfied, 55 per cent of the osteoplastic ridge were on level, 16 per cent were retracted, and 29 per cent overlapped, 19 per cent non union or ridge lysis, 21 per cent glenohumeral osteophytosis. As far as clinical results are concerned, no significant difference was noted associated to osteoplastic ridge position. Internal rotation was assessed by measuring the distance hand to back (lift-off test). On the operated side it averaged 6 cm (0-18 cm), on the other side 13 cm (2-21 cm). The difference between each side was statistically very significant (p = 0.0001). Strength in internal rotation on the operated side averaged 3 kg (0-8 kg), on the other side, 6 kg (2-10 kg). The difference between each side was statistically very significant (p < 0.0001). CT was carried out on thickness and degeneration of the subscapular muscle (n = 29). Thickness of the subscapular muscle (operated side) average 10.5 (5-17 mm) after surgery, and 14.6 mm before surgery. It was thimer than on the contralateral shoulder 21 mm (10-33 mm). In both cases (shoulder before and after surgery, operated and contralateral shoulder), the difference was statistically significant. Degeneration of the subscapular muscle showed 4 stage 0, 13 stage 1, 5 stage 2, 6 stage 3, and 1 stage 4. A non statistical correlation was noted, between muscle degeneration and functional result, strength in internal rotation, distance hand to back. DISCUSSION This series confirms efficiency and low morbidity of Latarjet procedure. Nevertheless, assessment of the subscapular muscle shows that 50 per cent of its strength and 50 per cent of its thickness were lost, 4 years after surgery. A significant degeneration (stages 2.3.4) was found in 41 per cent of the patients. This limitation is related to the trans-subscapular approach and to the absence of internal rotation postoperative rehabilitation. CONCLUSION A randomized study comparing the vertical trans-subscapular approach to the horizontal trans-subscapular one would determine the better procedure.