Anterior shoulder instability: histomorphometric study of the subscapularis and deltoid muscles.

Recurrent traumatic anterior shoulder dislocation results in soft tissues lesions around the glenohumeral joint. The subscapularis muscle is a major active stabilizer of the shoulder and the hypothesis of the current study is that one would expect pathologic changes within its substance secondary to the trauma. A histomorphometric study of the subscapularis muscle was done of 52 patients operated on for recurrent traumatic anterior shoulder dislocation. At the time of surgery biopsy specimens were taken of the subscapularis muscle and the ipsilateral deltoid muscle as a comparison and to see if any changes were present. The results revealed interstitial fibrosis within the subscapularis muscle compatible with muscle scarring, and modifications in the ratio of fiber types as usually is seen with disuse atrophy. Both of these findings may alter strength and stability and therefore the function of the glenohumeral joint. The histologic findings were not compatible with a denervation pattern. After traumatic anterior shoulder dislocation rehabilitation of the subscapularis muscle is recommended.