The deltoid muscle origin. Histologic characteristics and effects of subacromial decompression.

The histologic characteristics of the deltoid muscle attachment to nine cadaveric acromia were studied using light microscopy. The deltoid muscle attaches to the anterior and lateral acromion primarily by direct tendinous attachment. The muscle attaches to the dorsal side of the acromion by periosteal fiber attachment. In the specimens studied, a hypothetical acromioplasty of 4 mm would release, on average, 41% of the direct fiber attachment, and a 6-mm acromioplasty would release 69% for all zones examined histologically. The functional and clinical effects of these findings are not known, but the deltoid muscle would be released by arthroscopic acromioplasty in areas where bone is removed.