Histological and ultrastructural changes in the undersurface of the acromion with subacromial impingement

Abstract

Background We examined histological changes in the undersurface of the acromion in patients with symptoms of subacromial impingement, in order to clarify whether or not these changes are the main cause of rotator cuff tear. Methods We studied 39 shoulders. The undersurface of the acromion and the coracoacromial ligament were examined by light microscopy and transmission electron microscopy. Results The distinct four-layer structure seen in the undersurface of the acromion of normal subjects was not found in any of our patients. In patients with full-thickness cuff tear, the extent of the tear had a greater association with the degree of degeneration in the undersurface of the acromion than age or the duration of illness. There was little association between structural changes in the coracoacromial ligament and the extent of or the presence of full-thickness cuff tear, or the duration of illness, but there was a strong association with patient age. Interpretation The histological changes in the undersurface of the acromion in patients without cuff tear were merely minute changes compared to those in patients with full-thickness cuff tear. We conclude that the advanced degenerative changes in the undersurface of the acromion result from full-thickness cuff tear.