These authors studied the contractility of muscle fibers from biopsy specimens of supraspinatus muscles of 13 patients with chronic full-thickness posterosuperior rotator cuff tears, comparing the results to healthy vastus lateralis muscle fibers.
They found that chronically torn supraspinatus muscles had a 30% reduction in maximum isometric force production and a 29% reduction in normalized force compared with controls. They identified disordered sarcomeres along with an accumulation of lipid-laden macrophages in the extracellular matrix surrounding supraspinatus muscle fibers.
Comment: The figures in this paper are quite striking. These results show that in addition to the re-estabishment of a durable tendon attachment to bone, recovery from the repair of a chronic rotator cuff tear would hopefully include reversion of the muscle force generation and sarcomere architecture towards normal.
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