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  1. K Lundgreen1,
  2. Ø Lian2,
  3. A Scott3,
  4. L Engebretsen4
  1. 1Lovisenberg deaconal hospital, Oslo, Norway
  2. 2Kristiansund Sykehus HNR, Kristiansund, Norway
  3. 3Department of Physical Therapy, University of British Columbia, Vancouver, Canada
  4. 4Department of Orthopaedic Surgery, University of Oslo, Norway


    Introduction Rotator cuff tendinopathy is a significant source of musculoskeletal disability. Accompanying muscle changes may be important determinants of the prognosis. The aim of this study was to compare histological muscle changes in partial-thickness to full-thickness tears of the supraspinatus tendon.

    Methods Muscle biopsies of nine partially torn and 15 fully torn supraspinatus tendons were compared histologically. H&E staining was performed to assess degenerative changes. Immunohistochemistry was used to assess slow and fast myosin heavy chains (type I and II fibres; Anti-slow skeletal myosin heavy chain antibody and Anti-fast skeletal myosin heavy chain antibody), satellite cells (CD56), proliferation (Ki67) and apoptotic cells (activated caspase-3; Asp175).

    Results Full-thickness tears demonstrated significant atrophy of both slow (type I) and fast (type II) myosin heavy chains compared to partial tears. The area ratio of type II to type I was doubled in full-thickness tears. Partial thickness tears revealed significantly more satellite cells and proliferative activity than full-thickness tears. There was no detectable apoptosis using an antibody recognising active caspase-3.

    Discussion Progression of rotator cuff tendinopathy is accompanied by a change in muscle fibre phenotype from endurance type I fibres to type II fibres more prone to fatigue, illustrating an aspect of muscle disuse. The rotator cuff muscle's ability to regenerate appears to be reduced when a full-thickness tear is established. Apoptosis does not appear to be of importance in muscle changes accompanying rotator cuff tendinopathy.

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