title: Muscle biopsies from the supraspinatus in retracted rotator cuff tears respond normally to passive mechanical testing: a pilot study.
abstract: OBJECTIVE
  The aim of the present study was to assess the function of the isolated muscle component in retracted rotator cuff tears.
  
  
  METHODS
  Muscle biopsies were harvested from the supraspinatus and the ipsilateral deltoid in seven patients undergoing surgery for a large, retracted rotator cuff tear. Single fibres and fibre bundles were subjected to passive stretching in vitro with subsequent recordings of tension and sarcomere lengths using the laser diffraction technique. Stress-strain curves were plotted, and the elastic modulus was calculated for all preparations. Morphology was evaluated with regard to collagen fraction, ratio between fast and slow fibres, fibre size and fibre size variability using standard staining techniques.
  
  
  RESULTS
  Intra-individual comparisons of the stress-strain curves showed a high degree of conformity in terms of both shape and tangent values, and there were no statistically significant differences in the elastic modulus for single fibres and bundles in the deltoid and supraspinatus muscles, respectively, supported by the analysis of the observed confidence interval of the differences between the paired values of the elastic modulus. There were no differences in collagen content, fibre size and ratio between fast and slow fibres in the deltoid and supraspinatus muscles, respectively.
  
  
  CONCLUSIONS
  We conclude that muscle biopsies from the supraspinatus in retracted rotator cuff tears respond normally to mechanical testing in vitro.
authors.affiliation: Lundberg Laboratory for Orthopaedic Research, University of Gothenburg, 413 45, Gothenburg, Sweden. fredrik.einarsson@vgregion.se
authors.forename: Fredrik
authors.initials: F
authors.lastname: Einarsson
authors.forename: Eva
authors.initials: E
authors.lastname: Runesson
authors.forename: Jón
authors.initials: J
authors.lastname: Karlsson
authors.forename: Jan
authors.initials: J
authors.lastname: Fridén
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001707:Biopsy, Needle; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000473:pathology* / Q000503:physiopathology*; D010865:Pilot Projects; D012016:Reference Values; D017006:Rotator Cuff / Q000601:surgery; D000070636:Rotator Cuff Injuries; D012494:Sampling Studies; D018709:Statistics, Nonparametric; D013314:Stress, Mechanical; D013708:Tendon Injuries / Q000473:pathology* / Q000601:surgery; D013718:Tensile Strength