title: Effect of supraspinatus tendon injury on supraspinatus and infraspinatus muscle passive tension and associated biochemistry.
abstract: BACKGROUND
  Injury to the supraspinatus and infraspinatus tendons and the associated atrophic changes to the muscle remain a common clinical problem. Specifically, increased muscle stiffness has been implicated in failure of the repair and poor functional outcomes. We present a comparison of the passive mechanical properties and associated biochemical studies from patients with and without torn supraspinatus tendons.
  
  
  METHODS
  Muscle biopsy samples (n = 40) were obtained from twenty patients undergoing arthroscopic shoulder surgery. Passive mechanical tests of both individual fibers and fiber bundles as well as analysis of titin molecular weight and collagen content were performed.
  
  
  RESULTS
  At the fiber-bundle level, a significant increase in passive modulus was observed between intact supraspinatus samples (mean [and standard error], 237.41 ± 59.78 kPa) and torn supraspinatus samples (515.74 ± 65.48 kPa) (p < 0.05), a finding that was not observed at the single fiber level. Within the torn samples, elastic moduli in the supraspinatus were greater than in the infraspinatus at both the single fiber and the fiber-bundle level. There was a significant positive correlation between bundle elastic modulus and collagen content (r(2) = 0.465) in the supraspinatus muscle as well as a significant positive correlation between tear size and bundle elastic modulus (r(2) = 0.702) in the torn supraspinatus samples.
  
  
  CONCLUSIONS
  Supraspinatus muscle passive tension increases in a tendon tear size-dependent manner after tendon injury. The increase in muscle stiffness appears to originate outside the muscle cell, in the extracellular matrix.
  
  
  CONCLUSIONS
  Muscle stiffness after rotator cuff tendon injury is more severe with large tears. This finding supports the concept of early intervention, when tendon tears are smaller, and interventions targeting the extracellular matrix.
authors.affiliation: Departments of Orthopaedic Surgery (M.D.S., A.D.C., A.J.C., E.L., J.A.C., R.L.L., and S.R.W.), Radiology (S.R.W.), and Bioengineering (R.L.L. and S.R.W.), University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0610. E-mail address for S.R. Ward: srward@ucsd.edu.
authors.forename: Morgan D
authors.initials: MD
authors.lastname: Silldorff
authors.affiliation: Departments of Orthopaedic Surgery (M.D.S., A.D.C., A.J.C., E.L., J.A.C., R.L.L., and S.R.W.), Radiology (S.R.W.), and Bioengineering (R.L.L. and S.R.W.), University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0610. E-mail address for S.R. Ward: srward@ucsd.edu.
authors.forename: Alexander D
authors.initials: AD
authors.lastname: Choo
authors.affiliation: Departments of Orthopaedic Surgery (M.D.S., A.D.C., A.J.C., E.L., J.A.C., R.L.L., and S.R.W.), Radiology (S.R.W.), and Bioengineering (R.L.L. and S.R.W.), University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0610. E-mail address for S.R. Ward: srward@ucsd.edu.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Choi
authors.affiliation: Departments of Orthopaedic Surgery (M.D.S., A.D.C., A.J.C., E.L., J.A.C., R.L.L., and S.R.W.), Radiology (S.R.W.), and Bioengineering (R.L.L. and S.R.W.), University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0610. E-mail address for S.R. Ward: srward@ucsd.edu.
authors.forename: Evie
authors.initials: E
authors.lastname: Lin
authors.affiliation: Departments of Orthopaedic Surgery (M.D.S., A.D.C., A.J.C., E.L., J.A.C., R.L.L., and S.R.W.), Radiology (S.R.W.), and Bioengineering (R.L.L. and S.R.W.), University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0610. E-mail address for S.R. Ward: srward@ucsd.edu.
authors.forename: J Austin
authors.initials: JA
authors.lastname: Carr
authors.affiliation: Departments of Orthopaedic Surgery (M.D.S., A.D.C., A.J.C., E.L., J.A.C., R.L.L., and S.R.W.), Radiology (S.R.W.), and Bioengineering (R.L.L. and S.R.W.), University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0610. E-mail address for S.R. Ward: srward@ucsd.edu.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Lieber
authors.affiliation: COAST Surgery Center, 3444 Kearny Villa Road, Suite 100, San Diego, CA 92123.
authors.forename: John G
authors.initials: JG
authors.lastname: Lane
authors.affiliation: Departments of Orthopaedic Surgery (M.D.S., A.D.C., A.J.C., E.L., J.A.C., R.L.L., and S.R.W.), Radiology (S.R.W.), and Bioengineering (R.L.L. and S.R.W.), University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0610. E-mail address for S.R. Ward: srward@ucsd.edu.
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Ward
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001706:Biopsy; D003094:Collagen / Q000032:analysis; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000503:physiopathology*; D009133:Muscular Atrophy / Q000473:pathology / Q000503:physiopathology; D017006:Rotator Cuff / Q000503:physiopathology / Q000601:surgery; D000070636:Rotator Cuff Injuries; D012782:Shoulder / Q000601:surgery; D000070599:Shoulder Injuries; D013708:Tendon Injuries / Q000473:pathology / Q000503:physiopathology
chemical_list: D003094:Collagen