title: Muscle architectural changes after massive human rotator cuff tear.
abstract: Rotator cuff (RC) tendon tears lead to negative structural and functional changes in the associated musculature. The structural features of muscle that predict function are termed "muscle architecture." Although the architectural features of "normal" rotator cuff muscles are known, they are poorly understood in the context of cuff pathology. The purpose of this study was to investigate the effects of tear and repair on RC muscle architecture. To this end thirty cadaveric shoulders were grouped into one of four categories based on tear magnitude: Intact, Full-thickness tear (FTT), Massive tear (MT), or Intervention if sutures or hardware were present, and key parameters of muscle architecture were measured. We found that muscle mass and fiber length decreased proportionally with tear size, with significant differences between all groups. Conversely, sarcomere number was reduced in both FTT and MT with no significant difference between these two groups, in large part because sarcomere length was significantly reduced in MT but not FTT. The loss of muscle mass in FTT is due, in part, to subtraction of serial sarcomeres, which may help preserve sarcomere length. This indicates that function in FTT may be impaired, but there is some remaining mechanical loading to maintain "normal" sarcomere length-tension relationships. However, the changes resulting from MT suggest more severe limitations in force-generating capacity because sarcomere length-tension relationships are no longer normal. The architectural deficits observed in MT muscles may indicate deeper deficiencies in muscle adaptability to length change, which could negatively impact RC function despite successful anatomical repair. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2089-2095, 2016.
authors.affiliation: Department of Bioengineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, California.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Gibbons
authors.affiliation: Department of Bioengineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, California.
authors.forename: Eugene J
authors.initials: EJ
authors.lastname: Sato
authors.affiliation: Department of Orthopedic Surgery, University of California, La Jolla, California.
authors.forename: Damien
authors.initials: D
authors.lastname: Bachasson
authors.affiliation: Department of Orthopedic Surgery, University of California, La Jolla, California.
authors.forename: Timothy
authors.initials: T
authors.lastname: Cheng
authors.affiliation: Department of Orthopedic Surgery, University of California, La Jolla, California.
authors.forename: Hassan
authors.initials: H
authors.lastname: Azimi
authors.affiliation: Department of Orthopedic Surgery, University of California, La Jolla, California.
authors.forename: Simon
authors.initials: S
authors.lastname: Schenk
authors.affiliation: Department of Bioengineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, California.
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Engler
authors.affiliation: Department of Orthopedic Surgery, Southern California Kaiser Permanente, San Diego, California.
authors.forename: Anshuman
authors.initials: A
authors.lastname: Singh
authors.affiliation: Department of Orthopedic Surgery, University of California, La Jolla, California.|Department of Radiology, University of California, 9500 Gilman Drive, Mail Code 0610, La Jolla, California.
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Ward
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D000070636:Rotator Cuff Injuries / Q000473:pathology*; D012518:Sarcomeres / Q000473:pathology*
keywords: muscle architecture; muscle mechanics; rotator cuff tear; sarcomere