title: Restoration of shoulder biomechanics according to degree of repair completion in a cadaveric model of massive rotator cuff tear: importance of margin convergence and posterior cuff fixation.
abstract: BACKGROUND
  Complete repair in massive rotator cuff tear may not be possible, allowing for only partial repair. However, the effect of partial repair on glenohumeral biomechanics has not been evaluated. Therefore, the purpose of this study was to compare the rotational range of motion (ROM), glenohumeral kinematics, and gap formation at the repaired tendon edge following massive cuff tear and repair according to the degree of repair completion.
  
  
  OBJECTIVE
  Posterior fixation will restore the altered biomechanics of massive rotator cuff tear.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Eight cadaveric shoulders were tested at 0°, 30°, and 60° of abduction in the scapular plane. Muscle loading was applied based on physiological muscle cross-sectional area ratios. Maximum internal (MaxIR) and external rotations (MaxER) were measured. Humeral head apex (HHA) position and gap formation at the repaired tendon edge were measured using a MicroScribe from MaxIR to MaxER in 30° increments. Testing was performed for intact, massive cuff tear, complete repair, and 4 types of partial repair. A repeated-measures analysis of variance was used to determine significant differences.
  
  
  RESULTS
  Massive tear significantly increased ROM and shifted HHA superiorly in MaxIR at all abduction angles (P < .05). The complete repair restored ROM to intact (P < .05), while all partial repairs did not. Abnormal HHA elevation due to massive tear was restored by all repairs (P < .05). Release of the anterior single row alone and release of the marginal convergence significantly increased gap formation at the anterior tendon edge (P < .05).
  
  
  CONCLUSIONS
  This study emphasizes the importance of anterior fixation in massive cuff tear to restore rotational range of motion and decrease gap formation at the repaired tendon edge and of posterior fixation to restore abnormal glenohumeral kinematics due to massive cuff tear.
  
  
  CONCLUSIONS
  If complete repair of massive cuff tear is not possible, posterior cuff (infraspinatus) repair is necessary to restore abnormal glenohumeral kinematics, and margin convergence anteriorly is recommended to decrease gap formation of the repaired tendon edge, which may provide a better biomechanical environment for healing.
authors.affiliation: Department of Orthopedic Surgery, Seoul National University College of Medicine, Korea.
authors.forename: Joo Han
authors.initials: JH
authors.lastname: Oh
authors.forename: Michelle H
authors.initials: MH
authors.lastname: McGarry
authors.forename: Bong Jae
authors.initials: BJ
authors.lastname: Jun
authors.forename: Akash
authors.initials: A
authors.lastname: Gupta
authors.forename: Kyung Chil
authors.initials: KC
authors.lastname: Chung
authors.forename: James
authors.initials: J
authors.lastname: Hwang
authors.forename: Thay Q
authors.initials: TQ
authors.lastname: Lee
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D017006:Rotator Cuff / Q000503:physiopathology / Q000601:surgery*; D000070636:Rotator Cuff Injuries; D012782:Shoulder / Q000503:physiopathology* / Q000601:surgery