title: Biomechanical analysis of articular-sided partial-thickness rotator cuff tear and repair.
abstract: BACKGROUND
  Articular-sided partial-thickness rotator cuff tears are common injuries in throwing athletes. The superior shoulder capsule beneath the supraspinatus and infraspinatus tendons works as a stabilizer of the glenohumeral joint.
  
  
  OBJECTIVE
  To assess the effect of articular-sided partial-thickness rotator cuff tear and repair on shoulder biomechanics. The hypothesis was that shoulder laxity might be changed because of superior capsular plication in transtendon repair of articular-sided partial-thickness rotator cuff tears.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Nine fresh-frozen cadaveric shoulders were tested by using a custom shoulder-testing system at the simulated late-cocking phase and acceleration phase of throwing motion. Maximum glenohumeral external rotation angle, anterior translation, position of the humeral head apex with respect to the glenoid, internal impingement area, and glenohumeral and subacromial contact pressures were measured. Each specimen underwent 3 stages of testing: stage 1, with the intact shoulder; stage 2, after creation of articular-sided partial-thickness tears of the supraspinatus and infraspinatus tendons; and stage 3, after transtendon repair of the torn tendons by using 2 suture anchors.
  
  
  RESULTS
  Articular-sided partial-thickness tears did not significantly change any of the shoulder biomechanical measurements. In the simulated late-cocking phase, transtendon rotator cuff repair resulted in decreased maximum external rotation angle by 4.2° (P = .03), posterior shift of the humeral head (1.1-mm shift; P = .02), decreased glenohumeral contact pressure by 1.7 MPa (56%; P = .004), and decreased internal impingement area by 26.4 mm(2) (65%; P < .001) compared with values in the torn shoulder. In the acceleration phase, the humeral head shifted inferiorly (1.2-mm shift; P = .03 vs torn shoulder), and glenohumeral anterior translation (1.5-mm decrease; P = .03 vs torn shoulder) and subacromial contact pressure (32% decrease; P = .004 vs intact shoulder) decreased significantly after transtendon repair.
  
  
  CONCLUSIONS
  Transtendon repair of articular-sided partial-thickness supraspinatus and infraspinatus tears decreased glenohumeral and subacromial contact pressures at time zero; these changes might lead to reduced secondary subacromial and internal impingements and consequently progression to full-thickness rotator cuff tear. However, repair of the tendons decreased anterior translation and external rotation and changed the positional relationship between the humeral head and the glenoid.
  
  
  CONCLUSIONS
  Careful attention should be paid to shoulder laxity and range of motion when transtendon repair is chosen to treat articular-sided partial-thickness rotator cuff tears, specifically in throwing athletes.
authors.affiliation: Orthopaedic Biomechanics Laboratory, Long Beach VA Healthcare System, Long Beach, California, USA Department of Orthopedic Surgery, Osaka Medical College, Takatsuki, Japan Katsuragi Hospital, Kishiwada, Japan Daiichi Towakai Hospital, Takatsuki, Japan tmihata@yahoo.co.jp tmihata@poh.osaka-med.ac.jp.
authors.forename: Teruhisa
authors.initials: T
authors.lastname: Mihata
authors.affiliation: Orthopaedic Biomechanics Laboratory, Long Beach VA Healthcare System, Long Beach, California, USA.
authors.forename: Michelle H
authors.initials: MH
authors.lastname: McGarry
authors.affiliation: Orthopaedic Biomechanics Laboratory, Long Beach VA Healthcare System, Long Beach, California, USA Department of Orthopedic Surgery, Tamanagayama Hospital, Nippon Medical School, Tokyo, Japan.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Ishihara
authors.affiliation: Orthopaedic Biomechanics Laboratory, Long Beach VA Healthcare System, Long Beach, California, USA.
authors.forename: Christopher N H
authors.initials: CN
authors.lastname: Bui
authors.affiliation: Orthopaedic Biomechanics Laboratory, Long Beach VA Healthcare System, Long Beach, California, USA.
authors.forename: Damon
authors.initials: D
authors.lastname: Alavekios
authors.affiliation: Department of Orthopedic Surgery, Osaka Medical College, Takatsuki, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Neo
authors.affiliation: Orthopaedic Biomechanics Laboratory, Long Beach VA Healthcare System, Long Beach, California, USA University of California at Irvine, Irvine, California, USA.
authors.forename: Thay Q
authors.initials: TQ
authors.lastname: Lee
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D058430:Humeral Head / Q000503:physiopathology; D017746:Joint Capsule / Q000601:surgery; D008297:Male; D008875:Middle Aged; D011312:Pressure; D016059:Range of Motion, Articular; D012399:Rotation; D017006:Rotator Cuff / Q000503:physiopathology* / Q000601:surgery; D000070636:Rotator Cuff Injuries; D012785:Shoulder Joint / Q000503:physiopathology* / Q000601:surgery; D013708:Tendon Injuries / Q000503:physiopathology* / Q000601:surgery
keywords: articular; partial thickness; repair; rotator cuff; tear