title: Partial-thickness tears involving the rotator cable lead to abnormal glenohumeral kinematics.
abstract: OBJECTIVE
  The objective of this study was to determine the biomechanical function of the rotator cable when a partial-thickness (>50%) tear is present. We compared intact specimens with partial tears of the anterior cable followed by partial anterior and posterior tears in regard to glenohumeral kinematics and translation. The hypothesis was that partial-thickness tears will lead to abnormal glenohumeral biomechanics, including glenohumeral translation and path of glenohumeral articulation.
  
  
  METHODS
  Five fresh frozen cadaveric shoulders with intact labrum, rotator cuff, and humerus were tested using a custom shoulder testing system in the scapular plane. Glenohumeral translation was measured after applying an anterior load of 30 N at different angles of external rotation. The path of glenohumeral articulation was measured by calculating the humeral head center with respect to the glenoid articular surface at 30°, 60°, 90°, and 120° of external rotation.
  
  
  RESULTS
  With an anterior force of 30 N, there was a significant increase in anterior and total translation at 30° of external rotation after the anterior cable was cut (P < .05). When the tear was extended to the posterior cable, there was a significant increase in anterior, inferior, and total translation at 30° and 120° of external rotation (P < .05). With respect to the path of glenohumeral articulation , the humeral head apex was shifted superiorly at 90° and 120° of external rotation after the posterior cable was cut (P < .05).
  
  
  CONCLUSIONS
  Partial-thickness articular-sided rotator cuff tears with a thickness >50% involving the rotator cable increased glenohumeral translation and changed kinematics in our cadaveric biomechanical model.
authors.affiliation: Kerlan-Jobe, Los Angeles, CA, USA. Electronic address: gpinkowsky@gmail.com.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Pinkowsky
authors.affiliation: Kerlan-Jobe, Los Angeles, CA, USA.
authors.forename: Neal S
authors.initials: NS
authors.lastname: ElAttrache
authors.affiliation: Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, Long Beach, CA, USA.
authors.forename: Alexander B
authors.initials: AB
authors.lastname: Peterson
authors.affiliation: Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, Long Beach, CA, USA.
authors.forename: Masaki
authors.initials: M
authors.lastname: Akeda
authors.affiliation: Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, Long Beach, CA, USA; Department of Orthopaedic Surgery, University of California, Irvine, CA, USA.
authors.forename: Michelle H
authors.initials: MH
authors.lastname: McGarry
authors.affiliation: Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, Long Beach, CA, USA; Department of Orthopaedic Surgery, University of California, Irvine, CA, USA.
authors.forename: Thay Q
authors.initials: TQ
authors.lastname: Lee
mesh_terms: D000368:Aged; D002102:Cadaver; D005260:Female; D061165:Glenoid Cavity; D006801:Humans; D058430:Humeral Head; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology*; D000070636:Rotator Cuff Injuries / Q000503:physiopathology*; D012785:Shoulder Joint / Q000503:physiopathology*
keywords: Shoulder; basic science; biomechanics; overhead athlete; rotator cable; rotator cuff