title: Effects of the glenoid labrum and glenohumeral abduction on stability of the shoulder joint through concavity-compression : an in vitro study.
abstract: BACKGROUND
  Although the glenohumeral joint is the most mobile articulation of the human body, it is known to exhibit ball-and-socket kinematics. Compression into the glenoid labral concavity keeps the humeral head centered. The purpose of the present study was to determine the effects of joint position on glenohumeral stability through concavity-compression.
  
  
  METHODS
  Ten cadaveric shoulders were tested. The glenoid was mounted horizontally onto a six-component load-cell while the humerus was clamped to a vertically unconstrained slide. An x-y stage translated the load-cell with the glenoid underneath the humeral head in eight different directions. Compressive loads of 20, 40, and 60 N were applied. The tests were repeated in 0 degrees, 30 degrees, 60 degrees, and 90 degrees of glenohumeral abduction with and without the labrum. Relative translations between the glenoid and the humeral head and the forces resisting translation were recorded. Then the stability ratio, defined as the peak translational force divided by the applied compressive force, was calculated.
  
  
  RESULTS
  The average stability ratio was higher in the hanging-arm position than it was in glenohumeral abduction. The highest stability ratio was detected in the inferior direction (59.8% 7.7%) when the labrum was intact and in the superior direction (53.3% 7.9%) when the labrum had been resected. Under both conditions, the anterior direction was associated with the lowest stability ratio (32.0% 4.4% with the labrum and 30.4% 4.1% without the labrum). Resection of the glenoid labrum resulted in an average decrease in the stability ratio of 9.6% 1.7%. With increasing compressive load, the average stability ratio slightly decreased.
  
  
  CONCLUSIONS
  Glenohumeral stability through concavity-compression was greater in the hanging-arm position than it was in glenohumeral abduction. The average contribution of the labrum to glenohumeral stability through concavity-compression was approximately 10%, about one-half of the value previously reported. With the labrum intact, the glenohumeral joint was most stable in the inferior direction. Without the labrum, it was most stable in the superior direction. Under both conditions, it was least stable in the anterior direction. Glenohumeral joint stability through concavity-compression decreases with higher compressive loads.
authors.affiliation: Division of Orthopedic Surgery, Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55905, USA
authors.forename: A M
authors.initials: AM
authors.lastname: Halder
authors.forename: S G
authors.initials: SG
authors.lastname: Kuhl
authors.forename: M E
authors.initials: ME
authors.lastname: Zobitz
authors.forename: D
authors.initials: D
authors.lastname: Larson
authors.forename: K N
authors.initials: KN
authors.lastname: An
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D007593:Joint Instability; D008297:Male; D011187:Posture / Q000502:physiology*; D011312:Pressure; D016059:Range of Motion, Articular / Q000502:physiology*; D012680:Sensitivity and Specificity; D012785:Shoulder Joint / Q000033:anatomy & histology / Q000502:physiology*; D013314:Stress, Mechanical