title: In vivo articular cartilage contact at the glenohumeral joint: preliminary report.
abstract: BACKGROUND
  Little is known about normal in vivo mechanics of the glenohumeral joint. Such an understanding would have significant implications for treating disease conditions that disrupt shoulder function. The objective of this study was to determine articular contact locations between the glenoid and humeral articular surfaces in normal subjects during shoulder abduction with neutral, internal, and external rotations. We hypothesized that glenohumeral articular contact is not perfectly centered and is variable in normal subjects tested under physiological loading conditions.
  
  
  METHODS
  Orthogonal fluoroscopic images and magnetic resonance image-based computer models were used to characterize the centroids of articular cartilage contact of the glenohumeral joint at various static, actively stabilized abduction and rotation positions in five healthy shoulders. The shoulder was investigated at 0 degrees , 45 degrees , and 90 degrees abduction with neutral rotation and then at 90 degrees abduction combined with active maximal external rotation and active maximal internal rotation.
  
  
  RESULTS
  For all the investigated positions, the centroid of contact on the glenoid surface for each individual, on average, was more than 5 mm away from the geometric center of the glenoid articular surface. Intersubject variation of the centroid of articular contact on the glenoid surface was observed with each investigated position, and 90 degrees abduction with maximal internal rotation showed the least variability. On the humeral head surface, the centroids of contact were located at the superomedial quarter for all investigated positions, except in two subjects' positions at 0 degrees abduction, neutral rotation.
  
  
  CONCLUSIONS
  The data showed that the in vivo glenohumeral contact locations were variable among subjects, but in all individuals they were not at the center of the glenoid and humeral head surfaces. This confirms that "ball-in-socket" kinematics do not govern normal shoulder function. These insights into glenohumeral articular contact may be relevant to an appreciation of the consequences of pathology such as rotator cuff disease and instability.
authors.affiliation: Bioengineering Laboratory, Massachusetts General Hospital, Harvard Medical School, GRJ-1215, 55 Fruit Street, Boston, MA, 02114, USA.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Boyer
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Massimini
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Gill
authors.forename: Ramprasad
authors.initials: R
authors.lastname: Papannagari
authors.forename: Susan L
authors.initials: SL
authors.lastname: Stewart
authors.forename: Jon P
authors.initials: JP
authors.lastname: Warner
authors.forename: Guoan
authors.initials: G
authors.lastname: Li
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D002356:Cartilage / Q000033:anatomy & histology / Q000502:physiology; D005471:Fluoroscopy; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D016059:Range of Motion, Articular / Q000502:physiology*; D012785:Shoulder Joint / Q000033:anatomy & histology / Q000502:physiology*; D055815:Young Adult