title: Characterization of the Walch B3 glenoid in primary osteoarthritis.
abstract: BACKGROUND
  The type B3 glenoid is an addition to the Walch classification. A potential etiologic theory is that it is a progression of the B2. It is characterized by uniconcavity, absent paleoglenoid, medialization, retroversion, and subluxation. The purpose of this study was to describe the morphology of B3 glenoids.
  
  
  METHODS
  Fifty-two patients with B3 glenoids underwent 3-dimensional analysis of computed tomography data. Glenoid measurements (retroversion, inclination, medialization) and humeral head subluxation according to the scapular and glenoid planes were determined. The measured variables were compared between male and female patients.
  
  
  RESULTS
  The mean B3 retroversion, inclination, and medialization were 24° ± 7°, 8° ± 6° superior, and 14 ± 4 mm, respectively. The mean posterior subluxation was 80% ± 8% and 54% ± 6% according to the scapular and glenoid planes, respectively. There were no differences in B3 characteristics between sexes (P > .05). A significant correlation existed between glenoid retroversion and humeral head subluxation relative to the scapular plane, with every 1° increase in retroversion translating to a 1% increase in subluxation (P < .001). In contrast, when referencing the glenoid plane, the humeral head remained concentric to the erosion.
  
  
  CONCLUSIONS
  The B3 is uniconcave and retroverted. As glenoid retroversion increases, posterior humeral head subluxation significantly increases as referenced to the scapular plane; however, when referenced to the glenoid plane, the head remains concentric to the erosion. This appearance of "concentricity" is acquired secondary to the wear pattern, creating a uniconcave glenoid. Therefore, surgeons should be aware that the visualized concentricity is a product of the erosion pattern and thus may conceal a greater amount of subluxation potential.
authors.affiliation: Roth|McFarlane Hand and Upper Limb Center, St. Joseph's Health Care, Western University, London, ON, Canada.
authors.forename: Kevin
authors.initials: K
authors.lastname: Chan
authors.affiliation: Roth|McFarlane Hand and Upper Limb Center, St. Joseph's Health Care, Western University, London, ON, Canada.
authors.forename: Nikolas K
authors.initials: NK
authors.lastname: Knowles
authors.affiliation: Telecom Bretagne, Plouzané, France.
authors.forename: Jean
authors.initials: J
authors.lastname: Chaoui
authors.affiliation: Centre Orthopédique Santy, Lyon, France.
authors.forename: Marc-Olivier
authors.initials: MO
authors.lastname: Gauci
authors.affiliation: Roth|McFarlane Hand and Upper Limb Center, St. Joseph's Health Care, Western University, London, ON, Canada.
authors.forename: Louis M
authors.initials: LM
authors.lastname: Ferreira
authors.affiliation: Centre Orthopédique Santy, Lyon, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Walch
authors.affiliation: Roth|McFarlane Hand and Upper Limb Center, St. Joseph's Health Care, Western University, London, ON, Canada. Electronic address: gathwal@uwo.ca.
authors.forename: George S
authors.initials: GS
authors.lastname: Athwal
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000000981:diagnostic imaging*; D012783:Shoulder Dislocation / Q000000981:diagnostic imaging; D012785:Shoulder Joint / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed
keywords: B2; B3; Osteoarthritis; biconcave; posterior subluxation; retroversion; shoulder arthroplasty