title: Quantification of the position, orientation, and surface area of bone loss in type B2 glenoids.
abstract: BACKGROUND
  The purpose of this computed tomography-based study was to quantify erosions in B2 glenoids. We hypothesized that erosions do not occur symmetrically and that they have a predictable orientation.
  
  
  METHODS
  This study evaluated 55 type B2 glenoid cases. Computed tomography data were used to create three-dimensional reconstructions, and point coordinates were extracted from each reconstruction for morphologic analysis of the osteoarthritic glenoid and humerus.
  
  
  RESULTS
  There was a significant difference between the mean orientation angle (28° ± 11°) of the posterior glenoid line of erosion and the superoinferior axis (P < .001), which resulted in the average erosion being directed toward the 8-o'clock position. On average, the erosion started 1.6 ± 3.4 mm posterior to the glenoid center point. In 35% of B2 cases, the line of erosion was curved. The mean surface area was 763 ± 296 mm(2) for the neoglenoid and 957 ± 276 mm(2) for the paleoglenoid, indicating that the neoglenoid occupied 44% ± 12% of the total glenoid area. In this cohort, the mean radius of the humeral head neoarticulation was 32 ± 6 mm, the neoglenoid radius was 37 ± 8 mm, and the paleoglenoid radius was 34 ± 7 mm. The radius of the humeral head was significantly less than that of the neoglenoid (P < .001) and the paleoglenoid (P = .009). In addition, the radius of the neoglenoid was significantly greater than the radius of the paleoglenoid (P = .012).
  
  
  CONCLUSIONS
  Type B2 glenoids have a predictable wear pattern, which is not axisymmetric to the glenoid superoinferior axis. In addition, the identified anatomic characteristics of B2 erosions will aid surgeons in the operative management of bone loss and may assist manufacturers in the design of augmented components.
authors.affiliation: Roth/McFarlane Hand and Upper Limb Centre, Surgical Mechatronics Laboratory, St. Josephs Health Care, London, ON, Canada; Department of Mechanical and Materials Engineering, Western University, London, ON, Canada.
authors.forename: Nikolas K
authors.initials: NK
authors.lastname: Knowles
authors.affiliation: Department of Orthopaedic Surgery, Washington University/Barnes-Jewish Hospital, St. Louis, MO, USA.
authors.forename: Jay D
authors.initials: JD
authors.lastname: Keener
authors.affiliation: Roth/McFarlane Hand and Upper Limb Centre, Surgical Mechatronics Laboratory, St. Josephs Health Care, London, ON, Canada; Department of Mechanical and Materials Engineering, Western University, London, ON, Canada. Electronic address: louis.ferreira@uwo.ca.
authors.forename: Louis M
authors.initials: LM
authors.lastname: Ferreira
authors.affiliation: Roth/McFarlane Hand and Upper Limb Centre, Surgical Mechatronics Laboratory, St. Josephs Health Care, London, ON, Canada.
authors.forename: George S
authors.initials: GS
authors.lastname: Athwal
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D061165:Glenoid Cavity / Q000000981:diagnostic imaging*; D006801:Humans; D058430:Humeral Head / Q000000981:diagnostic imaging; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D010003:Osteoarthritis / Q000000981:diagnostic imaging*; D015203:Reproducibility of Results; D012785:Shoulder Joint / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed
keywords: Glenoid; augmented implants; biconcave; osteoarthritis; posterior erosion; shoulder arthroplasty; type B2