title: Mechanical characteristics of a novel posterior-step prosthesis for biconcave glenoid defects.
abstract: BACKGROUND
  Posterior glenoid defects increase the risk of glenoid component loosening after total shoulder arthroplasty (TSA). The goal of this work was to evaluate the mechanical performance of a novel posterior-step glenoid prosthesis, designed to compensate for biconcave (type B2) glenoid defects. Two prototypes ("Poly-step" and "Ti-step") were constructed by attaching polyethylene or titanium step-blocks onto standard (STD) glenoid prostheses. We hypothesized that the mechanical performance of the experimental prostheses in the presence of a B2 defect would be similar to that of an STD prosthesis in the absence of a defect.
  
  
  METHODS
  Fifteen normal shoulder specimens were consistently loaded under simulated muscle activity while peri-glenoid bone strains were measured. In 5 specimens, arthroplasty was performed with an STD glenoid prosthesis. In the remaining 10 specimens, a 20° B2 glenoid defect was created before arthroplasty was performed with the Poly-step or Ti-step prosthesis.
  
  
  RESULTS
  Load-induced peri-glenoid strains after TSA with either the STD or Poly-step prosthesis did not show statistical differences as compared with the native joints (P > .05). A posterior defect decreased superior glenoid strain as compared with the intact specimens (P < .05). The change in strains after Poly-step prosthesis implantation in the presence of a biconcave glenoid defect was not different than the change induced by STD prosthesis implantation in the absence of a defect. In contrast, strains after Ti-step prosthesis implantation were statistically different from those induced by the STD and Poly-step prostheses (P < .05).
  
  
  CONCLUSIONS
  The Poly-step prosthesis may be a viable option for treating posterior glenoid defects.
authors.affiliation: Biomechanics Laboratory, The Pennsylvania State University, University Park, PA, USA.
authors.forename: Yatin M
authors.initials: YM
authors.lastname: Kirane
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Lewis
authors.forename: Neil A
authors.initials: NA
authors.lastname: Sharkey
authors.forename: April D
authors.initials: AD
authors.lastname: Armstrong
mesh_terms: D019643:Arthroplasty, Replacement / Q000379:methods*; D001696:Biomechanical Phenomena; D002102:Cadaver; D006801:Humans; D006811:Humerus / Q000601:surgery*; D007592:Joint Diseases / Q000503:physiopathology / Q000601:surgery*; D007595:Joint Prosthesis; D008422:Materials Testing; D011474:Prosthesis Design; D012785:Shoulder Joint / Q000503:physiopathology / Q000601:surgery*