title: Posterior augmented glenoid implants require less bone removal and generate lower stresses: a finite element analysis.
abstract: OBJECTIVE
  Glenoid retroversion can be corrected with standard glenoid implants after anterior-side asymmetric reaming or by using posterior augmented glenoid implants with built-in corrections. The purpose of this study was to compare 2 augmented glenoid designs with a standard glenoid design, measure the amount of bone removed, and compute the stresses generated in the cement and bone.
  
  
  METHODS
  Finite element models of 3 arthritic scapulae with varying severities of posterior glenoid wear were each implanted with 4 different implant configurations: standard glenoid implant in neutral alignment with asymmetric reaming, standard glenoid implant in retroversion, glenoid implant augmented with a posterior wedge in neutral alignment, and glenoid implant augmented with a posterior step in neutral alignment. The volume of cortical and cancellous bone removed and the percentage of implant back surface supported by cortical bone were measured. Stresses and strains in the implant, cement, and glenoid bone were computed.
  
  
  RESULTS
  Asymmetric reaming for the standard implant in neutral version required the most bone removal, resulted in the lowest percentage of back surface supported by cortical bone, and generated strain levels that risked damage to the most bone volume. The wedged implant removed less bone, had a significantly greater percentage of the back surface supported by cortical bone, and generated strain levels that risked damage to significantly less bone volume.
  
  
  CONCLUSIONS
  The wedged glenoid implants appear to have various advantages over the standard implant for the correction of retroversion.
  
  
  METHODS
  Basic Science Study; Computer Modeling.
authors.affiliation: Division of Orthopaedic Surgery, Scripps Clinic, La Jolla, CA, USA.
authors.forename: Jared J
authors.initials: JJ
authors.lastname: Allred
authors.affiliation: Shiley Center for Orthopaedic Research & Education at Scripps Clinic, La Jolla, CA, USA.
authors.forename: Cesar
authors.initials: C
authors.lastname: Flores-Hernandez
authors.affiliation: Division of Orthopaedic Surgery, Scripps Clinic, La Jolla, CA, USA.
authors.forename: Heinz R
authors.initials: HR
authors.lastname: Hoenecke
authors.affiliation: Shiley Center for Orthopaedic Research & Education at Scripps Clinic, La Jolla, CA, USA. Electronic address: ddlima@scripps.edu.
authors.forename: Darryl D
authors.initials: DD
authors.lastname: D'Lima
mesh_terms: D000369:Aged, 80 and over; D000072228:Arthroplasty, Replacement, Shoulder / Q000295:instrumentation*; D060751:Bone Retroversion / Q000601:surgery*; D000071556:Cancellous Bone / Q000601:surgery; D003198:Computer Simulation; D000071538:Cortical Bone / Q000601:surgery; D005260:Female; D020342:Finite Element Analysis; D061165:Glenoid Cavity / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D012785:Shoulder Joint / Q000601:surgery; D000072227:Shoulder Prosthesis; D013314:Stress, Mechanical
keywords: Total shoulder arthroplasty; arthritis; finite element analysis; glenoid; posterior augment wedged; retroversion; stepped