title: Load transfer after cemented total shoulder arthroplasty.
abstract: BACKGROUND
  Glenoid loosening is the primary reason for failure after a total shoulder arthroplasty (TSA), but the failure mechanism is not yet known. This study determined how the load transfer and stress distribution are affected by the introduction of a glenoid implant.
  
  
  METHODS
  We developed a finite-element model of a scapula with and without a virtually implanted modern glenoid prosthesis design. Two load magnitudes were considered: normal and high. Loading locations were simulated at the center and at 4 eccentric positions on the glenoid. A metal-backed implant was also simulated to understand the effect of fixation stiffness.
  
  
  RESULTS
  In the intact glenoid, for both center and eccentric loading, the majority of stress was distributed in the cancellous bone, whereas after a reconstruction, stresses in that region were lower. Metal-backed implants further decreased the joint load carried by the bone. Stresses in the cement layer increased during eccentric and high-magnitude loading.
  
  
  CONCLUSIONS
  This study provided a basic understanding of the load-sharing phenomenon after a TSA that could explain glenoid loosening failure. Our results suggest that with reconstruction of the glenoid with a contemporary implant, the load transfer pattern is significantly altered, with eccentric and high-magnitude loads increasing stresses in the cement indicating potential for failure. The use of a metal-backed implant reduces the load carried by the bone, which may be detrimental to long-term TSA survival.
authors.affiliation: Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY, USA.
authors.forename: Radhika J
authors.initials: RJ
authors.lastname: Patel
authors.affiliation: Hospital for Special Surgery, New York, NY, USA.
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Wright
authors.affiliation: Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY, USA. Electronic address: yg75@cornell.edu.
authors.forename: Yingxin
authors.initials: Y
authors.lastname: Gao
mesh_terms: D000369:Aged, 80 and over; D019643:Arthroplasty, Replacement; D001843:Bone Cements; D002484:Cementation; D003198:Computer Simulation; D019544:Equipment Failure Analysis; D005260:Female; D020342:Finite Element Analysis; D006801:Humans; D007595:Joint Prosthesis; D011474:Prosthesis Design; D011859:Radiography; D012540:Scapula / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D013314:Stress, Mechanical
chemical_list: D001843:Bone Cements
keywords: Total shoulder arthroplasty; eccentric loading; finite-element analysis; glenoid loosening; load transfer; stress distribution