title: Finite element analysis and physiologic testing of a novel, inset glenoid fixation technique.
abstract: OBJECTIVE
  The success of shoulder arthroplasty surgery has been limited by a common complication: glenoid implant loosening. Eccentric loading of the glenoid due to migration of the humeral head is considered to be the major cause of glenoid loosening and is referred to as the rocking-horse phenomenon. Glenoid implant loosening may cause pain, limitation of function, and the need for complicated revision surgery. Our hypothesis was that an inset fixation technique could offer increased fixation strength and minimize the effects of the rocking-horse phenomenon on glenoid loosening.
  
  
  METHODS
  Fixation strength and stress distribution were analyzed using two methods. First, mechanical simulation of physiologic in vivo cyclic loading was performed on 1 inset glenoid implant design and 2 standard onlay glenoid implant designs currently on the market. Second, 3-dimensional finite element analysis was performed to compare an inset glenoid implant and a standard onlay glenoid implant with a keel and a standard onlay pegged implant.
  
  
  RESULTS
  After cyclic loading to 100,000 cycles, no glenoid implants demonstrated signs of loosening. Mechanical testing after cyclic loading demonstrated less distraction of the glenoid rim using an inset technique compared with an onlay technique. Finite element analysis results indicated that the inset technique achieved up to an 87% reduction in displacement.
  
  
  CONCLUSIONS
  Mechanical tests and finite element analysis support the concept of inset glenoid fixation in minimizing the risk of glenoid loosening.
authors.affiliation: Howard Memorial Hospital, Willits, CA, USA. sbgunther@aol.com
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Gunther
authors.forename: Tennyson L
authors.initials: TL
authors.lastname: Lynch
authors.forename: Desmond
authors.initials: D
authors.lastname: O'Farrell
authors.forename: Christian
authors.initials: C
authors.lastname: Calyore
authors.forename: Andrew
authors.initials: A
authors.lastname: Rodenhouse
mesh_terms: D019643:Arthroplasty, Replacement / Q000379:methods; D001696:Biomechanical Phenomena; D020342:Finite Element Analysis; D006801:Humans; D007595:Joint Prosthesis; D008422:Materials Testing; D010003:Osteoarthritis / Q000601:surgery*; D011475:Prosthesis Failure; D012785:Shoulder Joint / Q000503:physiopathology / Q000601:surgery*; D013718:Tensile Strength