title: Analysis of severely fractured glenoid components: clinical consequences of biomechanics, design, and materials selection on implant performance.
abstract: BACKGROUND
  The longevity of total shoulder replacement is primarily limited by the performance of the ultrahigh-molecular-weight polyethylene (UHMWPE) glenoid component in vivo. Variations in glenoid design (conformity, thickness), biomechanics (joint kinematics), and UHMWPE material selection (sterilization, cross-linking) distinguish total shoulder replacements from hip and knee arthroplasty devices. These variables can lead to severe mechanical failures, including gross fracture.
  
  
  METHODS
  Sixteen retrieved glenoids with severe fracture were analyzed. The explant cohort included 3 material groups (gamma-sterilized Hylamer; gamma-sterilized UHMWPE; and gas plasma-sterilized, remelted, highly cross-linked UHMWPE [HXL]) and a range of conformities (0- to 10-mm radial mismatch). Analysis included fractography (optical and scanning electron microscopy) and Fourier transform infrared spectroscopy for oxidative analysis.
  
  
  RESULTS
  Fracture primarily occurred along the exterior rim for all 16 explants. Fourier transform infrared analysis and fractography revealed significant oxidative embrittlement for all gamma-sterilized glenoids. Fatigue striations and internal flaws were evident on the fracture surface of the HXL glenoid, with little oxidation detected.
  
  
  CONCLUSIONS
  Fracture initiated at the external rim of all devices. Elevated oxidation levels and visible material distortion for representative gamma-sterilized conventional and Hylamer devices suggest oxidative embrittlement as a driving force for crack inception and subsequent fracture. Brittle fracture of theHXL glenoid resulted from a combination of elevated contact stress due to a nonconforming surface, an internal flaw, and reduced resistance to fatigue crack growth. This demonstrates that glenoid fracture associated with oxidation has not been eliminated with the advent of modern materials (HXL) in the shoulder domain.
  
  
  METHODS
  Basic Science Study; Implant Retrieval Study.
authors.affiliation: Department of Mechanical Engineering, University of California, Berkeley, CA, USA. Electronic address: ansari.farzana@gmail.com.
authors.forename: Farzana
authors.initials: F
authors.lastname: Ansari
authors.affiliation: Department of Mechanical Engineering, University of California, Berkeley, CA, USA.
authors.forename: Taylor
authors.initials: T
authors.lastname: Lee
authors.affiliation: Department of Mechanical Engineering, University of California, Berkeley, CA, USA.
authors.forename: Louis
authors.initials: L
authors.lastname: Malito
authors.affiliation: Thayer School of Engineering, Dartmouth College, Hanover, NH, USA.
authors.forename: Audrey
authors.initials: A
authors.lastname: Martin
authors.affiliation: Department of Orthopaedic Surgery, Martha Jefferson Hospital, Charlottesville, CA, USA.
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Gunther
authors.affiliation: San Francisco Shoulder, Elbow & Hand Clinic, San Francisco, CA, USA.
authors.forename: Samuel
authors.initials: S
authors.lastname: Harmsen
authors.affiliation: San Francisco Shoulder, Elbow & Hand Clinic, San Francisco, CA, USA.
authors.forename: Tom R
authors.initials: TR
authors.lastname: Norris
authors.affiliation: Tahoe Fracture and Orthopaedic Clinic, Carson City, NV, USA.
authors.forename: Mike
authors.initials: M
authors.lastname: Ries
authors.affiliation: Thayer School of Engineering, Dartmouth College, Hanover, NH, USA.
authors.forename: Douglas
authors.initials: D
authors.lastname: Van Citters
authors.affiliation: Department of Mechanical Engineering, University of California, Berkeley, CA, USA.
authors.forename: Lisa
authors.initials: L
authors.lastname: Pruitt
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D019544:Equipment Failure Analysis; D005260:Female; D005583:Fourier Analysis; D005720:Gamma Rays / Q000009:adverse effects; D006801:Humans; D008297:Male; D008422:Materials Testing; D008875:Middle Aged; D010084:Oxidation-Reduction; D011095:Polyethylenes / Q000737:chemistry; D011474:Prosthesis Design / Q000009:adverse effects*; D011475:Prosthesis Failure / Q000209:etiology*; D000072227:Shoulder Prosthesis / Q000009:adverse effects*; D013242:Sterilization / Q000379:methods
chemical_list: D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene
keywords: Total shoulder arthroplasty; UHMWPE fatigue fracture; UHMWPE fatigue wear; glenoid failure; glenoid fracture; glenoid rim damage