title: The effect of stem surface treatment and material on pistoning of ulnar components in linked cemented elbow prostheses.
abstract: BACKGROUND
  The ulnar component of a total elbow replacement can fail by "pistoning." Stem surface treatments have improved stability at the stem-cement interface but with varied success. This study investigated the role of surface treatment and stem substrate material on implant stability under axial loading.
  
  
  METHODS
  Sixty circular stems (diameter, 8 mm) made of cobalt chrome (n = 30) or titanium (n = 30) had different surfaces: smooth, sintered beads, and plasma spray. The surface treatment length was either 10 mm or 20 mm. Stems were potted in bone cement, allowed to cure for 24 hours, and tested in a materials testing machine under a compressive staircase loading protocol. Failure was defined as 2 mm of push-out or completion of the protocol. Two-way analyses of variance compared the effects of surface treatment and substrate material on interface strength and motion.
  
  
  RESULTS
  Significant interactions were found between surface treatment and substrate material for both interface strength and motion (P < .05). For titanium, the 20-mm beaded stems had greater interface strength than all other stems (P < .05) and had less motion than the 10-mm plasma-spray and smooth stems (P < .05). For cobalt chrome, the 20-mm beaded stems showed greater interface strength (P < .05) and similar motion (P > .05) to the 20-mm plasma-spray stems (P < .05), which outperformed all other stems (P < .05). Mechanisms of catastrophic failure varied: smooth stems debonded at the stem-cement interface, beaded stems experienced debonding of the beads from the stem, and plasma-spray stems showed loss of frictional force between the surface treatment and cement.
  
  
  CONCLUSIONS
  Stem surface treatment can enhance ulnar component stability but is dependent on substrate material.
authors.affiliation: Biomedical Engineering Graduate Program, Western University, London, Ontario, Canada.
authors.forename: Yara K
authors.initials: YK
authors.lastname: Hosein
authors.forename: Graham J W
authors.initials: GJ
authors.lastname: King
authors.forename: Cynthia E
authors.initials: CE
authors.lastname: Dunning
mesh_terms: D057929:Arthroplasty, Replacement, Elbow / Q000295:instrumentation*; D001843:Bone Cements; D002858:Chromium Alloys; D058569:Elbow Prosthesis; D006801:Humans; D008422:Materials Testing; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013499:Surface Properties; D014025:Titanium; D016474:Weight-Bearing
chemical_list: D001843:Bone Cements; D002858:Chromium Alloys; D014025:Titanium
keywords: Basic Science; Biomechanical Study; Surface treatment; implant fixation; implant stability; plasma spray; sintered beads; ulnar component