title: Effect of radial head implant shape on joint contact area and location during static loading.
abstract: OBJECTIVE
  To examine the effect of implant shape on radiocapitellar joint contact area and location in vitro.
  
  
  METHODS
  We used 8 fresh-frozen cadaveric upper extremities. An elbow loading simulator examined joint contact in pronation, neutral rotation, and supination with the elbow at 90° flexion. Muscle tendons were attached to pneumatic actuators to allow for computer-controlled loading to achieve the desired forearm rotation. We performed testing with the native radial head, an axisymmetric implant, a reverse-engineered patient-specific implant, and a population-based quasi-anatomic implant. Implants were inserted using computer navigation. Contact area and location were quantified using a casting technique.
  
  
  RESULTS
  We found no significant difference between contact locations for the native radial head and the 3 implants. All of the implants had a contact area lower than the native radial head; however, only the axisymmetric implant was significantly different. There was no significant difference in contact area between implant shapes.
  
  
  CONCLUSIONS
  The similar contact areas and locations of the 3 implant designs suggest that the shape of the implant may not be important with respect to radiocapitellar joint contact mechanics when placed optimally using computer navigation. Further work is needed to explore the sensitivity of radial head implant malpositioning on articular contact. The lower contact area of the radial head implants relative to the native radial head is similar to previous benchtop studies and is likely the result of the greater stiffness of the implant.
  
  
  CONCLUSIONS
  Radial head implant shape does not appear to have a pronounced influence on articular contact, and both axisymmetric and anatomic metal designs result in elevated cartilage stress relative to the intact state.
authors: Hand and Upper Limb Centre, Western University, London, Ontario, Canada.
authors: Hannah L
authors: HL
authors: Shannon
authors: Hand and Upper Limb Centre, Western University, London, Ontario, Canada.
authors: Simon R
authors: SR
authors: Deluce
authors: Hand and Upper Limb Centre, Western University, London, Ontario, Canada.
authors: Emily A
authors: EA
authors: Lalone
authors: Hand and Upper Limb Centre, Western University, London, Ontario, Canada.
authors: Ryan
authors: R
authors: Willing
authors: Hand and Upper Limb Centre, Western University, London, Ontario, Canada. Electronic address: gking@uwo.ca.
authors: Graham J W
authors: GJ
authors: King
authors: Hand and Upper Limb Centre, Western University, London, Ontario, Canada.
authors: James A
authors: JA
authors: Johnson
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D057929:Arthroplasty, Replacement, Elbow; D001696:Biomechanical Phenomena; D004551:Elbow Joint / Q000502:physiology; D058569:Elbow Prosthesis; D005260:Female; D006801:Humans; D008297:Male; D011474:Prosthesis Design; D011884:Radius / Q000502:physiology
keywords: Biomechanics; computer-assisted orthopedic surgery; elbow; joint contact; radial head arthroplasty