title: The effect of radial head implant shape on radiocapitellar kinematics during in vitro forearm rotation.
abstract: BACKGROUND
  A number of radial head implants are in clinical use for the management of radial head fractures and their sequelae. However, the optimal shape of a radial head implant to ensure proper tracking relative to the capitellum has not been established. This in vitro biomechanical study compared radiocapitellar joint kinematics for 3 radial head implant designs as well as the native head.
  
  
  METHODS
  Eight cadaveric upper extremities were tested using a forearm rotation simulator with the elbow at 90° of flexion. Motion of the radius relative to the capitellum was optically tracked. A stem was navigated into a predetermined location and cemented in place. Three unipolar implant shapes were tested: axisymmetric, reverse-engineered patient-specific, and population-based quasi-anatomic. The patient-specific and quasi-anatomic implants were derived from measurements performed on computed tomography models.
  
  
  RESULTS
  Medial-lateral and anterior-posterior translation of the radial head with respect to the capitellum varied with forearm rotation and radial head condition. A significant difference in medial-lateral (P = .03) and anterior-posterior (P = .03) translation was found between the native radial head and the 3 implants. No differences were observed among the radial head conditions except for a difference in medial-lateral translation between the axisymmetric and patient-specific implants (P = .04).
  
  
  CONCLUSIONS
  Radiocapitellar kinematics of the tested radial head implants were similar in all but one comparison, and all had different kinematics from the native radial head. Patient-specific radial head implants did not prove advantageous relative to conventional implant designs. The shape of the fixed stem unipolar radial head implants had little influence on radiocapitellar kinematics when optimally positioned in this testing model.
authors.affiliation: Hand and Upper Limb Centre Bioengineering Laboratory, St. Joseph's Health Care, Western University, London, ON, Canada.
authors.forename: Hannah L
authors.initials: HL
authors.lastname: Shannon
authors.affiliation: Hand and Upper Limb Centre Bioengineering Laboratory, St. Joseph's Health Care, Western University, London, ON, Canada.
authors.forename: Simon R
authors.initials: SR
authors.lastname: Deluce
authors.affiliation: Hand and Upper Limb Centre Bioengineering Laboratory, St. Joseph's Health Care, Western University, London, ON, Canada.
authors.forename: Joshua W
authors.initials: JW
authors.lastname: Giles
authors.affiliation: Hand and Upper Limb Centre Bioengineering Laboratory, St. Joseph's Health Care, Western University, London, ON, Canada.
authors.forename: James A
authors.initials: JA
authors.lastname: Johnson
authors.affiliation: Hand and Upper Limb Centre Bioengineering Laboratory, St. Joseph's Health Care, Western University, London, ON, Canada. Electronic address: gking@uwo.ca.
authors.forename: Graham J W
authors.initials: GJ
authors.lastname: King
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D004551:Elbow Joint / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D004838:Epiphyses; D005542:Forearm; D006801:Humans; D066298:In Vitro Techniques; D007595:Joint Prosthesis; D008297:Male; D011474:Prosthesis Design; D011885:Radius Fractures / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D016059:Range of Motion, Articular; D012399:Rotation; D014057:Tomography, X-Ray Computed
keywords: Arthroplasty; implant design; in vitro; kinematics; patient specific; radial head