title: Capitellar excision and hemiarthroplasty affects elbow kinematics and stability.
abstract: BACKGROUND
  Capitellar hemiarthroplasty is proposed as a reconstructive option for isolated capitellar deficiency, but there is limited data on its effect on elbow biomechanics. This study assessed the effect of capitellar excision with and without replacement on elbow kinematics and stability, and evaluated 2 different implant surface shapes.
  
  
  METHODS
  Ten cadaveric arms were tested with an upper extremity joint simulator. Each arm underwent computer tomography scanning for implant sizing and computer-assisted implantation. Kinematic data were obtained using an electromagnetic tracking system during elbow flexion, with the arm oriented in the valgus, varus, and vertical positions. Implants were placed through an extended lateral epicondylar osteotomy using computer-assisted techniques. A repeated-measures design compared 2 implants (anatomical and spherical) to the native capitellum control and capitellar excision states. Outcomes were maximum varus-valgus laxity and rotation of the ulna with respect to the humerus.
  
  
  RESULTS
  Excision of the capitellum increased the varus-valgus laxity up to 3.1° in active elbow flexion, with the forearm in pronation but not in supination. Both capitellar implant designs maintained normal varus-valgus laxity in both active and passive elbow flexion. Excision of the capitellum increased external ulnar rotation during active flexion in the vertical and valgus positions up to 1.5°, while both implants restored normal ulnar rotation. The kinematics and stability of the elbows were similar for both implant designs.
  
  
  CONCLUSIONS
  The capitellum appears to have a role as a valgus and external rotational stabilizer of the ulnohumeral joint. This instability was corrected by both designs of capitellar hemiarthroplasty.
authors.affiliation: Hand and Upper Limb Centre, St Joseph's Health Care, London, ON, Canada.
authors.forename: Marlis T
authors.initials: MT
authors.lastname: Sabo
authors.forename: Hannah L
authors.initials: HL
authors.lastname: Shannon
authors.forename: Simon
authors.initials: S
authors.lastname: Deluce
authors.forename: Emily
authors.initials: E
authors.lastname: Lalone
authors.forename: Louis M
authors.initials: LM
authors.lastname: Ferreira
authors.forename: Jim A
authors.initials: JA
authors.lastname: Johnson
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; D004550:Elbow / Q000000981:diagnostic imaging*; D004551:Elbow Joint / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery*; D058569:Elbow Prosthesis; D005260:Female; D062785:Hemiarthroplasty / Q000379:methods*; D006801:Humans; D021621:Imaging, Three-Dimensional; D007593:Joint Instability / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D010027:Osteotomy / Q000379:methods*; D011474:Prosthesis Design; D011859:Radiography; D016059:Range of Motion, Articular / Q000502:physiology; D012680:Sensitivity and Specificity