title: Determination of correct implant size in radial head arthroplasty to avoid overlengthening: surgical technique.
abstract: BACKGROUND
  Insertion of a radial head implant that results in radial overlengthening has been associated with altered elbow kinematics, increased radiocapitellar joint forces, capitellar erosions, early-onset arthritis, and loss of elbow flexion. The purpose of this study was to identify clinical and radiographic features that may be used to diagnose overlengthening of the radius intraoperatively and on postoperative radiographs.
  
  
  METHODS
  Radial head implants of varying thicknesses were inserted into seven cadaver specimens, which were then assessed clinically and radiographically. Eight stages were examined: the intact specimen (stage 1); repair of the lateral collateral ligament (stage 2); radial head resection with repair of the lateral collateral ligament (stage 3); insertion of an implant of the correct thickness (stage 4); and insertion of an implant that resulted in radial overlengthening of 2 mm (stage 5), 4 mm (stage 6), 6 mm (stage 7), or 8 mm (stage 8). The specimens were tested with and without muscle loading to simulate resting muscle tone and surgical paralysis, respectively. At each stage, radiographs were made to measure the ulnohumeral joint space and the lateral ulnohumeral joint was visually assessed.
  
  
  RESULTS
  We identified no difference, with regard to medial ulnohumeral joint incongruity as seen radiographically, among stages 1 through 6 during the tests with muscle loading. A significant difference in medial ulnohumeral joint incongruity was found in stages 7 (p = 0.003) and 8 (p < 0.001). The clinical (visually assessed) lateral ulnohumeral joint space gap was negligible in stages 1 through 4 but increased significantly at all stages involving overlengthening (gross gap, 0.9 mm with 2 mm of erlengthening [p = 0.005], 2.3 mm with 4 mm of overlengthening [p < 0.001], 3.4 mm with 6 mm [p < 0.001], and 4.7 mm with 8 mm [p < 0.001]).
  
  
  CONCLUSIONS
  Incongruity of the medial ulnohumeral joint becomes apparent radiographically only after overlengthening of the radius by ≥6 mm. Intraoperative visualization of a gap in the lateral ulnohumeral joint is a reliable indicator of overlengthening following the insertion of a radial head prosthesis.
authors.affiliation: Hand and Upper Limb Centre, St. Joseph's Health Care, 268 Grosvenor Street, London, ON N6A 4L6, Canada. gathwal@uwo.ca
authors.forename: George S
authors.initials: GS
authors.lastname: Athwal
authors.forename: Simon G
authors.initials: SG
authors.lastname: Frank
authors.forename: Ruby
authors.initials: R
authors.lastname: Grewal
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Faber
authors.forename: James
authors.initials: J
authors.lastname: Johnson
authors.forename: Graham J W
authors.initials: GJ
authors.lastname: King
mesh_terms: D019643:Arthroplasty, Replacement / Q000379:methods; D004551:Elbow Joint / Q000601:surgery; D005500:Follow-Up Studies; D018460:Fractures, Comminuted / Q000601:surgery*; D006801:Humans; D057072:Intra-Articular Fractures / Q000601:surgery; D007595:Joint Prosthesis; D011183:Postoperative Complications / Q000517:prevention & control; D011474:Prosthesis Design; D011885:Radius Fractures / Q000601:surgery*; D016059:Range of Motion, Articular / Q000502:physiology; D018570:Risk Assessment; D016896:Treatment Outcome