title: Reconstruction of the coronoid using an extended prosthesis: an in vitro biomechanical study.
abstract: BACKGROUND
  When repair of comminuted coronoid fractures is not possible, prosthetic replacement may restore elbow stability. The purpose of this biomechanical study was to determine whether a coronoid implant with an extended tip would improve elbow stability compared with an anatomic prosthesis in the setting of collateral ligament insufficiency.
  
  
  METHODS
  Passive elbow extension was performed in 7 cadaveric arms in the varus and valgus positions and active and passive extension in the horizontal position by use of an elbow motion simulator. Varus-valgus laxity of the ulna relative to the humerus was quantified with a tracking system with a native coronoid, a 40% coronoid deficiency, an anatomic prosthesis, and an extended prosthesis, with the collateral ligaments sectioned and repaired.
  
  
  RESULTS
  Laxity significantly increased after a 40% coronoid deficiency with both repaired and sectioned collateral ligaments (P ≤ .01). With the ligaments repaired, there was no significant difference in laxity between the native coronoid, the anatomic implant, or the extended implant. Ligament sectioning alone produced severe instability, with a mean laxity of 42.75° ± 11.54° (P < .01). With insufficient ligaments, the anatomic prosthesis produced no change in laxity compared with the native coronoid, whereas the extended implant significantly reduced laxity by 21.56° ± 17.70° (P = .02).
  
  
  CONCLUSIONS
  An anatomic coronoid implant with ligament repair restores stability to the coronoid-deficient elbow to intact levels. In the setting of ligament insufficiency, an extended implant improves stability relative to an anatomic implant, but the elbow remains significantly less stable than an intact elbow. Studies are needed to evaluate the feasibility of these designs.
authors.affiliation: Hand and Upper Limb Center, University of Western Ontario, London, Ontario, Canada.
authors.forename: Bashar
authors.initials: B
authors.lastname: Alolabi
authors.forename: Alia
authors.initials: A
authors.lastname: Gray
authors.forename: Louis M
authors.initials: LM
authors.lastname: Ferreira
authors.forename: James A
authors.initials: JA
authors.lastname: Johnson
authors.forename: George S
authors.initials: GS
authors.lastname: Athwal
authors.forename: Graham J W
authors.initials: GJ
authors.lastname: King
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D057929:Arthroplasty, Replacement, Elbow / Q000379:methods*; D001696:Biomechanical Phenomena; D002102:Cadaver; D004551:Elbow Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D058569:Elbow Prosthesis; D006801:Humans; D007593:Joint Instability / Q000517:prevention & control; D008023:Ligaments, Articular / Q000601:surgery*; D008297:Male; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011859:Radiography; D016059:Range of Motion, Articular / Q000502:physiology*; D019651:Plastic Surgery Procedures / Q000379:methods; D013314:Stress, Mechanical