title: Effect of radial head malunion on radiocapitellar stability.
abstract: BACKGROUND
  Management for Mason type II radial head fractures is controversial. We hypothesized that angulation or depression of a marginal radial head fragment would affect radiocapitellar stability similarly to fragment excision.
  
  
  METHODS
  A Mason type II radial head fracture was created in 6 cadaveric elbows by excising a segment from the anterolateral quadrant that was 30% of the diameter of the articular surface. Radiocapitellar stability was recorded under 5 sets of conditions: (1) intact radial head (intact), (2) 30% surface area fragment resected (partially excised), (3) anatomic fragment fixation with screws (fixed), (4) fragment fixation with 2 mm of depression relative to the articular surface (depressed), and (5) fragment fixation after a 30° wedge resection (angulated).
  
  
  RESULTS
  The forces required to subluxate the joint were greatly reduced after fragment excision (5 ± 1 N; P = .0001) and restored to normal (21 ± 1 N; P = .9) after anatomic fixation of the excised fragment. The peak forces were significantly reduced with fragment depression (4 ± 1 N) and angulation (4 ± 2 N; P = .0001).
  
  
  CONCLUSIONS
  A radial head fracture that is depressed 2 mm or angulated 30° may cause up to an 80% loss of concavity-compression stability of the radiocapitellar joint.
authors.affiliation: Biomechanics Laboratory, Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, USA.
authors.forename: Dave R
authors.initials: DR
authors.lastname: Shukla
authors.forename: James S
authors.initials: JS
authors.lastname: Fitzsimmons
authors.forename: Kai-Nan
authors.initials: KN
authors.lastname: An
authors.forename: Shawn W
authors.initials: SW
authors.lastname: O'Driscoll
mesh_terms: D001696:Biomechanical Phenomena; D004551:Elbow Joint / Q000503:physiopathology*; D017759:Fractures, Malunited / Q000145:classification / Q000503:physiopathology*; D006801:Humans; D007593:Joint Instability / Q000209:etiology / Q000503:physiopathology*; D011884:Radius / Q000293:injuries*