title: Radiocapitellar contact characteristics during prosthetic radial head subluxation.
abstract: BACKGROUND
  Metallic radial head prostheses are often used in the management of comminuted radial head fractures and elbow instability. We hypothesized that during radiocapitellar subluxation, the contact pressure characteristics of an anatomic radial head prosthesis will more closely mimic those of the native radial head compared with a monopolar circular or a bipolar circular radial head design.
  
  
  METHODS
  With use of 6 fresh frozen cadaver elbows, mean radiocapitellar contact pressures, contact areas, and peak pressures of the native radial head were assessed at 0, 2, 4, and 6 mm of posterior subluxation. These assessments were repeated after the native radial head was replaced with anatomic, monopolar circular and bipolar circular prostheses.
  
  
  RESULTS
  The joint contact pressures increased with the native and the prosthetic radial head subluxation. The mean contact pressures for the native radial head and anatomic prosthesis increased progressively and significantly from 0 to 6 mm of subluxation (native, 0.6 ± 0.0 MPa to 1.9 ± 0.2 MPa; anatomic, 0.7 ± 0.0 MPa to 2.1 ± 0.3 MPa; P < .0001). The contact pressures with the monopolar and bipolar prostheses were significantly higher at baseline and did not change significantly further with subluxation (monopolar, 2.0 ± 0.1 MPa to 2.2 ± 0.2 MPa [P = .31]; bipolar, 1.7 ± 0.1 MPa to 1.9 ± 0.1 MPa [P = .12]). The pattern of increase in contact pressures with the anatomic prosthesis mimicked that of the native radial head. Conversely, the circular prostheses started out with higher contact pressures that stayed elevated.
  
  
  CONCLUSIONS
  The articular surface design of a radial head prosthesis is an important determinant of joint contact pressures.
authors.affiliation: Department of Orthopaedics, Biomechanics Laboratory, Mayo Clinic, Rochester, MN, USA.
authors.forename: Dipit
authors.initials: D
authors.lastname: Sahu
authors.affiliation: Department of Orthopaedics, Biomechanics Laboratory, Mayo Clinic, Rochester, MN, USA.
authors.forename: James S
authors.initials: JS
authors.lastname: Fitzsimmons
authors.affiliation: Department of Orthopaedics, Biomechanics Laboratory, Mayo Clinic, Rochester, MN, USA.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Thoreson
authors.affiliation: Department of Orthopaedics, Biomechanics Laboratory, Mayo Clinic, Rochester, MN, USA.
authors.forename: Kai-Nan
authors.initials: KN
authors.lastname: An
authors.affiliation: Department of Orthopaedics, Biomechanics Laboratory, Mayo Clinic, Rochester, MN, USA. Electronic address: odriscoll.shawn@mayo.edu.
authors.forename: Shawn W
authors.initials: SW
authors.lastname: O'Driscoll
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D002102:Cadaver; D004551:Elbow Joint; D058569:Elbow Prosthesis; D004838:Epiphyses; D005260:Female; D006801:Humans; D004204:Joint Dislocations / Q000503:physiopathology*; D008297:Male; D011312:Pressure; D011474:Prosthesis Design; D011884:Radius; D013314:Stress, Mechanical
keywords: Anatomic radial head; biomechanics; malpositioning; radiocapitellar contact area; radiocapitellar contact pressures; radiocapitellar stability; subluxation