title: The effect of the annular ligament on kinematics of the radial head.
abstract: OBJECTIVE
  There is evidence that the radial head translates during pronation and supination. This study measured radial head movement and the location of the pronation-supination axis of the forearm with and without the annular ligament.
  
  
  METHODS
  Thirteen cadaveric arms were attached to a custom-built frame. Pronation and supination were achieved by actuation of the pronator teres and biceps tendons, respectively. Motion was captured by video cameras via marker arrays attached to the distal radius, distal ulna, humerus, and radial head. Three pronation-supination trials were performed with the annular ligament intact and the elbow positioned at 90 degrees . The sequence was repeated after transection of the annular ligament.
  
  
  RESULTS
  The radial head traveled an average of 2.1 mm in the anteroposterior direction and 1.6 mm in the mediolateral direction during forearm rotation. After annular ligament resection, travel of the radial head increased by an average of 44% in the mediolateral direction and by 24% in the anteroposterior direction. On average, the mean pronation-supination axis (screw displacement axis) passed 1.4 mm +/- 1.9 medial to the center of the capitellum and through the center of the ulnar head. Loss of the annular ligament did not change the location of the pronation-supination axis.
  
  
  CONCLUSIONS
  During forearm rotation, the radial head travels to a greater extent in the anteroposterior direction than in the mediolateral direction. Loss of the stabilizing effect of the annular ligament increases the travel mediolaterally more than anteroposteriorly. The pronation-supination axis of the forearm is nearly constant and is not affected by annular ligament transection.
authors.affiliation: Orthopaedic Biomechanics Laboratory, Allegheny General Hospital, 320 E. North Avenue, Pittsburgh, PA 15212, USA.
authors.forename: Karol
authors.initials: K
authors.lastname: Galik
authors.forename: Mark E
authors.initials: ME
authors.lastname: Baratz
authors.forename: Adrian L
authors.initials: AL
authors.lastname: Butler
authors.forename: Joseph
authors.initials: J
authors.lastname: Dougherty
authors.forename: Mark S
authors.initials: MS
authors.lastname: Cohen
authors.forename: Mark Carl
authors.initials: MC
authors.lastname: Miller
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D008023:Ligaments, Articular / Q000502:physiology / Q000601:surgery*; D008297:Male; D009068:Movement / Q000502:physiology; D011403:Pronation / Q000502:physiology*; D011884:Radius / Q000502:physiology*; D012399:Rotation; D013484:Supination / Q000502:physiology*