Hyperextension trauma to the elbow joint induced through the distal ulna or the distal radius: pathoanatomy and kinematics. An experimental study of the ligament injuries.

ABSTRACT

Loads applied to the forearm result in hyperextension of the elbow. The pathomechanics of hyperextension trauma with load applied to the distal radius and ulna were studied in 10 macroscopically normal cadaver elbow joint specimens to reveal patterns of injury with radial traction (n = 5) compared to ulnar traction (n = 5). The mean age of the donors was 60.8 years (range 33-74). Kinematic testing was performed in an experimental 3D-kinematic loading apparatus. The extension range of motion increased by 20.9 degrees +/- 2.9 degrees after joint loading. Hyperextension loads induced joint laxity during flexion of less than 60 degrees. In both groups, the changes were significant in joint flexion during forced valgus and external rotation, but were not significant in flexion during forced varus and internal rotation. In both groups, the same four lesions were produced 1) Anterior capsule rupture, 2) L-formed rupture of the origin of the pronator muscle with elongation of the anterior bundle of the medial collateral ligament, 3) partial rupture of the lateral collateral ligament and 4) small cartilage damage to the posterior or anteromedial edge of the ulna. In conclusion, hyperextension trauma to the elbow joint induced through the distal ulna or the distal radius produced the same pattern of injury as reported in hyperextension of the elbow with traction to the forearm when free rotation of the radius relative to the ulna was allowed.