Asynchronous growth of the canine radius and ulna: effects of cross pinning the radius to the ulna.

Kirschner wires were introduced into the diaphyseal region of the radius and the ulna in 4 Australian shepherd crossbred pups, and change in relationships between the bones during growth was demonstrated. The contributions to longitudinal growth of the radius from proximal and distal growth plates were also calculated. Over the period of growth, the proximal growth plate contributed approximately 40% of the length of the radius. A marked shifting of the radius in relationship with the ulna occurred. This normal shifting between radius and ulna was prevented in 6 dogs by cross pinning the radius to the ulna at 90, 111, 142, and 168 days of age. Marked change was produced in the elbow joint, where altered relationships of articular surfaces of the radius and the ulna resulted in displacement of the humeral condyle from the trochlear notch of the ulna. Changes in dogs cross pinned at 90 and 111 days of age were most severe and consisted of severe degenerative changes which were most marked on the lateral side of the distal half of the trochlear notch of the ulna.