Understanding Ulnar Coronoid Process Fractures

In this study cadavers are dissected to find out why small ulnar coronoid process fractures lead to an unstable elbow joint.

The elbow is a hinge joint made up of three bones. These include: 1) the humerus (the upper arm bone), 2) the ulna (the larger bone of the forearm, on the opposite side of the thumb), and 3) the radius (the smaller bone of the forearm on the same side as the thumb).

The end of the ulna at the elbow is called the coronoid process. It is shaped like a hook that fits around or hooks over the spool-shaped end of the humerus. Fractures of the tip of the coronoid process are called coronoid tip fractures.

This type of injury is fairly uncommon. Coronoid tip fractures can result in elbow instability. This occurs when the anterior joint capsule is disrupted and the elbow dislocates. Dislocation is more likely when a large portion of the tip breaks off.

The authors of this study explore why smaller fractures can become unstable. They looked at the anterior elbow capsule and tendons and ligaments that attach to the ulnar coronoid process. They wanted to see what happens to these structures when there's an unstable elbow from a small coronoid fracture.

They found that the location of the capsule as it inserts at the coronoid tip is the key factor in elbow instability after small coronoid fractures. It appears that the capsule inserts close to the tip of the coronoid process. So, even when only a small portion of the tip is fractured and dislocates, the capsule goes with it, leaving the joint loose and unstable.

The findings of this study point out why even small ulnar coronoid process fractures should be repaired surgically. The goal is to prevent elbow dislocation and instability. The larger the fragment size, the greater the need for surgical repair of this injury.

References: Robert H. Ablove, MD, et al. Ulnar Coronoid Process Anatomy. In Clinical Orthopaedics and Related Research. No. 449. Pp. 259-261.