Coronoid fracture or coronoid process fracture is fracture anterior projection of ulna in its superior part where together with the posterior projection of ulna, olecranon, it expands the articular area of the upper end of the ulna. Ulna articulates with the lower end of humerus in this articular notch.
Both coronoid and olecranon processes also provide stability to humerus by forming anterior and posterior supports by virtue of projections.
While fracture of olecranon is very common, a coronoid fracture is seen less commonly. Fractures of the coronoid process usually reflect severe trauma to the elbow.
Coronoid fracture usually occurs in association with other injuries of the elbow, namely elbow dislocation. Isolated coronoid fracture is less common.
Large coronoid fractures often are associated with persistent elbow instability even after reduction of the dislocation.
Coronoid fracture accounts for less than 1-2% of all elbow fractures. Coronoid fractures have been identified in 10-15% of elbow dislocations.
Mechanism of Coronoid Fracture
Previously, it was thought that these fractures were as a result of avulsion force acting on coronoid but now it is thought that they probably are due to direct impact of trochlea on the coronoid when a force acts.
The brachialis muscle, which was thought to put a force of avulsion, inserts much distally than the tip of the coronoid. However, it is not uncommon to find attached fibers of brachialis in a larger fragment distal to the coronoid process.
When the fragment of coronoid is large, it may cause dislocation of the elbow as the supportive buttress is no longer available [See classification]. But a small coronoid potentially severe trauma with possible acute recurrent dislocation.
Classification of Cornoid Fracture
The classification was suggested by Regan and Morrey who after a retrospective study, classified the fracture into three types.
Classification of coronoid fracture
Type I—small avulsion fracture at tip of coronoid
Type II—fragment involves 50% of the coronoid but does not extend to the base
Type III—Fracture at the base of the coronoid, likely including the insertions of the brachialis and the anterior band of the medial collateral ligament.
In spite of their type, the presence of a coronoid fracture should evoke concern for acute instability.
AP and lateral views of the elbow are sufficient for most of the cases. In complex injuries of the elbow with concomitant coronoid fracture, CT may be required.
Treatment of Coronoid Fracture
Fracture of the coronoid process are generally not amenable to closed treatment. Therefore open reduction is almost always the treatment of choice where the fragment is stabilized using either screw or wire fixation.
Because they are generally associated with elbow instability, open reduction with internal fixation of a significant coronoid fracture often provides the necessary stability to prevent further dislocation.
Operative intervention may also be considered for those fractures that interfere with joint motion. This can occur if the fragment is intraarticular or if it unites proximally and forms a significant bone block to flexion.
After the surgery, the limb is immobilized for a period of 3 to 4 weeks. Weekly follow up should be done with xray.
After this period , gentle elbow mobilization is begun.
Complications of Coronoid Fracture
- Neurovascular injury
- Heterotopic ossification
- Instability and recurrent dislocation
- Posttraumatic arthritis of the elbow