Practice Essentials
Fractures of the coronoid rarely occur in isolation. They are often seen as a part of complex elbow fracture-dislocations, usually involving a radial head fracture, a dislocation of the elbow, or both (terrible triad of the elbow) [1, 2, 3, 4] ; rarely, they may be seen in conjunction with high Monteggia fractures. Large coronoid fractures often are associated with persistent elbow instability even after reduction of the dislocation. There has been a trend toward fixation of these injuries to restore stability and facilitate initiation of an early range-of-motion (ROM) program. [5, 6, 7, 8, 9, 10]
Images depicting the elbow joint can be seen below.
Type 1 and most type 2 fractures (see Workup) usually are managed nonoperatively and do not require operative stabilization. Highly comminuted type 3 fractures pose a significant problem during open reduction and internal fixation (ORIF) and may be better treated with a hinged external fixator. A displaced coronoid fracture that presents with a block to elbow motion is a definite indication for surgical stabilization.
Anatomy
The coronoid acts as the anterior buttress of the greater sigmoid notch of the ulna. It provides attachment to the anterior band of the medial collateral ligament (MCL) and the middle portion of the anterior capsule. The anterior colliculus of the MCL is the primary stabilizer of the elbow against valgus strain in the functional arc of 20-120° of flexion. This ligament is most likely to become injured with a low coronoid fracture with the elbow in full extension. [11] A fracture of the coronoid, therefore, results in the loss of all of these supports.
The brachialis muscle is attached to the base of the coronoid process. [12] Dissection of the brachialis during fixation of these fractures contributes to the risk of heterotopic ossification in these cases.
Pathophysiology
Morrey et al, in their biomechanical study of the elbow, concluded that approximately 50% of elbow stability comes from the congruent articulation between the trochlea and the ulna. [13]
Closkey et al studied the stabilizing function of the coronoid process under axial load to the elbow. [14] They found no significant difference, at any flexion position, in posterior axial displacement between intact elbows and elbows in which 50% or less of the coronoid process was fractured (types 1 and 2; see Workup). Differences in posterior axial displacement were significant, across all flexion positions, between intact elbows and elbows in which more than 50% of the coronoid process was fractured (type 3).
The authors concluded that in response to axial load, elbows with a fracture involving more than 50% of the coronoid process displace more readily than elbows with a fracture involving 50% or less of the coronoid process, especially when the elbow is flexed 60º and beyond. [14]
Etiology
Coronoid fractures were believed to result from avulsion of a bony fragment of the coronoid by the brachialis, which inserts onto the coronoid process. This, however, does not explain the mechanism of type 1 and some type 2 fractures, as the brachialis attaches to the base of the coronoid process of the ulna. (See Workup, Imaging Studies, for a discussion of fracture types.) These fractures probably occur from shear forces at the time of the dislocation when the trochlea pushes off a piece of the coronoid.
Epidemiology
Coronoid fractures account for fewer than 1-2% of all elbow fractures. They have been identified in 10-15% of elbow dislocations. [15, 16] Radial head fractures are seen in about 5-10% of elbow dislocations. [17] Coronoid fractures, especially with large fragments, are associated with more instability and an increased incidence of complications.
Prognosis
The prognosis for a complex fracture-dislocation of the elbow is definitely poorer than that for a simple elbow dislocation, which has been shown to have good long-term results. [18, 19, 20, 21]
Prognostic factors include the following:
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Size of the fragment - Type 3 fractures have the worst prognosis, with only 20% having good results in the series presented by Regan et al [15]
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The degree of damage to the articular cartilage at the time of injury
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The extent of soft-tissue injury [22]
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The stability obtained at the time of reduction
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The duration of immobilization [23]
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Elbow joint, anterior view.
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Elbow joint, posterior view.
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Type 2 coronoid fracture: unstable elbow fracture dislocation with fracture involving <50% of coronoid height and associated radial head fracture.
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Type 3 coronoid fracture: fracture involving >50% of coronoid height.
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Type 1 coronoid fracture: avulsion fracture at tip of coronoid.
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Status post open reduction and internal fixation of coronoid with plate-and-screw construct. Courtesy of Kenneth Egol, MD.
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Status post open reduction and suture fixation of coronoid, as evidenced by drill holes in proximal ulna. Sutures are used as a lasso to capture coronoid fragment, passed through ulnar drill holes, and tied over posterior ulna bony bridge. Patient is also status post radial head replacement for comminuted radial head fracture. This is an example of typical operative management of "terrible triad" elbow injuries.
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Second example of plate-and-screw constructs for fixation of type 3 coronoid fracture. Courtesy of Kenneth Egol, MD.
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Chronic elbow fracture dislocation presentation films with type II coronoid fracture (left) and fixation films (right). Fixation consisted of radial head replacement and suture lasso fixation of coronoid fracture. Since the elbow remained unstable throughout the range of motion, a hinged external fixator was placed.
