Q: What are the characteristics of the coronoid process of the ulna?
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A: The ulna's coronoid process forms the anterior half of the greater sigmoid notch of the ulna and makes up the anterior margin of the ulnohumeral articulation. It articulates with the humeral trochlea and acts as a bony buttress to resist varus stress and prevent posterior elbow subluxation. It serves as the site of attachment of the elbow's anterior joint capsule, insertion of the medial ulnar collateral ligament (MUCL), and insertion of the brachialis muscle in its anterior aspect.
Q: Does the coronoid process play any role in elbow stability?
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A: The coronoid process plays an important role in elbow stability, serving as one of the primary restraints against varus-directed forces and, along with the radius, valgus-directed forces.
Q: Which are the segments of the coronoid process of the ulna?
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A: The ulna's coronoid process has different segments, including the tip, the anterolateral facet, and the anteromedial facet. The sublime tubercle is in the anteromedial facet of the ulna's coronoid process, and it serves as the site of insertion of the medial ulnar collateral ligament (MUCL) complex.
Q: How is the mechanism of a coronoid process fracture?
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A: The specific mechanism of coronoid fracture is varied and can involve twisting and flexion, and hyperextension. The most common cause of fracture of the ulna's coronoid process occurs due to a fall on an outstretched hand (FOOSH) from standing height. Most coronoid process fractures occur with elbow dislocation associated with comminuted proximal ulna fractures and radial head fractures. Isolated coronoid process fractures are uncommon.
Q: How is the initial imaging evaluation of coronoid process fracture?
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A: The initial evaluation should consist of anteroposterior and lateral views of the elbow and a radio-capitellum view (Greenspan view) to investigate an associated radial head fracture.
Q: Can a fracture of the coronoid process of the ulna be missed on radiographs?
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A: Fractures of the coronoid process are relatively uncommon and can be missed on radiographs, especially when they are small or non-displaced. The ulnar coronoid process overlaps the radial head on lateral X-ray film so that these fractures can be easily missed. Besides, it can be hard to distinguish from radial head fractures. These fractures often occur in association with elbow dislocations, and they play an important role in elbow instability.
Q: How can CT and MRI help to investigate coronoid process fracture?
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A: In cases where plain radiographs are not definitive, computed tomography (CT) or magnetic resonance imaging (MRI) is helpful. CT can show the fracture's site and extent, fracture fragment morphology and size, displacement of the fragments, the degree of anteromedial facet and coronoid base involvement, and intraarticular bodies. MRI can be used for radiographically occult fractures, to detect bone edema, and to evaluate associated injuries and soft tissue injuries of the capsuloligamentous structures.
Q: How is the O'Driscoll system classification for coronoid process fractures
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A: In the O'Driscoll system, coronoid process fractures are of three main types, each of which comprises several more specific subtypes. Type I transverse coronoid tip fractures. Type II fractures involve the anteromedial facet, with subtypes varying according to the fracture's location along this facet and the sublime tubercle's degree of involvement. Type III fractures involve the coronoid process base, with disruption of more than 50% of the coronoid body.
Q: How is the treatment of coronoid process fractures?
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A: The type of coronoid fracture is relevant in the selection of surgical methods of fixation. Type I transverse coronoid tip fractures in the classification of O'Driscoll are usually treated without surgery if stability is maintained. The risk of instability increases with the increasing size of fracture fragments, and, therefore, in some cases, surgical treatment is necessary. Types II and III nearly always require surgical repair to maintain elbow stability, and the surgical approach varies by fracture type.
Q: What is the terrible triad of the elbow?
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A: A terrible triad injury is when there is a combination of posterior or posterolateral elbow dislocation with radial head and coronoid process fractures. The terrible triad is a constellation of findings that invariably needs surgical stabilization and is usually associated with ligament damage resulting in poor outcomes due to severe chronic instability, post-traumatic osteoarthritis, and impaired elbow function if inadequately treated.
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