Orthonotes
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I: tip avulsion; II: <50% height; III: >50% height. II–III indicate elbow instability, commonly part of terrible triad → fixation required.
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The coronoid process of the ulna is the anterior projection of the proximal ulna that forms the anterior buttress of the ulnohumeral (trochlear) joint. It is the most important bony stabiliser of the elbow against posterior translation — it acts as a `bony stop` that prevents the trochlea from riding posteriorly over the coronoid. Coronoid fractures occur in the context of elbow dislocations (the coronoid is sheared off by the trochlea during the dislocation mechanism) and in complex elbow injury patterns. The Regan-Morrey classification (1989) grades coronoid fractures by the height of the fragment as a proportion of the coronoid height, predicting elbow stability and guiding surgical management. The classification is used in conjunction with assessment of the accompanying soft tissue injuries (lateral collateral ligament, medial collateral ligament, radial head) to determine the appropriate surgical approach.
| Type | Fragment Height | Description | Stability Implications | Treatment |
|---|---|---|---|---|
| Type I — Tip fracture | <50% of coronoid height; only the tip is avulsed; involves the anterior capsule insertion | A small avulsion of the coronoid tip; the anterior joint capsule inserts at the tip and is avulsed with the fragment; the fragment is typically very small (a few millimetres); visible as a small fragment anterior to the coronoid on the lateral elbow X-ray; easy to miss on plain X-ray — CT delineates the fragment size and position better | In ISOLATION: relatively low instability risk if the lateral and medial collateral ligaments are intact; HOWEVER, in the context of the `terrible triad` (coronoid + radial head + posterior elbow dislocation), even a Type I coronoid fracture must be repaired because the anterior capsular attachment at the tip is the ONLY remaining anterior stabiliser of the elbow (after the radial head fracture has removed the lateral stabiliser and the elbow has dislocated the MCL) | In ISOLATION (simple elbow dislocation with Type I coronoid): conservative — range of motion brace, early motion at 1–2 weeks; In TERRIBLE TRIAD: surgical repair — suture lasso technique (sutures are passed through the anterior capsule and the coronoid fragment, then through bone tunnels in the proximal ulna, and tied over the dorsal cortex); screw fixation is usually not possible for the small Type I fragment |
| Type II — 50% or less of height | ≤50% of the coronoid height is fractured; the fragment is larger than a tip avulsion but involves less than half the process | A more substantial coronoid fracture involving up to 50% of the coronoid height; the fragment is large enough to be visible on plain X-ray; the anterior capsular attachment is included in the fragment; the MCL attachment (at the sublime tubercle) may be partially involved depending on the exact fracture level; CT is recommended to assess the fracture morphology and the extent of articular surface involvement | SIGNIFICANT INSTABILITY — a Type II coronoid fracture substantially compromises the anterior bony stabiliser of the elbow; in the context of elbow dislocation or the terrible triad, elbow stability is severely compromised; the elbow will subluxate or redislocate posteriorly without surgical repair of the coronoid AND the associated soft tissue injuries | SURGICAL REPAIR typically required, particularly in the context of elbow instability; options: (1) screw fixation (if the fragment is large enough for a small screw — typically a 2.0–2.7 mm screw placed from anterior through the fragment into the coronoid body, or from posterior through bone tunnels); (2) suture lasso technique (if the fragment is too small or comminuted for direct screw fixation); (3) plate fixation for the anteromedial facet variant (see O`Driscoll classification below) |
| Type III — >50% of height | >50% of the coronoid height is fractured; more than half the coronoid process is separated from the proximal ulna | A LARGE coronoid fracture involving more than half the process; the MCL attachment at the sublime tubercle is invariably included in the fragment (because the sublime tubercle is located at the anteromedial base of the coronoid — a Type III fracture at this height necessarily includes this attachment); the brachialis muscle insertion may also be partially involved; the entire anterior buttress of the elbow is fractured | PROFOUND INSTABILITY — biomechanical studies demonstrate that a Type III coronoid fracture (>50% of height) creates an elbow that cannot be maintained in a reduced position without internal fixation; the trochlea will subluxate posteriorly without the anterior bony block; this type is the most challenging to manage and has the highest complication rates (post-operative stiffness, re-dislocation, post-traumatic arthritis) | MANDATORY SURGICAL FIXATION — ORIF of the coronoid fragment is essential; options: (1) anterior buttress plate (a small plate applied anteriorly to the coronoid fragment — provides the most rigid fixation and is the preferred technique for large Type III fragments); (2) lag screws from posterior to anterior through the coronoid body; (3) the McK-E approach (medial approach with elevation of the flexor-pronator mass to expose the coronoid medially); the MCL must also be assessed and repaired if torn; hinged external fixation may be needed if the elbow remains unstable after fixation of all fractures and repair of all ligaments |
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