Coronoid process fractures

The coronoid is the anterior buttress of the trochlear notch: with the anterior capsule and brachialis attached to it, it stops the ulna sliding backwards, and its anteromedial facet carries the sublime tubercle where the medial collateral ligament (anterior bundle) inserts. A coronoid fracture is almost never an isolated injury: it is the marker of an elbow that has dislocated or subluxed.

Mechanism

Posterolateral rotatory instability (fall on the outstretched hand with valgus and supination): the trochlea shears off the tip, often with a radial head fracture (terrible triad). Varus posteromedial rotation: the trochlea impacts the anteromedial facet (with a lateral ligament tear). Transolecranon fracture-dislocations break the base.

Clinical findings

• Elbow dislocation or a history of one; check for instability, crepitus and a block to motion.
• Varus posteromedial instability can look deceptively benign: a small anteromedial fragment on the lateral X-ray and a joint that subluxes in varus.
• Neurovascular examination, especially the ulnar nerve.

Imaging

• AP and true lateral of the elbow, before and after reduction.
• CT with 3D reconstructions for every coronoid fracture: tip, anteromedial facet or basal, fragment size and associated radial head injury.

• AP and true lateral of the elbow after reduction: the coronoid fragment is often a small triangle in front of the trochlea ("double crescent" on the lateral suggests an anteromedial facet fracture).
• CT with 3D reconstructions for every suspected coronoid fracture: size, type (tip, anteromedial, basal) and associated injuries determine treatment.

Classification

2U1B

AO/OTA 2018: coronoid fractures are partial articular fractures of the proximal ulna; use O’Driscoll for the pattern.

Regan–Morrey

I avulsion of the tip; II up to 50% of the coronoid height; III more than 50%. Each A without or B with elbow dislocation.

O’Driscoll

Tip (subtype 1 ≤ 2 mm, 2 > 2 mm); anteromedial facet (1 rim, 2 rim and tip, 3 rim and sublime tubercle); basal (1 body and base, 2 transolecranon basal).

Types shown in 3D

Regan–Morrey I

Tip avulsion (O’Driscoll tip): a small shear fragment, the hallmark of a posterior dislocation. Part of the terrible triad when the radial head is also broken.

Regan–Morrey II

Up to half of the coronoid height. The anterior capsule attaches here; with a dislocation the elbow tends to slip back out: repair (lasso suture or screws).

Regan–Morrey III

More than half of the coronoid (basal type): the ulnohumeral joint loses its anterior buttress and the brachialis insertion. Rigid fixation (screws or plate).

Anteromedial facet

O’Driscoll anteromedial facet fracture from varus posteromedial rotation, with a lateral ligament tear. The facet carries the sublime tubercle (MCL insertion); left untreated the elbow subluxes in varus and wears out quickly.

Terrible triad

Posterior dislocation with fractures of the radial head and the coronoid tip. Unstable and prone to stiffness and arthritis: repair the coronoid and capsule, fix or replace the head, then repair the lateral ligament.

Treatment

Non-operative

Small tip fractures in an elbow that is stable after reduction and on CT has no anteromedial component: short splinting and early motion in an overhead (gravity-assisted) protocol, with close radiographic follow-up for subluxation.

Terrible triad

Operative in most, through a lateral approach and working from deep to superficial: repair the coronoid (suture lasso through drill holes for tip fragments, screws for larger ones) and anterior capsule through the radial head defect, then fix or replace the radial head, then repair the lateral collateral ligament complex to the epicondyle. If the elbow is still unstable: medial ligament repair or a hinged external fixator.

Anteromedial facet

Usually fixed through a medial (flexor carpi ulnaris split or over-the-top) approach with a buttress plate or screws, together with repair of the lateral ligament; small stable fragments in a congruent joint may be treated non-operatively with close follow-up.

Basal and large (Regan–Morrey III)

Anatomical reduction and fixation with screws or a plate (posterior or medial approach), often as part of a transolecranon fracture-dislocation where the olecranon is plated too.

Aftercare

Early active motion in a stable arc; avoid varus stress (shoulder abduction) after anteromedial injuries and keep the forearm pronated after lateral ligament repair.

Complications

• Recurrent instability or persistent subluxation (missed anteromedial fracture)
• Post-traumatic arthritis
• Stiffness and heterotopic ossification
• Ulnar neuropathy