Radial Head Fractures

Radial head fractures are the most common adult elbow fracture, around 33% of elbow fractures and around 4% of all fractures.

Who. The median age is around 43 years, and population data show no consistent sex predominance. Fractures in women tend to be lower-energy falls; fractures in men occur in younger patients and at higher energy. Consider an osteoporosis assessment in an older patient with a low-energy injury.

Mechanism. A fall on the outstretched hand. Axial load with a valgus force drives the radial head into the capitellum. With the forearm in pronation the fragment is anterolateral, the most common pattern; extension produces a posterior dislocation.

Biomechanics. The head contributes to stability in three ways:

• Load transfer - radiocapitellar contact is a primary stabiliser and carries 60% of load transfer
• Valgus stability - a secondary stabiliser, contributing 30% of valgus stability and resisting valgus when the MCL is incompetent
• Longitudinal stability - it prevents proximal migration of the radius

The head and its ligaments. The radial head sits against the capitellum, encircled by the annular ligament, and its rim contacts the lesser sigmoid notch of the ulna through pronation and supination. The lateral collateral ligament complex, the lateral stabilisers, is often torn in Type IV injuries and is repaired after the head is fixed.

Blood supply. The radial recurrent artery supplies the head with retrograde flow, which puts neck fractures at risk of AVN and non-union.

The safe zone. Roughly three-quarters of the rim is articular margin that meets the lesser sigmoid notch, and hardware there impinges on the proximal radioulnar joint and blocks rotation. The remaining arc, facing antero-laterally away from the ulna, does not articulate with the proximal radioulnar joint, and plates and prominent screw heads go there. It is quoted as a 90-110° arc: Smith and Hotchkiss's cadaveric dissection defined approximately 110°, and 90° is a deliberately conservative version of the same idea. With the forearm in neutral it roughly corresponds to the lateral aspect of the head.

Finding it in theatre. Surface landmarks have been offered as reference marks: the radial styloid, said in some citations to correspond to the midpoint of the zone but unreliable, and alignment with Lister's tubercle. The best method is to mark the radial head in full pronation and full supination relative to the sigmoid notch; the area that never articulates with the lesser sigmoid notch is the safe zone.

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The Kocher interval runs between anconeus (radial nerve) and ECU (PIN). It is not a true internervous plane, since both muscles are supplied by branches of the radial nerve, but it is a reliable intermuscular interval. It is safe distally, but the posterior interosseous nerve, the motor nerve to the extensors, crosses the radial neck proximally within the supinator and is the structure at risk. Pronation moves the PIN anteriorly, away from the radial neck and the surgical field, which makes the dissection safer.

The Kaplan interval lies between ECU and EDC. It gives better access to the anterolateral coronoid and the anterior capsule, which is why it is often preferred for terrible triad injuries, but it puts the PIN and LCL at higher risk if extended proximally.

Mason's classification, modified by Broberg and Morrey, is the shared vocabulary. Types I to III describe the head; Type IV adds a dislocation, and with it the problem of instability.

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Associated injuries. Check the wrist, test the medial side, and get a CT.

• MCL injury - assess valgus stability
• Coronoid or capitellum fractures
• Essex-Lopresti - DRUJ injury with an interosseous membrane tear

The terrible triad. Radial head fracture, coronoid fracture and elbow dislocation with LCL injury. Fractures often come in threes, the rule of threes: find one component and look for the other two. The dislocation is posterolateral, the radial head fracture is usually Mason III or IV, and the coronoid fracture usually Regan-Morrey type I or II. The elbow is extremely unstable, and treatment runs inside-out: fix the coronoid, then fix or replace the radial head, then repair the LCL.

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The Essex-Lopresti lesion. Longitudinal radioulnar dissociation: a radial head fracture with a tear of the interosseous membrane and dislocation of the DRUJ. The radius migrates proximally and the ulna impacts at the wrist, which is where the patient hurts. Treatment restores radial length by replacing the head, with pinning of the DRUJ if needed. Never excise the head.

The coronoid is one of the terrible triad's three components, and two complementary systems are examinable.

Each Regan-Morrey type is subdivided A (no dislocation) or B (with dislocation).

The O'Driscoll classification is anatomic and more useful for instability:

• Tip fractures - the terrible-triad pattern, often managed through the radial head and LCL repair
• Anteromedial facet fractures - even a small fragment destabilises the elbow into varus posteromedial rotatory instability (VPMRI), is easily missed on plain films, and usually needs a buttress plate or fixation rather than non-operative care
• Basal fractures - large body or base fragments, often with olecranon or proximal ulna injury

History. Lateral elbow pain, worse with pronation and supination. Locking or clicking suggests loose bodies. Ask specifically about wrist pain, which points to an Essex-Lopresti injury.

Examination. Palpate the radial head, the LCL origin and the DRUJ at the wrist. Assess flexion-extension and pronation-supination, and decide whether any loss of motion is a hard mechanical stop or pain inhibition. Test stability with valgus stress for the MCL and the pivot shift for the LCL. Always document a non-tender DRUJ, or get wrist radiographs.

The aspiration test. Pain inhibition can mimic a mechanical block, and the aspiration test separates them.

Radiographs. Three views: AP, lateral and the radiocapitellar (Greenspan) view. Look for cortical disruption, a step-off and the fat pad (sail) sign, which may be the only radiological sign, and check the DRUJ context. Radial head fractures are best profiled on a true lateral and the radiocapitellar view.

The radiocapitellar view is taken with the beam angled 45 degrees to the shoulder. It profiles the radial head without overlap from the coronoid and ulna, which makes it excellent for detecting subtle fractures.

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CT assesses complexity and plans the operation. It is indicated for:

• Comminuted fractures (Type III)
• Associated coronoid fractures
• Dislocation or subluxation
• Surgical planning, ORIF versus replacement

MRI is rarely needed: only for a subtle ligamentous injury, or an occult fracture if CT is equivocal. Ligament injury is mostly a clinical diagnosis.

The decision. The mechanical block is the primary indication for surgery in a Type II fracture: if it resolves after aspiration the fracture is treated non-operatively, and if it persists the answer is surgery. The indications for surgery are:

• Mechanical block to motion that persists after local anaesthetic
• Loose bodies - intra-articular fragments
• Open fracture - requires washout and fixation
• Complex instability - Type IV (terrible triad) or Essex-Lopresti

Displacement over 2 mm is controversial and not, on its own, an absolute indication (see Controversies).

Judging height. The native radial head does not project proximal to the coronoid. The prosthetic articular surface should match the coronoid level on the lateral view, sitting at, or about 1-2 mm distal to, the proximal edge of the lesser sigmoid notch and the lateral edge of the coronoid. Judge it against the coronoid and ulnohumeral congruity; judging the implant against the contralateral radius is unreliable.

Why it matters. Overstuffing leads to capitellar wear and loss of extension.

Radiographic signs on a true AP of the elbow:

• Asymmetric widening of the medial ulnohumeral joint space, the cardinal sign. The medial and lateral spaces should be symmetric; the over-long implant tilts and levers the ulna so the medial joint gaps open
• The radial head sitting proximal to the coronoid reference level
• Ulnohumeral incongruity and, over time, capitellar erosion

The 'more than 3 fragments' rule. Traditional teaching fixes a head with fewer than 3 articular fragments and mandates arthroplasty once it has more than 3. A retrospective series of 35 Mason III/IV fractures found comparable QuickDASH and Broberg-Morrey scores and equal reoperation rates whether 2, 3 or 4 fragments were fixed (Walsh, PMID 35545488): selected comminuted heads fixed by experienced surgeons do as well as simple patterns. Fragment count guides but does not decide.

Excision or replacement. Despite widespread enthusiasm for arthroplasty, pooled meta-analysis data show no clear superiority over excision in a stable, isolated Mason III elbow with an intact MCL and interosseous membrane. The two give similar Mayo Elbow Performance Scores and complication rates, with a slightly better arc after excision. Replacement is favoured where stability is needed (terrible triad, Essex-Lopresti) and in younger patients, because of the long-term arthritis concern; excision is reserved for low-demand, stable elbows. Cost, implant availability and patient age drive the decision more than functional score.

The 2 mm threshold. The historical 2 mm step-off as a surgical trigger is not evidence-based, and many displaced Mason II fractures do well non-operatively. A true mechanical block, confirmed after aspiration and local anaesthetic, is the more reliable indication.

Routine MCL repair in the terrible triad. Whether to repair the MCL after LCL repair and bony fixation is debated. Most protocols achieve stability with LCL repair alone; MCL repair or a hinged external fixator is reserved for residual instability tested intra-operatively.