Elbow Dislocations

The elbow is the second most common large joint to dislocate, after the shoulder. The injuries it produces range from simple ligamentous injuries to complex fracture-dislocations with significant instability.

Mechanism. A fall on the outstretched hand with the elbow slightly flexed. The axial load arrives with a valgus and supination moment, which drives the ulna posterolaterally on the humerus, and that is why posterolateral displacement is the commonest pattern.

• FOOSH - the most common mechanism
• Direct trauma - less common
• Sports injuries - common in young adults
• Motor vehicle accidents - often high-energy, with complex patterns

Simple or complex. Simple means ligament injury with no fracture; complex means a fracture as well, and takes in the terrible triad, radial head fracture-dislocation, coronoid fracture-dislocation and the transolecranon pattern. The division decides the treatment and most of the prognosis, which is why it is the first thing said about any dislocated elbow.

The bony architecture. The ulnohumeral joint is the primary source of stability and works as a hinge; the radiocapitellar joint is a secondary stabiliser. The trochlea sits in the greater sigmoid notch, buttressed in front by the coronoid and behind by the olecranon, so the notch is a socket for only as long as both of its walls are intact.

Why the elbow comes out. A semi-flexed elbow is the vulnerable one. As the trochlear centre rises relative to the coronoid buttress, a smaller posteriorly directed force is enough to lever the ulna out of the joint.

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The lateral collateral complex. The lateral ulnar collateral ligament (LUCL) is the component that matters: it runs from the lateral epicondyle to the supinator crest of the ulna and is the primary restraint to posterolateral rotatory instability. The radial collateral ligament blends with the annular ligament, and the annular ligament holds the radial head to the ulna.

The medial collateral complex. Here the anterior bundle is the important one, running from the medial epicondyle to the sublime tubercle as the primary valgus stabiliser. The posterior bundle tightens in flexion, and the transverse ligament contributes little.

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Static and dynamic. The ligaments and the bony congruity are the static stabilisers. The muscles crossing the joint - triceps, biceps, brachialis and the flexor and extensor origins - are the dynamic ones. The column model below groups the two kinds together: the anterior and posterior columns contain the coronoid, olecranon, capsule, brachialis and triceps, the lateral and medial columns the radial head, collateral ligament complexes, coronoid and flexor-pronator or extensor origins.

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The Horii circle. O'Driscoll's account of how the soft tissue fails: disruption travels from lateral to medial, taking the LCL complex first, then the anterior and posterior capsule, then the MCL. Two things follow. The LCL complex is always injured in a posterolateral dislocation, and how far round the circle the injury has travelled is exactly what the O'Driscoll stages number.

The classifications answer different questions, and an examiner will want all of them: whether a bone is broken, which way the ulna went, how far round the soft-tissue circle the injury travelled, and what shape the coronoid fragment is.

Simple vs ComplexCoronoid FractureDirectionO'Driscoll StagesComplex Patterns

The primary division, and the one that sets both the treatment and the prognosis.

Simple

Definition

No fracture, ligament injury only

Incidence

50-60%

Complex

Definition

With associated fracture(s)

Incidence

40-50%

Type	Definition	Incidence
Simple	No fracture, ligament injury only	50-60%
Complex	With associated fracture(s)	40-50%

Simple. Ligamentous injury alone, usually stable after closed reduction, and with an excellent prognosis provided motion starts early.

Complex. A fracture as well as the dislocation - the terrible triad, a radial head pattern, a coronoid pattern or a transolecranon injury. Usually operative, and with higher complication rates.

Two classifications, and the newer one exists because height does not tell you what to do.

Regan-Morrey grades by the height of the fragment on the lateral radiograph:

I

Fragment

Tip avulsion only

II

Fragment

50% or less of coronoid height

III

Fragment

More than 50% of coronoid height

Type	Fragment
I	Tip avulsion only
II	50% or less of coronoid height
III	More than 50% of coronoid height

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O'Driscoll grades by location, which is what actually determines the instability pattern, the approach and the implant:

Tip

Location

Transverse, small

Why it matters

The terrible-triad fragment; capsule attaches to it

Anteromedial facet

Location

Sheared off the medial edge

Why it matters

Varus posteromedial rotatory instability - see below

Base

Location

Body / basal, into the sublime tubercle

Why it matters

Large, takes the MCL footprint; usually a fracture-dislocation of the proximal ulna

Type	Location	Why it matters
Tip	Transverse, small	The terrible-triad fragment; capsule attaches to it
Anteromedial facet	Sheared off the medial edge	Varus posteromedial rotatory instability - see below
Base	Body / basal, into the sublime tubercle	Large, takes the MCL footprint; usually a fracture-dislocation of the proximal ulna

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The Anteromedial Facet Fracture - Small on Film, Serious in the Joint

This is the coronoid fracture that gets missed. The mechanism is varus, axial load and posteromedial rotation, not the posterolateral pattern that produces a terrible triad. It shears the anteromedial facet, which overhangs the ulnar shaft unsupported, and it usually goes with an avulsion of the lateral collateral ligament - so the elbow has lost its medial bony buttress and its lateral ligament at once.

Why it is missed. On the AP and lateral it looks like a small fleck, and Regan-Morrey grades it as a Type I "tip" fracture - a grade whose whole teaching is that it can be left alone. It cannot. Get a CT on any coronoid fracture you are considering treating non-operatively, and look at the sagittal and 3D reconstructions.

What happens if you leave it. The joint collapses into varus, the ulnohumeral joint loses congruity, and post-traumatic arthrosis follows quickly - within months, not years.

Treatment. Approach medially (over-the-top or a Hotchkiss flexor-pronator interval), support the facet with a buttress plate rather than lag screws alone, and repair the lateral collateral ligament. Check the elbow tracks concentrically in varus before you close.

Posterolateral

Incidence

90%

Mechanism

FOOSH, valgus + supination

Posterior

Incidence

Rare

Mechanism

Direct posterior force

Lateral

Incidence

Rare

Mechanism

Varus force

Anterior

Incidence

Rare

Mechanism

Direct blow to flexed elbow

Medial

Incidence

Rare

Mechanism

Valgus force

Divergent

Incidence

Rare

Mechanism

Radius and ulna separate

Direction	Incidence	Mechanism
Posterolateral	90%	FOOSH, valgus + supination
Posterior	Rare	Direct posterior force
Lateral	Rare	Varus force
Anterior	Rare	Direct blow to flexed elbow
Medial	Rare	Valgus force
Divergent	Rare	Radius and ulna separate

In the posterolateral pattern the ulna comes to lie posterior and lateral to the humerus. The others are all rare, and each has its own mechanism, which is the reason to name the direction before attempting a reduction.

The stages count how far round the Horii circle the soft tissue has failed, and they map onto what the joint does.

1

Description

PLRI

Structures Involved

LCL complex

2

Description

Perched/incomplete

Structures Involved

LCL + capsule

3A

Description

Complete, anterior MCL intact

Structures Involved

LCL + capsule + posterior MCL

3B

Description

Grossly unstable

Structures Involved

All ligaments

Stage	Description	Structures Involved
1	PLRI	LCL complex
2	Perched/incomplete	LCL + capsule
3A	Complete, anterior MCL intact	LCL + capsule + posterior MCL
3B	Grossly unstable	All ligaments

Stage 1 subluxates posterolaterally and no more. Stage 2 is the perched elbow: the coronoid rests on the trochlea, incompletely dislocated. Stage 3A is a complete dislocation with the posterior bundle of the MCL torn and the anterior bundle still holding; by 3B the entire MCL has gone and the elbow is grossly unstable.

Terrible triad. Elbow dislocation, radial head fracture and coronoid fracture, with LCL disruption always. Four structures, not three, which is the point most candidates miss.

Mason type IV. A radial head fracture with dislocation, either as part of a terrible triad or on its own.

Transolecranon fracture-dislocation. An olecranon fracture with ulnohumeral dislocation, sometimes taking the coronoid with it.

Divergent. The radius and ulna separate from each other, the interosseous membrane is disrupted, and the elbow is very unstable.

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History. Ask the mechanism and whether the elbow reduced itself before arrival. Then the time since injury, any previous elbow problem, and hand dominance and occupation.

Examination. The limb is held deformed with the olecranon prominent behind, and the diagnosis is rarely the difficulty; what gets missed is everything that should be recorded beside it. These go in the notes, and the first of them twice, before and after the manipulation:

1. Neurovascular status - median, ulnar and radial nerves, and the brachial artery
2. Skin integrity - open or closed
3. Associated injuries - the rest of the ipsilateral limb
4. Deformity pattern - it predicts the direction

The nerve and the vessel. The ulnar nerve is the one most commonly injured, and its paraesthesiae are usually transient and settle with reduction. Brachial artery injury is rare but does happen, particularly with an anterior or an open dislocation.

What else it could be. A deformed, painful elbow that has already reduced, or one whose films are hard to read, is where the mimics live. Each has its own discriminating feature and its own confirmatory test.

Before reduction. Get an AP and a lateral, accepting that a true view is often impossible through the deformity. They confirm the dislocation and its direction, show any associated fracture of the radial head or coronoid, and show where a displaced fragment has come to lie.

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After reduction. Repeat the AP and lateral and read them properly, because this is where a simple dislocation gets reclassified as complex:

• Radial head fracture - often subtle
• Coronoid fracture - usually visible on the lateral
• Joint widening - suggests an interposed fragment
• Radiocapitellar alignment - the test of a truly concentric reduction

CT. Get one when the plain films leave a question:

• A suspected associated fracture that is not clear on radiographs
• A complex dislocation pattern
• Surgical planning
• Any joint incongruency on plain films

It characterises the radial head and coronoid fractures, counts and sizes the fragments, and picks up the associated injuries.

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The decision. Reduce the elbow, then answer two questions: is a bone broken, and will the joint stay in? The answers sort the patient into one of three groups - stable simple, unstable simple, or complex - and each has its own pathway.

Algorithm

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Reduction. The manoeuvre reverses the displacement that produced the injury, and the sequence below is what that looks like at the bedside.

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Stiffness. The commonest complication, and the reason the whole treatment plan is built around early motion. The usual pattern is a flexion contracture; once it is established the options are physiotherapy, dynamic splinting and surgical release.

What blocks what. Posterior radial-head and capitellar osteophytes block extension, and anterior osteophytes block flexion. Imaging the elbow through its arc shows which prominence is doing the blocking, and lets the release be a targeted osteoplasty rather than an indiscriminate one.

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Posterolateral rotatory instability. The chronic sequela of an LCL that was never repaired or never healed properly. The patient describes apprehension or frank instability, and the treatment is LCL reconstruction.

Heterotopic ossification. The risk rises with head injury, burns, delayed surgery and aggressive physiotherapy. Prophylaxis is indomethacin 25mg TDS for 3 weeks, or radiation, and bone that is mature and limiting function is excised.

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Entrapment of the medial epicondyle. The fragment can be drawn into the joint during reduction, where it blocks full extension. Miss it and the elbow stays unstable and stiff; it has to be extracted and fixed.

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After a simple dislocation. The programme below is for the elbow that held its reduction through a useful arc, and it is deliberately front-loaded: the protection comes off as soon as the joint can be trusted.

After an LCL repair or a complex reconstruction. More protection early: a hinged brace with an extension block if one is needed, motion started early but kept inside the safe arc, and progression governed by the stability and the healing rather than by the calendar.

What to expect. The pattern sets the ceiling, and the simple stable dislocation sits at the top of it.

What moves a patient within it. Beyond simple versus complex, the outcome turns on the time to reduction and the quality of that reduction, on how soon motion started, on the associated injuries, and on whether the patient does the rehabilitation.

Global epidemiology

Elbow dislocation is the second most common large-joint dislocation after the shoulder and is predominantly an injury of active adolescents and young adults.

Guidance and evidence, side by side

There is no single dedicated international society guideline for elbow dislocation comparable with hip-fracture pathways; practice is driven by high-level trial and consensus evidence that is broadly concordant across regions.

Registry evidence

Elbow dislocation is a soft-tissue / fracture-dislocation injury and is not tracked by the arthroplasty joint registries (NJR, AJRR, AOANJRR, SHAR, NZJR), which capture joint replacement rather than acute trauma. Epidemiology therefore derives from national injury-surveillance datasets (e.g. the US NEISS database) rather than implant registries.

Global practice variation

• High-resource settings: ready access to fluoroscopy, CT for complex patterns, radial head arthroplasty and hinged external fixators; early supervised hand-therapy-led mobilisation is standard.
• Limited-resource settings: reliance on plain radiographs and closed reduction; restricted access to radial head prostheses and hinged fixators may favour fixation or, where unavoidable, excision strategies and longer protected mobilisation.
• Convergent core: across all settings the principles are identical - reduce promptly, document neurovascular status before and after, classify simple versus complex, test the stable arc, and mobilise early.