Ankle fractures: Weber, Lauge-Hansen and the question of stability

The anatomy of stability

The talus sits in a mortise formed by the tibial plafond and the medial and lateral malleoli. It is held there by three groups of ligaments: the deltoid ligament medially, whose deep part is the main restraint to lateral talar shift; the lateral ligaments (anterior talofibular, calcaneofibular and posterior talofibular); and the syndesmosis, made of the anterior and posterior inferior tibiofibular ligaments, the interosseous ligament and the inferior transverse ligament.

Think of a ring of bone and ligament around the talus. A single break leaves the ring stable; two breaks, for example a fibular fracture with a deltoid rupture, allow the talus to shift. Ramsey and Hamilton (1976) showed that a millimetre of lateral talar shift sharply reduces the tibiotalar contact area, which is why talar shift is not accepted.

Classification

Lauge-Hansen (1950) is a mechanistic system: the first word is the position of the foot at injury and the second the direction of the deforming force. Each type has stages that occur in sequence, so the stage predicts which structures are injured.

Imaging and judging stability

• Who needs an X-ray. The Ottawa ankle rules: pain in the malleolar zone with bony tenderness at the posterior edge or tip of either malleolus, or inability to bear weight both immediately and in the department.
• Views. BOAST 12 asks for radiographs centred on the ankle, with a true lateral and a mortise view, and whole-leg films if a proximal fibular (Maisonneuve) fracture is suspected.
• Medial clear space. Widening between the medial malleolus and the talus on the mortise view, conventionally more than 4–5 mm or wider than the superior clear space, means talar shift.
• Stress and weight-bearing views. Medial tenderness and bruising are poor predictors of a deltoid injury. For an isolated Weber B fracture a weight-bearing radiograph, or a gravity or external rotation stress view, shows whether the talus stays reduced.
• CT. BOAST 12 notes that CT helps define complex patterns, particularly involvement of the posterior malleolus.

Treatment

• Stable fractures (BOAST 12): analgesia, a splint or boot, and weight bearing as tolerated; further follow-up may not be necessary. In a Finnish trial (Kortekangas, BMJ 2019) three weeks in a cast or orthosis was non-inferior to six weeks in a cast for Weber B fractures that were stable on stress testing.
• Uncertain stability: review within two weeks with repeat radiographs, weight bearing if possible.
• Clinically deformed ankles: reduce and splint urgently, taking radiographs first unless that would cause an unacceptable delay; repeat the neurovascular examination and confirm the reduction on radiographs.
• Unstable fractures under 60: early fixation, on the day of or the day after injury. External fixation is occasionally needed for gross instability with soft-tissue compromise.
• Unstable fractures over 60: close contact casting is an option when the reduction can be held. In the AIM trial (Willett, JAMA 2016) it gave equivalent function to surgery at six months, with fewer infections and wound problems but more radiological malunion.

Principles of fixation

• Fibula. Restore length and rotation: a lag screw with a neutralisation plate, or a posterolateral antiglide plate, for a Weber B fracture.
• Medial malleolus. Partially threaded cancellous screws or a tension band. Whether a ruptured deltoid ligament needs repair is debated.
• Posterior malleolus. Fixation is no longer decided by fragment size alone. Fix it when it compromises the congruity or stability of the joint, or when its attachment of the posterior inferior tibiofibular ligament is needed to stabilise the syndesmosis; CT guides the approach.
• Syndesmosis. BOAST 12 asks for the syndesmosis to be assessed after bony fixation and stabilised if it is unstable. Test it with a hook (Cotton) test or an external rotation stress under fluoroscopy, reduce it carefully, because malreduction is common, and hold it with screws or a suture-button device.
• Weight bearing. BOAST 12 allows most patients to bear weight as tolerated in a splint or cast, unless the fixation, peripheral neuropathy or the soft tissues give cause for concern. Patients are seen within six weeks of surgery to check for complications and confirm that the reduction is maintained.

Patterns that need recognising

Maisonneuve injury

A proximal fibular fracture with disruption of the syndesmosis and the interosseous membrane, and a medial injury. The treatment is reduction and fixation of the syndesmosis, not of the proximal fibula.

Bimalleolar equivalent

A lateral malleolar fracture with a deltoid ligament rupture. Behaves like a bimalleolar fracture and is unstable.

Bosworth fracture-dislocation

The proximal fibular fragment is trapped behind the posterior tibia and the injury is irreducible by closed means; it needs open reduction.

Pilon fracture

An axial-loading injury of the tibial plafond. It is excluded from BOAST 12 and managed on soft-tissue principles, often with staged fixation.

Diabetes and neuropathy

BOAST 12 asks for diabetes, peripheral neuropathy, peripheral vascular disease and other comorbidities to be documented at presentation because they change the outcome. Patients with diabetic neuropathy have more wound breakdown, infection, loss of fixation and Charcot neuroarthropathy. Many surgeons use stronger constructs (for example extra syndesmotic fixation or a hindfoot nail in frail patients), protect weight bearing for longer and follow them up more closely.