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Ankle Mortise – Anatomy, Injuries and Treatment

The ankle mortise is the fork-shaped bony structure of the upper ankle joint, formed by the medial and lateral malleoli. It cradles the talus and provides essential joint stability.

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The ankle mortise is the fork-shaped bony structure of the upper ankle joint, formed by the medial and lateral malleoli. It cradles the talus and provides essential joint stability.

What Is the Ankle Mortise?

The ankle mortise (also called the malleolar fork) refers to the fork-shaped bony socket of the upper ankle joint (articulatio talocruralis). It is formed by the medial malleolus, which is part of the tibia (shinbone), and the lateral malleolus, which is part of the fibula (calf bone). Between these two bony projections sits the talus (ankle bone), which is held and guided within the mortise. This structure allows controlled movement of the foot, primarily dorsiflexion (lifting the foot upward) and plantarflexion (pointing the foot downward).

Anatomy and Structure

The ankle mortise is composed of three key bony components:

Medial malleolus: The inner projection of the tibia, forming the medial wall of the mortise.
Lateral malleolus: The outer projection of the fibula, which extends slightly more distally than the medial malleolus and forms the lateral wall.
Tibial plafond: The distal articular surface of the tibia, forming the roof of the mortise where it articulates with the superior surface of the talus.

The mortise is further stabilized by strong ligamentous structures, most notably the syndesmosis -- the fibrous joint connecting the tibia and fibula just above the ankle. This connection is critical for maintaining the integrity of the mortise.

Function

The ankle mortise serves several important biomechanical functions:

It guides the talus during ankle movement, preventing lateral displacement.
It transfers body weight from the lower leg to the foot.
Together with the surrounding ligaments, it ensures ankle joint stability during walking, running, and jumping.

Common Injuries of the Ankle Mortise

Ankle Fractures (Malleolar Fractures)

Injuries to the ankle mortise are among the most common fractures seen in clinical practice. These include:

Lateral malleolus fracture: The most frequent type, often caused by an inversion (rolling inward) injury of the foot.
Medial malleolus fracture: Less common in isolation; often occurs in combination with other injuries.
Bimalleolar fracture: Simultaneous fracture of both malleoli.
Trimalleolar fracture: Fracture of both malleoli plus the posterior tibial margin (posterior malleolus).

The Weber classification (Types A, B, and C) is widely used to categorize fibula fractures based on their relationship to the syndesmosis, which helps guide treatment decisions.

Syndesmosis Injury

A disruption of the syndesmosis can lead to widening of the ankle mortise, significantly compromising joint stability. This injury, known as a syndesmotic rupture or high ankle sprain, often requires surgical intervention to restore mortise congruency.

Ligament Injuries

In addition to bony injuries, the ligaments surrounding the mortise can be stretched or torn. The lateral ligament complex -- comprising the anterior talofibular ligament, calcaneofibular ligament, and posterior talofibular ligament -- is most commonly affected. These injuries are often referred to as ankle sprains and range from mild stretching to complete rupture.

Diagnosis

Various diagnostic methods are used to assess the ankle mortise and any associated injuries:

X-ray: The standard initial investigation; typically performed in two planes (anteroposterior and lateral) plus a mortise view to assess mortise congruency and detect fractures.
Computed Tomography (CT): Used for complex fractures or when detailed bony anatomy is required.
Magnetic Resonance Imaging (MRI): Valuable for evaluating ligament injuries, cartilage damage, and occult (hidden) fractures.
Clinical Examination: Palpation, stability testing, and functional assessment help determine the nature and severity of the injury.

Treatment

Conservative Management

Stable, non-displaced fractures and isolated ligament injuries can often be managed without surgery. Conservative treatment typically involves:

Immobilization using a brace or cast
Non-weight-bearing with crutches
Physiotherapy to restore strength and range of motion

Surgical Treatment

Unstable fractures or fractures with joint involvement generally require surgery. Common procedures include:

Open reduction and internal fixation (ORIF): Realignment and stabilization of bone fragments using plates, screws, or wires.
Syndesmotic fixation: Stabilization of a widened ankle mortise using a positional screw or suture button device to restore mortise integrity.

Following surgery, a structured rehabilitation program with physiotherapy is essential to regain full ankle function and prevent long-term complications.

References

Rockwood and Green's Fractures in Adults, 9th Edition. Wolters Kluwer Health, 2020. Chapter: Fractures of the Ankle (Buckley, R. & Moran, C.).
Egol, K.A., Koval, K.J. & Zuckerman, J.D. - Handbook of Fractures, 5th Edition. Wolters Kluwer, 2015.
van Dijk, C.N. et al. - Diagnosis and management of ankle fractures. EFORT Open Reviews, 2018; 3(1): 1-7.

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