Syndesmotic Injury of the Ankle
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Direct answer
A syndesmotic injury of the ankle is a disruption of the ligaments binding the distal tibia and fibula, often called a high ankle sprain. The squeeze and external rotation tests reproduce the pain, and a widened tibiofibular clear space on the mortise view supports the diagnosis. Unstable injuries are fixed with a syndesmotic screw or a suture-button device to restore the mortise.
What you must remember
- Key structure: the anterior-inferior tibiofibular ligament is the first and most commonly torn, supported by the interosseous membrane and the posterior tibiofibular ligament.
- Mechanism: external rotation of a planted foot, often with dorsiflexion, is the commonest cause, typical of tackles and twisting sports injuries.
- Squeeze test: compressing the tibia and fibula at mid-calf reproduces pain at the syndesmosis.
- External rotation test: rotating the foot outwards with the knee flexed reproduces pain at the distal tibiofibular joint.
- Radiographic sign: a widened tibiofibular clear space on the mortise view indicates disruption of the syndesmosis.
- Stress views and CT: weight-bearing or stress films and CT help when the diagnosis or the degree of widening is borderline.
- Fixation options: a syndesmotic screw or a suture-button device, with the fibula reduced into the tibial incisura and the position confirmed on films.
A stepwise pathway from sprain to fixation
A 25-year-old rugby player is tackled with his foot planted and externally rotated, and reports pain above the ankle that prevents weight bearing. The steps below show how the injury is confirmed, graded and treated, in the order a sports orthopaedic team would follow.
- Suspect the injury. Pain above the ankle after a planted, externally rotated foot is the classic pattern, and the athlete often cannot bear weight.
- Examine the syndesmosis. Perform the squeeze test and the external rotation test, noting pain and instability at the distal tibiofibular joint.
- Image the ankle. Take AP, mortise and lateral views of the ankle, and add stress views or CT if the widening is borderline.
- Decide on stability. Treat a stable injury with immobilisation and graded rehabilitation, and reserve fixation for an injury that is unstable on examination or imaging.
- Fix the syndesmosis. Use a syndesmotic screw or a suture-button device, reduce the fibula into the incisura, and confirm the position on films.
- Plan the return to sport. Rehabilitate with protected weight bearing, and decide later whether to remove a screw, which is debated and depends on symptoms.
Where the exam tries to catch you
Syndesmotic questions test whether the candidate recognises the injury above the ankle and understands when to fix it.
- Trap: labelling every high ankle sprain as a simple sprain. Correct: a syndesmotic injury can destabilise the ankle and lead to arthritis if the mortise is not restored.
- Trap: relying on the static mortise film alone. Correct: stress films or CT detect subtle widening that the static view can miss.
- Trap: fixing every syndesmotic injury routinely. Correct: fixation is reserved for injuries that are unstable on examination or imaging, while stable injuries are managed by immobilisation.
Frequently asked questions
What is a high ankle sprain?
A high ankle sprain is a syndesmotic injury that tears the ligaments binding the distal tibia and fibula above the ankle joint. It typically follows external rotation of the foot and causes pain above the ankle rather than over the lateral ligaments.
Which tests diagnose a syndesmotic injury of the ankle?
The squeeze test and the external rotation test diagnose a syndesmotic injury of the ankle. Both reproduce pain at the distal tibiofibular joint, and the diagnosis is confirmed with radiographs or stress views.
When is a syndesmotic injury of the ankle fixed?
A syndesmotic injury of the ankle is fixed when it is unstable on examination or imaging, for example when the tibiofibular clear space is widened. Stable injuries are managed with immobilisation and graded rehabilitation.
What is the difference between a syndesmotic screw and a suture-button device?
A syndesmotic screw holds the distal tibia and fibula rigidly, while a suture-button device allows a small amount of physiological movement. Both aim to restore the mortise, and the choice depends on surgeon preference and the injury pattern.