What is the syndesmosis?
A syndesmosis injury is a commonly missed injury that involves damage or tearing to the ligaments, that bind the two bones of the lower leg together (tibia and fibular). It can also involve damage to a soft tissue membrane that holds these two bones together. Syndesmosis injuries, account for approximately 11% of all ankle injuries, with a higher occurrence in sporting activities that involve twisting or cutting maneuvers (e.g. soccer).
Before we get stuck into the details of syndesmosis…lets first talk a little bit of anatomy.
In the ankle and foot there are many ligaments. When someone tells you they’ve sprained their ankle, often they are referring to damaging the lateral ligaments of the ankle which is referred to as a lower lateral ligament sprain. These ligaments include the posterior talofibular ligament, calcaneofibular ligament and anterior talofibular ligament. These ligaments are labelled 1, 2 & 3 in the image below.
However, syndesmosis injury includes the ligaments and connective tissue that sit higher up the ankle and therefore it is sometimes termed ‘high ankle sprain’ due to it involving the ligaments that sit just higher up the ankle. By definition the syndesmosis is a joint where two bones are connected by strong ligaments and a strong membrane. The ligaments can be seen in the image below which include the anterior tibiofibular ligament and the posterior tibiofibular ligament. The reason why it is commonly missed is it often mistaken for being a lower ankle “lateral” ankle sprain, however as I have explained, a normal lateral ankle sprain sits anatomically lower down the foot and involves a different set of structures and ligaments.
How do syndesmotic injuries present?
Generally speaking, a syndesmotic injury or ‘high’ ankle sprain will often show less swelling than a usual lateral ligament ankle sprain with any swelling or bruising present tending to sit on the front of the ankle joint (lower lateral sprains tend to have a more swelling and bruising located on the outside of ankle).
Pain is often across the front of the ankle with tenderness over the anterior tibiofibular ligament and along the interosseus membrane. Often pain is aggravated with rotating the foot outwards, pointing the foot upwards (dorsiflexion) and pointing the foot downwards (plantarflexion). Often there is difficult weightbearing through the foot.
This is because Syndesmosis injuries often occur due to external rotation and sudden dorsiflexion of the foot. A sudden dorsiflexion movement causes one of the bones in the foot (the talus) to act as a wedge which essentially forces the tibia and the fibular bones apart. When the external rotation component is added, the syndesmosis ligaments can rupture.
Looking at the image above, you can imagine the talus wedging up between the two bones which then pushes the tibia and fibula apart and therefore can strain or rupture ligaments. Rupture or strain can involve any of the following structures: anterior inferior tibiofibular ligament, posterior inferior tibiofibular ligament, interosseous membrane (which sits between the two bones to keep them bound together), interosseous ligament and inferior transverse ligament.
A more severe injury will often commonly present with a fracture to either the tibia or the fibula therefore these areas should be examined by your physiotherapist.
Something I must stress is you should seek early professional advice and treatment after any ankle sprain, but especially this one.
There are specific tests that your physiotherapist will carry out to confirm or rule out a high ankle sprain and determine whether an x-ray is required. If instability is noted on the x-ray, an MRI may be required to determine the extent of damage to the ligaments.
A correct examination and assessment carried out by your physiotherapist and relevant imaging will indicate if surgery is required or whether treatment with physiotherapy is appropriate.
Diagnosis is crucial for determining whether the syndesmosis is stable or unstable and therefore which pathway of treatment (physiotherapy or surgery) should be taken. An unstable injury can lead to chronic instability and result in arthritis is left untreated, therefore it is important to receive professional advice for this injury. Unstable high ankle sprains will often require “tightrope” surgery to improve the stability between the two long bones of the lower leg.
If the injury is deemed to be stable no surgery is required, and conservative rehab through physiotherapy can produce good results.
Rehab is crucial for syndesmosis injuries as often they take up to twice as long to heal than lower lateral ankle ligament sprains. In fact, not doing rehab is associated with a high recurrence rate and chronic ankle instability.
A stable injury will generally involve a period of immobilisation in a non-weightbearing cast or walk boot for 4-6 weeks, however this is dependent on patient’s presentation and their ability to weight bear.
Injured your ankle? Make sure to get it checked to rule out a syndesmosis injury.
Written by William Lewis (Physiotherapist)