Injuries to the syndesmosis often occur in conjunction with acute bony injuries to the ankle joint, however subtle ligamentous injuries to the syndesmotic complex can also occur in the setting of low energy trauma to the ankle, including athletic activity.
The tibiofibular syndesmosis refers to the bony articulation between the distal aspect of the fibula and tibia, as well as the ligamentous structures that support the articulation. The syndesmosis is a true joint, with articular cartilage covering the medial aspect of the distal fibula and the lateral aspect of the tibia, also known as the fibular incisura. The ligamentous structures of the syndesmosis provide a majority of the stability for the complex, and consist of four separate components: the anterior inferior tibiofibular ligment, the posterior inferior tibiofibular ligament, the interosseous membrane and the transverse ligament. The transverse ligament is also sometimes considered the deep component of the posterior inferior ligament. The anterior inferior tibiofibular and transverse ligaments are the two stronger components of the complex.
The tibiofibular syndesmosis has two main functions. The first is to maintain the relationship between the fibula and the tibia, which provides stability to the ankle mortise during weightbearing activities. This also allows for some transmission of weightbearing through the distal fibula. The second function is to allow for expansion and contraction of the ankle mortise in the coronal plane, which allows the variable width of the talar dome to engage the ankle mortise at varying degrees of dorsiflexion and plantarflexion. The anterior aspect of the talar dome is wider than the posterior portion, meaning the ankle mortise must widen slightly when the ankle is in dorsiflexion.
Injuries to the syndesmotic complex are usually seen in the setting of low energy rotational injuries to the ankle joint. In most cases, they come in conjunction with bony injuries to the ankle mortise, as well as with other ligamentous injuries to the ankle, namely the deltoid ligament. However, pure ligamentous injuries can be encountered as well.
The most common mechanisms of injury to the syndesmosis involve external rotation or forced dorsiflexion of the ankle. External rotation moments on the ankle, depending on the position of the foot at the time of the injury, can cause fractures to the distal fibula or the posterior tibia that lead to disruption of the syndesmotic ligaments. External rotation can also lead to isolated ligamentous disruption. Forced dorsiflexion of the ankle joint causes the wider anterior talar body to act as a wedge that can cause injury to the syndesmotic complex. Once these ligaments are incompetent, the mortise can be rendered unstable, allowing for nonphysiologic motion of the talus and abnormal contact pressures on the articular surfaces of the ankle joint. Fractures of the proximal fibula can also result in propagation of energy through the interosseous ligament, leading to disruption of the syndesmotic complex.
Most patients with a syndesmotic injury will present with a history of a traumatic incident to the ankle. If accompanied by bony injuries, the patient can have a significant amount of swelling and pain around the ankle joint. However, more subtle injuries may only present with mild symptoms. Most patients will complain of pain in the anterior or lateral aspect of the ankle or distal leg. They may also complain of feelings of instability in the ankle joint, particularly with weightbearing activities. Instability can be specifically noticeable with lateral or cutting type maneuvers, encountered in many athletic activities. Patients with chronic syndesmotic instability will often present with symptoms of arthritis in the ankle joint, such as stiffness and impingement, in addition to pain and swelling.
Acute syndesmotic injuries can be classified into three categories: Stable, dynamic instability and static instability.
- Stable: Patients with stable injuries will present with symptoms of pain and swelling, however they will likely be able to weightbear with some support of the ankle.
- Dynamic Instability: Patients with dynamic instability will also present with symptoms in the ankle.
- Static Instability: Patients can present with chronic injuries, which can lead to degenerative changes in the syndesmosis and the tibiotalar joint depending on the chronicity of the condition.
Treatment of acute syndesmosis injuries depends on the stability of the joint complex.
Stable syndesmotic injuries can be treated conservatively, with immobilizaiton and protected weightbearing for 4-6 weeks. Activities can then be progressed with bracing and formal physical therapy to focus on proprioceptive activities and strengthening.
In the medically stable individual, clinically unstable injuries are usually treated surgically. Surgical intervention involves open reduction of the syndesmosis with some form of internal fixation.
Chronic injuries that do not demonstrate degenerative changes radiographically can be treated with reconstructive procedures. These may involve open debridement of the syndesmosis with reduction and fixation, as well as open reduction with allograft reconstruction. Chronic injuries that demonstrate degenerative changes can be treated with an arthrodesis of the syndesmosis.
Written by Brian Clowers, MD Reviewed by Casey Humbyrd, MD Last reviewed June 2015