The syndesmosis is the name of the ligament that connects two bones of the leg. These bones, the tibia and fibula, are between the knee and ankle joints. The tibia is the larger shin bone that supports most of the weight of body, and the fibula is the smaller bone on the outside of the leg. Connecting these bones is a ligament called the syndesmosis, also called the syndesmotic ligament.
Syndesmosis ligament injuries often occur in conjunction with other ankle injuries, including sprains and fractures. If a damaged syndesmosis is left untreated, poor results often occur. The ankle joint is held in proper alignment by the ends of the tibia and fibula, which wrap around the inner and outer side of the ankle. If the syndesmosis is damaged, the ankle joint may become unstable.
A syndesmosis injury occurs when the foot twists outwards relative to the leg -- a so-called external rotation injury. This type of injury can occur when the ankle is forcefully twisted outwards, or when the foot is planted, and the leg twists inwards.
Symptoms of Syndesmosis Injuries
As mentioned, syndesmosis injuries often occur in conjunction with ankle injuries. Therefore, anyone with an ankle sprain or fracture should also be evaluated for a possible injury to the syndesmosis.
Typical symptoms of a syndesmosis injury include:
- Pain above the ankle
- Calf pain
- Inability to place weight on the leg
X-rays should be obtained if an injury to the syndesmosis is suspected. Because normal x-rays may not show a syndesmosis injury, a special type of x-ray called a stress x-ray is often obtained. In a stress x-ray, the examiner will apply a force to the ankle to determine if the syndesmosis shifts when the force is applied. If there is still question of an injury, either a CT scan or MRI can also be helpful in making the diagnosis.
Types of Syndesmosis Injuries
The most common type of syndesmosis injury that occurs is called a "high ankle sprain". A high ankle sprain simply refers to the damage to the ligaments above the ankle joint -- the syndesmotic ligament. Treatment of a high ankle sprain depends on the stability of the ankle. If the x-rays show a stable ankle joint, most patients are treated with immobilization and crutches, and can expect a 6-8 week recovery. If the syndesmosis is unstable, treatment must ensure the syndesmosis can be held in a stable position while healing. This may require casting a protection from weight on the leg, or it may require a surgery to stabilize the ankle joint.
Syndesmosis injuries can also occur in association with ankle fractures. As with high ankle sprains, the critical information for determining treatment is if the ankle joint is unstable. When the syndesmosis is damaged in association with a fracture of the ankle, surgery is usually necessary to restore the stability to the ankle joint. Surgery is often performed to repair the fracture or to stabilize the syndesmosis, and sometimes both.
Surgery for Syndesmosis InjuriesWhen the syndesmosis is repaired surgically, this is usually done with metal screws that pass through the fibula and in to the tibia. These screws must be positioned once the syndesmosis has been placed in proper position and alignment. Either one or two screws may be used, depending on the type of injury and your surgeon's preference. Often, your surgeon will recommend removing the screws after about 3-4 months. If the screws are not removed, they will eventually loosen or break. While this may not present any issues, many patients don't want a loose or broken screw in their leg, and would therefore have them removed before that time.
Zalavras C and Thordarson D. "Ankle Syndesmotic Injury" J Am Acad Orthop Surg June 2007 ; 15:330-339.