High Ankle Sprain Syndesmotic Injury

Description

Above the talocrual joint the distal tibia and fibula come together and are reinforced by a series of ligaments to form a sydesmosis. While the ankle joint is one the most frequently injured joints, especially in athletes, a syndesmotic injury, better known as a high ankle sprain, occurs in a very small portion of those injuries and rarely occurs independtly of other injuries within the ankle.

Anatomy

The ankle syndesmosis contains both bony and soft tissue components. The bony component is the attachment of the medial aspect of the distal fibula and the lateral aspect of the distal tibia. There are four ligaments that make up the soft tissue component of the syndesmosis and help to make the bony junction stronger and prevent abnormal movement between the distal tibia and fibula. In a high ankle sprain the first ligament to rupture due to an external rotation force is the anterior-inferior tibiofibular ligament as it is the weakest of the four ligaments^3,4. Another ligament of the ankle syndesmosis is the transverse ligament. While some debate does exist as to whether or not it is a separate ligament the majority believe that it is³. The remaing two ligaments are the posterior-inferior tibiofibular ligament, which is the strongest of the four ligaments, and the interosseous ligament, which blends with the interosseous membrane and acts as a spring to allow a little movement between the distal tibia and fibula³.

Indications

Mechanism of injury can be a good indication as to whether or not the syndesmosis is affected. Most commonly external rotation of the foot or excessive dorsiflexion lead to involvement of the ankle syndesmosis. External rotation of the foot causes the fibula to externally rotate on the tibia thus, when in excess can cause the syndesmosis to fail. In dorsiflexion a gap is created betweeen the tibia and fibula which if too large the ligaments will fail. However, the most common way to sprain an ankle, plantarflexion and inversion, can also create disruption in the syndesmosis^1,4,5.

Incidence/Prevalance

High ankle sprains occur in only about 10% of the total amount of ankle sprains suffered. Within the athletic population especially in high contact sports the number of high ankle sprains jumps up to 40% of total ankle sprains suffered^1,4,5.

Clinical Presentation

Syndesmotic injuries can be difficult to diagnosis, especially if they occur independently of other ankle injuries because swelling and pain can decrease rapidly potentially allowing immediate weight bearing and only slight pain with ambulation¹⁰. Even though not always present swelling can be an indication as well as brusing which is why it is important to begin the physical examination with observation. The patient may also walk with a limp as it could be painful or they could be experiencing a feeling of instability. painful palpation of the lateral collateral ligaments, anterior inferior tibiofibular ligament, and deltoid ligaments. Tenderness may also be present above both the lateral and medial malleoli. As far as bony palpation goes the meadial and lateral malleoli, the navicular and the base of the fifth metatarsal will also be painful^4,5.

Potential Etiologies

Athletes are more prone to sustaning syndesmotic injuries than non-athletes because of the contact factor and all of the cutting and quick movements required of them by their respective sports.

Diagnostic Tests

Proper diagnosis of a syndesmotic injury is crucial because even a 1mm widening of the ankle mortise can decrease the contact area of the mortise by 42%³. Aside from the palpation and observation mentioned above, diagnosis of a syndesmotic injury can be done using X-ray imaging, CT scans, MRI's or ultrasound. When using X-ray's three different views are used: anterioposterior, mortise and lateral, it is also beneficial to look at the full length of the tibia and fibula⁵. indications of a syndesmotic injury using X-rays are: an increase in tibiofibular clear space, decreased tibiofibular overlap, and increased medial clear space¹². For more information concerning the radiographic spaces referr to http://www.jaaos.org/content/15/6/330.full.pdf+html. If plain X-rays are not sufficient to identify an injury, stress X-rays are also used to help better identify syndesmotic injuries. CT scans and MRI's can help to identify tears in the ligaments of the ankle syndesmosis. Ultrasound is a cheaper and equally accurate tool for diagnosis when compared to a CT and MRI. Ultrasound provides an easier way to accurately confirm a diagnosis by way of imaging⁷.

Evaluation/Special orthopedic Tests

For high ankle sprains there are three different classifications that exist and they are: 1) sprain without diastasis 2) diastasis that is only apparent after stress radiographs and 3) frank diastasis, which is more often than not accompanied by a fracture⁴. These classifications are important to understand as they will play a role in the evaluation and findings of the special tests.
Four special tests exist for a syndesmotic injury: external rotation test, dorsifelxion-compression test, tibia/fibula compression test and the stabilization test.

1. External rotation test - Patient is short sitting. The therapist stabilizes the leg with one hand and then passively externally rotates the foot and ankle with the other hand while the ankle is in a neutral or slightly dorsiflexed position. A postitive sign is pain over the syndesmotic ligaments.

2. Dorsifelxion-compression test - Patient is standing and actively dorsiflexes the ankle while weight bearing. Patient reports any pain produced in the area of the syndesmosis. The test is positive if the pain is reduced when the therapist using both hands compresses both malleoli in such a way as trying to push them together.

3. Tibia/fibula squeeze test - Patient lies supine, the therapist squeezes the patients leg at the mid calf which pushes the tibia and fibula together proximally but gaps them distally. The test is positive is pain is produced in the ankle syndesmosis.

4. Stabilization test - The therapist applies tape around the ankle syndesmosis which brings them closer together and prevents separation. A positive test is if pain is decreased with the tape in place.

Conservative Treatment, Physical Therapy Management and Modalities

Physical Therapy Management of a High Ankle Sprain (Syndesmotic Injury)

Surgery & Post-op Treatment

Surgical procedures for syndesmosis fixation are relatively similar in the sense that screws are used to reunite the tibia and fibula and regain stability. However there is dispute about size of screws, material of screws, and number of screws. Disagreement also exists about post-op treatment because metal screws can break and the stability of the joint can be compromised if such an event happens before healing is complete. The most important factor in surgery is making sure the fibula is of proper length and that screws are placed in properly. As malalignment could lead to a fibula that is too short or too long and affect over all ankle function. First the mortise is reduced and held in place with bone-clamps. In some studies a 4.5mm screw is used in others a 3.5mm screw is used. The screws can either be stainless steel noncannulated cortical screws or they can be bioabsorbable screws^5,8,11. Stainless steel screws need to be removed after the healing is complete and the syndesmosis is stable, but in 15% of patients the screws break between 6 weeks and 3 months⁸. The bioabsorbable screws are made from non-toxic materials and are broken down and absorbed by the body, which eliminates the need for surgery to remove the screws as well as eliminating the risk of a screw breaking. It is important to be aware of the fact that ankle function does not appear to be very different between ankles with and without broken screws⁸. Post-op management calls for non-weightbearing for at least 12 weeks, which is the minimum time before the screws are removed. Pre-mature screw removal has been linked to instances of reinjury and chronic ankle instability⁵. It is important to focus on scar healing in the early stages of post-op rehabilitation. Ankle ROM and proper biomechanics are also important because the patient will be non-weightbearing for such a great amount of time. Isometric strength training is also important for the same reason. Once the screw is removed rehabilitation will progress faster and will follow the same guielines and the conservative treatment. An agressive post-op rehabilitation protocol does exist with a main focus of getting athletes back to their respective sports quicker. Patients are in a splint for 1 week post-op and are encouraged to do ROM exercises and use a walking boot as tolerated. No restrictions are set, patients progress through weight bearing, stregthening exercises and proprioceptive exercises as tolerated and as functional goals are met. The walking boot is replaced with an air cast at 3 to 4 weeks and is used during all activities. Return to sport occurs when strength in the involved leg is equal to the uninvolved leg and the athlete is comfortable with all sport specific activities. Treatment is complete at 6-weeks and success has been shown with such a protocol¹¹. Surgery and post-op management are different across the board because of physician and physical therapists preferance, but the most important factor is a successful rehabilitation for each individual patient.

Additional Web Based Resources

http://www.mc.uky.edu/athletic_training/publications%20folder/Management%20of%20Syndesmotic%20Ankle%20Sprains.lnk.pdf
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC155405/
http://www.sportsinjuryclinic.net/cybertherapist/front/ankle/highankle.php
http://www.aafp.org/afp/2001/0101/p93.html
http://www.mdmercy.com/footandankle/syndesomosisinjury2.html

References

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