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The Elusive 'High Ankle Sprain'

Treatment for this stubborn injury requires hands-on tests and definitive classification

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Vol. 21 • Issue 12 • Page 21
Associated Table

High-profile athletes Sidney Crosby, Carson Palmer, Terrell Owens and Dirk Nowitzki are recent cases of an uncommon yet troublesome injury that can strike an athlete in the prime of their career, leaving them to face months of rehab, and possibly surgery.

Ankle syndesmotic injuries can occur with or without ankle fractures. In the absence of an ankle fracture, they're referred to as "high" ankle sprains. They're most common in hockey, football and to a lesser degree, basketball and slalom skiing. High ankle sprains often demand longer recovery periods than the more common lateral ankle sprain, and can have significant long-term complications. Because of this, rehab therapists working with an active population should be familiar with its presentation and remain up-to-date on evidence-based treatments.

How it Happens

The most commonly described mechanism of injury surrounding a syndesmotic injury involves a swift external rotation force to the ankle. A common example is a football player on his knees while another player lands on the posterolateral aspect of his heel, driving it to the ground and causing an external rotation force at the ankle. Another common scenario is a slalom skier who catches his inside ski on a gate, causing a rapid external rotation force.

Abduction at the ankle can be a contributing or isolated force causing this injury, and a hyperdorsiflexion mechanism has also been theorized. The injury may cause damage to the anterior syndesmosis only, while maintaining an intact posterior tibiofibular ligament, thus giving an "open book" type injury. Less common is when all the ligaments are involved, causing anterior and posterior diastasis.

In 1984, Edwards and Delee classified syndesmotic sprains on radiographic interpretation, which can help guide treatment regimens.1 Type 1: Sprain without diastasis on X-ray;

Type 2: Sprain with frank diastasis (seen on initial X-ray);

Type 3: Sprain with latent diastasis (normal initial X-ray, but diastasis is noted when syndesmosis is stressed with an external rotation/abduction force).

Syndesmotic sprains are comparatively rare, but impact sports and high-level competition raise the risk. A large study of more than 1,300 cadets with ankle sprains found that syndesmotic injuries made up just 1 percent of all ankle sprains.2 However, a study of Minnesota Vikings football players with ankle sprains found that 18 percent were syndesmotic injuries.3

Making the Diagnosis

An understanding of high ankle sprains requires a review of ankle ligament anatomy. Ankle syndesmotic ligaments are made up of four ligaments-the anterior inferior tibiofibular (AITFL), interosseous (IOL), posterior inferior tibiofibular (PITFL), and inferior transverse ligament (ITL). The syndesmotic ligaments are stronger than the lateral collateral ligaments.

The interosseous membrane actually makes up very little of the ankle's syndesmotic stability. A cadaveric study demonstrated that rupture of specific syndesmotic ligaments increased syndesmotic gapping by certain amounts: AITFL = 2.3 mm, AITFL and IOL = 4.5 mm, and all four ligaments ruptured caused 7.3 mm of diastasis.4 The bony anatomy also contributes to the stability of the syndesmosis, where the fibula is contained within the tibia in a triangular-shaped fibular recess known as the incisura fibularis. This concave groove in the tibia is bounded anteriorly and posteriorly by tubercles of varying size, and therefore provides varying stability based on this.

The syndesmosis prevents excessive gapping at the distal tibia and fibula. However, a certain amount of motion is allotted for normal gait mechanics. As the ankle moves from full plantarflexion to dorsiflexion, there is a 1.5 mm widening at the syndesmosis. The fibula migrates distally up to 2.4 mm in the stance phase. The fibula has 2-5 degrees of rotation, and 1-3 mm of posterior translation with normal biomechanics. The syndesmotic ligaments help control excessive fibular motion; however, this is a mobile region with some normal physiologic motion.

Diagnosing a high ankle sprain relies on a combination of information-injury mechanism, physical exam and radiographic examination. The mechanism of injury can be very helpful to delineate a syndesmotic injury. For example, an external rotation force mechanism is the common reason for syndesmotic injuries, while the more common lateral ankle sprain results from an inversion mechanism. However, in competitive athletes, the injury is often of such high velocity and force that many athletes aren't able to give specifics on what happened.

On examination, look for swelling at the level of the syndesmosis, specifically over the AITFL. Patients often experience pain with dorsiflexion and eversion. Tenderness will be noted over the syndesmosis, specifically the AITFL, while minimal-to-no tenderness is felt over the lateral ligaments (ATFL/CFL). There is often tenderness medially over the deltoid ligament, because of the strain placed on it, with diastasis of the ankle.

There are several specific manual tests for syndesmotic sprains. These should be performed in combination with the talar tilt test and the anterior drawer test, in order to rule out lateral ankle ligament injury.

External rotation test. This is the most reliable test, with highest inter-rater correlation. With the knee at 90 degrees and ankle neutral, forced external rotation causes pain at the syndesmosis. This can be used for acute or chronic stages.

Squeeze test. Compressing proximally to the mid-calf produces pain distally at the syndesmosis, caused by separation at the origin/insertion of the AITFL.

Cotton test. Also known as the tibiofibular shuck test, the distal leg is steadied with one hand while the plantar heel is grabbed with the other. Moving the talus from side to side in mortise, the clinician feels for excessive motion.

Treatment Guidelines

A significant syndesmotic injury can cause lateral subluxation of the talus in the ankle mortise. This can lead to severe arthritis at a later date. Therefore, appropriate classification of these injuries is critical in order to devise a treatment regimen. Again, classification is based on diastasis on initial (without stress) and stress X-rays. The absence of an ankle fracture does not necessarily mean that surgical intervention is not needed. However, the majority of syndesmotic sprains can be treated conservatively.

Type 1: No diastasis. If there is only a sprain with no diastasis seen on initial or stress X-rays, then a conservative trial is appropriate. This includes rest, ice and elevation, with consideration for a walking boot or cast, depending on severity. After three to six weeks of rest, physical therapy interventions consisting of proprioception training, strengthening and Achilles stretching would be appropriate, with an eventual focus on sport-specific re-integrating exercises. Counsel your patient that syndesmotic sprains often take twice as long to recover from, compared to lateral ankle sprains.

Type 2: Frank diastasis. The patient that has frank diastasis noted on initial X-rays would likely benefit from surgical fixation. Surgical fixation includes a screw or Endobutton that runs from the fibula into the tibia to prevent excessive gapping at the distal tibia-fibula interspace. The Endobutton is a new procedure that, in theory, would allow for more physiologic motion at the fibula without allowing pathologic diastasis to occur.

Some surgeons use one or two metal screws or one or two Endobuttons to stabilize this area, followed by a short period of immobilization and restricted weight bearing. Often the screws will break once weight bearing resumes; however, this is of little clinical significance. In fact, most patients do better when syndesmotic screws break, especially those treated with concominant ankle fractures.

For this reason, some surgeons will remove the screws once they feel comfortable that the ligaments have been given sufficient time to heal-usually after a three- to six-month period-as this allows the fibula to resume normal physiologic motion. Again, physical therapy is important after surgical treatment, as well as resuming proprioceptive activities, motion and strength.

Type 3: Latent diastasis. If the patient has no diastasis on initial X-ray, but stress X-ray causes gapping at the tibiofibular interspace, then the treatment plan lies within a gray area. In the high-level athlete, surgical fixation may be the treatment of choice for a quicker return to sports, and to ensure stability at the ankle for future prevention of ankle arthritis. However, a less active patient may do well with immobilization and a trial of conservative measures in hopes that the ligaments can scar in, resulting in a stable ankle.

While you may not encounter a high degree of syndesmotic sprains during day-to-day clinic operations, they do account for a sizeable portion of impact sports injuries. Proper classification and structured, type-driven treatment progressions will get athletes back on the field sooner, with a higher likelihood of long-term ankle stability.

References available at www.advanceweb.com/PT or by request.

Jeremy Bruce is an orthopedic surgery resident at the University of Tennessee-Chattanooga.




     

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