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High ankle sprains require a high index of suspicion: careful clinical assessment is needed to provide appropriate care.

Article Excerpt
Although high ankle (syndesmosis) sprains are not as common as low ankle (medial or lateral) sprains, they are a significant injury. Differentiating between the types of sprains, understanding the anatomy and biomechanics of the ligaments that provide stability to the ankle and distal tibiofibular joint, and applying this knowledge to the physical examination are essential to making the diagnosis. Syndesmosis injuries are a diagnostic challenge--a high level of suspicion and careful clinical assessment are needed to provide appropriate care.

In this 2-part article, we provide the salient points of clinical evaluation of ankle sprains to differentiate between low and high sprains and, as a result, provide patients with proper treatment. The first part ("Differentiating low and high ankle sprains," The Journal of Musculoskeletal Medicine, September 2008, page 438) focused on low ankle sprains. In this second part, we discuss diagnosis and management of high ankle sprains.

FREQUENCY OF INJURY

Syndesmosis injuries are seen most frequently in athletes and soldiers. Athletes who participate in American football, lacrosse, rugby, skiing, basketball, and hockey are at highest risk for these injuries. Injuries to the syndesmosis represent 10% to 20% of ankle sprains among athletes. (1) The extent of injury ranges from a simple sprain (soft tissue injury only) to frank disruption of the syndesmosis with a concomitant ankle fracture. (1,2)

ANATOMY AND BIOMECHANICS

The primary role of the syndesmosis is to maintain the relationship of the talus to the tibia under physiological loads. (3) To accomplish this goal, the distal tibiofibular joint must maintain its stability, which is provided by both osseous congruity between the distal tibia and fibula and the integrity of the syndesmotic ligaments.

The distal-medial aspect of the tibia has an anterior and a posterior process. The groove between these processes provides a resting place for the distal fibula and confers bony stability between the 2 bones. (4) During plantar flexion and dorsiflexion of the ankle joint, the talus and malleoli must maintain congruity. Otherwise, a lateral shift of the talus, as little as 1 mm, results in a 42% decrease in contact area at the tibiotalar joint, leading to an increase in forces across the joint. (5,6)

There are 4 syndesmotic ligaments: the anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL), inferior transverse ligament (ITL), and interosseous ligament (IOL). (4,7) Cadaveric studies on the syndesmotic ligaments revealed that the AITFL, ITL, IOL, and PITFL provide 35%, 33%, 22%, and 8%, respectively, of ankle stability. (8) In addition, sectioning of the AITFL, PITFL, and IOL allows for a mean of 4.7[degrees] of pathological external rotation at the ankle joint. (7) The deep portion of the deltoid ligament also...

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