Definition

Chronic ankle instability is a condition characterized by a constellation of symptoms, typically including pain, weakness, and a feeling that the ankle episodically gives way, that persist after an acute lateral ankle sprain. Although chronic ankle instability may occur after a single ankle sprain, it is more commonly a sequela of repeated sprains. It has been reported to occur in up to 40% of individuals with a history of ankle sprain and as late as 61⁄2 years after an initial injury [1]. Anatomic lateral ankle ligament laxity and mechanical instability, peroneal muscle weakness, and ankle proprioceptive deficits are three primary factors thought to cause and to perpetuate symptoms. Arthrogenic muscle inhibition of the peroneal and soleus muscles has also been implicated as a possible contributing factor [2]. These causative factors may coexist with other pathologic processes of the ankle (such as those listed in the differential diagnosis section), which may serve to amplify and to perpetuate symptoms of functional instability. The establishment of additional diagnoses does not preclude a diagnosis of chronic ankle instability.

Symptoms

Usual symptoms are ankle pain, swelling around the lateral malleolus, weakness of the ankle evertors, and a feeling that the ankle is episodically unstable. The term functional instability describes the subjective sensation of “giving way” that often persists after ankle sprains [3]. Functional instability may occur in the absence of true mechanical ligament laxity and vice versa. Symptoms can continue for months or years after the original injury, range from mild to severe, and often are manifested as recurrent acute lateral ankle sprains.

Physical Examination

Objective findings are variable and can often be minimal. Potential examination findings in patients with chronic ankle instability may include reduced passive or active ankle range of motion, lateral ankle swelling, ecchymosis, lateral ankle tenderness (typically over the lateral ligament complex or peroneal tendons), weakness of the peroneal muscles, proprioceptive deficits (manifested by decreased ability to perform a single-leg stance), and mechanical laxity (demonstrated by increased motion on anterior drawer or talar tilt test compared with the contralateral ankle) [4]. Abnormal alignment, such as calcaneal varus, calcaneal valgus, or pes planus, may be evident. A limp may also be observed. Examination of the affected ankle should always be compared with the contralateral unaffected ankle.

Findings of the neurologic examination, including sensation and deep tendon reflexes, are commonly normal. Results of manual muscle testing should also be normal, with the exception of muscles surrounding the ankle that may exhibit weakness from disuse or because of pain. Balance testing commonly demonstrates deficits in the affected limb but may also reveal impairments in the contralateral ankle, making it unclear whether these findings represent a preexisting risk for injury or are the result of previous inversion injuries [5].

Functional Limitations

Affected persons may have difficulty participating in sports, particularly high-demand sports that require quick starts and stops, cutting, and jumping (such as soccer, football, and basketball) as well as sports that involve a lot of lateral movement (such as tennis). When symptoms are severe, limitations can include difficulty with climbing steps, ambulation, and activities that require prolonged standing. It is estimated that functional instability prevents 6% of patients from returning to their occupation; 5% to 15% remain occupationally disabled 9 months to 61⁄2 years later, whereas 36% to 85% of patients report full recovery within a period of 3 years [1,2,6,7].

Diagnostic Studies

The diagnosis is made by confirming a history of prior sprain with subsequent development of typical symptoms of functional instability in conjunction with consistent examination findings. Adjunctive diagnostic testing can be helpful in establishing the diagnosis, particularly by identifying pathologic changes and conditions that may produce similar symptoms. Testing that may be useful when the diagnosis of chronic ankle instability is being considered includes routine radiography, stress radiography, computed tomography, bone scan, magnetic resonance imaging, ankle arthrography, and magnetic resonance arthrography.

Routine radiographs are useful to rule out old or chronic fractures (most commonly of the fibula, tibia, talus, and fifth metatarsal), to assess the integrity of the ankle mortise, and to assess for ankle arthritis. A routine radiographic series should include anteroposterior, lateral, and mortise views. Widening of the ankle mortise may indicate a syndesmotic disruption or significant deltoid ligament tear. Radiographs should be obtained in all cases with a history of significant trauma at initial injury.

Stress radiographs may be helpful in determining the presence of chronic mechanical instability. Although the routine use of stress radiographs remains controversial, a finding of more than 5 mm of anterior displacement of the talus during anterior drawer testing is considered to be abnormal [8]. Inversion stress radiographs are considered abnormal with a finding of more than 5 degrees of side-to-side difference in tibiotalar tilt [7]. However, a review found the published data regarding stress radiographs too variable to determine accepted normal values for acute and chronic sprains [9]. The sensitivity of stress radiographs in diagnosis of chronic lateral ligament tears (surgically confirmed) is low, although specificity is high [8].