The lateral ankle ligamentous complex is made up of three distinct ligaments: the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL), and the posterior talofibular ligament (PTFL). Other structures contributing to overall lateral ankle stability are the inferior extensor retinaculum and subtalar ligamentous complex.

The ATFL, which blends with the anterolateral joint capsule, is 15 to 20 mm long, 6 to 8 mm wide, and 2 mm thick.

The ATFL originates from the anterior and distal fibula to insert on the lateral body of the talus, forming an angle of about 75 degrees to the floor.

The CFL is 20 to 30 mm long, 4 to 8 mm wide, and 3 to 5 mm thick. It originates from the posteromedial portion of the inferior fibula to travel within the peroneal tendon sheath, under the tendons, and attaches to the lateral wall of the calcaneus. The orientation is 10 to 45 degrees posterior to the longitudinal axis of the fibula. The angle formed between the ATFL and CFL is 100 to 105 degrees.

The PTFL is the largest of the lateral ankle ligaments, at 30 mm in length, 5 mm in width, and 5 to 8 mm in thickness. It has a broad insertion on nearly the entire posterior lip of the talus.

The ATFL has the lowest load to failure of the three ligaments. Conversely, it has a much higher capacity to withstand strain than the CFL or PTFL, thereby allowing the greatest deformation before failure of all three structures.¹⁷

The ATFL is taut with the ankle in plantarflexion, whereas the CFL is relatively loose. The reverse is true for the dorsiflexed ankle. The strength of the CFL and the stability afforded by the bony mortise at the malleoli in a neutral or dorsiflexed ankle make maximal plantarflexion the position of vulnerability for lateral ankle ligament injuries.¹,³

The subtalar ligamentous structures include the lateral talocalcaneal ligament, cervical ligament, interosseous talocalcaneal ligament—thought to provide the greatest contribution to stability of the subtalar joint, and the CFL. These provide some measure of stability to the lateral ankle.

Ankle instability is thought to be either acquired, as a result of repetitive trauma, or inherited due to ligamentous laxity, biomechanical abnormality (eg, heel varus, cavus foot position), or a combination of both.

The ATFL is most commonly injured, accounting for about 75% of injuries to the ligaments of the ankle, followed by the CFL, which accounts for about 20% to 25% of these injuries. Injury to the ligaments occurs when they are either stretched or completely torn, either by avulsion from bone, or, more commonly, from midsubstance tearing.

Neuromuscular deficits also result from these inversion injuries, leading to slower firing of the peroneal muscles in response to inversion stress, decreased responsiveness in the peroneal nerve branches, weakness, and restricted dorsiflexion range of motion due to inadequate muscle forces.

Repetitive injury can result in accumulated scarring leading to anterolateral mechanical impingement or even sinus tarsi involvement.⁷,¹⁵

Subtalar ligaments also may be injured, although usually to a lesser extent.

Even though most ankle sprains and instability receive some form of treatment, there is little consistency in treatment regimens. The natural history is sketchy as to what would happen in the truly untreated situation.

In one long-term study, one-third of patients treated functionally for ankle sprains had continued complaints of pain, swelling, or instability in the form of recurrent sprains.¹¹

Nearly three-fourths had some level of impairment on return to sporting activity, with almost 20% incurring repeated sprains and 4% with pain at rest or severe disability.

Dysfunction after an acute sprain will persist for 6 months in 40% of injured athletes.⁶

Although it has been suggested that long-term lateral ankle instability and repeated traumatic events to the ankle can lead to advanced stages of degenerative disease, there is no actual proof of this theory.

Nevertheless, it is presumed that continued ankle injuries as a result of lateral ankle instability can, and often will, lead to osteochondral injuries, abnormal joint mechanics, and neuromuscular dysfunction, predisposing the individual to risk of more severe injury to the extremity or disabling degenerative arthritis of the ankle and, possibly, the subtalar joints.

Patients experiencing acute ankle sprains often describe a painful tearing or pop after sustaining an inversion type injury. Longer standing instabilities will cause complaints of lack of confidence in the joint under high demands or frequent giving way; pain and swelling often are less severe and are of secondary concern to the patient.

Findings on examination in the acute situation are reliably present and include anterolateral ankle pain, swelling, and pain on passive plantarflexion or inversion. In the patient with a chronically unstable ankle, the examination focuses more on the anterior drawer and talar tilt tests and the “suction sign.”

Assessment for structural abnormalities also is important. Heel position should be examined in every patient, by looking at the patient from behind while he or she is standing, to determine the possible presence of varus malalignment.

Neuromuscular function is another important part of the examination. Peroneal muscle group function, specifically, is critical. Strength and stability of the peroneals should be assessed by resistive muscle grading against plantarflexion and eversion. Provocative maneuvers such as the plantarflexion eversion stress test also should be performed to ensure that the peroneal tendons do not subluxate from the retrofibular groove.

Sensory nerves should always be inspected to ensure no neurapraxia has taken place as a result of the traction from the injury.

Syndesmotic integrity should be tested with palpation, the “squeeze” test, and dorsiflexion-external rotation provocative manipulations.

According to the Ottawa Ankle Rules,¹² nearly 100% sensitivity is approached if the following criteria are used in the acute setting:

If radiographs are required, anteroposterior (AP), lateral, and mortise views, preferably weight bearing, should be performed, looking for avulsion fractures of the tip of either malleolus or, less frequently, the lateral calcaneus. One also should inspect for osteochondral fractures, joint malposition, and other fractures that may mimic lateral ankle sprains (see Differential Diagnosis).

Stress views can be obtained in either the AP (talar tilt) or lateral (anterior drawer) position. Performing the study while stressing the ankle (as described in the section on examination of the patient) can give meaningful information regarding the stability of the joint. Significant controversy exists on what constitutes an abnormal study, but on the basis of the cumulative review of literature on this topic, more than 15 degrees of varus tilt and 5 mm of anterior translation are reasonably considered abnormal.

Magnetic resonance imaging (MRI) is valuable for determining whether the ligamentous structures have been injured and in what time frame. Attenuation, wavy fibers, or disruption in the face of fluid accumulation suggests recent injury, whereas thickening or intrasubstance signal change gives rise to suspicion for a more remote injury. Infrequently, an absence of ligament tissue is noted, reflecting repeated injuries leading to degeneration of the complex.

Acute

Chronic

Nonoperative management is the mainstay of treatment for both acute and chronic instabilities. Most patients will respond to conservative management; consequently, it is essential that appropriate conservative treatment be tried for all patients before surgery is suggested.

Acute swelling and pain, whether from a new injury or recent repeat injury, are best managed with RICE. Immobilization in a walking cast or boot should be considered for anyone, demonstrating a positive drawer or talar tilt after an acute episode or recurrence.

Once the acute symptoms have subsided, functional strapping, taping, or bracing should be instituted along with an exercise regimen emphasizing peroneal strengthening, proprioceptive training, and Achilles tendon stretching.

In the patient with a chronically unstable ankle, shoe wear modifications can be added as the individual returns to sports or activities. Orthoses with lateral heel and sole wedges or flare on the lateral sole of the shoe can promote
a valgus moment and help avoid injury in the vulnerable patient. Reducing heel height and stiffening the sole of the shoe also can be helpful.

Prophylactic brace wear or taping has been shown to have some benefit in prevention of injury. It also has a positive effect on reduction in severity of sprains if reinjury occurs while these measures are in effect.

Surgery rarely is indicated for an initial acute injury.

Chronic instability failing appropriate conservative measures is more complex.