Ankle Instability

Ankle Instability

R. Todd Hockenbury


  • An ankle sprain is a tear of the ligaments supporting the ankle joint.

  • Ankle sprains are common. They constitute 25% of all sports-related injuries (33).

  • Ankle sprains make up 21%-53% of basketball injuries and 17%-29% of all soccer injuries (13,19).

  • An age of 10-19 years old is associated with higher rates of ankle sprain. Nearly half of all ankle sprains occur during athletic activity, with basketball (41.1%), football (9.3%), and soccer (7.9%) being associated with the highest percentage of ankle sprains during sports (61).



  • The ankle, or talocrural, joint consists of the talus, tibial plafond, medial malleolus, and lateral malleolus. The distal tibia and lateral malleolus form a mortise, in which the talus sits.

  • The talus is wider anteriorly than posterior, thus resulting in a tighter fit and more stable articulation between the talus and mortise during ankle dorsiflexion.

  • Ankle joint stability depends on joint congruency and the supporting ligamentous structures.

  • The lateral ankle ligaments are the anterior talofibular ligament (ATFL), calcaneofibular ligament (CFL), and posterior talofibular ligament (PTFL). The medial ankle ligaments are the deep and superficial portions of the deltoid ligament.

  • The relative strengths of the ankle ligaments from weakest to strongest are ATFL, CFL, PTFL, and deltoid (4).

  • The syndesmotic ligaments connect and stabilize the distal fibula to the distal tibia. The syndesmotic ligaments are the anterior tibiofibular ligament, posterior tibiofibular ligament, transverse tibiofibular ligament, interosseous ligament, and interosseous membrane.

  • The subtalar (talocalcaneal) joint lies inferior to the ankle joint and is responsible for hindfoot inversion and eversion. Up to 50% of clinical ankle inversion occurs at the subtalar joint (51).

Joint Mechanics

  • The ankle is a hinge joint that permits flexion, extension, and rotation. The talus externally rotates with ankle dorsiflexion and internally rotates during plantarflexion (46).

  • The distal fibula externally rotates during ankle dorsiflexion and moves distally during weight bearing, thus deepening and stabilizing the ankle mortise (60).

  • The ankle mortise widens with ankle dorsiflexion and with weight bearing.

  • The ATFL and CFL act synergistically to resist ankle inversion forces. The ATFL resists ankle inversion in plantarflexion, and the CFL resists ankle inversion during ankle dorsiflexion.

  • The CFL spans both the lateral ankle joint and lateral subtalar joint, thus contributing to both ankle and subtalar joint stability (51).

  • The PTFL limits posterior talar displacement and external rotation (48).

  • The deltoid ligament resists ankle eversion, external rotation, and plantarflexion. In cases of distal fibular fracture and mortise instability, it restrains lateral talar translation (23).

Injury Mechanisms

  • The most commonly sprained ankle ligament is the ATFL, followed by the CFL and then the PTFL. An isolated CFL or PTFL tear is rare. A tear of the ATFL almost always precedes a CFL tear. The ATFL is almost always torn, the CFL and PTFL are torn 50%-75% of the time, and the PTFL is torn in < 10% of ankle sprains (16).

  • Lateral ankle sprains occur as a result of landing on a plantar flexed and inverted foot. These injuries occur while running on uneven terrain, stepping in a hole, stepping on another athlete’s foot during play, or landing from a jump in an unbalanced position.

  • A syndesmotic ankle sprain, or “high ankle sprain,” occurs as a result of forced external rotation of a dorsiflexed foot or during internal rotation of the tibia on a fixed planted foot. A common mechanism is a direct blow to the back of the ankle while the patient is lying prone with the foot externally rotated (64).

  • Isolated deltoid ligament sprains are rare and are usually accompanied by a lateral malleolar fracture and/or a syndesmotic injury. The deltoid ligament is injured through a mechanism of external rotation or eversion.

Injury Prevention

  • A balance training program has been shown to reduce the rate of ankle sprains in high school soccer and basketball players by one-third to one-half (14,34).

  • Studies are mixed regarding the efficacy of prophylactic bracing of athletes. A retrospective study of female college volleyball players who wore bilateral double-upright padded ankle braces showed a 93% reduction in ankle sprain incidence compared to the overall ankle injury rate in the National Collegiate Athletic Association (NCAA) (38). A prospective study of high school volleyball players found that ankle bracing did not overall decrease the incidence of sprains, except in those players who had not had a previous sprain. Players with a previous history of ankle sprain did not benefit from prophylactic bracing to prevent additional sprains. Players who had never had a sprain did show a lower incidence of initial ankle sprains with bracing (18).

Ligament Pathophysiology

  • Ligamentous injuries undergo a series of phases during the healing process: hemorrhage and inflammation, fibroblastic proliferation, collagen protein formation, and collagen maturation (1,9).

  • Early mobilization of joints following ligamentous injury actually stimulates collagen bundle orientation and promotes healing, although full ligamentous strength is not reestablished for several months (36,56,58).

  • Early treatment focuses on limiting soft tissue effusion, which speeds the healing process by lessening the amount of extracellular fluid and hematoma to be reabsorbed (24,43,55).


  • Lateral ankle swelling and ecchymosis are present and are proportional to the degree of ligament damage.

  • Careful one-finger palpation is essential to define areas of tenderness and avoid misdiagnosis of associated fractures or tendon ruptures.

  • Common fractures that mimic ankle sprains are fractures of the lateral malleolus and medial malleolus, fifth metatarsal base, anterior process of the calcaneus, lateral process of the talus, posterior talar process, talar dome, and navicular.

  • Commonly missed tendon injuries are Achilles ruptures, peroneal tendon tears, peroneal tendon subluxation/dislocation, posterior tibial tendon injuries, anterior tibial tendon tears, and flexor hallucis longus tendon ruptures.

  • A careful neurologic examination is essential to rule out loss of sensation or motor weakness, because peroneal nerve and tibial nerve injuries are sometimes seen with severe lateral ankle sprains (35).


Anterior Drawer Test

  • Tests the integrity of the ATFL.

  • Performed by stabilizing the anterior tibia just above the ankle with one hand while grasping the posterior heel with the other hand and applying an anteriorly directed force, and therefore attempting to translate the talus anteriorly.

  • The test should be performed on a relaxed leg with the knee bent and the ankle held in slight plantarflexion.

  • Normal anterior talar translation is less than 5 mm. The contralateral asymptomatic ankle should also be tested as a baseline.

Inversion Stress Test or Talar Tilt Test

  • Tests the integrity of the ATFL and CFL.

  • Performed by grasping the heel and inverting the ankle. A clunk may be heard or palpated in unstable ankles, as the medial talar dome impacts the distal tibial medial articular surface, indicating injury to one or both ligaments.

  • This test should be performed with the ankle in both dorsiflexion (to test the CFL) and plantarflexion (to test the ATFL).

Suction Sign

  • Tests the integrity of the ATFL.

  • During performance of the anterior drawer test, an unstable ankle will produce a dimple in the anterolateral ankle as the talus reaches it full anterior excursion. The dimple is formed by negative pressure within the ankle joint (26).

Squeeze Test

  • Tests the integrity of the syndesmotic ligaments.

  • The squeeze test is performed by placing the fingers over the proximal half of the fibula and thumb around the tibia and squeezing the two bones together. Pain in the distal ankle may indicate a syndesmotic injury (28,42).

External Rotation Stress Test

  • Tests the integrity of the syndesmotic ligaments.

  • The external rotation stress test is performed on the seated patient by externally rotating the foot while stabilizing the tibia with the other hand. Medial ankle pain or lateral talar motion indicates that a syndesmotic injury may be present.

  • Confirmatory anteroposterior and lateral external rotation stress radiographs will document widening of the syndesmosis and lateral talar subluxation (12,65).


Ottawa Ankle Rules (52)

  • Every sprained ankle does not require screening radiographs.

  • Anteroposterior, lateral, and oblique radiographs should be obtained if any of the below criteria are present:

    • Lateral or medial malleolar bone tenderness is present.

    • Patient is unable to bear weight for four steps both immediately after injury and in the emergency department.

  • The Ottawa ankle rules do NOT apply in the following settings:

    • Age less than 18 years

    • Multiple painful injuries

    • Pregnancy

    • Diminished sensation due to neurologic deficit

  • These criteria have been found to be 100% sensitive for detecting fracture while decreasing the incidence of unneeded radiographs (52).


  • If radiographs are warranted, they should be examined closely for the following fractures that mimic ankle sprains:

    • Medial or lateral malleolus

    • Talar dome

    • Posterior malleolus (posterior distal tibia)

    • Posterior talar process

    • Lateral talar process

    • Anterior calcaneal process

    • “Flake fracture” off the posterior distal fibular rim, indicating a tear of the superior peroneal retinaculum and peroneal tendon dislocation

    • Navicular fracture

    • Widening of the medial clear space between the medial talar facet and medial malleolus, produced by lateral talar subluxation indicative of a tear of the deltoid ligament and probable syndesmotic ligament instability

Stress Radiographs

May 22, 2016 | Posted by in SPORT MEDICINE | Comments Off on Ankle Instability
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