Ankle Instability

Introduction

Ankle sprains are common injuries accounting for up to 40% of all athletic injuries. It has been estimated that 75% of ankle sprains involve the lateral ligamentous complex. More than 23,000 ankle sprains occur per day in the United States affecting both males and females at approximately the same rates. Previous studies demonstrate that ankle sprains account for up to 53% of basketball injuries and 29% of soccer injuries. Most injuries respond well to conservative treatment with physical therapy emphasizing proprioceptive training, restoration of motion, and strengthening of the supporting musculature. Unfortunately, up to 34% of patients will resprain their ankle and up to 33% of ankle sprains will develop mechanical instability (MI) or functional instability (FI) that may ultimately lead to chronic ankle instability. Previous studies have demonstrated associated intra-articular pathology in upward 93% of patients with ankle instability, with up to 78% of patients developing posttraumatic arthritis. ^, Therefore proper diagnosis and management is critical in order to prevent long-term sequelae of ankle instability.

Anatomy/Biomechanics

The lateral ligament complex of the ankle is composed of the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL), and the posterior talofibular ligament (PTFL) ( Fig. 13.1 ).

The ATFL, which is the weakest of the three ligaments, originates 10 mm proximal to the tip of the fibula and inserts onto the lateral talar neck just distal to the articular surface. The CFL is an extra-articular ligament originating on the distal tip of the fibula and inserting onto the calcaneus 13 mm distal to the subtalar joint. The CFL forms the floor of the peroneal tendon sheath. The PTFL is the strongest of the lateral ligaments and extends from the posterior border of the distal fibula to the posterolateral tubercle of the talus.

The ATFL functions as the primary restraint to inversion in plantar flexion and resists anterolateral translation of the talus. It is the most commonly injured ligament in lateral ankle sprains. The CFL is the primary restraint to subtalar inversion in neutral and dorsiflexed positions. Although the PTFL limits posterior talar displacement, it does not play an integral role in ankle stability when both the ATFL and CFL are intact.

The most common mechanism of injury to the lateral ankle ligament complex involves excessive supination of the rearfoot about an externally rotated lower leg after contact with the ground. Plantar flexion during injury increases the likelihood of injury. The ATFL is typically the first ligament injured during an ankle sprain. Attarian et al. conducted a biomechanical study evaluating 20 human cadaver ankles and performed cyclic loading of each isolated bone-ligament-bone preparation, constant velocity load-deflection tests at varying deflection rates, and extremely rapid load to failure tests. The authors demonstrated that maximum load to failure for the CFL was 2–3.5 times greater than that for the ATFL, further supporting the increased rate of injury to the ATFL when compared with the CFL. The CFL is involved in 50%–75% of ankle sprains, whereas the PTFL is involved in less than 10% of all ankle sprains.

Risk Factors

Several studies have examined the relationship between intrinsic and extrinsic risk factors for ankle sprains. Extrinsic risk factors include training errors, type of sport, type of equipment, level of competition, and environmental conditions. Intrinsic risk factors include age, gender, weight, aerobic fitness, alignment, strength, range of motion, proprioception, joint laxity, and foot morphology. McKay et al. conducted a study evaluating the risk of ankle sprain in elite and recreational male and female basketball players and demonstrated an increased risk in patients who had a history of ankle injury and in patients who failed to stretch before games. Insufficient rehabilitation and earlier perceived healing of the injury may contribute to this increased risk. Baumhauer et al. demonstrated that individuals with a muscle strength imbalance and a smaller dorsiflexion-to-plantar flexion ratio had a higher incidence of ankle sprain. Willems et al. performed a prospective study evaluating risk factors for inversion ankle sprains in collegiate physical education female students aged 17–26 years. The authors identified several risk factors including less accurate passive joint inversion position sense, less postural control, and higher extension range of motion at the first metatarsophalangeal joint. Sport activities that involve running, jumping, and cutting movements place athletes at an increased risk for inversion sprains. Previous studies have demonstrated that ankle sprains most commonly occur in basketball, football, and soccer.

Clinical Presentation

Patients with acute ankle ligament injuries typically present with lateral ankle pain and swelling, and they often describe a sensation of “rolling over” his or her ankle. Patients may be unable to bear weight on the affected extremity during the initial presentation. In cases of chronic instability, patients report experiencing recurrent ankle sprains and describe a sensation of the ankle “giving way.”