Ankle sprain

Although ankle sprains are the second most common sports injury (after knee injuries), in a study of over three million ankle sprains just over half (51.7%) occurred during non-athletic activities. Most ankle sprains (80%) involve the outer (lateral) ankle joint as a result of excessive inward rolling of the foot (inversion injury). The pain is immediate and may be associated with an audible ‘snap’ or ‘pop’, due to the tearing or over-stretching of the ligaments.

Recurrence rates are extremely high, in fact, in some sports such as basketball, recurrence rates have been reported to exceed 70%. Repetitive sprains have been linked to increased risk of ankle osteoarthritis. Studies show the biggest risk factor for an ankle sprain is a previous ankle sprain. It is believed this is due to inadequate treatment and the persistence of underlying avoidable risk factors.

Appreciation of the complex anatomy and mechanics of the ankle joint and the underlying causes related to ankle instability is integral to effectively evaluating and treating ankle injuries.

Ankle anatomy 101

Your ankle is a strong complex mechanical structure consisting of four bones. The lower end of your two leg bones (the tibia and fibula) sit on your anklebone (talus), which in turn sits on your heel bone (calcaneus). These bones are stabilised by a number of very strong ligaments, which help prevent extreme movement of your ankle joints. There are a number of muscles which control and brace your ankle and are the first line of ankle stabilization.

Ankle instability

Of prime importance in ankle stability during activity is the even distribution of forces on the ankle bones. Having your weight focused towards the inner side (medial) of your foot places your ankle at greater risk of a lateral sprain. During weight bearing your foot is part of a closed mechanical chain so that what happens at the hip joint largely determines how the ankle (and knee) behaves including the forces acting on it. In this way, assessment of hip and knee mechanics is an essential part of a comprehensive ankle evaluation.  

There are three ligaments that passively bind the outer ankle, one at the front, one in the middle and one at the back of the ankle joint. The most commonly injured ligament is the one at the front (the anterior talofibular). If the force is more severe, the middle ligament (the calcaneofibular ligament) is also damaged. The posterior talofibular ligament is less likely to be damaged. A complete tear of all ligaments may result in a dislocation of the ankle joint and an accompanying fracture.

The most important muscles for protection against lateral ankle sprain are the peroneal muscles. Most ankle injuries involve an underlying condition with these muscles and their tendons, called peroneal tendinopathy, a condition that gradually develops over time.

In this state these muscles are prone fatigue, lose control, give way, strain or tear when placed under extra pressure. This exposes the ligaments and bone to overwhelming twisting forces. If factors that lead to peroneal tendinopathy remain unaddressed, an ankle injury is likely to become a chronic problem.

In addition to the peroneals, the muscles of the front (anterior) compartment of the lower leg (tibialis anterior and extensor digitorii) also contribute to the dynamic stability of the lateral ankle complex.

On the inner side of the ankle (medial), the joint is stabilised by a thick, strong fibrous ligament called the deltoid ligament. Sprains to the deltoid ligament as a result of the foot excessively rolling outward (eversion sprains) account for less than 20% of all ankle sprains.