Ankle sprains usually occur as a result of either a sudden twisting or rolling action of the ankle during either contact (tackles) or non-contact situations.
The most commonly injured structures are the lateral ligaments, however other tendons, muscles, nerves and bones can also be injured depending on how bad the injury is.
The most common injury mechanism for ankle injuries is 'inversion' where the ankle rolls under the sole of the foot and this often results in a sprain of the lateral ligament on the outside of the ankle.
The ankle can also be sprained from excessive eversion (involving the the ankle turning outwards) and this can occasionally coincide with a concurrent fracture of the fibula bone in the lower leg. These injuries take considerably longer to heal and recover from compared to inversion injuries, however they are much less common.
It is well known that the main cause for ankle injuries is poor proprioception. This is the ability of the muscles around the ankle joint to react quickly enough to prevent excessive movement of the joint. Think of it like walking along a road and stepping on a large stone – the quicker the ankle corrects itself, the smaller the injury to the ankle. In addition to this, another aspect of proprioception is the ability of the brain to know where the joint is in space (called joint awareness) and from this, be able to detect when the joint is at risk of injury from excessive movement and “fire” the correcting muscles accordingly.
One possible cause of ankle sprains is weakness of the supporting muscles however this lacks evidence and is in fact more related to proprioception. The surrounding muscles can be strong but if they are unable to react quickly enough then they are unable to prevent an ankle sprain.
Another possible cause that is often attributed to ankle sprains is footwear. It has been suggested that inappropriate footwear that does not provide the ankle and foot with sufficient support increases the risk of injury. An example of this in every day life is wearing high heels, where the base of support is small and the height of the heel causes instability of the ankle joint and thereby increasing the risk of an ankle sprain. The example in a sporting context is wearing the wrong studs for a particular type of surface / weather conditions or wearing heavily worn running shoes that doe not control the movement of the foot and ankle sufficiently. This is an easy factor to address by simply wearing the right footwear for the sport and conditions.
The ankle is made up of three separate joints – the talotibial joint, the tibiofibular joint and the subtalar joint and involves four different bones (talus, tibia, fibula and the calcaneus).
The most common joint to be injured is the tibiotalar joint and it is supported by a number of ligaments to prevent excessive movement. There are 3 ligaments on the outside of the joint - anterior talofibular (ATFL), posterior talofibular (PTFL) and the calcaneal fibular (CFL) and these form the lateral ligament complex and are most commonly injured in ankle sprains. Mild ankle inversion sprains often cause damage to only one of the ligaments whereas moderate to severe injuries usually damage two or three of the
In addition to the lateral ligaments complex, there is also a set of ligaments on the inside (medial aspect) of the ankle and collectively these are called the deltoid ligament (tibionavicular, tibiospring, and deep posterior tibiotalar ligaments). Finally, there are also ligaments above the ankle joint that connect the tibia and fibula bones and these form the syndesmotic complex (anterior tibiofibular ligament, posterior tibiofibular ligament and the interosseus membrane). Considering the large amount of force that is transmitted through the ankle during walking and running, these ligament complexes are vital in providing stability to the ankle.
In addition to these ligaments, there are a number of muscles that also support the ankle and can be injured in an ankle sprain. The muscles on the inside of the ankle are tibialis posterior and tibialis anterior and these invert the ankle (turn the soles of the foot inwards) and the muscles on the outside are the peroneals (longus/brevis and tertius) which evert the foot (turn the foot out). All of the muscles mentioned above are important to stabilize the ankle and act as 'guy ropes'.