Ankle inversion describes a specific movement of the foot where the sole turns inward. This motion primarily occurs at the subtalar joint. It is a natural and controlled action that plays a part in daily activities like walking and maintaining balance on uneven surfaces.
Understanding Ankle Movement
The ankle joint, also known as the talocrural joint, is formed by three bones: the shin bone (tibia), the calf bone (fibula), and the talus. These bones form a hinge-like joint, allowing for two primary movements: dorsiflexion (moving the foot upwards, towards the leg) and plantarflexion (moving the foot downwards, away from the leg). The tibia and fibula create a socket, or mortise, into which the talus fits.
Ligaments are tissues that connect these bones, providing stability. On the outer (lateral) side of the ankle, there are three main ligaments: the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL), and the posterior talofibular ligament (PTFL). A triangular deltoid ligament supports the inner side of the ankle.
Ankle inversion is distinct from eversion, the opposing movement where the sole of the foot turns outward. While both are normal movements, inversion has a greater range of motion due to the ankle’s anatomical structure and the strength of its inner ligaments. The muscles responsible for inversion are primarily the tibialis anterior and tibialis posterior, located on the front and inner side of the lower leg. Eversion is mainly controlled by the peroneal muscles (peroneus longus and peroneus brevis) on the outer side of the lower leg.
When Inversion Goes Too Far
Excessive ankle inversion is the most frequent cause of ankle sprains, often referred to as “rolling the ankle”. This injury occurs when the foot rolls too far inward, causing the ligaments on the outside of the ankle to stretch or tear. The anterior talofibular ligament (ATFL) is the most commonly injured ligament in inversion sprains, often followed by the calcaneofibular ligament (CFL).
When an inversion sprain occurs, common symptoms include pain, especially with weight-bearing. Swelling and bruising are present around the ankle. Individuals may experience tenderness and a decreased range of motion, making walking difficult. The severity of symptoms can vary based on the extent of ligament damage, ranging from mild stretching to a complete tear.