The foot is the lowermost point of the human leg. The foot’s overall shape, along with the body’s natural system of balance-keeping, make each person capable of not only walking, but also running, climbing, and countless other activities.
Sinus tarsi syndrome (STS) is a condition that mainly affects the lateral side of the foot and ankle and is most commonly caused by traumatic injury to the ankle / foot (ankle sprain), or through overuse, such as repetitive standing or walking. Sinus tarsi syndrome may also occur in a person who has a pes planus or an over-pronated foot (flat foot) posture, which can cause excessive compression in the sinus tarsi.
The sinus tarsi area is found in between the talus and the calcaneus bones and contains structures that are responsible for stability. The joint between the talus and calcaneus is known as the subtalar joint. Also known as the talocalcaneal joint, this joint forms a bridge between the foot and ankle.
The subtalar joint allows you to move your foot side-to-side (laterally), pivot to change directions, and stay balanced as you move across uneven terrain. Without this joint, you would constantly roll your ankles when you run, jump, or walk. Also, the subtalar joint is multi-articular, meaning that it can move in more than just one direction. Additionally, it has three articulated facets that provide a surface for the joint to glide, such as:
- Anterior subtalar joint – This allows the joint to glide forward.
- Medial subtalar joint – The medial subtalar joint allows the joint to glide side-to-side.
- Posterior subtalar joint – This joint allows the glide backward.
Moreover, ruptures or damage to the ligaments of the subtalar joint results in increased movement at the subtalar joint, causing instability. Hence injury to this area can affect our balance and predispose us to future ankle injuries.