The sinus tarsi is an opening on the outside of the foot between the ankle and heel bone. It is often referred to as the “eye of the foot” because it opens towards the outside of foot. STS (sinus tarsi syndrome) was first described by Denis O’Connor in 1957 as a problem that can occur after an inversion ankle sprain or due to a “pinching” or impingement of the soft tissues in the sinus tarsi due to a very pronated (rolling in) foot.
Patients typically present with localized pain in the sinus tarsi region with a feeling of instability aggravated by weight bearing activity. Inverting the ankle or moving it into a position where it is turned inwards like it would go with an ankle sprain can cause severe pain. Patients may feel instability in ankle joint especially while walking on uneven surfaces and repetitive strain can aggravate the condition.
Medication and therapies that reduce swelling and inflammation are recommended as well as correction of any underlying biomechanical problems that contribute to the way the ankle bones move restricting the space in the sinus tarsi channel. Strengthening exercises for the ankle are suggested and helpful. When treated early, the outlook for recovery is good but without appropriate, early intervention the condition can lead to chronic pain.