Sinus tarsi syndrome is a rare injury to the subtalar joint, the joint just below the ankle joint. The sinus tarsi is a tunnel or opening between the talus and calcaneus, the two bones in the foot that make up the subtalar joint. Several ligaments, nerves and blood vessels pass through the sinus tarsi. When any of these structures becomes injured, sinus tarsi syndrome may result. If the normal position and function of the subtalar joint is disrupted, the sinus tarsi tunnel will be affected and can result in pain and discomfort. The subtalar joint and the sinus tarsi also play an important role in proprioception. Proprioception is the awareness of the body in space and goes hand-in-hand with balance and stability.
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Symptoms
Pain on the outside of the foot that is difficult to pinpoint can be indicative of sinus tarsi syndrome. The area of pain is similar to that of an ankle sprain and often occurs in conjunction with a traumatic sprain of the ankle joint. The ankle and foot may feel stiff in the morning when first waking and improve as the day progresses. Pain associated with sinus tarsi syndrome typically develops over a period of time, not suddenly. In other words, if an ankle sprain does not seem to fully heal or continues to be problematic, it may be due to a resultant sinus tarsi syndrome, caused by the initial ankle sprain itself.
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Causes
Pain due to sinus tarsi syndrome can be caused by a traumatic injury or from overuse. An injury to the sinus tarsi following a traumatic ankle sprain can cause synovitis, which is an inflammation of the synovial lining of the joint. It can also cause permeation of fibrous scar tissue into the joint. If sinus tarsi syndrome is due to overuse caused by repetitive walking or standing, or overpronation of the foot, the subtalar joint will be abnormally positioned causing issues with balance and instability when walking. An overpronated subtalar joint causes compression of the sinus tarsi and if the two bones of this joint make contact with one another, arthritis and pain will result.
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Treatment
Early treatment and intervention are crucial to prevent long-term pain and discomfort. Rest and modification of the activities that aggravate the symptoms of sinus tarsi syndrome will help to relieve the pain. To control instability, ankle braces and taping offer support and lift the arch of the foot, opening up the sinus tarsi to reduce compression. Footwear that is designed to control pronation and increase stability are both important components of treatment. Surgical treatment is a last resort for chronic pain from sinus tarsi syndrome. If this syndrome is a result of severe flat feet and range of motion at the subtalar joint is limited, surgery may be required to reconstruct the foot and arch and reduce the compression within the sinus tarsi.
