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Two of the main bones that make up the rear portion of the human foot are the talus and the calcaneus. Between them runs a bony canal known as the sinus tarsi. This opening extends up from the heel of the foot into the ankle and contains a variety of structures important for the proper function of the foot.
Several ligaments run through the sinus tarsi, connecting bones within the ankle and the foot. The extensor digitorum brevis muscle runs through it; this muscle helps control the motion of several toes. Numerous blood vessels reside in the canal to bring nourishment to the talus bone. It also contains a high amount of synovial fluid, which is used as a lubricant within some joints to prevent friction.
Damage or inflammation of the tissues in the canal is known as sinus tarsi syndrome. This condition is often a result of an ankle sprain, usually when the foot rolls inward or outward excessively. In some cases, overuse of the joint can aggravate the sinus tarsi as well, particularly if the person has had a previous injury. Certain medical conditions that affect the joints, such as osteoarthritis or gout, may also be to blame.
Those suffering from sinus tarsi syndrome experience tenderness and pain around the location of the canal, particularly when the foot turns in or out. Any activity where the person puts weight on his or her foot will typically aggravate the situation. Damage to these tissues affects the stability of the foot and ankle, so sufferers may have difficulty navigating, particularly on uneven surfaces.
To confirm sinus tarsi syndrome, a doctor will often inject an anesthetic into it. This helps to verify that the pain is truly being caused by an injury of these tissues and not another portion of the foot. A follow-up MRI (magnetic resonance imaging), x-ray, or bone scan may also be used to help determine the extent of the damage.
Treatment for an injured sinus tarsi typically includes plenty of rest and minimizing any use of the affected foot and ankle. Inflammation and pain is usually addressed with ice packs and anti-inflammatory medications such as NSAIDs. Special shoes or an ankle sleeve may be necessary to help stabilize the joint, especially if the foot is prone to rolling. Physical therapy may be used to strengthen the ankle, which can help stop injuries from re-occurring. In rare cases, surgery may be required.