Sinus tarsi is a small depression or cavity that is located between the talus (ankle bone that articulates with the tibia and fibula) and the calcaneus (heel bone), on the outer side of the ankle. This Buzzle write-up provides information on the causes, symptoms, and treatment options of sinus tarsi syndrome.

Denis O'Connor, who first described sinus tarsi syndrome, also suggested the partial or complete removal of the contents of sinus tarsi as a treatment option. This procedure is referred to as the O'Connor procedure.The term 'sinus tarsi syndrome' is a clinical finding characterized by lateral hindfoot pain and instability, that might be experienced due to trauma to the foot, especially in case of lateral inversion injuries. The sinus tarsi is located between the ankle bone and the heel bone, and is filled with fat, ligaments, muscles, as well as nerve endings that play a vital role in proprioception of the ankle.

While an inversion ankle injury (rolled ankle or ankle sprain) is believed to be the most common contributory factor for sinus tarsi syndrome, poor foot biomechanics or structural foot abnormalities could also make a person susceptible to this condition. The diagnosis is confirmed after the elimination of other potential causes of pain in this region, such as fractures, ganglion cysts, etc. Radiological testing might be required to rule out heel bone fractures, talar fractures, subtalar arthritis, tarsal tunnel syndrome, peroneal tendonitis, etc., as these conditions could also cause pain in this region.

Common Symptoms
Runners, dancers, or athletes involved in sports such as long jump or triple jump are more susceptible to ankle sprains. Recurrent ankle sprains increase the risk of sinus tarsi syndrome, which in turn may give rise to symptoms such as:

➞ Pain over the lateral section of the ankle
➞ Localized swelling and tenderness in the sinus tarsi region
➞ Pain that worsens while walking or running
➞ Sensation of hindfoot instability
➞ Pain while walking or running on uneven surfaces
➞ Symptoms worsen on carrying out weight-bearing activities
Contributing Factors
More often than not, excessive movement of the subtalar joint damages the ligaments located in the sinus tarsi region, thereby causing this condition. This makes athletes highly susceptible to this ankle condition.

Ankle Sprains
Ankle sprains could be inversion or eversion sprains. Eversion sprains occur when the ankle gets twisted outwards. Majority of ankle sprains are inversion sprains, wherein the ankle twists inwards, thereby causing damage to the lateral ankle ligaments. Stress to the calcaneofibular ligament due to inward twisting of the ankle, followed by weakening of the lateral talocalcaneal ligament, is often the trigger for pain in the sinus tarsi region. If such injuries are left untreated, or the affected individual doesn't follow recommended self-care measures, the result can be chronic ankle pain. Pain and instability could force the affected individuals to change their lifestyle. They may even end up with an altered gait.

Poor Foot Biomechanics
The term 'pronation' is used with reference to the rotational movement of the foot and the arms. In case of the foot, it is the rotational movement in relation to the horizontal surface. In case of people with flat feet, the arch collapses on carrying out weight-bearing activities. Lack of proper arch support causes overpronation, or the excessive inward rolling movement while walking or running, thereby increasing the risk of inversion ankle sprains. Supination, which refers to under-pronation or outward rolling on the foot, is less common when compared to overpronation.

Inflammatory Conditions
People affected by inflammatory conditions such as subtalar arthritis, rheumatoid arthritis, etc., could also experience pain in the sinus tarsi region. At times, the symptoms might be experienced due to a degenerative joint disease. The inflammatory changes that take place in the sinus tarsi region could also lead to compression of the nerves located in this region, thereby leading to pain. The ligaments could also develop tears due to inflammatory processes. Pain could arise due to injuries to talocrural interosseous and cervical ligaments that lead to the inflammation of the synovial membrane, or scar tissue formation in the sinus tarsi region.

Besides the aforementioned conditions, structural abnormalities could also be contributing factors. For instance, foot abnormalities such as pes planus (abnormal foot due to flattened arches) and tarsal coalition (abnormal connection between two bones in the foot) could also make a person susceptible to sinus tarsi syndrome.
Treatment Options
Since ankle pain is common in many conditions that affect the foot, doctors often rely on diagnostic imaging procedures such as MRI or ankle arthroscopy to identify the cause of the pain in the sinus tarsi region. Once sinus tarsi syndrome has been identified as the reason for the pain and hindfoot instability, doctors can suggest treatment options, depending on the severity of the symptoms. Here are some of the common treatment options resorted to:

➞ Administration of a local anesthetic into the sinus tarsi is likely to provide relief.
➞ Since ankle sprain is one of the most common causes, it becomes essential to follow the RICE (Rest, Ice, Compression, Elevation) method for facilitating full recovery. Refrain from performing any activity that can put stress on the subtalar joint, and the other anatomical structures in this region. Application of ice for 15 minutes at an interval of 3 hours will help reduce the swelling, as will compression and elevation.
➞ Using an ankle brace or an orthotic device will limit the range of motion of the subtalar joint, thereby speeding up the healing process.
➞ It is extremely essential to wear the right kind of footwear, that can restrict excessive movement of the hindfoot.
➞ Foot orthotics are also required for people with poor foot biomechanics.
➞ As far as drug therapy is concerned, the use of non-steroidal anti-inflammatory drugs, or corticosteroid injections, is likely to provide relief from the pain.
➞ Physical therapy is also an integral part of rehabilitation.
➞ If conservative treatment options don't provide the desired results, arthroscopic evaluation, followed by debridement, is likely to be considered. The surgery involves removal of the contents of the sinus tarsi. At times, the removal of the interosseous talocalcaneal ligament maybe recommended.
Sinus tarsi syndrome is often a clinical finding observed in people affected by trauma to the foot or poor foot biomechanics. The best way to lower the incidence of this condition is to seek medical assistance for proper treatment of ankle sprains or other injuries. Correction or treatment of structural foot abnormalities will go a long way in lowering the risk of this foot problem.

Disclaimer: The information provided in this article is solely for educating the reader. It is not intended to be a substitute for the advice of a medical professional.