Where and what is the sinus tarsi:
The word “sinus” refers to a cavity, most often in bone. The cavity known as the sinus tarsi is located on the outside of the foot in front of and below the outside anklebone. The cavity is formed at the junction between the heel bone and the bone that sits over the heel bone called the Talus. The heel bone forms the floor of the cavity and the talus creates the roof.
Within the cavity there are blood vessels, nerves and ligaments. The ligaments function to hold the two bones together.
“Sinus Tarsi Syndrome” refers to a painful condition located in this cavity in the rear portion of the foot. The pain is made worse with weight bearing. The pain can become much more intense when walking, running or hiking on uneven surfaces.
Causes of Sinus Tarsi Syndrome:
The most common cause of sinus tarsi syndrome is an inversion injury to the foot. This occurs when the foot rolls inward and stretches the soft tissue in the cavity. When the foot is stressed by this inward motion a tear or strain occurs to the ligaments. The injury to these ligaments results in inflammation, swelling and thickening.
The other causes of this condition are structural as apposed to the injury noted above. One of these structural abnormalities that can occur is growths or masses of soft tissue. Over growth of nerve or fat tissues in the cavity can cause increased pressure and result in pain. The pain in this area can also be caused by deviations in the bone structure. For example, bone spurs; arthritis and bone bridges can be responsible for the development of sinus tarsi syndrome.
Diagnosing Sinus Tarsi Syndrome:
To make the diagnosis of this condition the podiatrist will listen to the history of how the symptoms began and then examine the area. Most of the time, that is all that is needed to confirm sinus tarsi syndrome. In addition to the history and physical exam an x-ray should be taken to rule out bone cyst, fractures, bone bridging and arthritis. In some cases if the condition does not resolve with conservative treatment an MRI or diagnostic ultrasound may be ordered to evaluate the soft tissues in the cavity.
Another helpful procedure to determine the exact location of the pain is to inject the sinus tarsi with a small amount of local anesthesia. If upon examination after the injection the pain is gone the diagnosis is confirmed. If however, the pain is still present following the injection the injury may be in another location in the foot.
Research has shown that a majority of the people with sinus tarsi syndrome will respond favorably to conservative management. Rest, ice and compression are suggested to reduce the inflammation. Oral anti-inflammatory medications can be prescribed to further decrease the pain and swelling.
Another treatment option is to tape the foot to attempt to limit the motion at the subtalar joint. If the taping successfully reduces the pain long term treatment with a custom orthotic can be used to control the motion of the rear foot. In most cases foot orthotics are sufficient to treat this condition, however in some cases an ankle foot orthotic may be necessary to fully control the motion.
Finally, a steroid injection into the sinus tarsi may be effective at relieving the pain.
In conservative measures have not helped to relieve the pain surgery may be needed. A common surgical procedure to threat this condition is decompression or removing the abnormal tissues from the cavity. If the MRI scans shows a soft tissue mass present in the sinus tarsi surgical removal of the mass will be needed.
After the surgery, protected weight bearing in a post-operative shoe or walking boot will be required for a period of approximately 2-4 weeks.
If this surgery fails or the patient has severe arthritis the bone in the rear foot may need to be fused.