The sinus tarsi, known as the “eye of the foot” is a small cavity located on the outside of the ankle between the talus and calcaneus bones. This can be felt as a deeper spot on the outside of the ankle that you can push your finger into.
This cavity contains numerous anatomical structures including ligaments, joint capsule, blood vessels, fatty tissue and nerve endings that play a vital role to the balance receptors in the ankle.
These structures within the sinus tarsi may be injured following an ankle sprain. Poor foot biomechanics and/or structural foot abnormalities could also make a person susceptible to this condition.
Inversion (rolling out) ankle sprains attribute to 70-80% of cases, the remaining 20-30% can be due to a “pinching” or impingement of the soft tissues in the sinus tarsi due to a very pronated (rolling in) foot.
In true Sinus Tarsi Syndrome, the structures in the canal will show pathology signs of inflammation, cellular damage, fibrosis (similar to scar tissue) and possible synovial cysts.
Treatment for Sinus Tarsi Syndrome should not be delayed. When the injury becomes chronic the rate of healing slows significantly, resulting in longer recovery times and an increased chance of future reoccurrence.
Causes of Sinus Tarsi Syndrome:
- Inversion ankle sprain (rolling out).
- Repetitive strain associated with walking or running.
- Excessively pronated flat foot (rolling in).
Contributing Factors of Sinus Tarsi Syndrome:
- Poor flexibility and/ or muscle weakness.
- History of ankle sprains and poor balance receptors and weakness in the ankle joint.
- Inappropriate training and/or inappropriate footwear.
- Poor foot biomechanics or structural abnormalities.
Signs and Symptoms of Sinus Tarsi Syndrome:
- Pain +/- swelling over the outside of the ankle, which may be difficult to pin point.
- Feeling of instability, especially when walking on slopes or uneven surfaces.
- Pain is frequently defined as a sharp sensation of pinching, when the foot is lifted up, for instance when walking-up stairs.
- Symptoms are typically worse in the morning and may present as pain and stiffness that slowly improves as the foot warms up.
- Pain may be exacerbated by inwards tilting of the heel.
- Reduced activity of the muscles on the outside of the leg during walking.
- MRI is the investigation of choice as this cavity is hard to investigate with X-ray and ultrasound alone. Fluid within this cavity may be seen as well as inflammation and fibrosis.
- The pain will be temporarily relieved by injecting local anesthetic into the canal. This is used as a diagnostic test only not a treatment.
Treatment for Sinus Tarsi Syndrome:
- R.I.C.E regime (rest, ice, compress, elevate) for acute injuries within the first 48 hours.
- Anti-inflammatory medication may be beneficial in the initial phase of this injury.
- Sufficient rest from any activity that increases pain levels.
- Prolotherapy into the joint has been found to be very beneficial along with Foot Mobilisation Therapy.
- Mechanical support to the foot, such as a customised foot orthoses to correct the poor function of the foot and tendons around the ankle, resulting in excessive movement.
- Functional rehabilitation of Achilles tendon, peroneal muscles and proprioception trainings, with a gradual return to activity, under the direct guidance of a podiatrist.
- Appropraite supportive footwear.
- Non-weightbearing boot, such as a cast walker may needed in very severe cases to allow healing without further tissue damage, due to weight bearing activities.
Note: Conservative treatment is usually effective and surgery is rarely needed and should be considered only after all conservative treatments have been exhausted.
Two Surgical Techniques for Sinus Tarsi Syndrome:
- Open surgery with excision of the entire contents of the sinus tarsi.
- Closed surgery with key hole examination and cleaning up of the posterior subtalar joint and sinus tarsi.