Sinus tarsi syndrome is an inflammatory reaction found within the sinus tarsi. The sinus tarsi is the lateral entry point to the subtalar joint. The subtalar joint consists of the talus on the top and the calcaneus (heel bone) on the bottom. Sinus tarsi syndrome is also referred to as sinus tarsitis. The onset of sinus tarsi syndrome is often preceded by trauma to the subtalar joint. Trauma may be due to an ankle sprain or a fall. In addition to a traumatic onset, sinus tarsi syndrome may also be due to chronic inflammatory conditions of the subtalar joint. Chronic inflammatory tissue can result from arthritis or cyst formation within the sinus tarsi or adjacent subtalar joint. Sinus tarsi syndrome is found equally in men and women. Sinus tarsi syndrome is found in adults between the ages of 18 to 50 years of age.
First described in 1958 by O’Conner, sinus tarsi syndrome was initially thought to be due to post traumatic scarring. The onset of sinus tarsi syndrome usually occurs in the second or third decade of life. Most contemporary clinicians believe that sinus tarsi syndrome is due to repetitive traumatic load applied to the subtalar joint resulting in forced inversion of the joint. Examples of repetitive inversion activities that would injure the subtalar joint include the trailing foot of a softball pitcher or bowler. Other examples include sitting with the feet tucked under the weight of your body. Each of these activities results in forced inversion of the subtalar joint and strain on the sinus tarsi.
Forced eversion of the subtalar joint can also contribute to the onset of sinus tarsi syndrome. Ballet is a good example of an activity that results in forced eversion of the subtalar joint. Each of the four positions of ballet result in one or both of the feet being placed in a position where the subtalar joint is in forced eversion placing strain on the sinus tarsi. This strain on the sinus tarsi results in sinus tarsi syndrome.
The sinus tarsi is a cone shaped area that lies between the talus to the top and calcaneus to the bottom. The sinus tarsi actually refers to the entry of the canalis tarsi, or deeper portion of the sinus. The canalis tarsi consists of the calcaneal portion called the sulcus calcanei. The dorsal or talar portion of the canalis tarsi is called the sulcus tali. The canalis tarsi separates the two segments of the subtalar joint. The subtalar joint consists of three different joint facets that are separated by the canalis tarsi. The anterior and middle facets lie distal to the canalis tarsi. The posterior facet lies proximal to the canalis tarsi.
The subtalar joint is held together by both internal supporting structures and external structures that traverse the joint. The cervical ligament, also known as the ligamanet of Farabeu, lies within the sinus tarsi. Deeper to the cervical ligament is an interosseous ligament that connects the talus and calcaneus. Both the cervical ligament and interosseus ligaments help to stabilize the subtalar joint during pronation (flattening of the foot) and supination (increasing the arch of the foot). The bifurcate ligament also originates in the sinus tarsi and extends across the top of the foot to the medial aspect of the foot. The bifurcate ligament is a two part, or Y shaped retinacular band that inhibits supination and prevents the extensor tendons on the top of the foot from 'bow stringing'. A fatty plug lies within the sinus tarsi. This fatty material is called Hoke's tonsile. Additional soft tissue found within the sinus tarsi includes the synovium of the subtalar joint.
Numerous small nerve endings are found in the canalis tarsi and are extensions of the posterior tibial nerve. Studies have shown that the nerve endings in the canalis tarsi are a source of nociceptive (pain) and proprioceptive (space orientation) neural sensation. Strain applied to the nerve endings of the sinus tarsi will stimulate a proprioceptive response and will initiate splinting of adjacent muscles and tendons in an attempt to limit excessive motion of the subtalar joint.
Causes and contributing factors
Compression of the tissues within the sinus tarsi occurs as the foot pronates (flattens). Testing has found that pronation significantly increases subtalar joint pressure and pressure within the sinus tarsi. It’s very common to find patients who experience sinus tarsi syndrome also suffer from pathological flatfeet and conditions such as tarsal coalitions or posterior tibial tendon dysfunction. Additional factors that contribute to sinus tarsi syndrome include activities that place prolonged strain on the subtalar joint. Examples of these activities include ballet, baseball and softball pitching and bowling.
The differential diagnosis for sinus tarsi syndrome includes;
Arthritis of the subtalar joint
Impingement within the ankle
Intermediate dorsal cutaneous nerve entrapment
Peroneal tendon rupture
Tarsal tunnel syndrome
The diagnosis of sinus tarsi syndrome is made by direct palpation of the sinus tarsi during range of motion of the subtalar joint. An injection of local anesthesia into the sinus tarsi is a common tool used to block the nerve sensation of the sinus tarsi. If pain relief is achieved following injection, the diagnosis of sinus tarsi syndrome is made. X-rays do not provide information specific to sinus tarsi syndrome, but x-rays are necessary to rule out fractures of the talus or calcaneus. Also, x-rays can be used to evaluate the integrity of the subtalar joint and rule out subtalar joint arthritis. MRI's can be useful in cases of sinus tarsi syndrome and can identify inflamed tissue within the sinus tarsi.
Treatment of sinus tarsi syndrome begins with identification of the activity that may be contributing to subtalar joint injury. Rest and bracing of the subtalar joint, using an ankle brace is helpful. Semi-rigid OTC arch supports and prescription orthotics do help to limit the range of motion of the subtalar joint thereby reducing pain.
It's important to recognize that most cases of sinus tarsi syndrome are due to mechanical load applied to the subtalar joint. Therefore, the most important aspect of caring for sinus tarsi syndrome is identifying and eliminating pathological loads applied to the subtalar joint. Inflammation within the sinus tarsi can be controlled with injectable cortisone. If cortisone and bracing prove ineffective, ablation (destruction) of the nerve can be accomplished by chemical or thermal means. Chemical ablation is performed using serial injections of 4% alcohol. Relief with chemical ablation is achieved after 4-6 injections. Thermal ablation involves the use of a thermal ablation unit that freezes the nerve of the sinus tarsi.
Surgical treatment of sinus tarsitis focuses on the removal of the soft tissue contents of the sinus tarsi. The soft tissue plug found in the sinus tarsi is called Hoke's tonsil. Removal of Hoke's tonsil acts to denervate the sinus tarsi. Denervation of the sinus tarsi does not correct the mechanical problems of the subtalar joint, but denervation removes the local sensory feedback from the sinus tarsi. Therefore, removal of Hoke's tonsile is simply used to eliminate the pain associate with sinus tarsi syndrome.
When to contact your doctor
Symptoms of sinus tarsi syndrome that fail to respond to conservative care should be evaluated by your podiatrist or orthopedist.
References are pending.
Author(s) and date
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Cite this article as: Oster, Jeffrey. Sinus Tarsi Syndrome. http://www.myfootshop.com/article/sinus-tarsi-syndrome
Most recent article update: September 13, 2017.
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