Sinus tarsi syndrome (STS) is a condition affecting the foot in which pain is often experienced on the outside of one’s foot where it joins the ankle. The condition is called a syndrome in that the pain that is often experienced can be due to one or more of several possible causes. In the majority of cases, the exact cause of the discomfort can be difficult or impossible to determine.
This particular disorder has in fact been described in some of the literature as being ‘nebulous’ in nature. Even the precise location of pain or tenderness that is being experienced can often be difficult to pinpoint.
A diagnosis of the condition can indicate anything from joint instability to ligament tears, to arthrofibrosis as well as a number of other disorders that can lead to pain or discomfort being experienced in the hind portion of each foot.
For this and other reasons, surgical intervention is generally considered an impractical approach since visual examination of the tissues that could be involved will often give little indication as to what the problem or the cause of the pain actually is.
Nevertheless, there are instances where exploratory surgery may be useful, especially if damage to the ligaments that are in close proximity to the joint appears to be a possibility. This syndrome tends to be more common among dancers and athletes but is also fairly common among those who are significantly overweight or flat-footed.
The syndrome is also more likely to occur in those individuals who have experienced one or more ankle sprains or some other injury to the ankle or foot.
Sinus Tarsi Anatomy and Function
The sinus tarsi also referred to in the literature as the tarsal sinus, is a cylindrical cavity between two of the bones in the hind part of one’s foot, the talus and the calcaneus. The talus is located on the top of each foot just in front of the ankle joint.
The calcaneus, most commonly referred to as the heel bone, is located on the bottom and hind parts of each foot. The point at which the talus and the calcaneus meet is called the subtalar or talocalcaneal joint. The tarsal sinus separates the anterior talocalcaneal joint from the posterior talocalcaneal joint and contains blood vessels, nerves, and a complex of ligaments.
This complex of ligaments is often looked upon as being a single structure called the fundiform ligament.
One of the problems encountered in attempting to properly diagnose the condition lies in the anatomy of the rear part of one’s foot. The motions of the talocalcaneal joint, and for that matter the entire rear portion of one’s foot, are not all that well understood. This is especially the case when the joints in each foot are attempting to accommodate to uneven surfaces, and the motions become even more complex when a person is running rather than walking over such surfaces. Not only ligaments but also connective tissues are involved. In simplistic terms, there are a number of things that could go wrong to cause pain. Part of the problem in understanding the various motions involved is the fact that the subtalar joint can be considered as actually consisting of two joints, the talocalcaneal joint itself and the talocalcaneal part of a companion joint, the talocalcaneonavicular joint. Taken together, these joints allow not only inversion and eversion of each foot but also dorsiflexion and plantarflexion. In other words, instead of controlling motion in two dimensions, three-dimensional motion is involved.
The fundiform ligament or ligament complex plays a major role in controlling the motion of the talus bone with respect to the calcaneus. This ligament complex also acts as a controlling mechanism when a longitudinal arch is formed in the foot during motion.
STS Symptoms and Diagnosis
In the majority of cases where athletes have been diagnosed with STS, they have had a prior history of injuries involving the ankle or foot. In addition to the pain they may be experiencing, most complain of a feeling of instability in the area where the ankle joins the foot. It is of some importance that the diagnosis be a correct one before treatment or therapy commences, especially therapy, since some of the more common therapeutic methods used to strengthen ankle joints will actually do very little to strengthen the talocalcaneal joint. In addition, some of the stretching exercises designed to reduce muscle stiffness that sometimes accompanies STS can at times make the condition worse.
Those who experience pain usually describe it as being a deep rather than a surface pain. Range of motion exercises may not give an indication of what the problem actually is unless testing is done at the extreme limits of range of motion, something that is not always easy to do given the complexity of movements that can occur in the area of the joint.
Often, an accurate diagnosis can be achieved by stabilizing the forefoot and moving the calcaneus through a prescribed set of motions. This exercise often makes it possible to detect any instability in the talocalcaneal joint. Having a patient to stand only on the affected foot and perform rotating motions on that foot, hopping up and down of one’s foot, or stepping up and down from a step can often provide clues that can lead to a correct diagnosis. When an athlete feels instability in the subtalar region, he or she will often try to compensate for this instability, which is something that can often be detected and assessed through the use of the Ankle Disability Index.
While correctly diagnosing the condition in terms of the exact cause can at times be difficult, one approach that is sometimes taken is to inject an anesthetic into the tarsal sinus itself to see if the pain goes away. Another less invasive approach is to conduct an magnetic resonance imaging (MRI) scan of the area to see if there has been an excessive buildup of fluid in the sinus tarsi canal.
Imaging is another diagnostic tool although the results are often inconclusive. Fluoroscopy can sometimes yield positive results but the best results are often obtained through MRI. MRI can sometimes reveal alterations and any degenerative changes that have taken place in the ligaments and in one’s talocalcaneal joint, respectively. X-ray techniques tend to be of little value in attempting to verify the presence of STS.
Treating the Disorder and Its Symptoms
Orthotics, special shoes, and various taping techniques, all of which are designed to provide stability and to limit motion in the area, can be helpful although they may not necessarily lead to a cure if the actual cause of the problem remains unknown. Any of these methods that serve to stabilize the rear part of the foot can however allow a person who has the condition to continue physical activities that might otherwise be painful or uncomfortable.
Therapy will at times involve training programs designed to strengthen the muscles that cross the subtalar joint and, in so doing, to provide an added measure of stability. These training programs usually consist of three phases, known as the Attain, Maintain, and Sustain phases. The Attain phase focuses on attaining the proper posture and foot position to achieve stability. The Maintain phase focuses on a series of coordinated isometric contractions of the muscles crossing the joint. The Sustain phase focuses on integrating the neuromuscular system for stability when performing specific physical activities. All three phases involve detailed sets of exercises during which the progress made towards healing the condition is continually being monitored.
Other forms of treatment that are often effective include periods of immobilization, cryotherapy, and the use of anti-inflammatory drugs. In those cases where the diagnosis reveals the presence of ganglion cysts, one of the known causes of STS, removing or aspirating the cysts can often result in a cure. In some instances, STS has been cured by injecting as anesthetic–cortisone solution into the tarsal sinus. This may need to be repeated one or more times before the issue can be totally resolved.
Surgical treatment will seldom be attempted unless there is a positive indication of tissue damage or degeneration or an abnormality in the anatomy of the region. When surgical treatment is deemed appropriate, the approach is most often that of arthroscopic techniques. Surgery tends to be a highly effective method of treating STS in cases involving ligament tears, soft tissue impingement lesions, synovitis, or arthrofibrosis. Synovitis is a condition in which the membrane surrounding a synovial joint becomes inflamed, and the subtalar joint is a synovial joint.
A Complicated Part of the Anatomy
From an anatomical perspective, this small part of the body where the foot meets the ankle is nevertheless one of the most complex parts. The ways in which the joints in the knees and elbows move are rather straightforward. While movement in the shoulder joint can be somewhat more complex, the movements that can take place within the shoulder joint are nevertheless quite well understood.
This is not the case with the subtalar joint and its immediate surroundings. An analogy of sorts could be drawn between the different motions that are possible in the region of the subtalar joint and the sinus tarsi and the many-body problem in physics, a problem that is virtually impossible to solve. To put it another way, it would require the power of a computer to simulate the ranges of motion possible in the subtalar region, but providing a computer with the information it would need to yield an accurate simulation of those movements would still be a significant challenge.
If the syndrome were life-threatening or if its symptoms were unbearable instead of tolerable, as is usually the case, STS would most likely have in the past been subjected to a great deal of study and a great deal more would be known about it than is presently the case. A syndrome is still a syndrome however, meaning that there are multiple causes, not all of which are known. Fortunately, in most instances, therapy, orthotics, rest, and injections quite often suffice to treat and sometimes cure this syndrome.