Often confused with an ankle sprain, sinus tarsi syndrome (STS) is a painful condition of the sinus tarsi, the opening on the outside of the foot between the ankle and heel bone. It is more often misdiagnosed than accurately identified. Sinus Tarsi Fat Pad Impingement Syndrome is another more appropriate, though rather lengthy, name for this painful condition.
Symptoms
When an athlete has a history of pain in the lateral/outside of the ankle and finds that the pain is usually made worse with exercise on uneven surfaces, the sinus tarsi should be considered. The condition is nebulous. Lateral ankle pain can be caused by arthritis in the ankle or in the foot, but usually exercise will make it feel somewhat better and discomfort will follow a period of rest. Sprains, or a series of “twisted ankles,” can cause lateral ankle pain and a general feeling of ankle instability. STS, however, usually causes pain immediately following exercise, and usually there is no memorable history of trauma. STS kind of sneaks up on the athlete, and usually without apparent reason. However, research has developed theories that support hyperpronation as a main cause. STS may also be a delayed result of recurring inversion ankle sprains, without ankle instability or damage to the lateral ankle ligaments. Whatever the prime cause, STS can be disabling.
Sinus Tarsi Anatomy
The heel bone, calcaneus, and the talus (best described as the foot bone inside your ankle) interface and form the talocalcaneal joint. This articulation moves with smooth, gliding motions that occur with every step. The 28 bones in the foot are designed to work in harmony, accepting shock and adapting to uneven, varied surfaces. The talocalcaneal joint is no exception. This strong joint is held together with stout ligaments called the medial, lateral, posterior, and interosseous talocalcaneal ligaments, which surround the joint, allowing only small slipping movements to occur between the calcaneous and talus. Injury to these ligaments can result in Sinus Tarsi Syndrome. The injury is thought to be caused by a series of small stresses within the joint, resulting from excessive motion. Hyperpronation is thought to be the main contributing factor in the creation of STS. The ligaments may become over stretched, a condition called “ligamentous laxity,” and it will cause the bones to move too much with every step. Chronic inflamation sets in and the result is pain. Added to the problem is the increased gravitational forces on the body and feet when running, which causes body weight to increase by as much as ten to twelve times. Also exacerbating the problem are shoes that have less than optimal biomechanical control for individual foot types.
Diagnosis
X-ray evaluations are often inconclusive. Subtalar arthrogram studies may be helpful and though the MRI is thought to provide only uncertain results, I believe that this test is best when correlated with the clinical findings of pain with digital pressure applied to the outside of the sinus tarsi, as well as a history of severe pain in the area during and after exercise. Combining X-ray, MRI, and clinical findings can produce enough evidence to establish a diagnosis and build a treatment plan.
Treatment
Adequate control of the biomechanical causes of hyperpronation is the first line of defense if you suspect STS. You should consult a professional and have a complete biomechanical exam with gait analysis. Then, make sure you have the proper shoes to compliment your individual biomechanical needs. In some instances, a review of repetitive moves should be examined. As an example, envision the basketball player making a simple jump shot, or the softball pitcher’s “follow foot” with every pitch. Every sport involves some repetitive motion that can stress joints beyond normal range. The runner who hyperpronates and is using less than adequate shoes will be at risk of overly stressing foot joints. The talar-calcaneal joint is an epicenter for risk, because pronation occurs here first. Pronation is normal and the body’s first shock absorbing motion as the foot strikes the ground. Hyperpronation is simply too much of a good thing, and causes excess stress on joints within the foot, as well as the knee.
The very first defense and treatment of Sinus Tarsi Syndrome has to include shoe recommendations and control of hyperpronation with a functional orthotic. If this conservative treatment program fails, trigger point injection therapy should be attempted. A series of one to three injections into the sinus tarsi should be utilized. This is an excellent application for a fast-acting cortisone. The injection should not be painful and the results are a miraculous absence of pain. I suggest using the injection treatment up to a maximum of three times spaced a month apart. Treatment outcomes are usually successful and complete but this hinges on the continuation of biomechanical control of hyperpronation. Surgery for Sinus Tarsi Syndrome is rarely required.
Summary
STS is painful and athletically disabling. The condition is thought to be caused from inflammation within the talar-calcaneal joint and structural ligament laxity, and can be the end result of hyperpronation or repeated inversion twists of the ankle. STS should be considered when pain persists on the outside of the ankle, when it occurs with no memorable trauma to the ankle, and when the pain follows exercise.
Robert Rinaldi is a board-certified podiatrist and podiatric surgeon at the Gifford Medical Center in Randolph, VT. He is a fellow and a founding member of the American Academy of Podiatric Sports Medicine, and a podiatric consultant to the Dartmouth College track and cross-country teams. He is a former nationally ranked long-distance runner having competed 25 world-class marathons. You can reach him at Gifford Sports Medicine and Surgery Clinics in Randolph, VT, or at the Sharon Health Clinic in Sharon, VT, 802-728-2490 or 802-763-8000 or at rrinaldi@giffordmed.com.
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