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Sesamoid bone injury not just for athletes

Conway McLean, DPM

The foot is a complex structure, with its plethora of ligaments and blood vessels, nerves and nails, subject to tremendous wear and tear over the years. When examined cumulatively, the physical stresses are incredible. To resist this wear, the skin on the bottom of the feet is unique, the thickest of the body. And specially shaped bones allow the body to walk, to run, to stand up to the rigors of being bipedal.

Every time you take a step, a simple stroll in the park, great force is experienced by the bottom of the foot. To be specific, nearly one and a half times body weight. This figure is greatly increased when sprinting, with a greater percentage impacting the forefoot as the body leans further forward. What about all the sports that involve running, or the activities entailing vigorous, quick movements. This is evidenced by a quick glance at the feet of a ballerina. Not a pretty site, I can tell you!

One of the regions of the foot most “impacted” by these kinds of activities is at the ball of the foot, at the base of the big toe. This structure is termed the first metatarso-phalangeal joint (since it joins the metatarsal bone with a toe bone, called a phalanx). This first joint is unique, experiencing special forces and providing special actions. One of the features that make it so is the presence of the two sesamoid bones. These small pea-shaped structures lie under the head of the first metatarsal bone, lying side-by-side, each positioned in an appropriately matching groove on the bottom of the metatarsal.

The sesamoids play an integral role in great toe function, absorbing weightbearing pressure, reducing friction and protect tendons. The functional complexity and anatomic location of these small bones make them vulnerable to injury from shear and loading forces. These two bones are embedded in the tendons running out to the big toe, preventing these tendons from rubbing against the metatarsal bone when walking or running. Thus, they function similarly to the kneecap, which has the same responsibility. Although you might not think of these small bones as being part of a joint, they each have an articular surface with joint cartilage, allowing each to articulate with the bottom of the first metatarsal bone, which has a matching joint surface.

But they have other tasks, also acting as a fulcrum, a pivot point, providing leverage when the big toe pushes off during gait. The sesamoids also serve as the weight-bearing interface between the supporting surface and the first metatarsal bone. Therefore, they are working to absorb the weight placed on the ball of the foot when in motion. In the athlete, forces up to three times body weight may be transmitted across the sesamoids.

These bones are without a good supply of arteries, meaning they don’t have an abundant blood supply. As is common knowledge, blood provides the essential nutrients and oxygen required for healing of inflammation or trauma. This often results in a delay in the resolution of pain from the immediate area, and when there is a bone injury, can mean enduring, chronic pain.

A host of different conditions can develop at this part of the body, from tendonitis to arthritis to a fracture of one of these bones. Each carries their own treatments, as well as their prognosis. An accurate diagnosis is critical, but can be challenging to arrive at. Along with all the many diagnostic tools available to us, good clinical suspicion is extremely important to accurately determining the cause of pain.

Because of the degree of physical trauma, this area frequently becomes symptomatic. Symptoms experienced by those suffering from some type of sesamoid injury or inflammation may include pain, limping and difficulty wearing shoes, all aggravated by even a simple activity like walking. In some, the pain will aching, but more commonly is a sharper-type pain.

Certainly, the stresses of many athletic activities entail great force to this region. Various structures can be traumatized, especially if this joint complex is moved forcibly out of position, past a safe amount of motion, as with an acute joint sprain. Typically, one of the multiple ligaments maintaining the position of these structures will be stretched, and with enough force, torn.

But athletic pursuits are not the only reason this problem develops. The positioning of the first metatarsal varies, and in some, it’s lower than it should be. This means it gets more of the pressure of standing and weight bearing. Alternatively, greater pressure is experienced by this region in the higher arched foot. Predictably, the sesamoids are often where the inflammation develops. The term used for this condition is, predictably, sesamoiditis. (The latter part of that word, ‘-itis’ simply means ‘inflammation’ and is added to the name of many structures, common examples including tendonitis, appendicitis, or bursitis.)

Treatment options for sesamoiditis are many, with the traditional “R.I.C.E.” being an early mainstay of therapies. Perhaps more effective for symptoms, as well as promoting healing, is the reduction of the pressures experienced by these structures in standing and walking. Immobilization is beneficial when it’s an acute traumatic injury to the area.

A stress fracture occurs when someone applies excessive repetitive stress to a healthy bone, or there is normal repetitive stress to a weakened bone. This kind of fracture is more common with certain athletic activities, especially long-distance running. Stress fractures account for 40 percent of all sesamoid injuries so obviously these are common. When these injuries occur, the sufferer will complain of increasing pain with increasing activities. When a stress fracture of a sesamoid bone occurs, the pain develops gradually. Generally, the faster you try to move, the more pain you will experience.

Acute fractures of these bones can also occur. These are not common, but are potentially debilitating. They usually are seen in the athlete from trauma to this region. Controlled studies have not been performed, so its difficult to say whether conservative care is better than surgery. In general practice, conservative care is typically successful when appropriately provided.

Many treatment options exist, with pressure relief being particularly helpful, providing some immediate relief. Long term redistribution of ground forces is best achieved with specially modified prescription foot supports (aka foot orthotics). The more rigid the sole of the shoe being worn, the less pain. If it is a fracture that has not healed after appropriate conservative care, and symptoms are sufficiently severe, surgical removal of the sesamoid may be needed. Another option with a fracture is to fix the two fracture fragments together in hopes that bony healing will occur.

In summary, pain from the ball of the foot, behind the big toe, could be due to a sesamoid condition. Some simple home measures, like use of an over-the-counter insole, may be sufficient to allow healing in milder cases. It’s very difficult to rest these structures (unless you’re really good at hopping!). Ignoring the pain can lead to further damage. Once again, the take home message? If your attempts at treatment fail, time to seek professional care. You don’t want to end up with something worse. (You could even get “sick sesamoid syndrome”, a real and debilitating condition!)

Editor’s note: Dr. Conway McLean is a physician practicing foot and ankle medicine in the Upper Peninsula, with a move of his Marquette office to the downtown area. McLean has lectured internationally on wound care and surgery, being double board certified in surgery, and also in wound care. He has a sub-specialty in foot-ankle orthotics. Dr. McLean welcomes questions or comments atdrcmclean@outlook.com.

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