The human foot has numerous combinations of dozens of different sesamoid bones. The largest and most commonly injured are the two bones beneath the great toe. These sesamoid bones rarely develop stress fractures, which is often confused with the more common problem of sesamoiditis combined with a congenital bipartite (split) sesamoid. When sesamoid stress fractures do occur, they usually result from an episode of increased repetitive loading such as an increase in running distance. Pain under the great toe that is aggravated by standing and walking is common. It is not unusual for patients who suffer a sesamoid stress fracture to have a high arched foot type. X-rays may be diagnostic although an MRI may be required to clarify the diagnosis. Non-displaced sesamoid stress fractures can be treated non-surgically with limited or no weight-bearing for 6-8 weeks. Displaced or chronic stress fractures may need surgery, which could include fixing the fracture or removing the affected bone.
Perhaps the first thing to realize about great toe sesamoid stress fractures is that in many instances they are not actually stress fractures of one of the two sesamoid bones, but rather, a “bipartite sesamoid” with an associated “sesamoiditis”. A bipartite sesamoid is a variant of a normal sesamoid where the bone remains separated into two fragments during development. “Sesamoiditis” is a general term that refers to pain under the great toe that occurs from repetitive loading to this area in a manner that is similar to metatarsalgia. Patients with deformities to the great toe, in which the sesamoid bones track abnormally, such as a bunion, can also develop a version of sesamoiditis.
However, sesamoid stress fractures do occur and also produce chronic pain under the base of the great toe similar to the symptoms seen in sesamoiditis. Research shows that sesamoid stress fractures are caused by repetitive loading to this area. This loading can occur during standing, walking or running, particularly in shoes that do not provide adequate protection. A painful sesamoid stress fracture may cause an individual to limp quite noticeably. Symptoms may settle over time, but they will reoccur if a person resumes repetitive load bearing activities, like running or playing sports. The pain is often quite localized and is associated with the involved sesamoid. It’s not uncommon for a sesamoid stress fracture to occur after a hard training run or another type of activity that is associated with more repetitive loading than normal, such as when an individual’s activity level or training level has increased noticeably.
Sesamoid stress fractures are associated with localized tenderness over the involved sesamoid. Movement of the great toe may exacerbate the symptoms. The pain is usually isolated to under the great toe region. It’s not uncommon for these injuries to occur in patients with high arched feet, as this foot shape tends to cause increased loading at the base of the great toe.
Routine x-rays of the foot can be very helpful. Typically they will demonstrate two sections of the sesamoid. What differentiates a stress fracture from the bipartite sesamoid is that the bone fragments of a bipartite sesamoid have a clearly identified margin. This is because the congenital nature of a bipartite sesamoid means that it has been present since development, whereas a sesamoid stress fractures has a fracture-like appearance on radiograph.
An MRI can help differentiate a bipartite sesamoid from a sesamoid stress fracture. An MRI may also help differentiate an acute sesamoid fracture from a chronic stress fracture. In addition, it may identify an area of avascular (dead) bone that develops in some sesamoid stress fractures. This happens in some circumstances as the sesamoid bones have a poor blood supply and a chronic stress fracture or bipartite sesamoid may leave one section of the sesamoid with a limited blood supply.
Treatment is more successful when the correct diagnosis is made; specifically, it is critical to determine whether the problem is from a sesamoid stress fracture or a bipartite sesamoid with overlying sesamoiditis. The general non-operative treatment principles are similar, although a true sesamoid stress fracture will tend to have a worse prognosis.
Non-operative treatment of a non-displaced acute sesamoid stress fracture requires a period of immobilization and protected weight bearing. The goal is to manage weight bearing through the heel for a period of six to eight weeks in order to give the sesamoid bones the best chance to heal properly. . Displaced acute stress fractures will need surgical intervention.
More commonly, a chronic stress fracture is present and these are managed non-operatively in a manner that is similar to treating sesamoiditis. Specifically, the area under the base of the great toe is protected. An orthotic that helps to offload this area is used. This is typically an orthotic with a recessed area under the base of the first metatarsal head. This is combined with the cushioned insole and a very stiff sole of the shoe with a slight contour. A stiff sole with a rocker bottom contour will allow for a smoother dispersion of the force away from the base of the great toe. In addition, activity modification to help prevent excessive loading to this area should be performed. Time will often help to settle this condition when combined with activity modification.
The results of surgical treatment are not routinely predictable. The treatment involves repairing the fracture with fixation and removing a portion of or the entire fractured sesamoid bone. Removing the sesamoid bone is performed in conjunction with a repair of the associated joint capsule. One of the issues with both operative and non-operative treatment is that the underlying foot shape (usually high arched) that often contributes to the development of this condition remains unchanged. Therefore, the area under the base toe is constantly and repetitively loaded during standing and walking activities.
Potential complications of surgery
There is an array of complications that can occur as a result of sesamoid surgery, including but not limited to:
Complications that are specific to sesamoid surgery include:
- Irritation to the nerve running to the inside of the big toe
- Persistence of symptoms as the loading to this area will continue.
- Great toe deformity (Bunion, hallux varus, cock-up toe)
If one sesamoid of the great toe is resected without adequate repair or reconstruction of the plantar capsule and flexor halluces brevis muscle, a secondary deformity can develop. Resection of the tibial sesamoid can lead to a bunion deformity. Resection of the lateral sesamoid can lead to Hallux Varus (medial devaiation the tip of the great toe.)
A Cock-up deformity of the big toes can occur if both sesamoids are resected and the capsule is not adequately repaired. In this instance, the big toe will tend to rise up out of position creating an uncomfortable deformity.