Peri-sesamoiditis and Sesamoid Fracture

The sesamoid bones of the foot are small, sesame-seed shaped bones that are found on the plantar aspect of the 1st metatarsal-phalangeal joint (underneath your big toe joint) within the tendon of the flexor hallucis brevis muscle (one of the muscles the bends your big toe downwards). Most people have 2 sesamoid bones, one is called the “tibial sesamoid”, as lies on the side of the tibia (closer to the inside edge of the foot) and the other the “fibular sesamoid”. The tibial sesamoid is slightly larger , longer and more distal (closer to the extremities) than the shorter, rounder, more proximal (away from the extremities) fibular sesamoid. Many people (perhaps 33% of sesamoid bones) have one or both sesamoids that are bipartite or tripartite, i.e. are made of two or three pieces, rather than a single sesame seed shaped bone. The sesamoid bones protect and absorb shock in both the joint and tendon. They also act like a pulley, which helps us during the propulsive phase of gait (when we push ourselves forward), while also providing additional strength to the tendons.

The sesamoid bones of the foot are tough little structures, and with good reason. Scientific research has shown that these bones have forces acting upon them that are approximately three times a person’s bodyweight…and that is when walking! This is likely to be much higher during high impact sports (such as running, tennis, or football) or when carrying heavy loads. The forces acting upon the tibial sesamoid are most often quite a bit higher than the fibular sesamoid, making this bone more likely to be injured. However, if a person has a hallux adducto valgus condition (aka. “a bunion”), then the deformity of the foot and the change in hallux (big toe) position moves the tibial sesamoid out of the way of the main focus of pressure, putting significantly more strain on the fibular sesamoid.

Prolonged biomechanical stress on a sesamoid bone, often in the form of elevated pressures leading to compression of the tissues, can lead to subchondral erosion (wearing away of the bone just below the joint cartilage) or fracture of the bone. This is more likely to occur in the tibial sesamoid due to its location and size, and is common in persons with a hallux limitis condition (not enough upward bend in the big toe) with either a rigid- or semi-rigid plantarflexed 1st ray.

When a sesamoid injury occurs, there may be limited dorsiflexion (bending upward) of the big toe as well as pain in the 1st metatarsal-phalangeal joint during this movement. I will now give a little more information about 4 types of sesamoid injuries in the foot:

  1. Peri-sesamoiditis: this is sometimes called just “sesamoiditis”, but “peri-sesamoiditis” is probably a better term, as it is the tissues surrounding the sesamoids that becomes injured in this condition. Repetitive stress and compression of the sesamoid and the 1st metatarsal-phalangeal joint can lead to inflammation of the structures around the sesamoids, causing conditions such as tendinitis of the flexor hallux longus (in the area beneath the 1st metatarsal-phalangeal joint), sesamoid bursitis, synovitis (inflammation of the synovial membrane of the joint), chondromalacia (abnormal changes to the cartilage). Treatment for this condition can include conservative options include therapeutic insoles, padding, and footwear changes to offload the affected sesamoid.
  2. Sesamoid Stress Fracture: high and ongoing levels of impact/compression stress can lead to a stress fracture of a sesamoid. This happens more frequently in people who run, play tennis and other court sports, and dancers. A plain X-ray 3 weeks after injury may show that the sesamoid is fractured. If a person has multipartite sesamoids (sesamoids of more than one part), then this can make a clear diagnosis more challenging. Sometimes a CT scan or bone scan may be needed to diagnose a sesamoid fracture, as it isn’t always easy to see these on an X-ray. Sesamoid fractures are often treated by below knee casting for 6 weeks followed by 6 weeks of protection using a special shoe (such as a surgical shoes or Cam walker) or running shoes with plenty of cushioning (not hard dress shoes or high-heels…sorry). In-shoe orthoses (insoles) are also advised to ensure healing and avoiding a delayed recovery, repeated injury, non-union fracture, or avascular necrosis (tissue death). Surgery is indicated in cases where the sesamoid is not healing properly.
  3. Acute fracture: occurs in dancers and sometimes other sports. X-rays can pick this up immediately due to the clearly defined borders of the fracture. Similar care is provided as for cases with a stress fracture. However, if the sesamoid (usually the tibial sesamoid) has been displaced, then surgery will be required to resolve this condition if it does not respond to conservative care.
  4. Chondromalacia of the sesamoid: if the synovial membrane is inflamed for a long time (chronic synovitis), this can lead to “freezing” of the sesamoids. The tissues surrounding the sesamoids and the joint capsule become more fibrous (“fibrosis”), which means the sesamoids can slide back and forth with the movement of the flexor tendon, reducing the range of movement in the 1st metatarsal=phalangeal joint. This causes a condition called “hallux limitus”, and eventually, “hallux rigidus” (no dorsiflexion in the big toe). Immobilising the foot, physical therapies, orthotics, and NSAIDs (non-steroidal anti-inflammatory drugs, such as ibuprofen) are required, and aggressive treatment called for if the person wants to avoid complications.

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