Hammertoe

Causes

The most common cause of hammertoe is the long-term use of poorly fitting shoes. Shoes that narrow toward the toes, have high heels, and are too small are the common culprits. Shoes that narrow toward the toes cause crowding of the smaller toes and push them into a flexed (bent) position. The condition can be aggravated by the feet rubbing against the small toe box, and this can lead to the formation of corns and calluses. High-heeled shoes increase the pressure placed on the ball of the foot and the toes. They force the toes down against the narrow toe box and increase the bend in the toe. With long-term use, the toe muscles weaken and lose the ability to straighten the toe. Risk of hammertoe also exists in children who continue to wear shoes that they have outgrown. The toes pay the price when a foot is squeezed into a shoe that is too small. Deformities can occur at both the interphalangeal joints (the joints in the toe) and the MTP joint.

While the majority of cases are attributed to poorly fitting footwear, a combination of other factors can also increase the risk of acquiring hammertoe. Anatomical problems such as a long second toe, bunions (hallux valgus), MTP joint instability, and previous toe trauma warrant attention.

• A long second toe causes shoes to fit improperly, because the toe is forced into a bent position (flexion) to accommodate the shoe. An abnormal motion of the second toe triggers excessive motion of the MTP joint, and this can lead to MTP synovitis (irritation of the joint capsule where the base of the toe connects to the foot). The joint support structures (i.e., muscles, tendons, and ligaments) weaken with abnormal motion, increasing the risk of MTP joint instability. Patients often complain of a lump at the ball of their foot and pain at the top of their foot near the base of the toes.
• Bunions present with an angulation of the big toe. The resultant pressure placed on the second toe can cause abnormal positioning and bending [Page 618]of the second toe, particularly while compressed into shoes.
• Prior trauma to a toe—such as a sprain, strain, fracture (broken bone), or dislocation—increases the risk of abnormal toe anatomy and the resultant positioning problems.

Medical conditions can also increase the risk of developing hammertoe. Studies have shown an association with connective tissue disorders, neuromuscular disease, degenerative disk disease, inflammatory joint diseases, and diabetes. Rheumatoid arthritis causes hammertoe deformity by progressive destruction of the MTP joint, leading to joint instability. Diabetics with peripheral neuropathy are prone to hammertoe because chronic nerve and muscle damage to the foot result in abnormal foot mechanics.

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