Causes / typical injury mechanism: The causes of hammer toe and claw toe deformities can vary, but common risk factors include overuse, ill-fitting shoes, nerve and muscle damage, arthritis, and genetics.

Classic history and presentation: Patients may present with pain and difficulty walking, along with visibly abnormal bending or curvature of the affected toe(s). Hammer toe presents with a hyperflexed proximal interphalangeal (PIP) joint in any of the lesser toes, commonly affecting the second or third toe. In claw toe, both the PIP and distal interphalangeal joint (DIP) are hyperflexed. These hyperflexed joints may be fixed or mobile.

Prevalence:

• Age – Can be seen in all ages, but incidence increases with age. Hammer and claw toe deformities have a prevalence of 35% and 9%, respectively, in populations aged 65 years.
• Sex / gender – Roughly equal prevalence in men and women. May have slightly higher female prevalence in some samples, due to higher rates of small joint osteoarthritis.

Risk factors: Risk factors for deformity of the lesser toes includes overuse, ill-fitting shoes, nerve and muscle damage, arthritis (particularly rheumatoid arthritis), and genetics.

Pathophysiology: Hammer toe and claw toe deformities are caused by a combination of factors including muscle imbalances, joint misalignment, and nerve damage. Over time, any of these pathologies can lead to progressive subluxation of interossei muscles and imbalances in tension between the flexor and extensor tendons of the lesser toes. This can lead to permanent bending of the toe(s) and difficulties with walking.

Grade / classification system: Lesser toe deformities can simply be classified as fixed or nonfixed. There is no commonly used or universal grading system.