Equinus is a condition in which the upward bending motion of the ankle joint is limited. Someone with equinus lacks the flexibility to bring the top of the foot toward the front of the leg. Equinus can occur in one or both feet. When it involves both feet, the limitation of motion is sometimes worse in one foot than in the other. There are several possible causes for the limited range of ankle motion. Often, it is due to tightness in the Achilles tendon or calf muscles (the soleus muscle and/or gastrocnemius muscle). In some patients, this tightness is congenital (present at birth), and sometimes it is an inherited trait. Other patients acquire the tightness from being in a cast, being on crutches or frequently wearing high-heeled shoes. In addition, diabetes can affect the fibers of the Achilles tendon and cause tightness. Sometimes equinus is related to a bone blocking the ankle motion. For example, a fragment of a broken bone following an ankle injury, or bone block, can get in the way and restrict motion. Equinus may also result from one leg being shorter than the other. Less often, equinus is caused by spasms in the calf muscle.