Hammertoe is when the middle joint in a toe bends and becomes stuck in that position. A common cause of hammertoe is a muscle/tendon imbalance resulting from structural changes in the foot over time. This most often occurs in women who wear shoes with a narrow toe box, forcing the toes against the front of the shoe and causing abnormal bending. Hammertoe can be the result of traumatic injury, or in some cases, hammertoe can be passed on genetically.