Small tumors called enchondromas can sometimes form in the bone beneath the toenail.

An enchondroma is a fairly common benign tumor, which is the most common bone tumor of the hands and feet. The tumor can involve large portions of the bones, causing thinning of the cortex. This can weaken the bone and cause it to break spontaneously. When enchondromas occur in the small bone in the end of the toe, they can cause pain that may mimic the pain of ingrown toenails. Ollier's Disease, also known as enchondromatosis, frequently occurs in the small bones in the hands and toes (phalanges) and the long bones behind the phalanges called metatarsals. Maffucci's Syndrome is a very rare form of enchondromatosis associated with multiple soft tissue hemangiomas. This tumor frequently occurs in the hands and feet, and has a greater tendency toward malignant transformation than Ollier's Disease.