Category M21.6, Other acquired deformities of ankle and foot, has been expanded to specifically identify bunion of right foot (M21.611), bunion of left foot (M21.612), and bunion of unspecified foot (M21.619). Prior to this change, bunion was an inclusion term at code M20.1, Hallux valgus (acquired). In addition, a new subcategory and new codes have been created to describe bunionette (tailor’s bunion). The new codes include bunionette of right foot (M21.621), bunionette of left foot (M21.622), and bunionette of unspecified foot (M21.629). Bunionette was previously not uniquely identified in ICD-10-CM.
A bunion is an unnatural, bony hump that forms at the base of the big toe. Often, the big toe will begin to lean towards the other toes. When this occurs, the base of the big toe pushes outward on the first metatarsal bone, forming a bunion. A bunionette, or tailor’s bunion, develops at the base of the little toe. This occurs when the toe (metatarsal) bends away from the foot, the little toe bends inward and the joint swells or enlarges. Because a bunion occurs at a joint, the entire body weight rests on the bunion at each step which can be very painful. A bunion deformity does not involve any overt positional movement of the first metatarsal or of the hallux. If such movement did occur, with associated hypertrophy of the medial condyle of the first metatarsal head and related edema and bursitis, then that deformity would be a hallux valgus deformity (M20.1-).