Valgus malformation of the great toe, commonly known as a bunion, is a very common and potentially painful and debilitating condition of unclear etiology. This topic review will provide an overview of the relevant anatomy, pathophysiology, diagnosis, and management of hallux valgus. Toe and foot injuries are discussed elsewhere. (See "Toe fractures in adults" and "Metatarsal shaft fractures".)
RELEVANT ANATOMY AND BIOMECHANICS
Basic forefoot anatomy — By convention, toes and their respective metatarsals are numbered from one (great toe) through five (little toe). The great toe has two phalanges, while the second through fifth toes typically have three (figure 1 and figure 2 and figure 3). Tendons and ligaments insert at the bases of each phalanx. The digital artery and nerve pass together along each side of each toe.
●Hallux valgus deformity – This deformity is defined as a lateral deviation of the hallux (great toe) on the first metatarsal (figure 4). The deviation of the hallux occurs primarily in the transverse plane. The deformity often also involves rotation of the toe in the frontal plane causing the nail to face medially (ie, eversion). These two deviations have led to the use of different terms to describe the deformity. In orthopedic texts, it is often called "hallux valgus" (HV) whereas many podiatry texts prefer the term "hallux abductovalgus (HAV)." The public is more familiar with the expression "bunion."
●Hallux abductus (or hallux valgus) angle – The angle created by the bisection of the longitudinal axis of the hallux and the longitudinal axis of the first metatarsal (figure 4 and image 1). Historically, a hallux abductus (HA) angle of greater than 15 degrees was considered abnormal, but such deformities are not always symptomatic, and some cases of an HA angle greater than 15 degrees occur naturally due to the shape of the articular surfaces involved [1,2]. Contemporary research suggests an HA angle of 20 degrees or greater is abnormal .
●Intermetatarsal (IM) angle – The angle determined by the bisection of the longitudinal axes of the first and second metatarsals (figure 4). An IM angle less than 9 degrees is considered normal.