Hallux valgus is one of the most common disorders of the foot, and is the most prevalent disorder of the bunion. Hallux valgus is a medical term, in addition to the terms “big toe” and “big goblet crutch”. A bunion is defined as an outward deviation of the bunion, where the angle between the proximal phalanx and the first metatarsal is greater than 15°. This angle is called the bunion angle. Bunion is a morphologic diagnosis and does not correctly define the pathologic process of a bunion. (I) Pathogenesis 1. The occurrence of genetic bunion deformity is related to congenital factors, and about half of the cases have genetic factors. lake believes that 1st metatarsal inversion is the main cause of the deformity. Many patients are seen to have a narrow medial wedge shape of the 1st cuneiform, resulting in an inward tilt of the metatarsophalangeal joint. However, in the author’s group of 76 foot bunions, only 9 feet had more than 12° of 1st metatarsal inversion. According to Carr’s standard, the angle between the 1st and 2nd metatarsal bones is 9°, and only a small number of people exceeded this standard, which shows that the metatarsal inversion is not congenital. In 11 of these 76 feet, the angle of the 1st and 2nd metatarsals was reduced by 2° to 4° after McBride’s procedure, apparently due to a reduction in the bowstring-like action of the thumb extensors and thumb flexors after correction of the bunion, as well as the effect of the adductor muscle moving to the 1st metatarsal. At the same time, after the bunion, the bowstring-like action of the muscles must produce the force that pushes the metatarsals inward. 2, wearing high-heeled pointed shoes is one of the main factors in the formation of bunions, pointed shoes are triangular in the front, high heeled standing, the front of the foot is stuffed into a narrow triangular area, the hard upper forces the bunion and slightly externally rotated, the little toe inversion slightly internally rotated, the middle 3 toes proximal interphalangeal joint strength flexion, metatarsophalangeal joint and distal interphalangeal joint over-extension. 3. Various inflammatory diseases, especially rheumatoid, often result in outward subluxation due to joint destruction and bunion deformity. (B) Pathogenesis The bunion rotates outward along its long axis to turn the toenail toward the midline and continues to worsen due to tension and pulling of the long bunion extensor, long bunion flexor and bunion retractor muscles. The medial head of the medial bunion and bunion flexor muscles and their internal seed bones are displaced outward and lose their abduction role, which in turn leads to contracture of the lateral head of the bunion and bunion flexor muscles, contracture and thickening of the lateral joint capsule, outward subluxation of the bunion, enlargement of the lateral seed bones and their displacement between the 1st and 2nd metatarsal heads, bunion valgus pushing the 1st metatarsal inward, widening the transverse arch of the foot to the point where the medial metatarsal head is squeezed and rubbed by the shoe upper and bunions occur. The bunion is painful, and the 1st metatarsal head becomes larger, forming a bony flank that protrudes medially. Due to strain on the bunion muscle, the transverse arch of the foot flattens and the 2nd and 3rd metatarsal heads collapse toward the lateral end of the metatarsal, which causes thickening of the skin and formation of callus due to weight bearing and friction. The bunion turns outward, squeezes the 2nd toe, occupies the position of the 2nd toe, lifts the 2nd toe and overlaps the bunion, causing the 2nd toe to overstretch the metatarsophalangeal joint and flexing the proximal interphalangeal joint, becoming a hammer toe, protruding from the dorsal side of the bunion and 3rd toe, and the dorsal side of the proximal interphalangeal joint is rubbed and squeezed by the shoe surface, also resulting in callus pain. The bunion-plantar toe joint is in a semi-dislocated position and gradually develops osteoarthritis under prolonged abnormal stress, with narrowing of the joint space, hardening of the bone and more pain. The pathological changes of bunion are summarized as follows: (1) bunion with metatarsophalangeal joint subluxation; (2) 1st metatarsal inversion and bunion; (3) callus at the 2nd and 3rd metatarsal heads; (4) hammer toe of the 2nd toe; (5) osteoarthritis of the 1st metatarsophalangeal joint.