Static subluxation of the first metatarsophalangeal joint results in this abnormal foot alignment. The process begins with the adduction of first metatarsal resulting in lateral deviation of the proximal phalanx. It progresses to subluxation and eventual early osteodegenerative changes in the first metatarsophalangeal joint.
Measurements on radiography
Two measurements may be utilized to quantify the extent of deformity:
- First metatarsophalangeal angle: The angle of deviation measured ideally between the centre of head of first metatarsal and centre of proximal phalanx articular surface. Any angle more than 15 degrees points to hallux valgus deformity.
- Intermetatarsal angle: the angle between the long axis of the first and second metatarsals. Any angle more than 9 degrees is suggestive of hallux valgus.