The Science of Hallux Valgus (Bunions)

Hallux valgus represents a complex three-dimensional deformity of the first ray involving lateral deviation of the hallux at the metatarsophalangeal joint, medial deviation of the first metatarsal, and pronation of the hallux. This progressive deformity results from a combination of intrinsic structural abnormalities and extrinsic environmental factors that disrupt the normal biomechanical balance of the first ray. The deformity typically begins with attenuation of the medial joint capsule and stretching of the medial collateral ligament, allowing progressive lateral drift of the proximal phalanx. Simultaneously, the first metatarsal deviates medially (metatarsus primus varus) due to the unopposed pull of the peroneus longus tendon and weakness of the tibialis anterior insertion. As the deformity progresses, adaptive changes occur throughout the first ray. The sesamoid complex becomes displaced laterally relative to the metatarsal head, creating a mechanical disadvantage for the flexor hallucis brevis and intrinsic muscles. The extensor hallucis longus and flexor hallucis longus tendons develop a bowstring effect, actually accelerating the deformity progression rather than providing corrective forces. The bursa overlying the medial eminence frequently becomes inflamed due to shoe pressure, creating the classic painful bunion presentation. Secondary arthritic changes develop within the metatarsophalangeal joint as the joint surfaces become incongruent. The altered mechanics also affect the entire forefoot, often leading to transfer metatarsalgia, lesser toe deformities, and compensatory gait changes that can affect the entire kinetic chain.