This review focused on the pathogenesis of hallux valgus by studying the pathoanatomy and aetiology (intrinsic and extrinsic factors) of the condition.
The first ray plays a key role in maintaining the structure of the medial arch and as the main load-bearing structure, it is subject to substantial forces during gait.
Failure anywhere along the first ray, from the distal phalanx to the talonavicular joint, can result in hallux valgus.
It is therefore worth considering the first ray biomechanics as a common factor to many of the key theories.
Morton believed that dorsal hypermobility of the first metatarsal segment was responsible for the widest array of foot deformity. However, several studies have questioned whether motion at the tarsometatarsal joint even exists.
The locus of the axis of rotation has to move in an arc that necessitates metatarsal motion proximally and plantarward in order to avoid compression at the metatarsophalangeal joint.
Prevention of this plantar flexion hinders dorsiflexion of the first metatarsophalangeal joint even when non-weightbearing.
Genetic inheritance and sex are important factors responsible for hallux valgus, but other anatomical and biomechanical factors such as anatomical metatarsal variants, including a long first metatarsal, a rounded articulation and metatarsus primus varus, play an important role too.
These variants increase the vulnerability to first-ray hypermobility, pes planus and ligamentous laxity.
The toe is at risk if loading is increased on the medial side; if the forefoot is in a narrow toe-box or pronated because of a hypermobile first ray or pes planus, the altered muscle pull can combine with the ground reaction forces and be sufficient to result in repetitive injury to the medial tissues.
It is in the interplay of the various intrinsic and extrinsic factors that come together in any one particular foot that determines the potential of these factors to become a risk factor in the development of the condition.
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