What causes bunions and hallux valgus?

Bunions and hallux valgus are virtually absent or extremely rare in habitually populations. Footwear that restricts the toes or disrupts natural arch–toe movement is their primary external cause.

Research consistently associates narrow or constrictive toe boxes with hallux valgus. A recent meta-analysis found narrow-toed footwear associated with more than twice the odds of hallux valgus, while the St. Helena study found the deformity was uncommon among people who had never worn shoes. 

A bunion and hallux valgus are closely related, but they are not exactly the same.

Footwear creates the external mechanical environment, while foot mechanics, anatomy, connective-tissue mobility, genetics, age, activity and accumulated loading history influence how quickly and severely the deformity develops.

How footwear contributes

During healthy weight-bearing, the arches dynamically lower and rise, the forefoot widens, and the great toe elevates and moves in coordination with the arches.

Several common footwear characteristics interfere with this movement:

• Narrow or tapered toe boxes hold the great toe toward the smaller toes and prevent natural toe splay.

• Shallow or stiff toe boxes restrict the great toe’s ability to rise during propulsion.

• Restrictive uppers and tight lacing inhibit the dynamic rise and fall of the arches.

• Elevated heels shift more body weight toward the forefoot.

• Stiff midsoles and outsoles restrict movement through the great-toe joint and substitute an external footwear rollover for natural toe movement.

Mechanical sequence: Footwear restriction → arch collapse and excessive pronation → restricted great-toe elevation → toe-out gait → first-metatarsal rotation → mechanically focused intermittent pressure, friction and shear against the shoe upper → adaptive soft-tissue and bony enlargement forming the bunion.

Pointed or tapered toe boxes directly force the toes together, creating the greatest displacement at the great toe—the hallux valgus orientation. Hallux valgus is a three-dimensional change in the alignment of the great toe and first metatarsal. The great toe shifts toward the smaller toes while the first metatarsal and its supporting structures change position and rotation. When footwear also restricts the great toe’s ability to rise during propulsion, the body turns the foot outward to move around the restriction. This creates rotational movement at the first metatarsal and focuses repeated pressure, friction and shear where the metatarsal contacts the shoe upper. These intermittent forces stimulate the soft-tissue and bony enlargement that forms the bunion.

Arch collapse and first-ray instability

When the weight-bearing arch excessively collapses, the foot pronates and the position of the first metatarsal changes relative to the great toe. This reduces the functional stability of the great-toe joint and changes the direction from which the surrounding muscles and tendons pull.

Once the great toe begins moving laterally, those muscular forces no longer act evenly across the joint. The altered alignment becomes self-reinforcing:

1. The arch collapses and the first metatarsal becomes less stable.

2. The great toe is displaced by the shoe and changing joint forces.

3. The muscles and connective tissues adapt to the altered position.

4. The medial aspect of the first-metatarsal head presses more firmly against the shoe.

5. Repeated intermittent pressure, friction and shear stimulate adaptive soft-tissue thickening and bony enlargement. As the bunion enlarges, the increased shoe contact can also produce irritation, inflammation, callusing and pain.

Over time, a functional alignment problem becomes an increasingly established structural deformity.

Addressing bunions and hallux valgus