What causes bunions?

While a number of theories exist as to what causes a hallux valgus (HV) deformity and the bunion associated with it, the exact cause remains unknown. It is believed that multiple factors may be at play ⁽¹⁾ including:

1. Genetics

For the most part, the development of bunions is thought to be predominantly genetic. While bunions themselves are not an inherited condition, abnormalities of the foot’s structure which lead to their development are more typically inherited or present at birth (i.e. congenital deformities). These include:

• Structural abnormalities of the first metatarsophalangeal joints
• Excessively flexible ligaments
• Overpronation of the foot (a turning inwards during landing while walking or running)
• Low arches
• Loose joints (joint hypermobility) and tendons
• Flat feet (an inherited foot type)

2. Abnormal biomechanics

Any abnormal biomechanics of the feet typically cause instability of the metatarsal phalangeal joint, as well as muscle imbalance, making a person more susceptible to the development of a deformity such as a bunion.

If a person’s one leg is longer than the other, additional stress may lead to the development of a bunion on the big toe of the longer limb due to overpronation (rolling inward) of the foot.

3. Trauma and injury to the foot

Injuries to the foot structure (due to sprains, fractures and nerve problems) can also lead to the development of bunions in those susceptible to structural changes.

4. Various health conditions

A variety of underlying health conditions may contribute to the development of bunions. These include:

Arthritic / Metabolic conditions

• Inflammatory conditions, such as arthritis (especially rheumatoid arthritis but also gouty and psoriatic arthritis) and inflammatory joint disease as a result of the stress these place on the joints of the feet.

Connective tissue disorders

• Down syndrome
• Marfan syndrome
• Ehlers-Danlos syndrome

Neuromuscular disorders

• Multiple Sclerosis (MS)
• Cerebral Palsy
• Charcot-Marie-Tooth disease (a hereditary disorder which damages nerves in the limbs)
• Polio

5. Choice of footwear

Shoes which are tight and narrow, or fit the feet poorly, tend to worsen a developed bunion, or potentially contribute to the development of these types of abnormalities in those who have an inherited structural defect.

As such, factors which may contribute to the worsening of bunions include:

• The wearing of shoes that are tight or too small / narrow (at the toes) place unnecessary pressure on the big toes and cause the others to crowd together (forcing the toes into an unnatural shape).
• The wearing of pointed shoes (at the toes), especially if heeled.
• Prolonged periods of standing.
• Signs of arthritis in the feet.

Who is most at risk of developing bunions?

Factors which may increase a person’s risk may include:

• A hereditary tendency (inherited structural abnormalities of the feet, like flat feet or low arches, as well as an abnormally shaped metatarsal head, which may be too rounded, making the joint less stable and more susceptible to deformity).
• Abnormal formation of the structural bones of the feet (a congenital condition).
• An existing medical health condition including inflammatory disorders, such as rheumatoid arthritis (which leads to damaged cartilage within the joint), connective tissue and neuromuscular disorders.
• The persistent wearing of high heeled (these shoes tip the body position / weight forward and thus force toes to the front of a shoe), pointy toed, tight, narrow or poorly fitted shoes.
• Individuals who stand or walk for long periods of time, such as those in nursing or teaching professions.
• Individuals who place severe repetitive stress on the feet, such as dancers (particularly ballet dancers).
• Pregnant women who experience a variety of foot problems during the gestation period due to hormonal changes which can flatten the feet and loosen up ligaments.

Reference:

^{1. US National Library of Medicine National Institutes of Health. 20 October 2012. Characteristics of foot structure and footwear associated with hallux valgus: a systematic review: https://www.ncbi.nlm.nih.gov/pubmed?term=22771775 [Accessed 28.11.2017]}