Bunions result from abnormal foot structure, specifically a deformity in the joint of the big toe called hallux valgus. This leads to changes in the structure of the joint and other areas of the foot. However, the exact cause of the deformation and development of bunions is not clear.
There appears to be a strong genetic link, suggesting that genetic inheritance of a certain gene may be involved as a causative factor. There are also other proposed causes of bunions, including certain health conditions, daily activities and ill-fitting footwear. Each of these is discussed in more detail below.
Individuals with a family history of bunions are more likely to develop bunions and a high proportion of people with bunions also have close family members that suffer from the same condition.
These observations suggest that the inheritance of a genetic mutation may be a significant determining factor for the likelihood of an individual to develop bunions. However, genetic inheritance is not believed to be the sole cause of bunions and some people with bunions are not aware of any family members with the condition. The specific gene mutations and inheritance pattern of bunions is currently unknown.
Abnormal Foot Structure
The structure of the foot and support to the toe joints is important for the foot to function properly and abnormal foot structure has been linked to increased risk of bunions. This includes:
- Flat feet
- Loose ligaments
- Flexible joints
- Low muscle tone
- Abnormal bone structure
There are several health conditions that result in changes in these characteristics of the foot (e.g. Marfan syndrome and Down’s syndrome) which are covered in more detail below.
Arthritis of the Feet
There are several types of arthritis of the feet that are associated with bunions, including rheumatoid arthritis, psoriatic arthritis and gout. Each of these involves pain and inflammation in the lining of the peripheral joints and may lead to a deformity in the bone of the joint, thus causing bunions.
Arthritis and bunions are closely related and both conditions have the potential to cause the other. Arthritis can lead to the presentation of bunions and, conversely, a complication of bunions is arthritis.
Other Health Conditions
Some neuromuscular conditions such as cerebral palsy, Charcot-Marie-Tooth disease and multiple sclerosis may also increase the risk of bunions. This can affect the movement and nervous activity in the feet, and have the potential to cause damage to the toe joint.
Additionally, disorders of the connective tissue such as Marfan syndrome and Down’s syndrome can contribute towards the development of bunions. These genetic conditions are associated with changes in the connective tissues that may weaken the support for the joint, predisposing and individual to bunions.
Anyone can develop bunions but they are more common in women than men. Based on this observation, it has been suggested that ill-fitting shoes that are more commonly worn by women, such as those with a pointed toe or high heel, may be a risk factor for the development of bunions. However, it is not clear if this causes the condition or worsens an existing structure abnormality.
Shoes that are thought to be particularly harmful to the structure of the include shoes that are tight fitting, high heeled or have a pointed toe.
Extended Periods on Feet
Finally, spending long periods of time standing up has also been linked to worsening of bunion symptoms, although this is not thought to be a primary cause of the condition.