What causes bunions?
Bunion: Hallux Valgus Deformity
Each toe is made up of bones called phalanges (singular, phalanx) connected at their interphalangeal joints. The big toe has two and each of the other toes have three. The first bone of the big toe (its first phalanx) is connected to a bone in the ball of the foot at an angle. This angle is small (<20°), such that the big toe’s general appearance is almost straight. There are no muscles that attach to this bone in the big toe to hold it at the proper angle when stressed by forces of habit, footwear, etc. If it pivots >20° over time toward the outer edge of the foot, toward the second toe, this pushes its joint out to the side and the visible lump there can swell from inflammation as what is popularly called a bunion.
This pivot or sliding outward at its joint–the first metatarsal-phalangeal (MTP) joint–also involves the whole big toe rotating toward the inner side of the foot. The medical term for these two conditions that are a bunion is a hallux valgus deformity.
Causes of Bunions
Depending on age, 23-36% of people have it, twice as commonly seen in women as in men. This and the fact that barefoot populations suffer from it less (but still get it) makes footwear, especially ill-fitting footwear, a likely contributor to an underlying bone or foot condition which is its main cause. Other causes may be unusual demands on the feet, as those from ballet foot positions, but because the true cause is a bony or mechanical abnormality, these contributing factors have not been conclusively proven.
Signs and Symptoms
The first MTP joint, where the big toe deviates and pivots, can have a number of complications that range from mild to severe. Technically, a bunion is an arthritis (inflammation of a joint), and it can present with
- Bursitis (inflamed covering over the joint): The most common symptom
- Synovitis: Inflammation in the synovial fluid of the MTP joint
- Cartilage degeneration: Over the bone under the big toe (metatarsal)
- Erosion of the bony parts that undergo friction
- Nerve entrapment: Entrapment of nerves that pass through the enlarged, inflamed bunion
- “Hammertoe”: Deformity of the second toe from the pressure from the deviated big toe
- Splinting pain in the rest of the foot: Pain to normal areas that are abused by the shifting of weight to avoid bunion pain
Complications of Bunions
Besides the bursitis, synovitis, pain, and further anatomical deviations initiating from the big toe’s displacement (e.g., hammertoe), complications are from associated injuries that arise from changes in weight-bearing when suffering from a bunion. Calluses and pressure sores can form due to the shifting of the weight burden; they can become infected. The way a person walks can be affected from this adjustment of stance or from the altered walking and in the elderly may contribute to balance problems or falls, which have their own additional morbidity and even mortality.