A bunion, also known as hallux valgus, is a common foot condition characterized by the misalignment of the bones in the big toe joint. The misalignment causes the first metatarsal bone to move out of its normal position and angle towards the second toe, and it forms a bony bump on the joint, at the base of the big toe. This bump is what is commonly referred to as the bunion.
This misalignment can cause inflammation and degeneration of the joint and surrounding soft tissues, leading to pain, stiffness and difficulty moving the big toe. The skin over the bunion may be red and warm to the touch, and the big toe may be angled towards the second toe, which can cause additional problems such as hammertoe or other toes overlapping.
The joint affected by bunion is the metatarsophalangeal joint (MTP), it's the joint where the first metatarsal bone and the first phalanx of the big toe meet. The MTP joint is a synovial joint, which means it has a capsule that surrounds it and it's lined by a synovial membrane which produces synovial fluid, a lubricant that helps to reduce friction and wear and tear in the joint.
It's important to note that the longer the bunion is left untreated, the more the joint will degenerate and the more difficult it will be to correct with non-surgical treatment options.