Typically, bunions begin as a bump or outward bend of the big toe that is only a cosmetic concern. However, the misaligned, outward-bending toe stretches the ligaments that connect the foot bones and pulls against the tendons, gradually drawing the toe farther out of line. Over time, the big toe continues to twist until it no longer lines up properly with its corresponding metatarsal and the end of the metatarsal may become enlarged.
Pressure from the first toe can result in deformity of the metatarsophalangeal joint in the second toe, pushing it toward the third toe. In some cases, the second toe may ride over or under the big toe. At this point, the range of motion in the big toe is decreased, which is a condition called hallux limitus.
The condition becomes painful at this stage. The bunion changes the shape of the foot and the biomechanics of walking become altered. Normally, the big toe can bend at least 65 degrees, enabling it to be the last part of the foot to leave the ground during walking. However, with hallux limitus, the big toe cannot function properly and the body weight is transferred to the bunion.
Painful bunions cause the patient to compensate by walking in an exaggerated toe-turned-out manner, so the painful hallux does not have to bend as far. Walking with the feet turned out steadily forces the hallux even farther out, worsening the condition. Without treatment, the deformity eventually becomes disabling.