Hallux valgus, commonly known as a bunion, is a progressive deformity of the foot that causes the big toe to deviate toward the second toe. The primary goal of surgical correction is to relieve pain and restore the foot’s proper mechanical alignment. This involves a series of carefully planned procedures to address the underlying structural and soft tissue abnormalities, rather than simply removing the visible bump.
Understanding the Hallux Valgus Deformity
The condition is characterized by two main structural changes at the base of the big toe, called the first metatarsophalangeal (MTP) joint. The big toe (hallux) shifts laterally, while the first metatarsal bone shifts medially. This misalignment is often referred to as metatarsus primus varus, where the first metatarsal spreads out from the others. The visible “bunion” is the head of the first metatarsal bone jutting out on the inner side of the foot. Chronic friction from footwear over this prominent bone can lead to the formation of an extra bony growth, known as an exostosis.
Addressing the Bony Prominence
The most direct answer to what is removed during hallux valgus surgery is the bony prominence, or exostosis, on the medial side of the metatarsal head. This procedure, sometimes called a bunionectomy, involves shaving off the excess bone to create a smooth contour. A surgeon uses a specialized burr or saw to resect the hypertrophic bone that causes the painful bump against shoes. Removing this lump reduces friction and swelling at the joint, which is a major source of discomfort. However, simply removing the bump alone, without correcting the underlying bone misalignment, is usually reserved for very minor deformities, as the deformity would likely recur.
Realignment of the Structural Bones
The core of hallux valgus correction involves surgically altering the position of the misaligned bones, a procedure known as an osteotomy. This means the surgeon cuts the first metatarsal bone to shift the head of the bone back into a proper position relative to the big toe.
For milder deformities, a cut might be made near the head of the metatarsal, such as in a Chevron osteotomy. More severe deformities often require a cut further back, closer to the midfoot, or a Z-shaped cut along the shaft of the metatarsal, like the Scarf osteotomy, to allow for greater correction.
The bone is not removed entirely; instead, a measured cut is made, the fragments are repositioned, and then stabilized in the new alignment. This repositioning corrects the angle between the first and second metatarsals, a key measure of the deformity’s severity. The newly aligned segments are fixed with small screws or plates, which remain permanently to allow the bone to heal correctly. In some cases, a wedge of bone may also be removed from the phalanx to finalize the straight alignment.
Soft Tissue Balancing
The structural correction of hallux valgus also requires altering the soft tissues, including the tendons, ligaments, and joint capsule. The deformity causes the soft tissues on the lateral (outer) side of the joint to become tight, while those on the medial (inner) side become stretched and loose.
To allow the toe to be straightened, the surgeon performs a lateral soft tissue release, which involves cutting or releasing the tight structures on the outer side. This release often includes the lateral joint capsule and the tendon of the adductor hallucis muscle, which is a significant deforming force pulling the toe out of alignment.
Conversely, the loose tissue on the inner side must be addressed to stabilize the correction. This is accomplished through a medial capsular plication or imbrication, where the stretched joint capsule is tightened with sutures. Releasing the contracted structures laterally and tightening the stretched structures medially rebalances the soft tissue envelope. This comprehensive approach to both bone and soft tissues is necessary to hold the big toe in its corrected position and prevent recurrence.