Hallux valgus, commonly known as a bunion, is a deformity where the big toe joint shifts outward, causing the first metatarsal bone to angle away from the other toes. This misalignment creates a prominent bony bump on the inner side of the foot. Surgical correction for this condition is not merely a cosmetic removal of the bump, but a complex procedure aimed at structurally realigning the entire joint to restore proper foot mechanics.
Removal of the Bony Prominence
The most visible part of the deformity, the bony bump on the side of the foot, is called the medial eminence. This prominence is removed through a procedure known as an exostectomy or bunionectomy. The surgeon uses a surgical saw or a chisel to carefully shave off this excess bone from the head of the first metatarsal.
While this step directly addresses the painful bulge that rubs against footwear, it is rarely the only component of the surgery. An isolated exostectomy corrects the symptom but leaves the underlying structural misalignment unaddressed. Consequently, the toe may drift back into the deformed position over time. The removal of the medial eminence provides access for the deeper, corrective procedures on the bone and soft tissues.
Bone Reshaping for Alignment
The core of hallux valgus surgery involves cutting and repositioning the misaligned bones, a procedure known as an osteotomy. This step is necessary to correct the abnormal angle between the first and second metatarsals, which is the true cause of the deformity. Bone is not simply removed; rather, precise surgical cuts are made to shift the bone segment back into proper anatomical alignment.
For milder to moderate deformities, the cut is typically made near the end of the metatarsal, close to the big toe joint. A common technique is the Chevron osteotomy, where a V-shaped cut is made in the metatarsal head. The head is then shifted laterally and secured to narrow the foot and push the big toe into a straight position. For more severe deformities, a mid-shaft cut, such as the Z-shaped Scarf osteotomy, or a cut closer to the ankle, may be necessary to achieve a greater degree of correction.
In some cases, an additional osteotomy may be performed on the proximal phalanx. This procedure, like an Akin osteotomy, involves removing a small wedge of bone from the toe to help straighten the joint. After the bone segments are shifted, they are fixed in their new position using specialized hardware. Small screws, pins, or plates are inserted to hold the realigned bone firmly until healing is complete. This fixation hardware is generally left in place permanently.
Soft Tissue Balancing and Release
Effective hallux valgus correction requires more than just realigning the bones; the surrounding soft tissues must also be balanced. The forces that keep the toe misaligned are created by contracted ligaments and tendons around the joint. Specifically, the soft tissues on the outer (lateral) side of the joint become tight and contracted.
During the surgery, a lateral soft tissue release is performed. This includes the lateral joint capsule and the tendon of the adductor hallucis muscle, which is a major deforming force. Releasing these contracted elements allows the surgeon to move the big toe and the first metatarsal head back into a neutral position without excessive tension.
Conversely, the joint capsule on the inner (medial) side of the foot often becomes stretched and lax. To stabilize the correction, the surgeon will tighten the medial capsule through a procedure called capsulorrhaphy or imbrication. This combination of releasing the tight lateral structures and tightening the lax medial structures maintains the stability of the joint.
Joint Surface Removal in Severe Cases
For patients with severe hallux valgus, especially those with advanced arthritis or significant joint damage, the strategy shifts from realignment to fusion. This procedure, known as arthrodesis, involves permanently fusing two bones together to create a single, stable unit. The most extensive form of “removal” in this context is the complete removal of the joint surfaces.
The surgeon removes the articular cartilage from both the head of the first metatarsal and the base of the proximal phalanx. Removing all of the cartilage ensures that the two bones can grow together, or fuse, permanently.
The fused joint is then held in the correct anatomical position with internal fixation, such as plates and screws, until the bones heal together. This fusion eliminates movement in the joint and provides stability. The Lapidus procedure is a similar fusion technique used further back in the foot for patients with excessive instability in the midfoot.