The Lapidus procedure is a surgical procedure used to treat a bunion deformity, also known as hallux valgus. It involves fusing the joint between the first metatarsal and one of the small bones in your midfoot, the medial cuneiform. Surgery includes removing the cartilage surfaces from both bones, correcting the angular deformity, then placing hardware (screws and often a small plate) to allow the two bones to grow together, or fuse. This surgery often is done to correct a bunion deformity with a very large angle, or when there is increased mobility through the tarsometatarsal (TMT) joint. When the TMT joint has too much looseness or movement, the condition is known as hypermobility or instability. When this joint becomes hypermobile, the first metatarsal moves too far in one direction and the big toe compensates by moving too much in the other direction. When this happens, a bunion can develop. 

The goal of the Lapidus procedure is to surgically treat hallux valgus that is caused by first TMT joint hypermobility. When the first TMT joint is fused, the first metatarsal will not move abnormally. This will allow the first toe to stay straight and decrease the risk of the bunion coming back.