What’s the difference between an open wedge and a closed wedge osteotomy? The surgeon explained it to me, but I don’t think I caught it all on the first go-round.

The osteotomy procedure is most often used for patients who have osteoarthritis in only one side of their knee joint. The operation helps realign the knee joint and shifts the weight off the load bearing side. This operation may increase the life span of the joint and prolong the time before a knee replacement surgery becomes necessary.

There are two methods to realign the knee joint. One involves taking out a wedge of bone; the other involves adding a wedge of bone. In a closing wedge osteotomy, the surgeon cuts though the tibia (lower leg bone) on the lateral side (side of the leg away from the other leg). A pie-shape or wedge of bone is removed. Pins or a metal plate and pins are used to close the open edges back together.

In an opening wedge osteotomy, the surgeon cuts though the tibia on the medial side (side closest to the other knee) and opens a wedge, adding a bit of bone graft to hold the wedge open. The bone graft is usually taken from pelvis bone, through an incision in the side of your hip. The bone graft is held in position with a metal plate or pins.

In either procedure, care is taken to protect the nerves and blood vessels that travel across the knee joint. The surgeon uses either X-rays or a fluoroscope, a special kind of X-ray machine that casts images on a fluorescent screen, to make sure the wedge is the right size and is placed correctly.