Osteotomy is the surgical procedure of "Cutting a bone". It is done to correct a deformity in a bone, or adjacent to a joint, to correct a deformity of the joint. As a surgical procedure, an osteotomy must be done very accurately, to ensure that the deformity is adequately corrected, but not over corrected. It may involve removing a wedge of bone to correct an angular deformity, or cutting the bone and turning it to correct a rotational deformity.

There are two situations when an osteotomy may be done to help manage an osteoarthritic joint.

Firstly, if there is a deformity  in a bone some distance from a  joint, the deformity will cause uneven loading on the joint, resulting in secondary osteoarthritis, or degenerative wearing of the over-loaded side of the joint. An example would be as the result of a past  fracture of a long bone, e.g. the tibia in the mid shaft region, joining with a bowed or angled deformity, leading to Osteoarthritis of the knee above, or the ankle below, or both joints. If the arthritic joint is treated by a replacement prosthesis, this prosthesis would be subject to the same forces that wore out the normal knee, and will fail prematurely. Therefore it would be usual to correct the deformity with an osteotomy, either before doing a joint replacement, or simulataneously with a replacement operation.

Secondly, osteoarthritis may begin sponteneously, and wear out one side of the knee joint more than the other, leading to a knee deformity, either a bow leg, or a knock knee. This deformity in turn leads to increased load on the worn side of the joint, and accelerates the arthritic wear, and increases the pain symptoms. In selected cases, a corrective osteotomy may be done to alter the pressures on the joint. For medial knee arthritis, an osteotomy of the upper tibia is done, for lateral knee arthritis an osteotomy of the lower femur is done.

An osteotomy is done for patients with osteoarthritis(OA) localised to one side of the joint, who otherwise have good knee function (full movemment) and who are too young or active to consider a joint replacement. It is more common for this operation to be done in younger males, and the numbers of osteotomies being done is falling, as more cases are selected for a Unicompartment knee replacement as an alternative.

An osteotomy is a complex operation, with surgical saws and chisels used to make the bone cuts, with X-ray control for accuracy. The bone is stabilised with plates and screws after cutting. The recovery is prolonged, depending firstly on healing of the bone, and later on regaining joint function. Recovery from an osteotomy can take 3 to 6 months. The symptomatic improvement in pain after an osteotomy will deteriorate after about 10 years, as the joint wears out further, and then a joint replacement will be done. An osteotomy will have "bought time" for a young arthritic patient, delaying the timing of a knee replacement, this is important, because if a joint replacement is done in a younger paerson, the likelihood of wearing the joint replacement out is high.