This is a type of joint preservation surgery meant for the aging varus or bow leggedd knee in which the medial compartment on the inside has osteoarthritis and the other parts in the front and the outside remain intact. 

This surgery aims to unload the degenerated part of the knee and shift the weight to the undegenerated surfaces of the knee.

For patients with mild osteoarthritis who are bowlegged with lateral weight-bearing surface still intact, arthroscopic examination will be done to confirm that the lateral compartment is still under generated before commencing with the osteotomy.

Normally the axis of weight-bearing in the knee should be in the middle of the knee as shown by the green line. Abnormal weight-bearing is shown by the red line in the inner medial compartment of the knee. 
The osteotomy is performed in the proximal tibia and the medial open wedge gap will be created and fixed in place with a plate and screws.
 
After the osteotomy is done, it is confirmed intraoperatively that the weight-bearing line is shifted to the midline of the knee.
 
The bone gap created will heal on its own and new bone formation will occur.