Osteotomy means "cutting of the bone," and a proximal tibial osteotomy refers to a specific cut that results in unloading or relieving pressure on the medial (inner aspect) of the knee joint. It is often done in the setting of a painful bow-legged deformity that has resulted in medial compartment osteoarthritis.
A wedge of bone is removed from the proximal tibia, under the healthy side of the knee. When the wedge is removed, the leg is then straightened. This results in the knee distributing weight more evenly within the joint.