Osteotomy is a medical term meaning 'to cut a bone'. High tibial refers to its location, just below the knee joint. So this operation's name pretty well describes what happens. But why cut the bone?
Osteotomies are done to change the alignment of a bone and hence the angle of a joint. If your knee is bow-legged, you are taking all of your weight through the inside half of your knee. This leads to much greater rates of wear and much more pain. A high tibial osteotomy aims to straighten out your leg to evenly share the load between the inside and outside of your knee.
The are two main types of osteotomy for knee osteoarthritis. Opening wedge and closing wedge.
In an opening wedge, a cut is made in the tibia and the two sides are separated. The wedge shaped space is filled with a bone graft.
In a closing wedge, two cuts are made and a wedge shaped piece of bone is removed. The two edges are then brought together creating the desired change angle.
Both types of operation then require the bone to be fixed, usually with a plate and screws.
A high tibial osteotomy does not make the joint unworn so is looking to decrease pain rather than completely relieve it. The operation is seen as a way of delaying a total knee replacement in those considered too young. It is not suitable for everyone so individual cases need to be discussed with your surgeon.