Prior to surgery, alignment X-rays are taken and entered into a computer programme, which calculates the amount of realignment required on each bone. What we have found since using the computer to plan our osteotomies it is not as straightforward as a lot of surgeons believe. They look at the long leg X-rays of the knee so they draw the lines on the X-rays using the old fashioned Miniacci technique, connecting the centre of the hip to the centre of the ankle. In varus mal-alignment that line will be going through on the medial compartment of the knee. They want to shift that weightbearing line into the lateral compartment. So they draw that in on the long leg film and then calculate a correction angle from that. And that is how surgeons have been planning their osteotomies for ages.
What this manual calculation technique doesn’t really do is that it doesn’t tell us where the deformity is. Some of the deformity may be in the femur and some of the deformity may be in the tibia, or all of the deformity may be in the tibia (the most common) or all of the deformity may be in the femur.
The newer computer software identifies exactly where the bone cuts need to be made, the exact amount of correction required and the relative contribution of the tibia and femur to the deformity. The image on the left shows the long leg X-ray with the computer generated marks where the bone cuts need to be made.
The most common type of osteotomy carried out around the knee is on the upper shin or proximal tibia. This is called a High Tibial Osteotomy or HTO.
The operation involves cutting the shin bone (tibia) just below the knee joint via either the opening wedge or closing wedge techniques that I went though in Part 1e of this course. The image on the right of an opening wedge high tibial osteotomy fixed with the Tomofix plate is reproduced with the permission of Synthes.
An opening wedge osteotomy involves making a single cut in the tibia and creating a gap, which in time heals with new bone. A closing wedge involves making two cuts and removing a wedge of bone to allow realignment of the tibia, while the two cut surfaces which are touching one another heal together by bony union.
The gap in this film shows up pale and the plate is dark. Usually in an X-ray it is the other way around, but the shades here have been reversed.
Distal femoral osteotomy is carried out at the bottom of the thigh bone. It is a procedure performed for treatment of lateral or outer compartment arthritis and is carried out in patients with knock-knees. It usually employs the closing wedge technique at the bottom part of the femur (thigh-bone), thereby straightening the leg and taking the pressure off the arthritic lateral (outer) compartment. A plate is used to fix the osteotomy at the end of the operation. The image on the right of an opening wedge distal femoral osteotomy fixed with the Tomofix plate is reproduced with the permission of Synthes.
Now the most common scenario with valgus lateral compartment osteoarthritis or damage is that the deformity is in the femur in the lateral compartment and they are in valgus. They say “It hurts on the outside of my knee” so you want to var-ise them and take the weighbearing line into the medial compartment. You do that by doing an osteotomy on the femur.
There are two different ways of doing it –
The femur is such a big bone it is asking a lot of any one plate to actually hold a gap open and get it to fill in with new bone - this isn’t the case in the tibia. There is a very new and extremely accurate jig which allows the surgeon to cut the bone to within a fifth of a mm of the desired amount, and although it is committing yourself surgically (inasmuch as once you have taken the wedge of bone you can’t change it) we are very confident in the software and in the new jig. Also, you achieve bone-on-bone apposition on the femur, which offers the best chance for bone healing. So we tend to do a closing wedge on a femoral osteotomy rather than an opening wedge, although sometimes we do perform an opening wedge on the lateral side.
Sometimes we need to do a combination of osteotomies – one on the femur and one on the tibia to actually correct the deformity in both areas, and that is a big operation but it is not that uncommon to do a double osteotomy in the same operation. Usually we do the tibia first and then we move onto the femur, and if you are very experienced in osteotomy surgery you can do it in the reverse and use the bone cut from the closing wedge on the femur and then pack that bone into the gap of the opening wedge of the tibia.