One of the problems with knee osteotomy is that it had a bad reputation in the past.
It used to be an operation very commonly performed in the UK, where it was done as the only surgical alternative to knee replacement. In fact it was the predecessor to knee replacement surgery, so before we had knee replacements all we could do was osteotomies.
The procedure was very crude – you took an osteotome (chisel), you took out a wedge of bone from the outside of the tibia, move the leg over and initially nothing was used to hold the new position other than plaster. Later on, metal plates or staples were used to secure the bone in the new position, but these were not strong enough to permit early walking. Patients were therefore put in plaster and told not to walk for six weeks, and even though the bone usually healed, patients did not go on to have good knee function. So the original popularity of the procedure gradually declined. In my training I always wanted to do knee surgery and even though I worked for some top knee surgeons, I only saw two or three osteotomies in six years of my registrar training.
These more sophisticated techniques enable the surgeon to carry out meticulous pre-operative planning. The patient has a series of long-leg X-rays and these are then entered into a computer system that works out the angles of the hip, the knee and the ankle. Then by looking at the computer images, the surgeon can plan exactly where he wants to put the weight-bearing line (which I discuss later in this course), and that computer programme then gives him a figure which he takes to the operating theatre. Here, using an image intensifier - which is a type of X-ray machine - wires are placed at the appropriate position across the tibia or the femur. Then the tibia or femur is realigned to exactly the right degree to the nearest millimetre or half-millimetre.
The way the TOMOfix is designed is that you have three screws at the top that lock into the top of the tibia, and then you have four screws below the osteotomy and finally you have one important screw that virtually sits in the osteotomy or preferably just above it. And for people under 60kg Synthes have developed a small low profile form of TOMOfix (specifically aimed at the Far Eastern market). The PEEK Plate by Arthrex is based on this, and is much smaller plate with fewer screws (see the box on the right below).
The double screw-hole is based around the idea of a locking plate. Before, our plates for fixing fractures just had simple screw holes and they were eccentric, meaning you could position the screw slightly differently and by doing so make the bones move apart needlessly.
In this photo the screws are all locked in. You can see the osteotomy site quite clearly. The very first screw below the osteotomy site you sometimes need to move into the non-locking position to actually pull the shin back onto the plate again to reduce it perfectly.
If you put one screw in at one edge and you place another screw at the other side of the fracture eccentrically, by tightening the screw the plate and screw can pull the bone in a certain direction. You can just move it very very slightly to actually close up a fracture and compress it. So basically we had these simple holes that were slightly eccentric so that you could alter the position of the screw within it slightly, but basically it was just a hole. And the TOMOfix is a locking plate so the screw actually locks into the plate itself. Each screw hole can be used for both locking and for non-locking.
So if you want to reduce a fracture and actually get the fracture fragments to move towards the plate, you have the non-locking option, so you just use a single screw. But if you really want to get a rigid fixation you use the locking option. It has that option at every single hole, so you can use the one or the other. We tend to lock all of them but there is a very clever trick that we use in the first hole below the osteotomy site – basically when you make the osteotomy you aim to sort of bring your cut not quite the full way across – so if you are doing it from the medial side you go almost all the way across and you stop approximately 5 mm short of the lateral cortex, and by doing that you create this hinge point. You don’t want to break through though.
Previously, if you broke through the other side of the bone (lateral cortex), that was a major complication and tricky to make right. The osteotomy construct would fall apart and the bone fragments would lose their position. With the new TOMOfix plate we can actually reduce the bone back onto the plate by using what we call ‘the golden screw’, which is a non locking screw. We can place this screw into the first hole below the osteotomy and we substitute it later in the operation. So if during the operation we break through the other side of the tibia (lateral cortex) and the tibia slips slightly, that can be relatively easily fixed by using a reducing screw to move the tibia back into the ideal position. That is the main purpose of the non-locking holes in the plate. All we have to do at the end is change that non-locking screw for a locking screw.
Once the osteotomy has been opened to our set level, the laminar spreaders are used to maintain that position and the plate is placed on the tibia. Once the ideal osteotomy gap is achieved the plate is safely secured with locking screws above and below the osteotomy, the laminar spreaders are removed and the wound is closed.