When surgically tackling complex issues in the knee, attention to alignment is often key to a successful outcome.
We can use the procedure of re-alignment osteotomy to -
- unload damaged areas in the knee
- re-tension ligaments
- improve movement, and
- as an adjunct to other procedures
With osteotomy, and especially complex osteotomy, everything is about planning. The techniques one can learn very easily, but the one step that the surgeon must not overlook is pre-op planning. The key is knowing the angles, understanding how to make a plan. We have these very nice trauma software packages that allow us to do 'virtual' osteotomy surgery before we carry out the procedure - to calculate where the deformity is and operate in the correct bone. We can simulate the osteotomy and even simulate the plate being placed.
Distance between the mechanical axis (yellow) and the anatomical axis (blue) on one side is 15 mm, indicating that that side has a varus deformity.
|In our planning we do a deformity analysis. If, for example, the mechanical axis deviation is medial more than 15mm, then there is a varus deformity. In that case, if the MPTA is small, which it usually is 80% of the time, the surgeon should do a tibial correction. If the LDFA, however, is big, the surgeon should do a femoral varus correction. And the same applies on the lateral side for a valgus deformity - most of the time the LDFA is small or reduced and we will carry out a femoral osteotomy, but 20% of the time we will need to carry out the osteotomy in the tibia.|
So 'which bone?' is crucial. Varus does not mean that the problem is definitely in the tibia. Valgus does not mean that the problem is definitely in the femur. It is really important that we follow the rules. Poor planning leads to a poor outcome.
Sometimes there is a problem in both bones. Or the amount of correction is too great to do the whole procedure on just the one bone. A double-level osteotomy means that some of the correction is made in the femur at the same time as some of the correction is made in the tibia. The plates can be put in through very small incisions with minimal disruptions to the soft tissues, and with this minimally invasive approach patients can do very well.
Bilateral Simultaneous Osteotomy
Doing an osteotomy on both sides at the same time is a rehabilitation challenge for the patient. However, I think with the advances that we have made in minimally-invasive osteotomy surgery - particularly with the use of a femoral head bone wedge - and with the accurate pre-operative digital planning that we are doing, the use of a GameReady cryotherapy device, together with the different types of anaesthetic that we use in terms of spinal and large volumes of local anaesthetic in and around targeted areas, we can achieve an operation that previously was very painful and leave the patient to rehabilitate with very little pain.
So what about changing the slope? Really we learn a lot in orthopaedics from other specialities - the dentists and also the vets. And the vets have taught us that changing the slope in dogs can sort out their cruciate issues, and we have heard some great talks already touching on this in terms of changing the sagittal plane. So we want to flatten for an ACL and create a slope for a PCL, and with this alone we often don't need to add in any further procedure.The magic figure is said to be around about 10-12 degrees in terms of where our cut-off is for doing slope-changing. We have these 'intelligent' plates - we are going to hear more about this from Andreas - this is his PEEK plate which is very clever for combined ligament surgery because of the multi-dimensional nature of the top three screws that allow you to put your screws where you want them so that you can carry out your ligament surgery in combination.
What about changing the slope from the front? This is an interesting concept. What we do is a 'virtual' osteotomy - we plan out the hinge point, we plan out where we would do our tubercle osteotomy, how big we were going to open the osteotomy and then we use a femoral head allograft and again simulate that in terms of what we are going to do. And then the really clever bit is using the tubercle as the plate. So the tubercle goes on at the front and all you do is fix this with is a series of screws.
A benefit of osteotomy is the the corrective surgery does not involve the actual knee joint. But there are times when it is necessary to involve the joint itself. In particular, bad fractures of the tibial plateau may require that we free and elevate a depressed portion of the plateau.