Total Knee Replacement in the Valgus Knee
– everyone seems to have differing ideas about what needs to be released
– Whitesides (CORR, October 1999) seems to have the most unified, organized approach to the soft tissue releases
– the soft tissues to consider: iliotibial band, posterolateral capsule, lateral collateral ligament, popliteus
1. The approach: some would argue about going laterally – all the anatomy is there, but once you’ve done all the releases, there may be nothing but skin to cover the prosthesis. Go medially. It can all be done from the medial side.
2. In the exposure, only go to mid-plateau on the medial side – don’t go stripping much farther back than that. The medial side is going to be relatively lax, and you don’t want to go destabilizing it any more than necessary.
3. Do a lateral release (the superior lateral geniculate artery is coming in at the musculotendinous junction of vastus lateralis – you can try to save it, but don’t sweat it if you cut it.)
4. Release around the lateral aspect of the tibial plateau – resect the meniscus, and cut the PCL. Even though Whitesides doesn’t cut the PCL, the valgus knee is a compelling place to do so, even for those who like PCL-retention.
5. KEY POINT – effective ligament balancing can only be done if you do the bony cuts properly. The first principle is to first make the cuts and align the components correctly so that the femoral joint surfaces are equidistant from the epicondylar axis, and the tibia is cut perpendicular to its mechanical axis. Remember – the key to doing the femur is remembering the epicondylar axis on both the distal femoral cut, and on the AP cutting block, where you dial in the external rotation of the femoral component. If you fuck up the cuts, it is unlikely that you will balance the knee.
6. When you make the cuts, use what is least destroyed/abnormal as your guide. The lateral condyle may be hypoplastic (leading to valgus) – use the medial femoral condyle to measure the distal cut. Similarly, the lateral tibial plateau may be worn away – more will then be cut from the medial side (opposite from doing a varus knee)
7. Now, once the cuts are made, you need a strategy to decide what to do. This is where Whiteside’s strategy comes in handy. He decides what is tight in flexion, and what is tight in extension, and bases the releases on that.
– the LCL and popliteus tendon attach near the axis through which the tibia rotates – if they are tight, they will be tight in both flexion and extension.
– the iliotibial band and posterolateral capsule are loose in flexion, but tight in extension
So if the lateral side is tight only in extension but not in flexion, then just release the IT band from Gerdy’s tubercle. If it is still tight, then release the posterolateral capsule completely.
But if the lateral side is tight in flexion and extension, the best place to start is by releasing the LCL and popliteus off their femoral insertions along the lateral femoral condyle. In about 50% of cases, this will be all that is required. If it is still tight in extension, release the IT band, and if still tight, the posterolateral capsule.
If the lateral side is tight only in flexion but not in extension, there is no sense in releasing the IT band – it is usually loose in flexion anyways! Instead, release the LCL, then the posterolateral capsule.