High Tibial Osteotomy – TKA Implications
First thing: the skin incision
– if there are multiple longitudinal incisions, pick the most lateral one
– if there is a transverse incision, can cross it at 90o.
– try not to create sharp flaps
– try to maintain an 8 cm bridge between a midline incision and the lateral one
Then, the exposure: patella infera will make patella difficult to evert and proximal tibia difficult to expose
– be prepared for rectus snip, quadriceps turndown, or even tibial tubercle osteotomy
– be prepared for a tougher time exposing around the tibia and doing the soft tissue releases laterally
Then, the hardware – you must consider how you are going to expose it and take it out; are you going to get it through the TKA incision, or get it through its previous incision
Then, the tibial cut:
– the coronal alignment is in valgus, so unlike the usual varus knee where you take more bone off laterally, in this case you’re going to take more bone off medially.
– the sagittal alignment must also be considered – normally there is a 10 degree posterior slope – but you don’t know if they took this into account when doing the HTO. Make sure you check on the lateral to see what the posterior slope is and make your cut accordingly.
As for the PCL:
– you might as well cut it right away to help with the exposure and plan to use a posterior stabilized. You’d be abit crazy to try keeping it. Most of it’s tibial insertion will be cut away anyways.
And finally, the tibial truncation
– with the tibia being cut proximal to the tubercle, there inevitably ends up being some “truncation” or “overlap” such that the tibial plateau is not quite centered over the tibial metaphysis. You need to accommodate to this with an offset stem if possible, and use an extramedullary guide when lining up the cut.