Approach to Revision Total Knee Replacement
– make sure you have a diagnosis! First of all – is it septic failure or aseptic failure?!??!!
– Aseptic Loosening: Failure of fixation? Malalignment? (varus is the most common malalignment leading to loosening and failure) or Polyethylene wear and osteolysis? (these three are not mutually independent)
– make sure you know how much and how big the osteolysis is
– Instability – why is it unstable? MCL or lateral ligament insufficienty? Poor tension on PCL?
– Stiffness – why is it stiff? Flexion/extension mismatch? Patellofemoral joint overstuffed?
1. Start with a diagnosis.
2. Get good exposure
3. Remove the prosthesis with minimal destruction of remaining host bone
4. Debride soft tissue and bone of cement and fibrinous/granulomatous material
5. Assess the bone stock
6. Assess the ligamentous balance
7. Prepare the trial components with stems, augments, or bone graft to restore the joint line
8. Balance the soft tissues – varus/valgus, flexion/extension spaces
9. Trial the components
Note: estimating the joint line – look at the other knee; measure from the tip of the fibula, and from the distal pole of the patella. Should be about a fingerbreadth from the distal pole of the patella, and 1.5 fingerbreadths from the tip of the fibula.
Managing Bone Defeciency
– small defects less than 5 mm can be cemented
– larger contained defects can be filled with morcellized graft
– larger uncontained defects should have structural allograft/autograft, or should be supported by augments – do not just cement them!
– when dealing with bone deficiency in the metaphysis, use stemmed components to share the load. They are press fit, and the cementing is done only at the metaphysis.
– establish the diagnosis
– then achieve exposure and non-destructive removal of implants
– re-establish mechanical alignment with bony cuts – both varus/valgus, and flex/extension
– re-establish stability with ligament balancing, or if insufficient, with a more constrained component