Femoral condylar lift-off in vivo in total knee arthroplasty

We carried out weight-bearing video radiological studies on 40 patients wit h a total knee arthroplasty (TKA), to determine the presence and magnitude of femoral condylar lift-off, Half (20) had posterior-cruciate-retaining (P CR) and half (20) posterior-cruciate-substituting (PS) prostheses. The sele cted patients had successful arthroplasties with no pain or instability. Ea ch carried out successive weight-bearing knee bends to maximum flexion, and the radiological video tapes were analysed using an interactive model-fitt ing technique. Femoral lift-off was seen at some increment of knee flexion in 75% of patie nts (PCR TKA 70%; PS TKA 80%). The mean values for Lift-off were 1.2 mm wit h a PCR TKA and 1.4 mm with a PS TKA, Lift-off occurred mostly Laterally wi th the PCR TKA, and both medially and laterally with the PS TKA, Separation between the femoral condyles and the articular surface of the tibia was re corded at 0 degrees, 30 degrees, 60 degrees and 90 degrees of flexion. Femo ral condylar lift-off may contribute to eccentric polyethylene wear, partic ularly in designs of TKA which have flatter condyles, Coronal conformity is an important consideration in the design of a TKA.