[Modification of the method of Figgie for determination of joint line shifting in total knee arthroplasty].

An important factor for a good result after total knee arthroplasty is the position of the patella in relation to the tibiofemoral joint line. The position of the patella itself is not influenced by arthroplasty, therefore any changes in the position of the tibiofemoral joint line are of special interest. The Figgie method to describe patella height delivers only absolute measurements, which makes it difficult to compare different radiographs. For this reason we developed a new JL/P quotient (JL: distance from the tibial plateau to the tibial tubercle, P: distance from the inferior pole of the patella to the tibial plateau) to enable better comparison. Furthermore, we modified the JL/P quotient and instead of taking the tibial plateau as the reference line, we constructed a tangent on the femoral condyle. With this modification, problems such as tibial inlays of different heights which have to be taken into account in the measurements, the slope of the tibial component or difficult assessment of the tibial joint surface in osteoarthritic knees do not arise. The JL/P quotient shows massive shift to cranialisation of the tibiofemoral joint line which does not correspond to reality. The modified method also shows cranialisation of the tibiofemoral joint line, but in a realistic way. Both methods show a minimal interobserver variability. The modified JL/P quotient seems to be a good method for determining the shift in the tibiofemoral joint line after total knee arthroplasty.