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Malposition of the Joint Line

- Discussion: 
    - see flexion and extension gaps:
    - quantification of joint line malposition:
             - joint line position lies about 3 cm distal to the medial femoral epicondyle and 15 mm above the fibular head;
             - if the opposite knee has not undergone TKR then measure the distance from the adductor tubercle to the distal edge of the femoral component;
             - if the opposite knee has undergone previous TKR (or has deformity) then the optimal joint line position often lies two finger breadths above the tibial tubercle;
             - at the time of surgery, the joint line position can be determined by looking for the old residual meniscus;
    - elevation of joint line:
             - common complication with primary and especially revision total knee replacement;
             - patella baja results from elevation of the joint line;
    - lowering of the joint line:
             - depth of tibial cut:
             - occurrs if tibial resection is made very distal & amount of femur resected was less than the thickness of component being used;
             - in this situation the knee is stable in extension but becomes progressively lax as it is flexed;
             - this situation occurs most often when, in the face of an asymmetrical tibial plateau defect, the surgeon attempts to obtain a flat tibial  surface by lowering the tibial resection line

The influence of patellofemoral location on function of the knee in patients with the posterior stabilized condylar knee prosthesis

Joint line displacement of a total knee replacement results in reduction of knee flexion. Cummings JF et al. Trans Orthop Res Soc. 1990;15:280.

Joint line position restoration during revision total knee replacement.