The level of the joint line after cruciate-retaining total knee replacement: a new coordinate system

This study assessed joint line changes after knee replacement surgery. Sixty consecutive cruciate-retaining total knee replacements were followed up. The height of the femorotibial joint line in extension and in 90 degrees flexion were analysed. A new coordinate system was used. It is based on two perpendicular axes applied to a lateral X-ray: one axis is drawn along the anterior cortex of the distal femur and the other axis overlies the intersection of the inter-condylar roof and the posterior femoral condyles. In patients with non-posterior stabilised implants, the landmarks chosen appear to be reliable and useful. In this study, the femorotibial joint line was displaced distally, and the surgical instrumentation was changed accordingly.