Posterior reference guides do not always maintain the size of posterior femoral condyles in TKA.

Abstract

Posterior reference guides are provided by many manufacturers. However, the true posterior femoral condyle bone resection thicknesses using posterior reference guides are not stated by the manufacturers. The purpose of this study was to analyse the influence of the posterior reference guide designs on the posterior femoral condyle bone resection thickness. Thickness of posterior femoral condyle bone resection and thickness of prostheses were investigated in 8 types of total knee prostheses using the production drawings provided by the manufacturers. Posterior femoral condyle bone resection thickness differed between prostheses. Change in size of the medial posterior condyle ranged from -0.5 to 1.4mm at 0° external rotation, from -2.9 to 1.4mm at 3° external rotation, and from -5.3 to 1.4mm at 6° external rotation. Change in size of lateral posterior condyle ranged from -0.5 to 1.4mm at 0° external rotation, from -0.4 to 3.4mm at 3° external rotation, and from -0.4 to 5.3mm at 6° external rotation. This study showed that posterior femoral condyle bone resection thickness was different for each posterior reference guide. The rotation centre of posterior reference guides influenced the bone resection thickness in the posterior femoral condyle. The size of the posterior femoral condyles increased in some guides but decreased in other guides. The maximum differences in size changes of the posterior femoral condyles between the guides were 1.9mm at 0° external rotation, 4.1mm at 3° external rotation, and 6.3mm at 6° external rotation. To control the size of posterior femoral condyles, the posterior reference guide design should be checked before use.