Accuracy assessment of a technique for contact point determination from planar radiographs.

The purpose of this study was to determine the accuracy, precision and repeatability of a simple radiographic method which might be used in in-vivo determination of joint contact points following total joint replacement (TKA). A model of a TKA was constructed from which the anterior/posterior location of the contact point could be mathematically calculated. A radiograph was taken of the model and two observers repeatedly determined the contact point using a parallel rule. The measured locations were compared to the calculated values. The accuracy and precision of the measurement locations in comparison to the calculated values were 1.6 mm and 0.4 mm, respectively. The mean inter-observer error was 0.2 mm.