Radiographic measurement of femorotibial rotation in weight-bearing. The influence of flexion and extension in the knee on the extensor mechanism and angles of the lower extremity in a healthy population.

PURPOSE: A system for examination and measurement of the weight-bearing knee was developed earlier on examination equipment used for QUESTOR Precision Radiography (QPR), adapted to computed radiography and to a picture archiving and communication system. In this study the same system was used to develop a method to define "patellar variables" including measurements of the rotation of the femur and the tibia and the patellar translation, between semiflexion and extension, as well as the Q-angle. The aim of this study was to evaluate the reproducibility of these patellar variables and also to establish "normal" reference values for both the patellar variables and the variables in the original QPR system.
MATERIAL AND METHODS: For evaluation of the reproducibility 10 volunteers with healthy knees were examined twice. To obtain the reference values, 80 volunteers with healthy knees, 10 females and 10 males within each decade between 20 and 59 years of age, were examined. RESULTS AND
CONCLUSION: The reproducibility of the rotation of the femur and the tibia and of the Q-angle was 2--3 degrees (SD) and of the patellar translation about 3 mm (SD). The result from the healthy volunteers will be a useful tool for evaluation of disorders in the knee joint.