[AT-TG (anterior tuberosity-trochlear groove): interobserver variability in CT measurements in subjects with patellar instability].

Measurements between the anterior tuberosity of the tibia and the trochlear groove of the patellar surface of the femur AT-AG) are recognized parameters for exploring patellar instability. Interobserver variability should be less than 4 mm and reproducibility should be greater than 85 per cent for valid measurements. We assessed interobserver variability with CT measurements.The radiography files (left and right knee) of thirteen patients with patellar instability were examined by six radiologists working in private practice after training in our university center.The results demonstrated major variability with acceptable reproducibility in only 15% of the measurements. Differences greater than 5 mm were observed for 14 groups of values (54 per cent) and greaterd than 8 mm in 5 groups (19 per cent). The spread was mainly related to determinations of the TG point in case of major dysplasia and in defining the precise contour of the tibial tuberosity. Surgical decisions made on the basis of these millimetric values should be made prudently.