To assess the accuracy of a new radiographic measurement of the distal tibia and fibula on the lateral view of the ankle in normal adults: the anteroposterior tibiofibular (APTF) ratio.
Thirty adults without history of trauma or disease of the ankle were included. Bilateral ankles were x-rayed with a true lateral view of the ankle. A line from the anterior tibial physis scar to the posterior tibial cortex, passing by the intersection of the physis and the fibula anterior cortex, was drawn. The APTF ratio was calculated as the ratio of the anterior segment to the posterior segment. The measurements were done by 3 independent evaluators. Intra- and interobserver reliability was obtained using intraclass correlation.
The APTF ratio was 0.94 ± 0.13 with a range of 0.63-1.31. Sex and age had no effect on the results. Inter- and intraobserver reliability was good to very good with an intraclass correlation between 0.6 and 0.8. A strong correlation between the left and the right APTF ratio was observed (r = 0.501 and P = 0.001).
The distal tibiofibular joint anatomy in the sagittal plane can be accurately assessed with a new reliable radiographic measurement, the APTF ratio. The reduction of this joint during surgery can be confirmed with a true lateral view of the ankle. The anterior fibula cortex crosses the tibial physeal scar at the center of the line crossing this point and the anterior cortex of the tibia at the level of the physeal scar in the normal ankle.