Purpose: The distal tibiofibular joint is implicated in ankle movement but has been the topic of less work than the talotibial joint. Its mobility within the talo-crural complex has not been described in detail as precisely as its static role. The purpose of this work was to develop a simple noninvasive method for characterising in vivo the mobility of the fibula at the ankle level between is positions in dorsal and plantar flexion.

Material and methods: We used 32 computed tomo-graphic studies of the ankle in 16 healthy volunteers (men and women), one study in each position of ankle flexion. We identified one cross-sectional slice through the syndesmosis in each of the two positions. A medio-lateral reference line was drawn tangent to the posterior cortical of the tibial metaphysis. The displacement of the fibula in relation to the tibia when moving between the two positions of ankle flexion was calculated using a remarkable landmark on the tibia, the anterior rim of the posterior tibial incisure, and the polar co-ordinates of the ends of the anteroposterior axis of the fibula.The repeatability and reproducibility of this method were tested.

Results: Repeatability was satisfactory for translation movements. Reproducibility was fair except for the reference line where it was good. When the ankle moved from dorsal flexion to plantar flexion, the fibula moved medially 1.25 mm (0.03–2.58 mm) (p< 0.0001) without correlation with the amplitude of the ankle flexion. Mean anterioposterior displacement was 0.46 mm (NS) with a wide range from −1.58 to +7.2 mm. It was correlated with lesser amplitude of ankle flexion.

Discussion: This dynamic method confirms published data concerning active mediolateral tibiofibular approach during plantar flexion. The results point out the variability of the anteroposterior movement of the fibula, the influence of the amplitude and the flexion position of the ankle, and the possible antepulsion effect of fibular tendons. The three-dimensional movement of the ankle joint merits further study including its tibio-fibular and talofibular components in view of potential prosthetic repair of the ankle.

Conclusion: Distal tibiofibular mobility is undeniable. We call for more work to achieve a better understanding of the lateral component of the talocrural complex.