Evaluation of tibiofibular motion under load conditions by computed tomography.

Evaluation of tibiofibular motion in vivo has been possible only by invasive methods. A new noninvasive method has been developed that uses computed tomography (CT). A special device was constructed for use on the CT table to study fibular motion with load placed across the ankle. From dorsal to plantar flexion the fibula moved 1.1 +/- 0.4 mm medially with an accompanying nonsignificant ventral shift and medial rotation. Application of load across the ankle did not significantly alter these findings. In a subgroup of predominantly females, plantar flexion of the ankle provoked a dorsal fibular motion of 0.7 +/- 0.8 mm. In this subgroup application of load across the ankle reduced the medial and dorsal motion during the accompanying plantar flexion. The mechanism of these different movements can be deduced from the morphology of the ankle joint and its ligamentous and muscular guidance mechanism. The variable axis of joint movement and the insertion of the lateral ligament forced the fibula anterior in plantar flexion. When external talar rotation is present, the normal fibular motion is prevented unless load is applied across the ankle. This new investigative procedure permits study of the sequelae of traumatic and iatrogenic injuries to the fibula.