Experimental instability of the ankle. A radiographic investigation.

For determination of the optimal position in examining the ankle joint for anterior drawer sign and talar tilting, 12 legs freshly amputated above the knee were radiographically examined after successive transection of the lateral ankle ligaments in three different sequences. Apparatuses secured the position of the ankle joint in 25 degrees of inward rotation and 10 degrees and 30 degrees, respectively, of plantarflexion. Examination for anterior drawer sign gave significantly greater displacement with the foot in 10 degrees than with the foot in 30 degrees of plantarflexion and was most pronounced after the cutting of the anterior talofibular ligament. Examination for talar tilt gave a non-significantly greater displacement at 10 degrees of plantarflexion, except when cutting both the posterior talofibular and the anterior talofibular ligament. Isolated cutting of the calcaneofibular ligament gave only little displacement irrespective of the method used. Radiographic examination should be performed with 10 degrees of plantarflexion to obtain maximal displacement and 25 degrees of inward rotation of the leg to obtain a free ankle mortise in the anteroposterior projection and concentric arcs of the joint surfaces in the side projection.