The effect of the syndesmotic screw on the extension capacity of the ankle joint.

To investigate whether, when inserting a syndesmotic screw, the foot position effects the range of motion in dorsal extention, 16 osteoligamentous lower-leg preparations were studied. The specimens were placed in a test frame where a constant dorsal extention force could be applied to the foot. The dorsal extention capacity was recorded with a syndesmotic screw inserted by a standardized technique in various plantar flexion positions. The dorsal extension capacity decreased by an average of 0.1 degree for every degree of increase in plantar flexion when the screw was being inserted. There was a correlation between a large decrease in range of motion and a limited dorsal extension capacity to start with. No correlation could be found between a large decrease in range of motion and a large difference in width between the anterior and posterior edges of the talar trochlea. The results suggest that the foot should be in maximal dorsal extension when a syndesmotic screw is inserted in order to decrease the risk of stiffness.