SYNDESMOTIC SCREW PLACEMENT - A BIOMECHANICAL ANALYSIS

At the present time, syndesmotic screw fixation is recommended when th ere is a tibiofibular diastasis, a Maisonneuve fracture, or syndesmoti c instability after fixation of distal tibia-fibula fractures. The aim /purpose of this study was to demonstrate the optimal level of syndesm otic screw placement before creation of a Maisonneuve fracture. Legs o f 17 embalmed cadavers underwent knee disarticulation. The legs were t hen dissected to expose the syndesmosis/interosseous membrane. The pai red cadaver legs were tested in two groups, In group I (10 pairs), the left legs were tested without any syndesmotic fixation and the right legs were tested with the syndesmosis fixed at 2.0 cm above the tibiot alar joint. In group II (7 pairs), the syndesmosis in each left leg wa s fixed at 3.5 cm above the tibiotalar joint and the right leg syndesm osis was fixed at 2.0 cm above the tibiotalar joint. After ligament se ction and syndesmosis fixation, each leg was then jig mounted with tra nsfixing wires through the proximal tibia and calcaneus. The ankle was placed in neutral with 15 degrees of pronation and a load of 150 poun ds and a strain gauge anchored medially and laterally. The proximal ti bia was internally rotated while the ankle was held fixed until syndes motic, bony, or hardware failure occurred. Torsional force, the degree of rotation and the amount of syndesmotic widening were quantitated. Two-tailed t-test comparing no fixation with fixation at 2.0 cm indica ted less syndesmotic widening with screw placed at 2.0 cm (P = 0.04). Two-tailed t-test comparing screw fixation at 2.0 cm and 3.5 cm indica ted less syndesmotic widening with screw placed at 2.0 cm (P = 0.07), It would seem reasonable to place a syndesmotic screw at 2.0 cm above tibiotalar joint.