TIBIOTALAR JOINT DYNAMICS - INDICATIONS FOR THE SYNDESMOTIC SCREW - ACADAVER STUDY

Pronation-external rotation ankle injuries involve varying degrees of disruption of the syndesmotic ligaments. The loss of ligament support and alteration in the stability of the mortise have been postulated to lead to an increase in joint reactive forces and traumatic arthritis. The purpose of this study was to determine the changes in tibiotalar joint dynamics associated with syndesmotic diastasis as a result of th e sequential sectioning of the syndesmotic ligaments to simulate a pro nation-external rotation injury. Dissections were conducted on 10 fres h-frozen, knee-disarticulated cadaveric specimens which were then axia lly loaded in an unconstrained manner. Tibiotalar joint forces were me asured at each level of sequential sectioning of the syndesmotic ligam ents, the interosseous membrane, and finally the deltoid ligament. Com plete disruption of the syndesmosis with the medial structures of the ankle intact resulted in an average syndesmotic widening of 0.24 mm an d no significant change in the tibiotalar contact area or the peak pre ssure. However, deltoid ligament strain increases with sectioning of t he syndesmosis. With the addition of deltoid ligament sectioning, ther e was an average syndesmotic diastasis of 0.73 mm, a 39% reduction in the tibiotalar contact area, and a 42% increase in the peak pressure. In a simulated unconstrained cadaveric model of a pronation-external r otation ankle injury that results in complete disruption of the syndes mosis, if rigid anatomic medial and lateral joint fixation is obtained and the deltoid ligament complex is intact, syndesmotic screw fixatio n is not required to maintain the integrity of the tibiotalar joint.