Session VII - Foot & Ankle

Overtightening of the Syndesmosis: Is It Really Possible?

Paul Tornetta, III, MD; Fletcher Reynolds, MD; Jeffery Spoo, MD; Cassandra Lee, MD, Boston Medical Center, Boston, MA

Purpose: It is a widely held belief that if syndesmotic fixation is performed the ankle should be held in dorsiflexion to prevent "overtightening". Clinically, however, a loss of dorsiflexion is not reported to be a significant problem after syndesmotic fixation, or even after syndesmotic fusion.

The purpose of this study was to determine if overtightening of the syndesmosis would lead to a loss of dorsiflexion in the ankle joint under physiologic forces.

Methods: 19 Cadaveric ankles were used for the study. The anterior soft tissues were removed exposing the distal tibia and talar neck. K-wires were placed vertically in the tibia and in the talar neck at an angle that would not interfere with full dorsiflexion. As cadaveric ankles are stiff, the tendoachilles was transected at the top of its tendinous portion. All capsular and ligamentous structures were preserved. The gross motion of each ankle was documented using a goniometer. A 6" fluoroscan portable c-arm was used for the remainder of the experiment. Each ankle was dorsiflexed by the same investigator using approximately 50-60 lbs. of force via a flat object at the bottom of the foot. A perfect lateral radiograph was obtained and printed >from the C-arm. A 4-corticle 4.5-mm (Synthes) lag screw with washer was then placed across the syndesmosis after overdrilling both cortices of the fibula. The lag screw was maximally tightened causing compression of the syndesmosis with the ankle in plantarflexion. The ankle was again dorsiflexed using the same force, and a perfect lateral radiograph was taken and printed. All screws were thought to have excellent purchase and could not be retightened after the test, indicating no loss of position. The angle between the pins was measured for each printed radiograph (pre- and post-syndesmotic lag screw placement) by one individual out of order and logged by a second individual.

Results: The gross range of motion of the ankles as measured by a goniometer was 11° ± 4° of dorsiflexion (5° - 20°), 44° ± 9° of plantarflexion (28° - 58°) with a total arc of motion of 55° ± 9° (39° - 69°). The difference between the dorsiflexion of the ankle before syndesmotic compression and after averaged 0.5° ± 1° with a range of (-2° - 3°). There was no difference in the dorsiflexion before and after maximal syndesmotic compression with a 4.5-mm lag screw.

Discussion: Although it is widely believed that compression of the syndesmosis leads to limitations in dorsiflexion, the evidence that this is in fact the case is very limited. Clinically, this does not seem to be a problem. This study examined the effect of maximal compression of the syndesmosis on dorsiflexion of the ankle. The difference in dorsiflexion with and without compression was evaluated by using pins fixed in the talus and tibia to isolate the ankle joint and remove any effects of the subtalar and midfoot joints. This allowed for exacting measurements of the difference in dorsiflexion, unlike previous work. The force used was equal to approximately 30% of full weight bearing to better mimic the clinical situation. There was no effect on ankle dorsiflexion. The previous recommendation to hold the ankle in dorsiflexion while fixing the syndesmosis seems to be unecessary. Additionally, because dorsiflexion of the ankle is accompanied by heel valgus and external rotation, an unstable syndesmosis may be opened during this maneuver, resulting in a widened mortise and possible instability after fixation. This study does need to be cautiously applied as it applies only to passive motion and does not address pain.

Conclusion: Compression of the syndesmosis does not lead to a decrease in dorsiflexion. Syndesmotic fixation should be performed with the syndesmosis anatomically reduced. The position of the ankle joint during syndesmotic fixation is not important with respect to dorsiflexion after fixation.