Effects of ligament sectioning on the kinematics of the distal tibiofibular syndesmosis: a radiostereometric study of 10 cadaveric specimens based on presumed trauma mechanisms with suggestions for treatment.

Background: Syndesmotic injuries of the ankle without fractures can result from external rotation, abduction and dorsiflexion injuries. Kinematic studies of these trauma mechanisms have not been performed. We attempted to describe the kinematics of the tibiofibular joint in cadaveric specimens using radiostereometry after sequential ligament sectioning, and resulting from different trauma mechanisms and axial loading, in order to put forward treatment guidelines for the different types of syndesmotic injuries.

Methods: We assessed the kinematics of the distal tibiofibular joint in fresh-frozen cadaveric specimens using radiostereometry in the intact situation, and after alternating and sequential sectioning of the distal tibiofibular and anterior deltoid ligaments. To assess which of the known trauma mechanisms would create the largest displacements at the syndesmosis, the ankle was brought into the following positions under an axial load that was comparable to body weight (750 N): neutral, dorsiflexion, external rotation, abduction, and a combination of external rotation and abduction.

Results: In the neutral position, the largest displacements of the fibula consisted of external rotation and posterior translation. Loading of the ankle with 750 N did not apparently increase or decrease the displacements of the fibula, but gave a larger variety of displacements. In every position, sectioning of a ligament resulted in some fibular displacement. Sectioning of the anterior tibiofibular ligament (ATiFL) invariably resulted in external rotation of the fibula. Additional sectioning of the anterior part of the deltoid ligament (AD) gave a larger variety of displacements. In general, sectioning of the posterior tibiofibular ligament (PTiFL) gave the smallest displacements. Combined sectioning of the ATiFL and the PTiFL resulted in a larger variety of displacements in the neutral position. Sectioning of the AD together with the ATiFL and PTiFL resulted in tibiofibular displacements in the neutral situation exceeding the maximum values found in the intact situation, the most important being fibular external rotation.

Interpretation: Sectioning of the ATiFL results in mechanical instability of the syndesmosis. Of all trauma mechanisms, external rotation of the ankle resulted in the largest and most consistent displacements of the fibula relative to the tibia found at the syndesmosis. Based on our findings and the current literature, we recommend that patients with isolated PTiFL or AD injuries should be treated functionally when no other injuries are present. Patients with acute complete ATiFL ruptures, or combined ATiFL and AD ruptures should be treated with immobilization in a plaster. Patients with combined ruptures of the ATiFL, AD and PTiFL need to be treated with a syndesmotic screw.