Triangular spinopelvic fixation for U-shaped sacral fractures and tile C pelvic disruptions: counter-nutation (anteflexion and rotation) load-bearing instability requires complementary anterior pelvic ring fixation.

Unstable trauma lesion of the spinopelvic junction, including U-shaped sacral fractures and Tile C pelvic ring disruptions, require surgical stabilization in order to realign the bone arches of the pelvis thus reducing the upcoming orthopaedic impairment during sitting, standing, and walking positions, decompress the nerves roots of the cauda equina in a view of reducing neurological impairment, and allow early weight bearing. Even though posterior open modified triangular spinopelvic fixation is particularly efficient for treating unstable trauma lesions of the spinopelvic junction, it may not be sufficient alone in order to prevent long-term counter-nutation, i.e. rotation and anteflexion deformity of the anterior pelvis under load bearing conditions. Such progressive deformation is caused by either the slight rotation of the iliac connectors within the head of iliac screws for spinopelvic constructs, or the slight rotation of sacral cancellous bone around transsacral screws in case of percutaneous procedure. Regardless of the posterior surgical technique that is used, complementary anterior pelvic fixation appears mandatory in order to prevent such deformation over time, which can lead to pelvic asymmetry and then gait imbalance.