In Vivo Syndesmotic Motion After Rigid and Flexible Fixation Using 4-Dimensional Computerized Tomography

Introduction: Maintaining reduction after syndesmotic injury is crucial to patient function; however, malreduction remains common. Flexible suture button fixation may allow more physiologic motion of the syndesmosis compared with rigid screw fixation. Conventional syndesmotic imaging fails to account for physiologic syndesmotic motion with ankle range of motion (ROM), providing misleading results. Four-dimensional computerized tomography (4DCT) can image joints through a dynamic ROM. Our purpose was to compare syndesmotic motion after rigid and flexible fixation using 4DCT. Methods: We analyzed 13 patients with syndesmotic injury who were randomized to receive rigid (n = 7) or flexible (n = 6) fixation. Patients underwent bilateral ankle 4DCT while moving between ankle dorsiflexion and plantar flexion. Measures of syndesmotic position and rotation were extracted from 4DCT to determine syndesmotic motion as a function of ankle ROM. Results: Uninjured ankles demonstrated significant decreases in syndesmotic width of 1.0 mm with ankle plantar flexion (SD = 0.6 mm, P < 0.01). Initial rigid fixation demonstrated reduced motion compared with uninjured ankles in 4 of 5 measures ( P < 0.01) despite all patients in the rigid fixation group having removed, loose, or broken screws by the time of imaging. Rigid fixation led to less motion than flexible fixation in 3 measures ( P = 0.02–0.04). There were no observed differences in syndesmotic position or motion between flexible fixation and uninjured ankles. Conclusion: Despite the loss of fixation in all subjects in the rigid fixation group, initial rigid fixation led to significantly reduced syndesmotic motion. Flexible fixation recreated more physiologic motion compared with rigid fixation and may be used to reduce rates of syndesmotic malreduction. Level of Evidence: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.