Four-Dimensional CT Analysis of Normal Syndesmotic Motion

Area of Science:

• Orthopedics
• Radiology
• Biomechanics

Background:

• The syndesmosis ligament complex is crucial for distal tibiofibular joint stability.
• Malreduction of syndesmotic injuries significantly impairs functional outcomes.
• Conventional computed tomography (CT) inadequately assesses dynamic syndesmotic reduction.

Purpose of the Study:

• To utilize four-dimensional CT (4DCT) to quantify in vivo syndesmotic motion across a range of ankle motion (ROM).
• To establish the reliability of syndesmotic measurements in uninjured ankles for potential application in injury assessment.

Main Methods:

• Bilateral 4DCT scans were performed on 58 uninjured ankles (patients with contralateral injuries and healthy volunteers).
• Ankles moved through maximal dorsiflexion and plantarflexion to capture dynamic changes.
• Custom software extracted syndesmotic width, sagittal translation, and fibular rotation during ankle ROM.

Main Results:

• Syndesmotic width decreased by 0.7–1.1 mm with ankle motion from dorsiflexion to plantarflexion (P < .001).
• External fibular rotation averaged 1.2 degrees with ankle ROM (P < .001).
• No significant sagittal plane motion was detected (P = .43), and side-to-side width differences were minimal.

Conclusions:

• 4DCT provides accurate in vivo measurement of syndesmotic motion with ankle ROM.
• Consistent side-to-side syndesmotic measurements validate using the contralateral ankle for templating reduction in cases of syndesmotic injury.