Detection of kinematic changes induced by sequential lateral ankle ligament section: a dynamic 4D-CT scan study

Purpose: Investigate the potential of 4D-CT to detect kinematic changes induced by sequential lateral ankle ligament section.
Methods and Materials: The tibia of two fresh frozen specimens were fixed on a custom-made device and the ankle joint was moved at a pace of 25 cycles/minute. The Anterior Talo-Fibular Ligament, the Calcaneo-Fibular Ligament and the Posterior Talo-Fibular Ligament were cut sequentially. Dynamic-CT scan image datasets of the intact ankle and after each ligament cut were acquired with a 256-slice GE Revolution CT-Scanner (80kV,25mA,tube rotation time 0.28s,z-axis coverage 120mm,scanning-time 3.92s). Rigid registrations of single bones (tibia,talus and calcaneus) were performed and transformation matrixes were derived. Using the global reference frame of the CT (x,y,z), the talo-crural (motion of talus relative to the tibia) and sub-talar (motion of calcaneus relative to the talus) joint kinematics were described as displacement of the centroid of the talus and calcaneus respectively. Radiation dose was also recorded.
Results: The difference between the displacement of the intact ankle and the cut scenarios was up to 2.90mm, 1.19mm, 1.37mm (sub-talar joint) and up to 2.63mm, 2.58mm, 5.46mm (talo-crural joint) for the x,y,z axes respectively. Comparing the intact and injured ankle, deflections in the centroid displacements curves occurred at different time points. Each acquisition required a radiation dose (CTDIvol) of 1.9mGy.
Conclusion: The present study showed that low dose 4D-CT may allow to detect motion changes of the talo-crural and sub-talar joint induced by lateral ankle ligament lesions. This highlights the potential of 4D-CT to investigate dynamic functional joint laxity.