The Kinematics Of In-Vivo Chronic Ankle Instability

Background and Objective:The ankle joint complex is comprised of tibiotalar and subtalar joint. It bears the whole body weight and plays critical role in daily activity and sports. Chronic ankle instability is usually resulted from ankle sprains and results in a series of pathologies such as altered kinematics, impingement, altered stress distribution, hindfoot malalignment and etc. These pathologies may lead to pain and swollen of the ankle, and osteochondral defect and/or progressive osteoarthritis in some patients. The pathologic presentations are closed related to the altered in-vivo kinematics. Thus a thorough understanding of the dynamic in-vivo kinematics is of critical importance. Methods:Dual fluoroscopic imaging system(DFIS) and 3D Vicon imaging system were used on 10 normal volunteers and 6 patients of chronic ankle instability while walking on a scientific treadmill at certain speeds. A thorough validation study was performed to test its bias and precision.The mobile videos captured by DFIS were matched with static shape images derived from CT scanning semi-automatically in 6 dimensional space to get the precise position of each bone. A CT and anatomic matrix transformation was then performed to get the bone to bone angling and translation. Thus the dynamic in-vivo kinematics of ankle joint complex was achieved. The same method was used on patients of chronic ankle instability, and the results were compared with those of the normal ankles. Results:Results demonstrated this technique is capable of quantifying in-vivo AJC kinematics with a mean positional error of 0.03±0.35 mm and a mean rotational error of 0.25±0.81°.In the normal population, the tibio-talar joint plays major role in dorsal-plantar flexion movement, while the subtalar joint plays major role in inversion-eversion movement. There’s more inversion-eversion and internal-external rotation in the period from late mid-stance to toe-off than from heel strike to early mid-stance.There’s more inversion, internal rotation and anterior translation in the period from heel strike to early mid-stance and more internal rotation in the period from late mid-stance to toe-off at tibia-calcaneal and tibia-talar joint. There’s no statistical difference between the two populations at the subtalar joint level throughout the two periods within the stance phase. Conclusion:The DIFS system and model based tracking can track the dynamic in-vivo kinematics of ankle joint complex with high accuracy. The kinematics of CAI patients alter while walking. The ankle joint presents more inversion, internal rotation and anterior translation at the period of time around heelstrike, which is likely an important factor leading to ankle impingement, osteochondral lesion, hindfoot malalignment and osteoarthritis.