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Ankle joint complex, consisting of talocrural and subtalar joints, provides stability and energy exchange for human walking. However, due to poor anatomical accessibility of talus, kinematics and kinetics of ankle joint complex had not been well studied. In the past, ankle motion was simulated with mathematical models and measured by cadaver specimen or using skin marker system. They usually treated ankle joint complex as a single hindfoot segment. Until recently, detailed analysis of subtalar joint motion during stance phase of normal walking was performed with skeletal markers and 3D motion analysis system. The video-based motion analysis system can provide a 3D analysis of joint motion and accurate real time dynamic study could be obtained by its fast sampling rate. With well-fixed smooth pins connected to reflective markers set, soft tissue movement which is more important in those joints with smaller range of motion such as subtalar and midfoot joints can be eliminated. Also, skeletal markers system made possible the kinematic study of small bones and those which cannot be easily approached such as talus, carpal bones and tarsal bones.
We assume ankle joint complex to be a three-segment linkage system and use skeletal marker system to separately evaluate talocrural and subtalar motion. The subject performed three kinds of open kinetic chain motion in sagittal, coronal and transverse planes, and walked in the motion laboratory. The images of markers were collected with six video cameras and digitized by ExpertVisionTM motion analysis system, then downloaded to a 586 PC for calculation of Euler angles and screw axis parameters using appropriate programs coded in MATLAB language. With minimal invasive procedure of inserting a smooth pin into talus, we can separately and accurately evaluate talocrural and subtalar joints kinematics. The pins were removed after experiment and only somewhat soreness sensation around pin holes during walking was noted. There left no significant complication or any sequela. As data showed, skin markers could detect calcaneal motion properly due to relatively small skin movement in this region. There was little translation in ankle joint complex occurred during normal walking.
Although the kinematic data obtained from a single subject in this experiment can tell us the trend of motion of ankle joint complex bothduring walking and in open kinetic chain movement, more information from more subjects is mandatory to draw more definite conclusions. In the meanwhile, kinetic analysis using force plate data and inverse dynamics can supplement kinematic analysis for presenting a comprehensive understanding of the ankle joint complex.
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