Abstract
ObjectiveThe objective is to assess the in vivo knee secondary motions intrinsic to flexion in isolation from actual displacements during a landing activity. For this purpose a “static zero position”, which denotes the normal tibiofemoral position to the static flexion angle, was introduced to describe the intrinsic secondary motion. MethodsThe three‐dimensional motion data of the healthy knee were collected from 13 male and 13 female young adults by using an auto motion analysis system and point cluster technique. First, the relationship between flexion and secondary motion in the static state was determined during a single-leg quasistatic squat. The static zero position during a single-leg drop landing was then calculated by substituting the flexion angle into the flexion-secondary relational expression obtained. ResultsAfter the foot-ground contact, the estimated static zero positions shifted monotonically in valgus, internal rotation, and anterior translation in the case of both the male and female groups. For the time-course change, noticeable differences between the actual displacement and estimated static zero position were found from the foot-ground contact up to 25ms after the contact for the valgus/varus and external/internal rotation, and between 20 and 35ms after the contact for the anterior/posterior translation. SummaryThe static zero position demonstrated relatively modest but not negligible shift in comparison with the actual displacement. The intrinsic tibiofemoral motion, or baseline shift, would be worth taking into account when examining the fundamental function and injury mechanics of the knee during an impulsive activity.
Highlights
IntroductionIn the tibiofemoral joint, an involuntary axial rotation occurs as the knee flexes or extends
Quasistatic squat was regarded as the static state sequence at the corresponding flexion angle; i.e., no dynamic effect on the secondary motion was observed
These secondary motions were similar in time-course tendency among the 3 trials for an individual subject, while remarkable variation was observed among the subjects by visual inspection
Summary
An involuntary axial rotation occurs as the knee flexes or extends. This is known as a “screw-home movement” (SHM) and was first demonstrated using a cadaver specimen [1,2,3,4]. The. SHM describes the coupled property in which the tibia automatically rotates externally relative to the femur during passive extension of the knee, and the reverse occurs during knee flexion. SHM describes the coupled property in which the tibia automatically rotates externally relative to the femur during passive extension of the knee, and the reverse occurs during knee flexion Regardless of whether this property is coupled, the rotational motions, i.e., valgus/varus and external/internal rotation, and the translational motions, i.e., lateral/medial translation, anterior/posterior translation, and superior/inferior translation, have been investigated as the knee motions that are intrinsic to flexion, recently termed secondary motions [5, 6]. The notion of coupled motion and that of the envelope conceptually oppose one another, both of these ideas share the view that the motion path is highly sensitive to the external load 7
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