The figure illustrates how joint subluxation or dislocation would result were a convex surface to roll on a fixed concave surface without gliding at the same time.
When the concave surface is fixed and the convex surface moves on it, the convex surface rolls and glides in opposite directions. Movements at joint surfaces (arthrokinematics) follow the rules of concavity and convexity.Įach joint or articulation involves two bony surfaces, one that is convex and one that is concave. Roll and glide, like all motions, are produced by forces. NB: Roll and glide do not occur in the direction they do because of the shape of the joint surfaces. We can predict and understand the relationship between bony shapes at a joint surface and the surfaces' movements by applying the rules of concavity and convexity (Kaltenborn 1989, p.27). Roll and glide must occur simultaneously to preserve joint integrity. If the moving joint surface rolls on its partner without simultaneously gliding, the surfaces would separate (gap or subluxate) in some places and impinge in others. The figure, a sagittal plane depiction of the knee (tibio-femoral) joint, illustrates roll, like the rolling of a tire on a surface, and glide, like a tire slipping without rolling. This discussion focuses on how joint surfaces roll and glide with respect to one another, and largely ignores the spin component. Joint surfaces move with respect to one another by simultaneously (1) rolling, (2) gliding, and (3) spinning. (Joint surface movements are sometimes called joint play motions or component motions). Normal joint surface movement is necessary to ensure long-term joint integrity. Joint axes' locations are fairly stable, but only because the joint surfaces move in a very specific way.ĪRTHROKINEMATICS is the general term for the specific movements of joint surfaces. We speak as if this joint axis is a fixed point, as if the center of rotation is stationary like an automobile axle. These terms describe the movements that occur around a center of rotation, namely the joint axis. We use OSTEOKINEMATIC terms, such as abduction or adduction, flexion or extension, to name the movements that occur between bones at synovial joints. Small amplitude motions of bones at joint surface Arthrokinematics and osteokinematics Arthrokinematics (contrasted with osteokinematics)
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