Joint Motion (Arthrokinematics)
Three fundamental motions occur at joint surfaces - roll, slide and spin.
Roll – multiple points along one rotating articular surface contact multiple points on another articular surface; analogy – a tire rotating over the road
Slide – a single point on one articular surface contacts multiple points on another articular surface; analogy – a tire that is not rotating skids on the icy road
Spin – a single point on one articular surface rotates on a single point on another articular surface; analogy – a rotating top spinning on one spot.
Arthrokinematic principles of movement:
• for a convex-on-concave surface movement, the convex member roles and slides in opposite directions
• for a concave-on-convex surface movement, the concave member rolls and slides in similar directions
Close packed position – position of maximum congruency of the joint; most ligaments and joint capsule are taut natural stability to a joint; eg full extension of the knee.
Loose packed position – not in position of maximum congruency; ligaments are not taut; some accessory movements are possible
Joint motion about axes:
• joints move about axes
• movement is perpendicular to the axis
Axes of motion