Lumbar Spine Biomechanics

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Movements

Bones can undergo translation and rotation

Movement	Description	Movement occurs when	Force
Translation	Every point on a bone moving in the same direction and to the same extent	Single force or net single force acts on a bone	Shear force
Rotation	All the points on a bone move in parallel around a curved path that is centred on a fixed point, but to different extents depending on their distance from the centre of rotation. May be due to two opposed muscular actions, or muscular action and ligamentous resistance, or gravity opposed by either muscular action or ligamentous resistance.	Two unaligned forces acting in opposing directions on different parts of the bone forming a force couple	Torque