Answer
Lateral and medial rotation are most easily described for upper and lower limbs bones. One defines these movement by starting from a standard position which enables one to define the anterior surface of a bone , say the humerus. To describe medial rotation , the upper limb is held in the standard position. In this position the aspect of the upper arm bone facing forward is the anterior aspect of the humerus. If one rotates the arm towards the trunx( the midline) that turning of the humerus around its longitudinal axis is a medial rotation. Rotation of the humerus around the same axis that moves the anterior surface of the bone away from the midline ( the trunk) is a lateral rotation of the humerus.
Work Step by Step
Rotation is the movement of an object/organ around its own longitudinal axis. Rotating the head from side to side is the non-verbal gesture for "No"( means "Yes" in some East Indian cultures). Is a rotation of the atlas at the atlanto-axial pivot joint-- between the first and second cervical vertebrae. The atlas is the first cervical vertebra, and it pivots(rotates) around the odontoid peg of the axis when we "shake our heads."
Defining medial and lateral rotation is most easily done by describing the toward-trunk (medial ) and the away-from-trunk (lateral) turning of the anterior surface of the humerus or femur.
