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Proximal Radioulnar Joint (Rotation) - proximal being the end of these bones that is nearest the elbow.
Bones: Head of Radius and Ulna closest to the humerus.
Cartilage: There is a capsule that connects all three bones of the elbow.
Ligaments: The annular ligament binds the radius to the ulnar.
Muscles: Pronator teres which attaches at the humerus and radius (from the inside of the elbow closest to the body) and then runs diagonally to the radius (the inside bone of the forearm) about three quarters of the way towards the writs, this muscle pronates the hand turning the palm down. Usually grouped as part of the elbow because of the muscle attachment to the humerus. The supinator (stretching from the tip of the humerus to the radius, covering close to a third of it) and assistance from the biceps brachii supinate the hand turning the palm downwards.
Joint type: Pivot joint.
Mechanics: The Ponator muscle is on the inside of the arm therefor when contracted turns the arm inwards pronating the palm of the hand downwards. The Supnator muscle is on the outside of the arm therefor when contracted turns the arm outwards supinating the palm of the hand upwards.
Range of motion: The mechanics of this pronator allows for the hand to turn from neutral to slightly over 90 degrees downwards and the reverse as with the supinator. When the complimentary muscles contract the opposite muscle must still provide enough elasticity for the total rotation of the forearm to be about 180 degrees.
Manipulation: These are fairly small muscles so a more than 90 degree force supination or pronation of the forearm will push the elasticity of the muscle and the connective alignments of the bones causing them to lock and a throw easy to follow or with a snap like force the destruction of ligaments and cartilage.
For information on additional joints please refer back to the Joints page.
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