Goniometry (distal forearm)
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Supination is a motion that occurs across three separate joints – the proximal radioulnar, distal radioulnar, and the elbow joint (specifically the radiocapitular portion of the elbow). Supination and elbow flexion occur together quite often. This makes sense muscularly as the biceps functions equally well as a supinator and an elbow flexor – and it is the strongest of all the muscles that motor each of these functions. Feeding oneself and using a telephone are good examples of these two motions together; supination occurs also for turning doorknobs, keys, screwdrivers, and positioning the hand to do such tasks as open windows, hold large bowls, trays and various other objects.
Biceps (C5-6), Supinator (C6), and Brachioradialis (C5-6) are all active in forearm supination. (Brachioradialis functions as a supinator only to the neutral position starting from a position of full pronation .)
· Test for Fair grade in the upright position, elbow flexed, shoulder adducted, forearm pronated, first observing full supination against gravity to test for a grade of Fair. It is a good idea to test for Fair, Good, and Normal with the subject holding a tennis ball (or other small light object) between the elbow and the trunk. This prevents the subject from substituting other shoulder muscles (ie, adductors) to "throw" the forearm into supination.
· Testing for Good and Normal grades, position yourself on the outside of the forearm. After supination occurs and the position is being held, resist the forearm along its length with one of your hands placed on the distal third of the volar forearm, thumb wrapped around the radius dorsally and fingers across the volar forearm. The other hand is similarly placed but more distally on the forearm – at the wrist. Attempt to twist the forearm back toward pronation, attempting to pull the radius back over the ulna with your thumbs, pushing down on the ulna with the fingertips while the subject tries to hold the position of full supination against your resistance.
· For Poor grade, the shoulder and elbow are each held in a position of 90 degrees (hand pointed upward toward ceiling) and full supination is attempted from a beginning position of full pronation.
· Palpate the biceps tendon or the supinator as marked on the picture (in yellow).
· Remember a good clinical test to determine whether the radial nerve is functioning (following injury and repair to the nerve proximal to the supinator) is to palpate the biceps tendon while the subject attempts slow and easy supination from a fully supported position of elbow flexion. The supinator should function alone in slow unresisted supination. Palpation of activity in the biceps tendon under this condition indicates the supinator (radial nerve) is not yet functioning and the job is taken over by the biceps (musculocutaneous nerve).