Muscle Test Group: Extensor carpi radialis longus and extensor carpi radialis brevis.
• Extensor carpi radialis longus and brevis are tested together as a muscle group.
• Muscle group extends the wrist with slight radial deviation (extensor carpi radialis longus).
• Extrinsic extensor muscles.
Extensor Carpi Radialis Longus: Extends and abducts the wrist. Assists in flexion of the elbow.
Extensor Carpi Radialis Brevis: Extends and assists in abduction of the wrist.
Extensor Carpi Radialis Longus: The base of the second metacarpal bone ulnar to the extensor pollicis longus tendon.
Extensor Carpi Radialis Brevis: The base of the third metacarpal bone.
Gravity-lessened Test: Position – the subject in sitting with the elbow either in slight flexion or flexion greater than 90º, forearm in neutral, wrist in flexion. The forearm is positioned resting on the table with the wrist on the edge and the hand off the edge. Stabilize – the forearm.
Anti-gravity Test: Same as the Gravity-lessened Test except the forearm is in pronation rather than in neutral position. Resist – against wrist extension with slight radial deviation (in the direction of wrist flexion and ulnar deviation). To differentiate the brevis from the longus, the test can be completed with the elbow in flexion of 90º or greater. This will increase the action of the brevis and put the longus at a disadvantage.
Possible Substitutions: Substitutions include extensor pollicis longus and the finger extensor muscles. To prevent these substitutions, keep the thumb and fingers relaxed during resistance.
Extensor Carpi Radialis Longus
• Roots: C5, C6, C7, C8.
• Nerve: Radial nerve.
• Innervation Route: C5, C6, C7, C8 → radial nerve → extensor carpi radialis longus branch.
Origin: Distal ⅓ of lateral supracondylar ridge of humerus and lateral intermuscular septum.
Insertion: Dorsal surface of base of second metacarpal bone, radial side.
Extensor Carpi Radialis Brevis
• Roots: C6, C7, C8.
• Nerve: Radial nerve.
• Innervation Route: C6, C7, C8 → radial nerve → extensor carpi radialis longus branch.
• There is some variability with the take off of this nerve branch. It can occasionally originate off the radial sensory nerve branch or the posterior interosseous nerve.
Origin: Common extensor tendon from lateral epicondyle of humerus, radial collateral ligament of elbow joint, and deep antebrachial fascia.
Insertion: Dorsal surface of the base of the third metacarpal bone.