How do you test the extensor carpi ulnaris (ECU) muscle?

From the Guidelines

To test the extensor carpi ulnaris (ECU) muscle, have the patient sit with their forearm pronated and resting on a table, then ask them to extend their wrist and deviate it ulnarly against resistance, which can help identify weakness, pain, or instability in the ECU tendon, as noted in studies discussing wrist and hand trauma evaluation 1. When performing this test, it is crucial to stabilize the forearm and apply resistance against the ulnar side of the patient's hand to effectively isolate the ECU muscle. The primary functions of the ECU muscle are wrist extension and ulnar deviation, making this test specific for assessing its integrity and function.

Key Points to Consider:

• The ECU muscle originates from the lateral epicondyle of the humerus and inserts on the base of the fifth metacarpal bone, which is important to consider when evaluating its function and potential sites of injury.
• Observing for asymmetry compared to the opposite side and pain that might indicate tendinopathy or instability of the ECU tendon in its groove on the distal ulna is essential during the test.
• If weakness is present without pain, potential nerve issues affecting the posterior interosseous nerve, a branch of the radial nerve that innervates the ECU, should be considered.
• Imaging studies like MRI or US can be used to evaluate extensor carpi ulnaris tendinopathy, tenosynovitis, and tendon rupture, but dynamic instability may be better assessed with dynamic maneuvers during the physical examination or with specific imaging sequences 1.

Testing Procedure:

• Have the patient sit comfortably with their forearm pronated and resting on a flat surface.
• Ask the patient to extend their wrist and deviate it ulnarly (toward the little finger side) against your resistance.
• Use one hand to stabilize the patient's forearm and the other to apply gentle but firm resistance against the ulnar side of the patient's hand.
• A positive test is indicated by weakness, pain, or an inability to maintain the position against resistance, suggesting potential issues with the ECU muscle or its tendon.

From the Research

Testing the Extensor Carpi Ulnaris (ECU) Muscle

To test the ECU muscle, several methods can be employed, including:

• The ECU synergy test: This test applies isolated tension to the ECU tendon without greatly stressing other structures, making it a useful diagnostic tool for evaluating chronic dorsal ulnar-sided wrist pain 2, 3.
• The carpal supination test: This test involves supination of the forearm and wrist, which can help to detect ECU tendinitis by increasing pressure and tendon strain in the sixth extensor compartment of the wrist 4.
• Ultrasound imaging: This can be used to evaluate the normal displacement of the ECU tendon within the ulnar groove in various forearm-wrist positions, helping to diagnose ECU tendinopathy 5.

Diagnostic Performance of the ECU Synergy Test

The ECU synergy test has been shown to have a sensitivity of 73.7%, specificity of 85.7%, positive predictive value of 82.4%, and negative predictive value of 78.3% in detecting sonographic ECU abnormalities in patients with chronic dorsal ulnar-sided wrist pain 3.

• The test results were significantly different between groups with and without ECU abnormalities (P < .01) 3.
• There was no significant difference in age, sex, or symptomatic duration between any of the groups 3.

Clinical Application of the ECU Synergy Test

The ECU synergy test can be used as part of a clinical algorithm to diagnose ECU tendonitis and differentiate it from other causes of ulnar-sided wrist pain 2.

• The test can help to minimize the need for wrist MRI and diagnostic arthroscopy by providing a simple and unique diagnostic maneuver for evaluating chronic dorsal ulnar-sided wrist pain 2.