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By Ben Benjamin, PhD

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The Ulnaris Muscles

Let's take a close look at the anatomy and injury profiles of the extensor carpi ulnaris and flexor carpi ulnaris. Two difficult injuries to differentiate.

The extensor carpi ulnaris is attach to the lateral epicondyle, and it has a second head originating at the posterior border of the ulna. From there, it extends downward, crossing over the forearm to insert at the base of the pinky (the fifth metacarpal). This muscle-tendon unit not only extends the wrist and moves the hand into ulnar deviation, but also helps to stabilize the ulnar side of the wrist. One motion that's particularly dependent on the extensor carpi ulnaris is accelerating a motorcycle; the wrist moves into extension, twisting the throttle grip toward you.

Resisted Ulnar Deviation - Copyright – Stock Photo / Register Mark Resisted Ulnar Deviation The position of the extensor carpi ulnaris, relative to the other structures in the wrist, will differ depending on whether the forearm is pronated or supinated. Injuries are more likely to occur during supination, particularly when combined with wrist flexion and ulnar deviation. Many extensor carpi ulnaris injuries occur when the wrist is placed in this vulnerable position during sports such as tennis and golf. Others result from a sudden lateral force affecting the wrist while the tendon is strongly engaged. A stereotypical case is when a golf club hits a hard object on the ground, interrupting the momentum of the swing and forcing the hand into radial deviation, while this muscle-tendon unit is contracted isometrically. Such injuries are more likely to occur distally near the wrist, either at the tendon attachment or in the tendon body, causing pain in the wrist. Other activities like a backhand in tennis tend to cause injuries at the proximal attachments, which cause pain at the elbow.

Like the extensor carpi ulnaris, the flexor carpi ulnaris has both a humeral head and an ulnar head. One attaches to the humerus at the medial epicondyle, via the common flexor tendon. Its second attachment is at the olecranon process (the bony "point" of the elbow) and the posterior border of the ulna. The distal tendon inserts on the pisiform, hamate, and fifth metacarpal bones.

carpi ulnaris - Copyright – Stock Photo / Register Mark Strenuous wrist flexion activities like hammering, squash, and racquetball can also contribute to injury of the flexor carpi ulnaris, especially when the wrist is cocked in an awkward position. Tendon tears at the distal attachment will cause pain near the wrist, and tears at the proximal attachments will cause pain at the elbow.

Assessment Tests

The primary assessment test is resisted ulnar deviation of the wrist. The same test causes pain for both the extensor carpi ulnaris and flexor carpi ulnaris injuries. With the client's palm facing the floor, grip the forearm an inch or two above the wrist with one hand, and grasp the outer portion of the hand with the other. Ask the client to hold their hand firmly in place as you try to pull the hand toward the thumb side of the hand.

Friction Therapy - Copyright – Stock Photo / Register Mark Friction Therapy of the Extensor Carpi Ulnaris If the pain is felt on the flexor surface or at the medial epicondyle it's the flexor carpi ulnaris, if it's felt at the extensor surface of the forearm or near the lateral epicondyle then it's the extensor carpi ulnaris.

Often, you'll be testing to differentiate between one of these injuries and either tennis or golfer's elbow. Pain felt on resisted extension of the wrist may indicate either the extensor carpi radialis brevis or longus (which is tennis elbow) or the extensor carpi ulnaris. Pain on both resisted extension and resisted ulnar deviation tells you that the extensor carpi ulnaris is injured. (Of course, it's also possible for both structures to be injured simultaneously.)

Friction Therapy - Copyright – Stock Photo / Register Mark Friction Therapy Flexor Carpi Ulnaris If the pain is felt on resisted flexion of the wrist, it may indicate either the flexor carpi radialis (which is golfer's elbow) or the flexor carpi ulnaris. Pain on both resisted flexion and resisted ulnar deviation tells you that the flexor carpi ulnaris is injured. (Again, it's also possible for both structures to be injured simultaneously.)

Treatment

Extensor and flexor carpi ulnaris injuries respond well to a combination of friction therapy, massage therapy and a combination of stretches and strength building exercises for the ulnaris muscles.

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