Posted on 15 Oct 2011 00:21
By Ground Up Strength
The extensor digitorum1 muscle gets its name from the Greek and Latin ex which means "out of", and the Latin tendere, which means "to stretch". So an extensor is a muscle that stretches out or straightens out a joint. The word digitorum is from Latin, indicating the digits or fingers. Communis is Latin for "common" and it refers to a muscle which has several branches or structures.1
The extensor digitorum muscle, also called the extensor digitorum communis, is an extrinsic hand muscle. Located in the posterior forearm, it is thicker at its proximal end and flattens out as it reaches the wrist. It may be the most apparent of all the forearm hand muscles as it is responsible for most of the shape of the dorsal (extensor) surface of the forearm and you can clearly see its tendons when you extend all four fingers. This may tell you its function, which is, in fact to extend the fingers, and it is the only muscle capable of extending all four.
Along with several other muscles it is part of the "extensor compartment" of the forearm. These other muscles are the extensor indicis, extensor digiti minimi, exensor pollicis longus, and extensor pollicis brevis. It also extends the wrist and is sometimes reported to weakly flex the elbow 2, 3 See also intrinsic hand muscles.
The Extensor Digitorum
Beginning at the distal humerus, the extensor digitorum runs down the dorsal surface of the forearm between the extensor carpi radialis brevis and the extensor carpi ulnaris muscles, which all arise from a common tendon. The muscle then gives way to four tendons on the four fingers. These tendons are united by a oblique bands over the back of the hand so that individual movement of the fingers by the muscle is limited, but not eliminated. The individual parts of the muscle are capable of producing independent finger extension, with the middle and ring extensors being the most symptomatic for trigger points. The tendons on the index and little fingers are commonly joined by thicker tendons from the extensor indicis and the digiti minimi muscles. 4
The action of the extensor digitorum in finger extension is significant and the muscle can be overworked by frequent forceful gripping or repetitive actions of the fingers. Strength trainees engaging in dedicated grip strength training, especially high volume repetitive training, can certainly overload this muscle as any powerful flexion of the fingers requires great activity of the antagonistic extensors, especially since, without them, strong flexion of the fingers while closing the grip would also cause the wrist to bend (flex). Trigger points in the extensor digitorum can cause pain in the forearm, hand, and fingers. 4
Extensor Digitorum Origin, Insertion, and Action
Origin: The common extensor origin which is a smooth area on the anterior distal aspect of the lateral epicondyle of the humerus. Its tendon is fused together with the tendons of the extensor carpi radialis brevis, the extensor digiti minimi, and the extensor carpi ulnaris. There are also attachments arising from the adjacent intermuscular septa and from the fascia of the forearm muscles which neighbor. 2, 5
The Extensor Tendons
Insertion: Four separate tendons form a myotendinous junction around one-third of the way up the distal forearm (2/3 of the way down the proximal forearm). Initially somewhat attached, the tendons separate at the extensor retinaculum and form complex attachments at base of the distal phalanx and middle phalanx of each finger, with attachments on the proximal phalanges also being possible (The tendons and the extensor mechanism they are a part of have many possible variations and are highly complex).
Locating the Extensor Digitorum
Actions: Extension of the four fingers, primarily at the metacarpophalangeal joints. Also some extension of the proximal interphalangeal joints, assisting the interossei and lumbricals. Some seperation (adduction) of the fingers. Wrist extension. 2,1
Extensor Digitorum Trigger Points Referred Pain, Symptoms, and Causes
Pain derived from trigger points in the extensor digitroum could be mistaken for arthritis pain in the fingers or even Tennis elbow because of symptoms at the elbow. Sore and "tender" fingers and aching forearms are also possible, even without actual pain in the joints. Overuse of the fingers in forceful activities such as with pianists, mechanics, carpenters, typists, etc. are likely to cause overload and trigger points in the ED muscle. Overuse of the grip, as in inappropriate grip strength training, are likely also to cause TrP's in the muscle. Although it would be easy to surmise that maximal grip crushing grip training, as with heavy duty hand grippers, would be the most likely to cause this, it is just as likely to be caused by light grippers used with high repetitions, or other types of grip training done with too much volume or frequency. Also, any kind of repetitive gripping or twisting motion of the hand may be responsible.
Typing on a computer keyboard causes the finger extensors to be active almost constantly since they must keep the fingers extended over the keyboard between keystrokes. Mouse clicking, likewise, presents the same problem.
A weak grip and painful and/or stiff fingers can be due to extensor digitorum trigger points. The pain is exacerbated when trying to grip any object strongly and upon such activities as shaking hands. Trigger points in this muscle radiate pain down the dorsal forearm, to the back of the hand, and into back of the fingers (dorsally). The pain does not reach the end of the fingers, but may reach as far as the proximal interphalageal joint. Symptoms will appear in the finger which corresponds to the involved area of the muscle, being the middle or ring finger extensor. The image below shows the approximate point that trigger points develop in the muscle.
Extensor Digitorum Trigger Point Locations
Trigger points in the middle finger appear most often. Pain from this extensor TrP radiates down the dorsal forearm and sends concentrated pain to the middle finger. Trigger points in the middle extensor are also capable of occasionally referring pain to the frontal or "volar" part of the wrist2 The image below shows the referred pain pattern of this TrP.
Middle Finger Extensor TrP Referred
TrP's in the ring finger extensor send pain down the dorsal forearm, crossing the back of the hand, and concentrating pain into the ring finger. The TrP's in this part of the muscle may also send pain upwards, toward the outer elbow at the lateral epicondoyle region so that symptoms similar to the pain of so-called "tennis elbow" is experienced. This condition, called lateral epicondylitis is actually due to pathology in the common extensor tendons rather than problems in the muscle bellies, whether due to TrP's or otherwise. However, in addition to the ring extensor of the extensor digitorum, other forearm muscle trigger points, such as the brachioradialis, supinator, and extensor carpi radialis longus, and brevis can send pain to lateral region of the epicondoyle.3
Since lateral epicondylitis, although initially causing pain only in the lateral elbow eventually tends to spread pain down the arm, pain that is actually being referred from the extensor digitorum or other forearm muscle trigger points can easily be misdiagnosed as lateral epicondylitis, even though no pathology is present in this region. 4,6 The image below shows the referred pain pattern of the ring finger extensor TrP.
Ring Finger Extensor TrP Referred
Finger Flexion Test for Extensor Digitorum
A finger flexion test can be used to help determine which, if any, parts of the extensor digitorum muscles are affected by trigger points. Since extensor digitorum trigger points can be associated with trigger points in the scalene muscles, the same test can be used to test for both, as described in the scalene trigger point article
If one of your fingers sticks out from the others during the finger flex test, and you are unable to get that finger to touch the volar pad without pain, this can indicated a trigger point in the area of the muscle attached to that finger.
Extensor Digitorum Trigger Point Treatment
Using the images above to locate the approximate areas of the trigger points, you should easily be able to palpate the muscle and find the area that elicit a response, which will typically be close to the surface where the taut band can be felt. Those with well developed forearms will be able to see the muscle working when wiggling or extending the fingers. Others can palpate the muscle two or three inches down from the elbow on the outer surface of the forearm and feel the muscle jumping when working the fingers. Once you locate the trigger points they can be treated with a number of simple devices. The fingers of the opposite hand can of course be used but a hard device that can exert deeper and firmer pressure will work best.
A tennis ball can be used against a wall but a small hard rubber bouncy ball, about 1.5 inches in diameter, like the kind sold in party supply or dollar stores, will work even better. Place the ball between a smooth wall and the affected forearm so that the back of your hand is facing the wall and your forearm is horizontal. Using the wall as a rolling surface, roll the ball along the muscle, starting at the middle of the forearm and ending at the elbow. Lean your body weight against the ball to increase pressure as needed. Concentrate the strokes on the most tender areas that house the trigger points.
A firm hand-held roller massage ball works well. Use a roller massage ball in the same manner except hold the support base of the ball in the opposite hand and rest the arm to be massaged comfortable against your stomach so that you can easily access the outer forearm with the ball and apply good pressure.
A Knobble [self-massage tool] will work well held in the hand, and can be used to work a deeper and smaller area. There are many other hand-held self massage devices that can be used, such as the Jacknobber and the Indexknobber. Use these in a manner similar to the roller ball.
You can perform multiple sessions throughout the day, but keep them to around a minute or two in length. 7
Extensor Indices Muscle
While you're treating the extensor digitorum muscle, go ahead and look for trigger points in the extensor indicis muscle, which are likely to be present. Both the EDC and the EI are usually considered together in trigger point treatment. Trigger points in this muscle sends pain to the radial side of the back of the hand (closer to the index finger). Feel for this muscle on the back of the forearm about three inches from the wrist. It is located between the radius and ulna bones, as shown in the image below. A contraction can be elicited by extending the index finger. 4, 7
Extensor Indicis Muscle
Extensor Indicis Trigger
Point and Referred Pain Pattern
Other Associated Trigger Points
Although it is possible for trigger points in the extensor digitorum finger extensors to develp alone, it is also likely that they will develop as part of the above-mentioned "tennis elbow" associated symptoms, which is characterized by trigger points in the supinator, brachioradialis, and extensor carpi radialis longus muscles. Refer to Simons and Travell's Myofascial Pain and Dysfunction: the Trigger Point Manual, Volume One: The Upper Extremities for more complete information. 4
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This page created 15 Oct 2011 00:21
Last updated 23 Feb 2015 19:38