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Ta k e 5 a n d t r y A B M P F i v e - M i n u t e M u s c l e s a t w w w. a b m p . c o m / f i v e - m i n u t e - m u s c l e s . 61 name for this group would be the common extensor belly/tendon because, as with the musculature of golfer's elbow, the bellies of the muscles of the common extensor tendon also blend together before their tendons do. As the name common extensor implies, these muscles are involved with extension. The two extensor carpi muscles cross the wrist joint posteriorly, so they extend the hand at the wrist joint. The extensor digitorum crosses the wrist joint posteriorly and the MCP and proximal and distal IP joints of fingers 2–5 posteriorly, so it extends the hand and fingers. The extensor digiti minimi crosses the wrist and the MCP and IP joints of the little finger, so it extends those joints. Only at the elbow joint does some of the mirror symmetry between the common flexor and common extensor groups disappear. The extensor carpi radialis brevis of the common extensor group actually flexes the elbow joint because it crosses it anteriorly (Image 4). All other wrist extensor muscles of the tennis elbow group cross the elbow joint posteriorly, so they extend the elbow joint as they extend the wrist and finger joints they cross. All of these joint actions place a stress on the musculature of this group, as well as on its attachment onto the lateral epicondyle of the humerus. Even though tennis elbow was originally described for its periosteal inflammation of the lateral epicondylar humeral attachment, before the humeral inflammation occurred, tennis elbow involved common extensor tendinopathy; and before the tendinopathy occurred, it began as an overuse and tightness of the myofascial tissue of the muscles involved. In addition to the stress of the joint motions just described, tennis elbow has another cause. Whenever the fingers flex to grip an object, the finger flexor muscles (flexor digitorum superficialis and flexor digitorum profundus) also cause the hand to flex at the wrist joint. To keep the wrist joint in a neutral anatomic position so (&5/ (&5% %UDFKLRUDGLDOLV Whereas golfer's elbow is caused solely by flexion, tennis elbow is often thought of as being caused solely by extension, but is also caused by activities that involve finger flexion. Lateral view of the right upper extremity. The extensor carpi radialis brevis (ECRB) of the common extensor muscle group actually crosses the elbow joint anteriorly, so it flexes the forearm at the elbow joint. Permission Joseph E. Muscolino, The Muscular System Manual, 4th edition, Elsevier, 2015. 4