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BIOMECHANICS The biomechanics of golfer's and tennis elbow can be nicely compared and contrasted because they are extremely similar, although they are somewhat mirror opposites of each other. The muscles of golfer's elbow have their proximal attachments on the medial epicondyle of the humerus, so golfer's elbow causes medial elbow pain; the muscles of tennis elbow attach onto the lateral epicondyle of the humerus, so tennis elbow causes lateral elbow pain. Golfer's elbow is an overuse condition of excessive fl exion of the hand at the wrist joint and fl exion of the fi ngers at the metacarpophalangeal (MCP) and interphalangeal (IP) joints, resulting in overuse of the anterior fl exor compartment of the forearm musculature. In contrast, tennis elbow is primarily an overuse syndrome of excessive extension of the hand at the wrist joint and extension of the fi ngers at the MCP and IP joints, resulting in overuse of the posterior extensor compartment of the forearm musculature. GOLFER'S ELBOW Golfer's elbow involves fi ve muscles that all attach to the medial epicondyle of the humerus and along the medial supracondylar ridge of the humerus. These fi ve muscles are the pronator teres, the three muscles of the wrist fl exor group (the fl exor carpi radialis, palmaris longus, and fl exor carpi ulnaris), and the fl exor digitorum superfi cialis (Image 1). These muscles attach to the medial epicondyle via what is known as the common fl exor tendon because the proximal tendons of these muscles blend into each other. Perhaps a better name might be the common fl exor belly/tendon because their bellies blend together before their tendons merge. As the name common fl exor implies, these muscles are involved with fl exion. The three muscles of the wrist fl exor group all cross the wrist joint anteriorly, so they fl ex the hand at the wrist joint. The fl exor digitorum superfi cialis crosses the 58 m a s s a g e & b o d y w o r k j a n u a r y / f e b r u a r y 2 0 2 0 Biceps brachii Brachialis Triceps brachii Medial epicondyle of humerus Pronator teres Flexor carpi radialis Wrist flexor group Flexor digitorum superficialis Flexor digitorum profundus Palmar carpal ligament Transverse carpal ligament (flexor retinaculum) Flexor digitorum superficialis Flexor digitorum profundus Brachioradialis Extensor carpi radialis longus Flexor pollicis longus Abductor pollicis longus Pronator quadratus Radial styloid Flexor pollicis longus Palmaris longus Flexor carpi ulnaris 1 Anterior view of the right upper extremity. Golfer's elbow causes pain at the medial elbow. The muscles of golfer's elbow common fl exor belly/tendon group are noted in red. Permission Joseph E. Muscolino, The Muscular System Manual, 4th edition, Elsevier, 2015.