Tennis elbow is caused as a result of specific strain or overuse of outer part of elbow. In medical term it is referred as lateral epicondylitis since it affects the lateral epicondyle of the humerus. Lateral epicondyle is a small, tuberculated eminence, giving attachment to the radial collateral ligament of the elbow joint and to a tendon originating in some of the extensor muscles. This extensor tendon is shared by a number of extensor muscles of the forearm. Some of the prominent muscles in this category are extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi and extensor carpi ulnaris.
Extensor carpi radialis brevis:
Extensor carpi radialis brevis originates from the lateral epicondyle of the humerus by a tendon common to it and other three muscles. The fibers of the muscles ends in the middle of the forearm and is supplied by a branch of the radial nerves. It helps in manipulating the wrist so that hand moves away from the palm and towards the thumb.
Extensor digitorium also arises from the lateral epicondyle of the humerus and divides into four tendons. These four tendons are diverged on the back of the hand and inserted into the second and third phalanges of the fingers. It extends the phalanges, then the wrist and finally the elbow. It tends to separate the fingers as it is involved in extending them.
Extensor digiti minimi:
The extensor digiti minimi is a slender muscle of forearm emerging from the anterior portion of lateral epicondyle of the humerus. It actually helps in extending the little finger at all joints.
Extensor carpi ulnaris:
Extensor carpi ulnaris is an extensor muscle which is situated on the posterior side of the forearm. It rises from the lateral epicondyle of the humerus and crosses the forearm to the medial side of ulna and inserts at the base of the 5th metacarpal. The main objective of extensor digiti minimi is to extend the wrist. When it is acting alone, hand is inclined toward the ulnar side. The elbow-joint shows extension during its continuous motion.
These are the main four muscles which are responsible for proper functioning of tennis elbow. A small dysfunction of any of the muscle can lead to the origin of tennis elbow.