It is on anterior aspect of lateral epicondyle of humerus and Extensor expansion of little finger-usually two tendons which are joined by a slip from extensor digitorum at metacarpophalangeal joint.
Origin: Common extensor tendon from lateral epicondyle of humerus, and deep antebrachial fascia. Insertion: By four tendons, each penetrating a membranous expansion of the dorsum of the second to fifth digits and dividing over the proximal phalanx into a medial and two lateral bands.  Origin: Common extensor tendon from latearl epicondyle of humerus and deep antebrachial fascia Insertion: into expansion of little finger with extensor digitorum tendon Action: Extend MCP joints and IP joints. Origin: Common flexor tendon from medial epicondyle ofhumerous, deep to antebrachial fascia insertion: flexor retinaculum and palmar aponeurosis action: Tenses palmar fascia, flex wrist assists in elbow flexion. Muscles, ligaments and tendons are the structural support for the elbow joint. The elbow is the location of origin for the muscle of the forearm, the common extensor muscles at the lateral epicondyle and the common flexor muscles at the medial epicondyle of the humerus. The biceps and brachioradialis muscles also attach to the elbow joint region. Lateral epicondylitis or “tennis elbow” is an overuse syndrome of the common extensor tendon of the forearm. This syndrome has been documented as one of the most prevalent disorders of the arm. This injury is seen as a degenerative syndrome of the extensor tendon at the lateral epicondyle. ORIGIN Common extensor origin on anterior aspect of lateral epicondyle of humerus. INSERTION Extensor expansion of little finger-usually two tendons which are joined by a slip from extensor digitorum at metacarpophalangeal joint.  Tennis elbow. Tendon pathology involving the common extensor tendon origin is the most common cause of elbow pain and/or disability, and is much more common than tendinous injury of the common flexor tendon origin. Tennis elbow is a clinical diagnosis and typically does not necessitate imaging. Findings include thinning, partial tearing or avulsion of the common extensor tendon origin at the lateral epicondyle. The common extensor tendon is a tendon that attaches to the lateral epicondyle of the humerus. It serves as the upper attachment (in part) for the superficial muscles that are located on the posterior aspect of the forearm: 1  extensor carpi radialis brevis. 2  Extensor digitorum. Posterior view of muscles of the forearm showing common extensor tendon (Suarez, C.A. and Vilensky, J., All-in-One Anatomy Exam Review. Structure Edit. It arises from the lateral epicondyle of the humerus, by the common tendon; from the intermuscular septa between it and the adjacent muscles, and from the antebrachial fascia. The extensor digitorum muscle (also known as extensor digitorum communis) is a muscle of the posterior forearm present in humans and other animals. Extensor tendinopathy or as it is most commonly know “tennis elbow” is pain in the outside of the elbow that comes from inflammation and degeneration of the tendons on the outside of the elbow. The tendons are part of the muscles that control movements of the wrist, hand and fingers. Extensor Tendinopathy is classified as an overuse injury occurring at the common extensor origin (CEO) on the outside of the elbow. The wrist extensor muscles are attached to the CEO via a common tendon. This overuse condition occurs due to repetitive forces at the CEO. 
http://classes.kumc.edu/sah/resources/handkines/muscles/eeextdigcomm.htm https://quizlet.com/4528082/muscles-of-the-hand-flash-cards/ http://morphopedics.wikidot.com/lateral-epicondylitis http://www.lumen.luc.edu/lumen/MedEd/GrossAnatomy/dissector/mml/edm.htm http://www.medscape.com/viewarticle/842224_3 https://en.wikipedia.org/wiki/Common_extensor_tendon https://en.wikipedia.org/wiki/Extensor_digitorum_muscle http://www.sportscarephysio.com.au/resources/extensor-tendinopathy-tennis-elbow/
common extensor tendon origin and insertion