Tennis Elbow - Anatomy

My regular readers will know that I believe anatomy to be the cornerstone of understanding an injury. This section may be wordy and technical for some of you. I apologize for that, but at least the pictures are pretty.

 Lateral epicondylitis was first described in 1973 by Runge and in 1883 Morris first attributed the condition to tennis - "lateral elbow pain in the tennis player." That gives us a pretty good idea of the area we will be looking at. Epicondylitis is a bit of a misnomer as studies have shown that there really isn't much of a inflammatory process, but more on that later.

The reason that the pain is felt in the lateral part of the elbow is because this the the common extensor origin for the forearm musculature. The muscles that originate here are responsible for wrist extension (as with a backhand in tennis) as well as radial deviation. Let's have a look at the lateral epicondyle.

The lateral epicondyle is the bony protuberance on the distal lateral humerus that articulates with the head of the radiuslat the lateral portion of the olecranon as it  This is where the common extensor origin is. The muscles that attach to the lateral epicondyle are as follows.

extensor carpi radialis brevis
extensor digitorum
extensor digiti minimi
extensor carpi ulnaris

These muscles all originate from a single tendon - hence the name "common extensor" - and branch into the separate muscles to attach to different parts of the wrist/hand. All of the muscles that origination for the common extensor tendon are innervated by by a branch of the radian nerve called the posterior interosseous nerve (PIN) from nerve roots C6-8. I'll talk a little more about the PIN in the next section.
The extensor carpi radialis brevis follows a superficial route along the lateral shaft of the radius to insert at the base of the 3rd metacarpal. It acts on wrist extension and radial deviation.
The extensor digitorum follows a superficial route on the posterior aspect of the forearm and inserts on the extension expansion where it splits to then insert into the distal phalanges 2-5. It acts mainly to extend the those phalanges.
The extensor ditigi minimi follows a superficial, posterio-medial route along the shaft of the ulnar just below the extensor digitorum and extensory carpi ulnairs. It inserts in the extension expansion where it continues to inserts on the tendon of the extensor digitorum at the dorsal base of the 5th phalanx. It acts synergistically with the extensor digitorum to extend the 5th phalanx.
Finally, the extensory ulnaris, which not only originates from the common extensor origin, but also the the middle third of the proximal ulna. It follows a superficial route along the posterio-medial shaft of the ulnar to insert at the dorsal base of the 5th metacarpal. it acts on wrist extension and ulnar deviation.
There is also literature that suggests that the lateral ulnar collateral ligament (LUCL) of the elbow also contributes to the pain of tennis elbow. The LUCL originates on the lateral epicondyle and inserts into the tubercle of the supinator crest of the ulna. It is under tension through the full range of elbow flexion as well as during supination. I'll explain why this matters in the next section. 

The literature on tennis elbow suggests that the muscle that contributes most the the pain felt with tennis elbow is the extensor carpi radialis brevis (ECRB). I'll elaborate a little more on this in the next section.

There may be more structures at play than what is mentioned above such as bursa's and granulated tissue. I'll talk briefly about this in the next section, but I will not include the bursae in the anatomy of tennis elbow because of a lack of literature that says it is a contributor to tennis elbow pain.
Let's sum all that wordiness above up.

Posterior Interoeseus Nerve - the deep motor branch of the radian nerve. nerve roots from C6-8

Extensor Carpi Radialis Brevis
Extensor Digitorum
Extensor Digiti Minimi
Extensor Carpi Ulnaris

Lateral Collateral Ulnar Ligament

Next up: Causes and Symptoms

Note: all images are sourced from Gray's Anatomy with minor alterations (shading of specific anatomy). Gray's Anatomy is public domain.

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