Pathology
In lateral epicondylitis, pain occurs in the lateral proximal forearm where the wrist extensors attach to the lateral epicondyle of the humerus. While many anatomy books indicate each of the extensor tendons as a separate attachment, their fibers actually blend together at this site; therefore, they are often referred to as having an attachment through the conjoined tendon at the lateral epicondyle. Despite the fact that these fibers blend together, it is sometimes clear that the primary pathology is more in one tendon than in others. Because of its angle of pull, the extensor carpi radialis brevis appears to take more of the load than the other tendons. Thus, it is more frequently the source of the primary complaint.

The name epicondylitis implies that the condition occurs from inflammation of the epicondyle because of the suffix "itis," which means inflammation. Yet, the problem is not the epicondyle itself, but the extensor tendons that attach to it.

For many years this condition has been treated as if it were an inflammatory tendinitis of the extensor tendons. Predominant theory suggested that constant tensile loading of the tendons from repetitive motion caused fiber tearing and a subsequent inflammatory response as the body attempted to heal the condition.

However, recent investigations into the nature of overuse tendon pathologies have come up with some interesting conclusions that alter our concept of tendinitis altogether. Almost all of the common overuse tendon injuries, such as patellar tendinitis, rotator-cuff tendinitis and lateral epicondylitis, are rarely inflammatory conditions and don’t occur from fiber tearing within the tendon. Electron microscopy has revealed that in most of these conditions there is an absence of inflammatory cells and no fiber tearing.

Most contemporary researchers now suggest that the word "tendinitis," which indicates an inflammatory condition, be replaced by "tendinosis." Tendinosis indicates an abnormal condition of the tendon, but does not specify that it is inflammatory in nature. What appears to be occurring in these tendon pathologies is a degeneration of the collagen matrix within the tendon. While most cases appear to be tendinosis, it is important to remember that true tendinitis (tearing of the tendon fibers) can occur; however, it is quite rare.

With this new understanding several factors related to the clinical picture of epicondylitis seem to make more sense. If this condition were occurring from a tearing of the tendon fibers, the subsequent injury-repair process would help the tissue heal in a relatively short period of time. However, many people have developed chronic cases that can go on for weeks or months. It just so happens that the process of rebuilding the damaged collagen is a much slower process, which explains the chronic nature of these problems.

The majority of problems in lateral epicondylitis come from excessive concentric wrist extension or eccentric wrist flexion. Either of these actions performed repetitively is likely to overwhelm the tendon fibers and lead to chronic collagen degeneration. This may happen during various occupational activities when the hands are doing a repetitive task, such as the grasping and moving of objects through a grocery store checkout line.

Tension in the wrist extensor muscles from isometric contractions may also cause fatigue and tendon degeneration. People who do a great deal of work with a computer mouse may experience these problems. In order to operate the mouse there are chronic isometric contractions in the wrist extensor muscles.

In addition to the more obvious movements of flexion and extension, there is evidence that repetitive supination and pronation of the forearm may lead to epicondylitis. This likely occurs because the flexor and extensor muscles act with strong isometric contractions to hold the hand in position during supination and pronation movements. Constant contractions in the wrist may also lead to the development of myofascial trigger points in the extensor muscles. These trigger points may produce symptoms similar to the pain from tendon-fiber degeneration and be a concurrent problem that needs treatment.

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