Pathophysiology
The pathophysiology of lateral epicondylitis is degenerative. Non-inflammatory, chronic degenerative changes of the origin of the extensor carpi radialis brevis (ECRB) muscle are identified in surgical pathology specimens. It is unclear if the pathology is affected by prior injection of corticosteroid.
Among tennis players, tennis elbow is believed to be caused by the repetitive nature of hitting thousands and thousands of tennis balls which lead to tiny tears in the forearm tendon attachment at the elbow.
The extensor digiti minimi also has a small origin site medial to the elbow which can be affected by this condition. The muscle involves the extension of the little finger and some extension of the wrist allowing for adaption to "snap" or flick the wrist – usually associated with a racquet swing. Most often, the extensor muscles become painful due to tendon breakdown from over-extension. Improper form or movement allows for power in a swing to rotate through and around the wrist – creating a moment on that joint instead of the elbow joint or rotator cuff. This moment causes pressure to build impact forces to act on the tendon causing irritation and inflammation.
The following speculative rationale is offered by proponents of an overuse theory of etiology: The extensor carpi radialis brevis has a small origin and does transmit large forces through its tendon during repetitive grasping. It has also been implicated as being vulnerable during shear stress during all movements of the forearm.
While it is commonly stated that lateral epicondylitis is caused by repetitive microtrauma/overuse, this is a speculative etiological theory with limited scientific support that is likely overstated. Other speculative risk factors for lateral epicondylitis include taking up tennis later in life, unaccustomed strenuous activity, decreased mental chronometry and speed and repetitive eccentric contraction of muscle (controlled lengthening of a muscle group).
Read more about this topic: Tennis Elbow