A potential factor in the pathophysiology of lateral epicondylitis: The long sarcomere length of the extensor carpi radialis brevis muscle and implications for physiotherapy.

Lateral epicondylitis is a chronic angiofibroblastic degeneration of the origins of the wrist extensor muscles and is characterized by diffuse elbow pain. Although it is the most common syndrome of the elbow joint, the most affected structure is the tendon of the extensor carpi radialis brevis (ECRB) muscle. Several theories have been proposed to explain the pathophysiology of lateral epicondylitis, however, there is no evidence to show that the sarcomere length and microanatomical features of the ECRB muscle can be affected by the elongated position of the muscle. We hypothesized that the tensile response may be the responsible mechanism in the pathophysiology of lateral epicondylitis due to the microanatomy of the ECRB muscle and its functioning in the elongated position. Elongated position leads to elongation of the sarcomere length by forming a functional traction angle in the ECRB muscle. The elongated sarcomere length negatively affects muscular microcirculation. Poor microcirculation triggers ischemia in the muscle and tendon and leads to an increase in immature Type III collagen synthesis. Disruption of the collagen continuity and the loss of load-bearing capacity initiate the neovascularization process. This situation accelerates the degeneration process in the tendon and prevents healing. Furthermore, based on our hypothesis, we recommend new physiotherapy approaches that may contribute to reducing the increased incidence of tendinopathy and to the healing process.