The clinical presentation is consistent with lateral epicondylitis, which is caused from pathologic changes at the origin of the extensor carpi radialis brevis (ECRB).
Physical exam findings consistent with lateral epicondylitis include tenderness over the lateral epicondyle at the origin of the ECRB, and pain that is reproduced with gripping, resisted long finger extension, resisted wrist extension while the elbow is fully extended, and maximum passive wrist flexion. This should be distinguished with the pain with resisted supination with the arm and wrist in extension characteristically seen with radial tunnel syndrome.
Nirschl et al looked at their surgical cohort of patients with lateral epidondylitis that were treated with surgery. They found the lesion that was consistently identified at surgery was immature fibroblastic and vascular infiltration of the origin of the extensor carpi radialis brevis (ECRB). There was an over-all improvement rate of per cent, and per cent of the patients returned to full activity including rigorous sports following surgical treatment.
Morris et al used indwelling EMG to look at muscle activity about the elbow during tennis strokes in nine professional and collegiate level players. They concluded the predominant activity of the wrist extensors in all strokes may be one explanation for predisposition to injury.
139 limbs from embalmed specimens were dissected to reveal the attachments of extensor muscles in the vicinity of the lateral epicondyle. M. extensor carpi radialis brevis was found to consist of a keel-shaped tendon with attachments to m. extensor carpi radialis longus, m. extensor digitorum communis, m. supinator; and to the radial collateral ligament, the orbicular ligament, the capsule of the elbow joint and the deep fascia. On 29 limbs, a prolongation of the muscle was identified attaching proximal to the lateral epicondyle. On nine specimens a bursa was evident between the capsule over the head of the radius and the overlying soft tissues. There was no evidence of variation in vascular or nerve supply to the region. Examination of m. extensor carpi radialis brevis while under tension across the elbow, forearm and wrist revealed the greatest muscle lengthening in pronation of the forearm with palmar flexion and ulnar deviation. The results of this study support the hypothesis that tennis elbow is primarily a mechanically-induced condition. When performing movements at the wrist, with the forearm in pronation, the muscle is at its maximum length. As its origin lies proximal to the axis of rotation for flexion and extension at the elbow, it is subject to shearing stress in all movements of the forearm, especially those involving power at the wrist. This is further compounded by the head of the radius rotating anteriorly against m. extensor carpi radialis brevis during pronation of the forearm. Additionally, a number of individuals may experience pain at the head of the radius during pronation, due to irritation of an underlying bursa.