The common extensor tendon originates on the lateral epicondyle and lateral supracondylar ridge of the humerus and consists of the fused tendons of the extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris (from lateral to medial). Nearly all forces associated with wrist extension are funneled through this tendon onto lateral epicondyle. The supinator muscle lies deep to the common extensor group, with some fibers attaching to the lateral epicondyle.  The common extensor tendon, particularly the extensor carpi radialis brevis (ECRB), is relatively hypovascular, creating a penchant for injury and hypoxic degeneration.

The pathogenesis of LE entails repetitive wrist extension causing micro-tearing of the common extensor tendon, ultimately leading to a failed healing response and degeneration. The primary site of injury is the extensor carpi radialis brevis (ECRB) tendon, 1-2 cm distal to its attachment on the lateral epicondyle.  While acute inflammation may accompany the earliest phase of tendon disease, it is unlikely to last more than a few days. In chronic cases, inflammatory cells are absent.  Researchers now recognize that repetitive microtrauma does not cause inflammation but rather a failure of the natural healing process, resulting in a disorganized pathological degeneration of the tendon called angioblastic degeneration. Since LE is primarily a degenerative condition rather than a chronic inflammatory process as once hypothesized, the term “tendinitis” has been replaced with “tendonosis” or “tendinopathy”. True tendinitis is rare compared to tendinopathy.  A degenerated tendon may be predisposed to partial or full-thickness tears as a result of ongoing strain, particularly rapid eccentric overload.

Symptoms often begin insidiously following overuse-type activity, without a history of specific trauma. The classic clinical presentation includes pain over the lateral aspect of the elbow.  Symptoms are typically provoked by activities that involve gripping and/or wrist extension.  Pain may vary from mild to sharp severe pain that limits the simplest activities- like picking up a coffee cup. Rest may provide relief.  Symptoms and objective progress may be tracked on a DASH questionnaire, or Patient-Rated Tennis Elbow Evaluation (PRTEE)

Pain is generally localized, and clinicians should consider the possibility of a peripheral neuropathy (radial tunnel syndrome) in patients whose symptoms radiate distally. Radial tunnel syndrome is entrapment of the radial nerve as it passes through the proximal forearm near the lateral epicondyle. Common sites of compression within the radial tunnel include the Arcade of Frohse, or within the supinator muscle. Research suggests that up to 10% of patients with tennis elbow have co-existent radial tunnel syndrome.  The similarities of lateral epicondylitis and radial tunnel syndrome can make differentiation of the two conditions challenging. The pain of radial tunnel syndrome should be more acute distally.  Nocturnal pain is more common in radial tunnel patients than those with lateral epicondylitis.

The classic clinical findings for LE include: pain on palpation of the lateral epicondyle, pain on resisted wrist extension, and pain on resisted middle finger extension.  Peak tenderness is located directly over, and slightly distal to, the lateral epicondyle- most specifically over the origin of the ECRB. Cozen’s test is basically wrist extension performed with the patient’s fist closed and elbow fully extended. Reproduction of pain upon this maneuver suggests LE. When Cozen’s maneuver produces pain when performed with the elbow slightly bent, the condition may be more challenging to manage. Mill’s test for LE involves passive stretching of the wrist extensors while the elbow is in extension. Resisted extension of the middle finger (Resisted long finger extension test) places tensile stress on the ECRB tendon and often provokes LE symptoms. Clinicians should consider radial tunnel syndrome when this maneuver is more painful than Mill’s test.

Neurologic assessment should be performed to identify the possibility of cervical radiculopathy or peripheral neuropathy. Radial tunnel syndrome may manifest as diminished sensitivity along the dorsal aspect of the forearm and/or thumb, or weakness of thumb extension.

Plain film radiography is of little diagnostic value for the assessment of soft tissue disorders.  Radiographs may be appropriate in the presence of “red flags” or a history of trauma, to rule out fracture, dislocation, infection, or neoplasm.  Occasionally, radiographs may demonstrate calcific tendinitis or the presence of intra-articular pathology.  MRI has the ability to demonstrate tendinosis as well as bony or soft tissue pathology. Diagnostic ultrasound is useful for evaluating the common extensor tendon for tendinitis or tearing.

The differential diagnosis of tennis elbow includes cervical radiculopathy, radial tunnel syndrome, osteoarthritis, fracture, infection, neoplasm, osteochondral loose body, elbow synovitis, triceps tendinitis, sprain/strain, myofascial pain syndrome, and inflammatory arthropathy.

The natural course of LE can be exasperating. Twenty percent of untreated patients demonstrate no improvement after one year.  Even those patients undergoing optimal management may require three to four months for a full recovery.  Evidence supports the use of traditional conservative measures, including manipulation, mobilization, exercise, friction massage, bracing, and modalities.

Initially, patients may require selective rest and avoidance of activities involving repetitive wrist extension, pronation, or supination. Counter-irritant creams may provide palliative relief. Ice or home ice massage may be helpful for acute “tendinitis” patients, but do little to alter the long-term course of chronic tendinopathy. Tennis players should look for ways to improve mechanics, including not leading with their elbow and switching to a 2-hand backstroke that limits pronation.  The use of a counter-force strap applied firmly approximately 10 cm distal to the elbow joint has been shown to decrease pain and improve grip strength. Counter-force braces should not be used in cases of concurrent radial tunnel syndrome, as the additional pressure will likely exacerbate compressive neuropathy symptoms. Some clinicians choose to employ a cock-up wrist splint, although this orthotic has less support in the literature.