Lateral epicondylitis, commonly known as tennis elbow, is a painful overuse injury affecting the tendons on the outside of the elbow. It is a frequent cause of elbow pain, often resulting from repetitive wrist extension or gripping activities. While Magnetic Resonance Imaging (MRI) can visualize the associated damage, it is typically not the initial diagnostic step. Advanced imaging is sometimes necessary, however, to confirm the full extent of the injury and guide treatment due to the complex anatomy of the elbow.
The Anatomy of Lateral Epicondylitis
The common extensor tendon group originates from the lateral epicondyle, a bony prominence on the outer side of the elbow. The extensor carpi radialis brevis (ECRB) is the primary tendon involved in tennis elbow. The ECRB stabilizes the wrist during gripping and repetitive motions, making it highly susceptible to strain.
The pathology is accurately described as tendinosis, indicating a degenerative process rather than acute inflammation (tendinitis). This condition involves microscopic tearing and disorganization of the tendon’s collagen fibers due to a failed healing response. This chronic microtrauma eventually leads to thickened, weakened tendon tissue where it attaches to the bone.
Clinical Examination and Initial Diagnosis
A diagnosis of lateral epicondylitis is usually established through a thorough patient history and physical examination, without immediate imaging. The physician looks for a history of repetitive activity and a gradual onset of pain localized to the outer elbow. The primary diagnostic finding is tenderness when palpating directly over the lateral epicondyle, which is the site of the common extensor tendon origin.
Specific pain provocation tests confirm the involvement of the ECRB tendon. For example, the Cozen’s test requires the patient to extend their wrist against resistance. Reproduction of sharp pain over the lateral epicondyle during this maneuver indicates a positive result. Other physical maneuvers, such as the Mill test or Maudsley test, may also be used to test the extensor muscles.
The Primary Purpose of MRI Assessment
MRI is generally reserved for cases where symptoms are persistent, or recalcitrant, despite several months of conservative treatment. If a patient fails to improve with physical therapy or bracing, imaging is ordered to determine if the injury is more extensive than initially believed. MRI’s superior soft tissue contrast is useful for evaluating the full extent of common extensor tendon damage and for pre-surgical planning.
Excluding Differential Diagnoses
A primary function of the MRI is to exclude other potential causes of lateral elbow pain, known as differential diagnoses. Identifying these other problems is important because they may require a different treatment approach than simple tendinosis.
- Radial tunnel syndrome (a type of nerve entrapment)
- Occult fractures
- Internal joint issues like osteochondral defects
The scan also assesses for coexisting injuries, such as damage to the nearby radial collateral ligament, which can complicate recovery.
Specific Findings Revealed by MRI and Ultrasound
The degenerative changes of tennis elbow are visible on an MRI, where the radiologist assesses alterations in the tendon’s appearance and signal intensity. Healthy tendon tissue normally appears dark on both T1- and T2-weighted MRI sequences. In tendinosis, the tendon shows abnormal thickening and an intermediate to increased signal intensity on the images, particularly on T2-weighted fat-suppressed sequences.
If degeneration has progressed to a tear, it appears as a fluid-filled gap within the tendon, showing high signal intensity on T2-weighted images. Partial-thickness tears can be graded based on the percentage of the tendon thickness involved, ranging from mild to severe. The scan may also reveal associated bone marrow edema, which is swelling within the bone at the point of tendon attachment, or the presence of calcification in chronic cases.
Comparison with Ultrasound
High-resolution musculoskeletal ultrasound is a common and cost-effective alternative to MRI that offers dynamic visualization of the soft tissues. Ultrasound can demonstrate tendon thickening, disorganized tissue structure (heterogeneity), and fluid-filled areas (hypoechogenicity) indicating tears.
While MRI provides a broader view of the entire joint and superior assessment of bone and deep structures, ultrasound allows the physician to observe the tendon in motion. Observing the tendon dynamically can sometimes reveal instability or painful impingement.