Plain film radiographic examination of the elbows should be the initialevaluation forpatients withchronicelbowpain. Radiographs can be useful for the assessment of calcium within the joint compartment or periarticular soft tissues. Standard frontal and lateral radiographs are used for the routine evaluation of the elbow joint. Radiographic examination of the elbow has a minimal RRL.
MRI has not been applied to the evaluation of elbow pathology as extensively as it has been to other large joints (17). However, improving imaging techniques and the use of surface coils permit superb visualization of the bony, ligamentous, muscular and neurovascular structures around the elbow. Common elbow injuries evaluated with MRI are usually related to sports (weightlifting, throwing, and racquet sports) or compartmental nerve entrapment.
FIGURE 6-9. Normal elbow as seen on T1-weighted MR images. A: The axial MRI displays the ulna (U), radius (R), annular ligament (AL), radial collateral ligament (RCL), brachial artery (BA), biceps tendon (BT), forearm flexor muscles (FM), forearm extensor muscles (EM), ulnar nerve (UN), and radial nerve (RN). B: The coronal MRI displays the humeroulnar joint (HUJ), humeroradial joint (HRJ), radial collateral ligament (RCL), ulnar collateral ligament (UCL), forearm flexor muscles (FM), and forearm extensor muscles (EM). C: The sagittal MRI through the humeroulnar joint demonstrates the biceps tendon (BT), brachialis (Br), and triceps (T).
Axial MRI views of the elbow region permit good visualization of the biceps, brachialis, triceps, and all the extensor and flexor muscles of the forearm (Fig. 6-9A). High–signalintensity fat planes and low–signal-intensity intermuscular septa permit clear delineation of each muscle and their tendons of insertion or origin. Axial images clearly depict brachial, ulnar, and radial arteries and all the subcutaneous and deep veins. They also allow identification of the ulnar nerve within the cubital tunnel and the radial nerve in the brachioradialisbrachialis interval and under the supinator muscle’s arcade of Frohse, where it is commonly entrapped. The median nerve is visualized at all its common elbow entrapment sites, including under the bicipital aponeurosis, between the heads of the pronator teres, and under the fibrous arch of the flexor digitorum superficialis.
The humeroulnar, humeroradial, and proximal radioulnar joint spaces and articular cartilages are well visualized on both coronal and sagittal MR images (Fig. 6-9B and C). The low–signal-intensity ulnar collateral, radial collateral, and annular ligaments are depicted on both axial and coronal MR images. Sagittal images delineate the anterior and posterior subsynovial fat pads.
MRI has the capability of directly visualizing degenerative or traumatic abnormalities of the annular and the radial and ulnar collateral ligamentous complexes. A sprain appears in MRI as thickened or thinned ligament with surrounding highT2 signal intensity. The collateral ligaments may show degeneration in association with adjacent epiocondylosis. The affected ligament commonly shows thickening and intermediate signal intensity. Full thickness of avulsion ligamentous tears appears as discontinuities of the low–signal-intensity ligament. The T2-weighted images disclose hyperintense edema and hemorrhage between the torn ends of the ligament extending into the joint interval and adjacent soft tissues. A partial thickness tear appears as high T2 fluid signal intensity within an uninterrupted ligament (Fig. 6-10).
FIGURE 6-10. Coronal MR T1WI with intra-articular contrast in a 22-year-old baseball player with medial elbow pain. There is a partial tear (arrowhead) at the insertion of the ulnar collateral ligament into the coronoid process of the ulna. Note the minimal amount of contrast extending between the bone cortex and the distal ligament attachment.
MRI also provides good visualization of the sites of muscle injury and denervation about the elbow (18) (Fig. 6-11A,B). Acute muscle denervation is demonstrated by increased T2-weighted signal intensity within the specific muscle group supplied by the injured or the affected nerve. Increased intramuscular T2-weighted signal intensity is due to muscle edema. Chronic muscle denervation is demonstrated by increased intramuscular T1-weighted signal intensity, related to muscle atrophy and fatty infiltration. Acute muscle injuries presents with intramuscular edema and hemorrhage. Increased thickening, increased signal intensity, and discontinuity of tendon fibers are the findings commonly observed in tendon tears (Fig. 6-12A,B).
FIGURE 6-11. Impingement to the anterior interosseous branch of the median nerve, Kiloh Nevin Syndrome. Axial STIR (short tau inversion recovery sequence) at the level of the distal forearm. On this fat suppressed sequence there is increased signal intensity to the fibers of the flexor pollicis longus muscle as can be appreciated with acute (stage I) or subacute (stage II) impingement. (Courtesy of Zehava Rosenberg, NY.)
FIGURE 6-12. Sagittal A and axial B FSE T2-weighted fat suppressed images of the distal arm in a patient with a complete biceps tear. A: The tendon free margin is retracted (long arrow in A). B: There is significant edema (arrow- heads) surrounding the retracted tendon (long arrow). B, biceps muscle; Br, brachialis muscle.
MRI has the ability to demonstrate tendinosis involving the common extensor and flexor tendon origins from the lateral and medial aspects of the humerus with findings similar to those described in tendinosis about the shoulder. It also can display abnormalities of the radial and ulnar collateral ligament complexes.