Role of dynamic ultrasound in assessment of the snapping elbow and distal biceps tendon injury

Abstract

Introduction: Ultrasound is useful in assessing patients with snapping syndromes around the elbow joint. The dynamic nature of the examination allows for direct visualisation of the underlying causative factor.Topic description: We discuss the role of dynamic ultrasound in assessing various snapping syndromes around the elbow, such as ulnar nerve instability, snapping triceps and less commonly, snapping brachialis. Ultrasound is also useful in evaluating the distal biceps tendon, particularly in differentiating partial from complete tendon injury.

Discussion: Ulnar nerve instability and snapping triceps can be assessed via a medial approach with the transducer placed transversely between the medial epicondyle and the olecranon. In ulnar nerve instability, the nerve can be seen crossing over the medial epicondyle on elbow flexion. In snapping triceps syndrome, both the ulnar nerve and the distal triceps can be seen dislocating over the medial epicondyle. Dynamic assessment of the distal biceps tendon using a lateral approach minimises anisotropy artefact often seen on the anterior approach. Passive pronation and supination of the forearm will reveal little or no movement in a completely torn tendon whereas moving tendon fibres will be appreciated in partial tears. In a snapping brachialis, the medial portion of brachialis will be seen abnormally translocating anterolateral to the medial border of the trochlea during elbow flexion and snapping back into its normal position on elbow extension.

Conclusion: Dynamic ultrasound of the elbow is valuable in diagnosing patients with snapping sensations around the joint and in evaluating the integrity of the distal biceps tendon.

Keywords: Musculoskeletal; brachialis; real-time imaging; tendinopathy; triceps; ulnar nerve.

Figure 1.

Normal ultrasound examination of the ulnar nerve within the cubital tunnel using a high-frequency (6–18 MHz) hockey stick probe. (a) Positioning of patient when scanning the elbow from a medial approach. This is ideally done by placing the patient’s elbow above a pillow or foam with the olecranon at the free edge allowing for optimum placement of the transducer and the examiner’s hand to assess the cubital tunnel structures. (b) Axial US image across the cubital tunnel showing the ulnar nerve (UN), medial triceps (MTr), medial epicondyle (ME) and olecranon (O) as well as the Osborne ligament running between the ME and O, forming the roof of the cubital tunnel (arrowheads).

Figure 2.

A 24-year-old woman with ulnar nerve instability (a) US image of ulnar nerve (UN) in transverse axis at the level of the cubital tunnel between the olecranon (O) and medial epicondyle (ME) in elbow extension position. (b) On elbow flexion, the ulnar nerve has crossed over the apex of the medial epicondyle to locate outside the cubital tunnel, confirming ulnar nerve dislocation. Note that the medial triceps (MTr) remains posterior to the ME on elbow flexion. See also Video 1.

Figure 3.

A 32-year-old woman with snapping triceps syndrome (a) US image of the ulnar nerve (UN) at the level of the cubital tunnel in elbow extension demonstrates an enlarged ulnar nerve with cross-sectional area (CSA) of 17.2 mm² (well above normal CSA cut off limit of 10 mm²). Note that the UN is also abnormally hypoechogenic with ill-defined fascicles. (b) On elbow flexion beyond 90°, both the UN and medial triceps (MTr) can be seen crossing beyond the apex of the medial epicondyle (ME), in keeping with medial triceps and ulnar nerve dislocation. See also Video 2.

Figure 4.

Normal ultrasound examination of the elbow via anterior and lateral approach for assessment of the distal biceps tendon using a high-frequency (5–14 MHz) linear probe. Figure legends at corner of image demonstrates patient and probe positioning for each image. (a) Anterior approach elbow US in transverse axis allows visualization of the (long) and (short) heads of the biceps tendon which are identified just lateral to the brachial artery (BA) and median nerve (MN). Note that the tendons are next to each other. (b) Anterior approach US image slightly more distally demonstrating the 90° rotation of the distal biceps tendon components to lie on top of each other. (c) Anterior approach elbow US in longitudinal axis demonstrating the normal distal biceps attachment to the radial tuberosity (RT). Note the anisotropy artefact (arrows) slightly limiting the assessment of the very distal attachment. (d) Lateral approach elbow US in longitudinal axis of the distal biceps tendon, demonstrating normal tendon appearance. Note the lateral approach allows for transducer placement parallel to the distal biceps tendon with minimal anisotropy and the edge artefact (asterisk) from the supinator muscle (S). The biceps tendon is curving deep to the radial neck (RN) and therefore the footprint attachment is difficult to visualize using this approach. See also Video 3.

Figure 5.

A 48-year-old man with partial-thickness tear of the distal biceps tendon. (a) US image of the distal biceps tendon via anterior-longitudinal approach demonstrates ill-definition and hypoechoic appearance of the distal biceps tendon (BT) fibres, with the impression of anechoic fluid deep to the tendon (Asterisks). Note the anisotropy limiting the assessment of the distal BT in this anterior-longitudinal approach. (b) Lateral approach ultrasound image confirms partial tear to one component of the distal biceps tendon (small arrow) and intact appearance to the other component (long arrow). Note there is a heterogeneous area of reduced echogenicity and architectural distortion within the extensor muscle (E) in keeping with low-grade muscle injury. See also Video 4. RH: radial head; RN: radial neck; RT: radial tuberosity.

Figure 6.

A 25-year-old woman with snapping brachialis. (a) US image of the brachialis muscle in transverse axis via anterior approach in elbow extension (as shown in figure legend) using a 5–14 MHz linear probe, demonstrating the medial portion of the brachialis muscle (arrow heads) located outside the medial border of trochlea (T). This is the normal position of the medial brachialis. (b) Upon elbow flexion, the medial portion of the brachialis (arrow heads) snaps to lie anterolateral to the medial border of trochlea (T). See also Video 6.