The distal biceps brachii tendon may show findings of tendinosis (hypoechoic enlargement), partial-thickness tear (anechoic clefts), and full-thickness tear (complete tendon discontinuity) (Fig. 2) associated with sports injuries [15]. Ultrasound imaging of the distal biceps brachii tendon is often difficult given the oblique course of the distal tendon and resulting anisotropy. Imaging the biceps tendon from a medial or pronator window approach, with possible elbow flexion, is often helpful [16]. Partial-thickness biceps tears may involve one of the two heads, commonly the more superficial short head, which can create refraction shadowing artifact possibly obscuring the deeper long head tendon. In differentiating partial-thickness from full-thickness tendon tear, the use of dynamic evaluation is helpful, either imaging from a medial or lateral approach [17]. With supination and pronation, lack of tendon movement to the same degree as radial tuberosity rotation is indirect evidence of full-thickness tear. Often full-thickness distal biceps brachii tendon tears will be associated with significant tendon retraction.

Distal triceps brachii tendon tear are also effectively evaluated with ultrasound. Partial-thickness tears often involve the superficial combined long and lateral heads, associated with an avulsed enthesophyte bone fragment (Fig. 3) [18]. The deeper medial head is often intact but may be erroneously interpreted as torn given that the medial head tendon is very short. Tendinosis may uncommonly involve the distal triceps brachii tendon, as well as distention of the overlying olecranon bursa.

Epicondylitis may also be diagnosed with ultrasound. With lateral (tennis elbow) more common than medial (golfer’s elbow), the term “epicondylitis” is a misnomer in that it is not a primary epicondyle problem and is not inflamed [19]. The underlying pathology, similar to other tendons, represents tendinosis, interstitial tear, or uncommonly full-thickness tear (Fig. 4). The presence of hyperemia on color Doppler imaging correlates with symptoms and represents neovascularity rather than an indirect sign of inflammation.

The ulnar collateral ligament is evaluated dynamically with ultrasound, and complements MR arthrography where the accuracy in diagnosis of tear is highest when both imaging methods are used [20]. With the elbow flexed at least 30 degrees, valgus stress is placed across the elbow. Asymmetric widening of the medial joint space between the humerus and ulna with valgus stress can indicate ligament tear [20].

Sports injuries of the hand and wrist are often ligamentous or related to the triangular fibrocartilage complex, which are best evaluated with MR or preferably MR arthrography; however, ultrasound can be used to evaluate focal tendon abnormalities. For example, intersection syndrome will appear as asymmetric hypoechoic swelling, edema, and possible hyperemia where the first extensor wrist compartment muscles (extensor pollicis longus and abductor pollicis brevis) cross over the second extensor wrist compartment (extensor carpi radialis longus and brevis) [21]. Full-thickness tendon tears are often associated with tendon retraction. Related to the extensor tendons, sagittal band injury at the level of the metacarpophalangeal joints is diagnosed when abnormal hypoechogenicity is seen with asymmetric location of the extensor tendon, best seen dynamically with flexion at the metacarpophalangeal joints, termed Boxer’s knuckle [22]. Related to the flexor tendons of the fingers, ultrasound is effective in evaluation of the pulleys of the digits. Non-visualization of a pulley can indicate injury; however, the finding of tendon bowstringing is an important indirect sign of pulley injury, which appears as an abnormal position of the flexor tendon not approximated to the phalanx (Fig. 5). Bowstringing is evaluated dynamically with active finger flexion against resistance where a distance between the flexor tendon and phalanx greater than 1 mm indicates pulley injury; a distance greater than 3 mm indicates a complete A2 pulley tear and a distance of 5 mm indicates a combined complete tears of A2 and A4 pulleys [23].

One ligament that is ideally evaluated with ultrasound is the ulnar collateral ligament of the thumb [24]. Injury to this ligament, termed skier’s or gamekeeper’s thumb, can range from sprain (hypoechoic swelling), partial tear (partial anechoic defect), and complete tear (discontinuous ligament), with the latter either being non-displaced or displaced [25]. A displaced ulnar collateral ligament tear with an interposed adductor aponeurosis is termed a Stener lesion. Ultrasound is able to diagnose a Stener lesion with 100% accuracy [24]. Key to evaluation is correct placement of the transducer in the coronal plane relative to the thumb with visualization of the characteristic bone contours at the expected attachments of the ulnar collateral ligament. The adductor aponeurosis is identified as a thin hypoechoic structure that normally overlies the intact ulnar collateral ligament, where flexion and extension at the interphalangeal joint causes isolated movement of the aponeurosis, which aides in its identification. The distal aspect of the displaced ulnar collateral ligament is identified as a hypoechoic round abnormality proximal to the metacarpal joint (Fig. 6), with a possible hyperechoic and shadowing avulsion bone fragment. The end of the torn ligament may be seen superficial to the adductor aponeurosis, or may be seen along the distal metacarpal shaft with the ligament coursing proximal.