Barbara Riccio Via Montebello 15, Torino (TO), Italy Ultrasonographic examination of the elbow and shoulder yields information about the soft tissue structures of elbow and shoulder joints, complementing the information that is obtained through radiography and nuclear scintigraphy. These areas have been traditionally difficult to examine properly in the field with radiography, and ultrasonographic examination can be helpful for the practitioner to obtain diagnostic information about conditions related to these areas. An upper limb lameness, a history of trauma, a swelling or local deformation, a hematoma, an abscess, a draining tract, or a lameness localized to the joint are all common indications for ultrasonography of the shoulder and elbow. In cases in which the lameness is localized to the elbow, ultrasonography is considered more sensitive than radiography for detection of early bone remodeling that is usually associated with osteoarthritis. As an ultrasound examination of the shoulder and the elbow is less commonly performed than in other regions, it is recommended to prepare both limbs in order to use the opposite limb for comparison. Sedation is usually not needed in adults, while young animals usually require a low dose of sedation. Routine skin preparation is used. Diagnostic images can be obtained with high-frequency linear transducers (5–10 MHz), but a convex probe can be useful at the cranial aspect of the elbow to study the distal insertion of the biceps brachii tendon. In cases of ultrasound-guided injections, a micro-convex probe is suitable. A standoff pad is required to improve contact with the lateral aspect of the elbow during examination of the lateral collateral ligament of the elbow joint. The elbow joint can be scanned from cranial, lateral, and medial approaches. Ultrasonography of the elbow is performed in the weightbearing position, but the evaluation of the medial aspect of the elbow joint is limited in this position. To allow better positioning of the transducer in this area the limb should be pulled forward, but nevertheless medial access in not easy. A complete sonographic examination of the elbow should involve the lateral and medial collateral ligaments, the triceps brachii tendon, the proximal tendon of the ulnaris lateralis, the distal biceps brachii tendon, the joint space, and the articular cartilage. Examination of the lateral collateral ligament, the triceps brachii tendon, the proximal tendon of the ulnaris lateralis, and the articular cartilage of the humeral trochlea is straightforward. The medial collateral ligament and the distal biceps brachii tendon require more expertise to assess. The elbow joint is formed by the articulation of the distal humerus with the radius and ulna. The distal humerus has two condyles that are unequal in size, with the medial condyle being significantly larger. They are separated by a groove that sometimes contains a synovial fossa (Figure 5.1). The epicondyles sit proximal and caudal to the condyles, and between the epicondyles is the olecranon fossa which interdigitates with the anconeal process of the ulna. The joint is supported medially and laterally by collateral ligaments and dorsally by a thick dorsal capsule, which includes the attachment of the proximal tendon of the extensor carpi radialis. At this level on the dorsal aspect, the humeral condyle is covered by three muscles (from medial to lateral): the biceps brachii muscle belly and distal tendon, the brachialis muscle, and the extensor carpi radialis muscle. The biceps brachii tendon and the brachialis muscles may appear hypoechoic as a function of the orientation of the probe. In a normal joint, no synovial fluid is present on the cranial aspect of the joint. The amount of synovial fluid and the articular margins are better evaluated on the lateral aspect at the level of the collateral lateral ligament. In the lateral recess of normal horses, it is possible to find a small amount of synovial fluid. The best site to perform an ultrasound-guided injection is at the level of the joint space, immediately caudal to the lateral collateral ligament, with the probe in transverse section. Figure 5.1 Normal images of the dorsal aspect of the elbow joint in transverse (A and B) (medial is to the left) and longitudinal (C) (proximal is to the left) sections. (A and B) The dorsal aspect of the elbow joint is characterized by a strong articular capsule with the attachment of the extensor carpi radialis tendon. By slightly changing the orientation of the probe, we can better visualize the articular cartilage and the biceps brachii becomes more echogenic as seen in (A). (C) Longitudinal section corresponding to the red line in Figure 5.1B. 1: skin; 2: extensor carpi radialis muscle; 3: brachialis muscle; 4: biceps brachii muscle; 5: dorsal aspect of the humeral condyle; 5a: medial ridge of the trochlea; 5b: groove; 5c: lateral ridge of the trochlea; 5d: capitulum; 6: dorsal articular capsule; 7: dorsal aspect of the proximal radius; 8: joint space. Abnormalities of the elbow joint other than septic arthritis are uncommon and septic arthritis is the most common abnormality seen. Septic arthritis is most common in foals, but occasionally is seen in older horses in association with trauma. The humerus, other than the deltoid tuberosity, is largely protected from the effects of direct trauma by muscles, but the olecranon of the ulna and the lateral aspect of the elbow are covered with minimal soft tissues and are therefore much more susceptible. With trauma to the lateral aspect of the elbow joint, wounds may easily extend into the elbow joint and sepsis should be considered. Ultrasonographically, this condition is characterized by a large amount of synovial fluid, which can appear hypoechogenic or echogenic due to an increased cellularity and/or the presence of fibrin (Figure 5.2). Figure 5.2 Septic arthritis of the elbow joint. (A) A 5-year-old draft horse with a severe swelling of the left elbow region caused by septic arthritis of the joint secondary to trauma. (B) Ultrasonogram of the lateral aspect of the left elbow. The lateral recess of the elbow joint is filled with a large amount of echogenic synovial fluid consistent with septic arthritis. The diagnosis was confirmed by synovial fluid analysis. 1: skin; 2: lateral recess of the elbow joint; 3: radius. In horses, osteoarthritis of the elbow joint is relatively unusual but can be seen in older sport horses, often with a history of trauma. Osteoarthritis can also be secondary to collateral ligament desmitis, osseous cyst-like lesions of the proximal aspect of the radius, olecranon fractures, post-sepsis, or some other primary insult to the joint. Periarticular bone modeling, osteophytes, and an increased amount of synovial fluid with echogenic spots consistent with fibrin are the most likely ultrasonographic findings (Figure 5.3). Figure 5.3 Osteoarthritis of the elbow joint. Ultrasonogram of the lateral aspect of the left elbow of a 10-year-old show jumper horse with a chronic intermittent left fore limb lameness. (A) Longitudinal sections of the joint slightly cranial to the lateral collateral ligament. The bone surface of the lateral aspect of the affected left radial condyle (LF) is irregular (arrows) compared to the unaffected contralateral right limb (RF). (B) Two longitudinal sections of the affected left fore limb showing similar abnormal findings to (A). (C) Two transverse images of the lateral recess of the elbow joint which is markedly distended. The synovial fluid contains multiple echogenic “spots,” consistent with fibrin. These findings are indicative of osteoarthritis with chronic synovitis. 1: skin; 2: lateral humeral condyle; 3: joint space; 3a: lateral recess of the elbow joint; 4: lateral radial condyle. The lateral collateral ligament of the elbow joint is short; it originates from the lateral humeral condyle and inserts distally on the lateral tuberosity of the radius just distal to the joint margin. The lateral collateral ligament is a strong ligament compared to the medial, which is thinner and weaker. The lateral collateral ligament is easily imaged under the lateral head of the triceps brachii muscle. This ligament is slightly heterogeneous because of its spiral fibers. The ligament has two portions with different fiber orientation: the deep portion which is shorter and travels obliquely in a disto-caudal direction and is less echoic, and a superficial portion which is longer and almost vertical. In a transverse section, it is possible to obtain three different images of the collateral ligament: at its proximal humeral enthesis, at the joint space, and at its distal radial insertion. The proximal part of this ligament appears ovoid/elliptic shaped and appears less homogeneous than distally (Figures 5.4 and 5.5). Figure 5.4 Normal longitudinal (left) and transverse (right) ultrasound scans of the lateral collateral ligament (LCL) of the elbow joint from its origin (A), just proximal to the joint space (B), at the level of the joint space (C), and at its distal insertion (D). The shape of the LCL is ovoid proximally and becomes more flat distally. In the transverse scan at the level of the joint space (C), it is possible to appreciate the articular cartilage layer (6). Longitudinal section: proximal is to the left, lateral is to top. Transverse section: cranial is to the left, lateral is to top. 1: lateral humeral condyle; 2: lateral collateral ligament; 3: skin; 4: joint space; 5: lateral radial tuberosity; 6: articular cartilage; R: radius. Figure 5.5 Normal longitudinal (left) and transverse (right) ultrasound scans of the lateral collateral ligament (LCL) of the elbow joint at the level of the joint space. (A) Longitudinal section (proximal is to the left, lateral is to top) and transverse section (cranial is to the left, lateral is to top). (B) Transverse section (cranial is to the left, lateral is to top). In transverse section, caudally to the LCL, there is the lateral recess of the elbow joint which shows a small amount of anechoic synovial fluid. 1: lateral humeral condyle; 2: joint space; 3: lateral radial tuberosity; 4: lateral collateral ligament; 5: skin; 6: synovial fluid in the lateral recess of the elbow joint; 7: ulnaris lateralis tendon; 8: articular cartilage. Compared to the lateral collateral ligament, the medial collateral ligament is longer and thinner so its ultrasonographic examination is more challenging. The muscular mass of the pectoralis muscles make its visualization more complicated. Pulling the limb forward and pushing back the pectoralis muscles may help in the examination of this area. The medial collateral ligament originates proximally from an eminence on the medial humeral epicondyle, and consists of a long superficial portion and a short deeper portion. The deep part inserts on the radial tuberosity; the longer branch ends more distally on the medial border of the radius, just distal to the interosseous space between the radius and the ulna. Figure 5.6 shows the medial collateral ligament at its proximal insertion and at the level of the joint space. The distal insertion can be more difficult to identify. The medial aspect of the radius is often irregular without clinical significance, and care should be taken in interpreting these findings. At the medial aspect of the elbow joint, superficially and adjacent to the medial collateral ligament, there are large neurovascular structures: the median arteries and veins, and the median nerve (Figure 5.7). Figure 5.6 Normal transverse ultrasound scan of the medial collateral ligament (MCL) of the elbow joint at the level of the joint space. When the transducer is perpendicular to the ligament fibers in transverse scans, the MCL looks homogeneous and echogenic. In longitudinal section, the MCL can appear more or less flat, depending on the position of the probe in the craniocaudal plane. Cranial is to the left, medial is to the top. 1: skin; 2: pectoralis transversus muscle; 3: MCL; 4: medial humeral condyle; 5: joint space; 6: medial aspect of the proximal radius. Figure 5.7 Normal transverse ultrasound scan of the medial aspect of the elbow joint at the level of the medial radial condyle showing the vessels and the median nerve. The irregularity of the radial bone surface is normal. 1: median nerve; 2: median arteries and veins; 3: medial radial condyle; 4: pectoralis transversus muscle; 5: antebrachial fascia. Collateral ligament injuries are uncommon and usually the result of trauma. Lesions to the collateral ligaments result in an enlarged hypoechoic collateral ligament with disruption of the normal fiber pattern. Sometimes avulsion fractures of the collateral ligaments from the humeral condyle or the distal radial insertion are seen, or periosteal new bone can be associated with collateral ligament desmitis. Figure 5.8 shows an example of chronic enthesopathy of the lateral collateral ligament. Figure 5.8 Proximal insertional desmitis of the lateral collateral ligament (LCL) of the elbow joint. The left LCL is enlarged and shows disrupted fiber pattern on transverse and longitudinal section (A and B). The bone surface of the left lateral humeral condyle is irregular (arrow) compared to the normal contralateral right fore limb (B and D). Transverse section (cranial is to the left, lateral is to top). Longitudinal section (proximal is to left, lateral is to top). (Source: Courtesy: Dr Roger Smith). The ulnaris lateralis muscle originates proximal to the lateral epicondyle of the distal humerus, caudal and deep to the lateral collateral ligament; its tendon then courses caudal to the lateral collateral ligament. For this reason, an ultrasound examination of the ulnaris lateralis is easier if it begins with the transverse section of the lateral collateral ligament just proximal to the joint space, and then the probe is moved slightly caudally (Figure 5.9). In cases with synovial distension of this lateral articular recess, the ulnaris lateralis tendon is separated from the lateral collateral ligament by a synovial fold. Figure 5.9 Normal ultrasound scans of the ulnaris lateralis (UL) at the lateral aspect of the elbow. (A) Transverse section of the lateral collateral ligament (left) and ulnaris lateralis tendon (right). (B) Transverse (left) and longitudinal (right) sections of the UL tendon. (C) Transverse (left) and longitudinal (right) sections of the UL tendon at the level of its enthesis on the lateral epicondyle. Longitudinal section: proximal is to the left, medial is to top. Transverse section: cranial is to the left, medial is to top. 1: skin; 2: lateral collateral ligament; 3: lateral aspect of the humerus; 3a: lateral humeral epicondyle; 4: ulnaris lateralis: 4a: tendon,; 4b: muscle; 5: lateral recess of the cubital joint with a small amount of synovial fluid. Figure 5.10 shows a rare case of avulsion of the ulnaris lateralis muscle following a fall over a fence. Figure 5.10 Avulsion of the ulnaris lateralis (UL) muscle following a fall over a fence. The abnormal right ulnaris lateralis muscle is severely swollen with a clear abnormal fiber pattern in transverse (C) and longitudinal (D) sections when compared to the normal UL on the left (A and B). On transverse section of the RF, it is difficult to identify the tendon and some bony avulsion fragments are present. (A) Transverse section (cranial is to the left, lateral is to top). Longitudinal section (proximal is to left, lateral is to top). 1: UL muscle belly; 2: UL tendon; 3: Lateral aspect proximal radius; 4: Lateral humeral epicondyle. Source: Courtesy: Dr Roger Smith In horses, the biceps brachii muscle is characterized by an intramuscular tendon continuing to its distal tendon. Because of the concave shape of this anatomical area, it is easier to examine the distal insertion of the biceps brachii with a convex transducer. To identify the biceps brachii enthesis, it is useful to begin with longitudinal scanning on the dorsal aspect of the elbow joint (see Figure 5.1) and then move the probe slightly medially to identify the insertion located at the craniomedial aspect of the elbow (Figure 5.11).
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Ultrasonography of the Elbow and Shoulder
Introduction
Elbow
Preparation and Scanning Technique
Ultrasonographic Anatomy and Ultrasonographic Abnormalities
Elbow Joint
Collateral Ligaments of the Elbow Joint
Ulnaris Lateralis Muscle
Distal Insertion of the Biceps Brachii
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