Ultrasonography of the Elbow and Shoulder
Studio Veterinario Associato Cascina Gufa, Merlino (LO), Italy
Introduction
Ultrasonographic examination of the elbow and shoulder yields information about the soft tissue structures of these 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 the latter case, 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.
Elbow
Preparation and Scanning Technique
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 is 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.
Ultrasonographic Anatomy and Ultrasonographic Abnormalities
Elbow Joint
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, 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 caudally to the lateral collateral ligament, in transverse section.
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).
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).
Collateral Ligaments of the Elbow Joint
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 less echoic, and a superficial one. 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).
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).
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.
Ulnaris Lateralis Muscle
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 5.8). 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.
Distal Insertion of the Biceps Brachii
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 5.9).
Enthesopathy of the biceps brachii insertion is caused by a tearing of its distal attachment on the cranioproximal aspect of the radius. In chronic cases, radiographic and ultrasonographic examination may identify periosteal new bone on the cranial tuberosity of the radius at the site of the insertion of the biceps brachii. Pathology of the biceps brachii is much more common in the shoulder region and will be discussed in the shoulder section.
Triceps Brachii Muscle and Distal Tendon
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