INDICATIONS:

• Joint effusion

• Tendon or ligament injury

• In select cases, fracture or joint dislocation

• Procedural guidance for arthrocentesis or hematoma block

The goal of musculoskeletal (MSK) ultrasound in the ED is to identify pathology based on a specific clinical question. While other ultrasound exams are performed more broadly, you are unlikely to find benefit from MSK ultrasound without narrowing your focus.

Anatomy:

Ultrasonographic appearance of MSK structures is intuitive but takes a solid foundation of basic anatomy. It is helpful to identify the anatomy in layers based on depth of appearance, which assists in orienting you to the structures being viewed.

 The structures you will encounter include:

1. Subcutaneous tissue & fat

2. Muscle

3. Tendon/ligaments

4. Nerves

5. Hyaline cartilage

6. Bone

Pro tip: Always scan the contralateral/unaffected side for direct comparison.

For the vast majority of MSK images, the linear probe is preferred. This high frequency transducer gives better resolution to superficial structures to help delineate the anatomy and identify pathology. However, in certain cases the curvilinear probe is preferred, such as with visualization of deeper structures like the hip or shoulder joint, or when excessive fatty tissue is present

Anisotropy is the most encountered sonographic artifact when scanning MSK structures. It occurs most frequently when visualizing nerves, tendons and ligaments. To obtain proper images of these structures, the ultrasound probe must be perpendicular to the axis of the nerve, tendon or ligament. When not maintained in perfect alignment, the ultrasound beam returns to the probe at an inappropriate angle and can cause the structure to appear hypoechoic. This can lead to misdiagnoses of fluid collections or tendon rupture. You can evaluate for anisotropy by changing the angle of the probe to match the axis of the structure and evaluate if this changes the image.

Technique/anatomy

In general, shoulder ultrasound is performed from an anterior or posterior approach. Each technique is described more below based on the pathology you are attempting to identify.

 Effusion

1. Best visualized with a posterior approach (consider using the curvilinear probe)

2. Identify the patient’s scapular spine

3. Place probe in transverse orientation at the lateral portion of the scapular spine and slide lateral toward the humeral head until the glenohumeral joint is visualized

4. Effusion appears as an anechoic collection between the humeral head and glenoid fossa

TENDONS and LIGAMENTS

 Proximal bicep tendon:

1. Position patient with elbow flexed, arm supinated and resting comfortably at his/her side

2. Place probe in transverse orientation on the proximal humerus and slide cranial until you identify the bicep tendon within the bicipital groove. The bicipital groove sits between the ridge-like contours of the greater and lesser tuberosity of the proximal humerus.

3. After obtaining a short axis view, rotate probe 90 degrees to obtain a long axis view.

Subscapularis tendon:

1. Position patient with elbow flexed, arm supinated and held in slight external rotation.

2. This is best done after identifying the bicep tendon, as external rotation of the shoulder brings the subscapularis tendon into view overlying the lesser tuberosity of the humerus.

3. Obtain a long axis view of the tendon. You may need to slide the probe medially.

Supraspinatus tendon:

1. Position patient with shoulder internally rotated and extended. Better understood as “hand in back pocket” position.

2. The tendon overlies the humeral head and inserts into the greater tuberosity. To obtain a long axis view, the probe will often be positioned obliquely over the humeral head, simulating the anatomical position of the supraspinatus tendon.

Infraspinatus tendon

1. Position patient with affected side reaching across body to rest on contralateral shoulder

2. Using a postero-lateral approach, place the probe in an oblique orientation to visualize the tendon on the back of the humeral head as it attaches onto the posterior aspect of the greater tuberosity.

Joint dislocation

Using ultrasound to assess for shoulder dislocation has become increasingly popular and several papers have described techniques and workflow to utilize this in the ED.1-5 

1. Use the posterior approach to visualize the glenohumeral space (consider using the curvilinear probe)

2. Identify the humeral head, which sits immediately lateral to the glenoid fossa. If there is no dislocation, you will see free movement of the humeral head within the glenoid with internal/external rotation of the shoulder.

3. In anterior dislocations, the humeral head will be located in the far field on the screen.

4. In posterior dislocations, the humeral head will be located in the near field on the screen.

Technique/anatomy

 Lateral approach:

1. Position patient with elbow flexed to 90 degrees, pronated, abducted and resting on table at patient’s side.

2. Place probe in longitudinal orientation at the proximal forearm, parallel to shaft of radius

3. Slide probe proximally until you visualize the radial head and lateral epicondyle

Posterior approach:

1. Position patient with elbow flexed at 90 degrees and arm internally rotated and held across stomach

2. Place probe in longitudinal orientation along the posterior upper arm

3. Slide distal towards elbow until you visualize the distal humerus and olecranon

Effusion

 An effusion appears as an anechoic collection located between the lateral epicondyle and radial head in the lateral approach, or between the distal humerus and olecranon in the posterior approach. Look for displacement of the fat pad superiorly to distinguish from normal articular cartilage.

Technique/anatomy

 The primary purpose for ultrasonographic evaluation of the wrist in the ED is to evaluate for an effusion. This is done by a dorsal approach.

1. Position patient with wrist in slight flexion by placing a rolled towel or kerlix underneath the wrist.

2. Place transducer in longitudinal orientation over the distal radius.

3. Slide probe distally until you visualize the joint space between the distal radius and scaphoid/lunate bones. Lister’s tubercle (bony projection that can be palpated on the distal radius) lines up anatomically with the middle of the scaphoid bone. Use this as your landmark.

4. An effusion appears as an anechoic collection between the joint space of the distal radius and carpal bones.

Fracture

 Fractured bone on ultrasound appears as a break in the smooth, hyperechoic bony cortex. In regards to distal radius fractures:

1. Place probe in longitudinal orientation along the shaft of radius.

2. Slide distal towards the wrist. A fracture appears as a disruption of the hyperechoic bony cortex with fractured fragments in malalignment, often with a surrounding hypoechoic collection representing a hematoma.

3. Make sure to assess the bone in multiple planes to ensure accuracy of the findings.

Technique/anatomy

 Imaging the hand/digits using the standard probe & gel approach often provides suboptimal images. The limited amount of soft tissue in these areas does not allow the adequate depth of penetration required for the ultrasound waves to travel and provide clear pictures. One way to combat this issue is to place the patient’s hand in a water bath and use the water as an ultrasound medium. Keep a small distance between the probe and patient – the probe shouldn’t be touching the patient with this technique.

Flexor tenosynovitis

Using the water bath as described above, obtain longitudinal images on the palmar surface of the symptomatic finger. Flexor tenosynovitis is suggested by visualization of hypoechoic peritendinous effusions and/or a hypoechoic and hyperemic thickened synovial sheath10,11.

Technique/anatomy

1.  Position patient in sitting or supine position with knee slightly flexed by placing a towel roll underneath the back of the knee

2. Evaluate the proximal knee in long and short axis by placing the probe just proximal to the patella, visualizing the course of the quadricep tendon as it runs toward the patella

3. Evaluate the distal knee in long and short axis by placing the probe just distal to the patella, visualizing the course of the patella tendon as it runs distal and inserts into the tibia

Effusion

Knee effusions are typically best seen on the proximal knee, appearing as an anechoic collection underneath the quadricep tendon. Use your non dominant hand to push fluid toward your probe, in order to more easily visualize the presence of an effusion.

Tendon/ligament injury (quad, patella tendon)

The quadricep tendon is visualized from the myotendinous junction proximally to its insertion in the patella distally. A ruptured tendon appears as loss of the normally visualized longitudinal fibers, typically with a surrounding hypoechoic hematoma. The patella tendon is viewed similarly, by identifying its insertion in the patella proximally and tibial tuberosity distally.

Technique/anatomy

 The primary goal of ankle ultrasound is to identify the presence/absence of an ankle effusion.

1. Position patient with foot flat on a surface and in slight plantar flexion to open up the joint space. This can be performed with patient in a sitting position or supine with the knees flexed.

2. Palpate for the tibialis anterior tendon. You will image the ankle joint directly underneath the tendon or just lateral to it.

3. Place probe in a longitudinal orientation along the distal tibia and slide distal until you visualize the tibiotalar joint.

Effusion

An ankle effusion will appear as an anechoic collection just above the talus with superior displacement of the fat pad. A common mistake is to confuse the articular cartilage for an effusion, so make sure to image the unaffected ankle for comparison.

Achilles Tendon

Position patient in either a supine or sitting position to easily access the posterior lower leg. Imagine the Achilles tendon in long access from its myotendinous junction at the distal gastrocnemius, distal to its insertion on the calcaneus. It is often easier to first find the Achilles as it inserts into the calcaneus and trace it proximal. An Achilles tendon tear/partial tear will appear as a disruption of the normal longitudinal fibers, often with surrounding hypoechoic fluid.