Dr. Shirley Chow was a 2017 ORADE Grant recipient. In this article, Dr. Chow shares her learnings from the EULAR Ultrasound Intermediate Course
It was a phenomenal opportunity to learn from leading ultrasonographers in the field and meet with other rheumatologists who are using ultrasound (US) in their practice. There were 5 courses: a basic, intermediate, and advanced Musculoskeletal (MSK) US course, a pediatric US course and a Teach the Teachers course. I was impressed with the number of attendees (30-50 per course), and the organization of teacher to student ratio 5-6:1 and patient volunteers. There was a good balance of lecture and hands-on learning (atleast 50% of the time)
I achieved my learning objectives to gain more knowledge on the doppler technology, common US pitfalls, understand the applications and limitations of MSK US, and develop my skills in MSK US.
Doppler physics:Power Doppler assesses the energy of flow, which is more sensitive for joint inflammation than Colour Doppler, which looks at velocity of flow. Doppler is best detected when flow is parallel to the probe. Pulse Repetition Frequency (PRF) is the number of images acquired by the probe per second, or the sampling frequency. Low PRF provides more detail, however, can have more noise.
Different types of artifacts/pitfalls:
1) Motion artifact between tissue and transducer
2) Mirror artifact: US a smooth area may act as a mirror eg. Bone.
3) Reverberation artifact: the US beam bounces in a hollow structure such as vessels or needle
4) Machine factory settings may not be reliable so adjust settings yourself.
5) Position: a neutral relaxed joint better than an activated joint for tendons
6) Pressure: too much pressure from probe may decrease sensitivity to flow and inflammation
7) Ensure Focus is in right place
8) Medications: use of NSAIDs may lower Doppler signal.
9) Temperature: cold joints may also have less flow which may affect doppler. Smoking may also affect detection. Diurnal variation and cardiac cycle should be considered
10) Location of power doppler: when assessing signal, closer to cartilage is more significant compared to a signal in the overlying tissue.
11) There is a feeding vessel in MCP head – this can be mistaken for power Doppler signal. Also children have a growth plate with neovascularization.
12) Effusions can be normal in certain joints, and not specific for synovitis. Eg. Foot
13) anisotropy of tendons
14) pulleys with retinaculum can be mistaken for tendinosis
15) be aware of septa
16) muscles can look like fluid- eg, lumbricals
Application and Limitations of MSK US
Power Doppler US is a reliable tool for assessing inflammatory activity of the MCP joints (Szkudlarek et al, Arthritis Rheum 2001). Doppler in MCP joints can be graded as 0 no signal, 1, 1 vessel, 2 <50% of area with Doppler signal, and 3 with >50% of area affected.
Asymptomatic rheumatoid arthritis (RA) patients can have subclinical synovitis on US (Brown et al, Arthritis Rheum 2006). Further studies show progression of disease in areas of power Doppler signal. In a study (Vreju et al. Clinical Experimental Rheumatology 2016), subclinical US synovitis in a particular joint was associated with US evidence of bone erosions in that same joint in rheumatoid arthritis patients in clinical remission.
There are limitations of US and power Doppler. Low flow and deep structures are hard to assess eg. 5MHz to assess greater trochanter, 4th MCP better seen by x-ray (Wakefield 2000). US may be less helpful in a destroyed joint. The activity of patient may effect doppler signal Eg. Jumper’s knee. Assess quantity but also quality of power Doppler signal.
Identifying the spectrum of MSK abnormalities on US
Difference between synovial hypertrophy and effusions: Fluid is displaceable and compressible but no doppler signal. Synovial hypertrophy: More significant because more reliable. It is not compressible and has positive power Doppler signal. You can have synovial hypertrophy without inflammation.
Synovitis is graded to help follow patient’s clinical status over time. Grade 0 is normal, Grade 1 has a slight elevation, Grade 2 has a concave appearance, and grade 3 has a convex appearance. This can be subjective.
Tenosynovitis is defined as thickening of tissue with fluid in 2 planes and power Doppler signal. Tendon grading: 0 is normal, 1 has slight widening, 2 has moderate widening and 3 has severe widening. Tenosynovitis grades 0 is normal, 1 has focal peritendon signal, 2 has multi tendon and peritendon involvement, and 3 has diffuse signal and intertendon signal.
Tendinosis is thickening of tendon with areas of hypoechoic signal. A tendon tear will have retraction. Acute stage may have fluid, subacute stage echogenic, and chronic phase there will be thinning of the tendon with retraction.
Erosions: US sensitivity in axial plane (trans) is 0.1mm depth, and sagittal (lateral) plane is 0.2mm width. Scan all around joint: dorsal, volar and lateral (especially 2nd MCP). Most common locations: distal ulna, radius, MCP 2 and 5 and MTP 5. Different definitions of erosions, but >2 mm break in cortex is significant, seen in 2 planes. Beware cysts which look like a shadow, but no cortical break. Beware the anatomic neck of metacarpal bones. Up to 1/3 of normals have “erosion-like” but these are usually less than 2mm (Zayat et al ARD 2014). If erosion <2mm, then follow over time, US trans view, compare right and left hands, and assess with power Doppler. In general, joints are better seen in longitudinal view and tendons in transverse view.
Enthesis is normal if there is normal bone and cartilage, normal insertion of tendon in bone, and no echogenicity. Enthesitis is defined by structural changes such as erosions, enthesophytes, calcifications, as well as inflammatory changes such as increase in thickness of the tendon, hypoechoic of insertion (dynamic), and doppler activity within <2mm of bony cortex. Tendinitis and bursa development is isolated and independent of enthesitis. Common sites include the lateral condyle, superior patella, inferior patella and Achilles.
Omeract definition of Enthesitis is positive power dopper signal within 2 mm of insertion with either hypoechoic tendon or increased thickness of tendon.
Dactylitis definition is tenosynovitis, soft tissue edema, and synovitis.
In summary, using MSK ultrasound has enhanced my practise by its utility in determining if there is joint inflammation or erosions in patients with a difficult physical exam eg. obese patients, damaged joints, those who have difficulty communicating, joints that are hard to examine such as hip effusions, and individuals who have pain but no physical exam evidence of synovitis. I routinely use ultrasound in my practise now to improve the safety and accuracy of my joint aspirations and injections, and to demonstrate to patients the presence or absence of pathology to help guide their treatment.