Musculoskeletal Ultrasound in

Rheumatology

Andrew Cairns MD MSc FRCP MFSEM and Allister Taggart MD FRCP, Musgrave Park Hospital, Belfast
Original article: 18/05/2004
Reviewed: 22/01/2009
Next review due: 22/01/2011

The past decade has seen a dramatic increase in the use of ultrasound as a clinical tool by rheumatologists. Ultrasound is a painless and harmless test, using sound waves that are emitted and then collected by a probe after reflecting off the body’s internal tissues, providing a detailed image of the structures beneath the skin (figure 1). Bone appears bright white and fluid black on the monitor. Most people will be familiar with the use of ultrasound to look at an unborn baby inthe womb. Recent advances in probe technology have enabled the use of ultrasound to examine the joints and surrounding soft tissues. Ultrasound is relatively inexpensive and safe, avoiding the exposure to radiation that is necessary for conventional x-rays, CT and MRI scans.

Traditionally, rheumatologists have referred patients to radiologists for all ultrasound examinations but recent developments have enabled them to conduct some scans themselves. The advent of portable ultrasound machines (figure 2)means that scans can be carried out at the bedside or in the outpatient clinic without the need for a second appointment in the x-ray department. This speeds up the process of investigation and allows the rheumatologist to plan treatment without delay.

Radiologists are expert at conducting detailed scans that often assist with a structural diagnosis. Rheumatologists tend to use ultrasound in a slightly different way. They may use it to guide them in carrying out difficult joint injections. They also use it to detect subtle inflammation around tendons and small knuckle joints. This is important because clinical examination may not always identify inflammation, particularly in early arthritis. The earlier the diagnosis of rheumatoid arthritis, the better the chance of dampening down inflammation and preventing joint damage.

There are a number of ways of imaging the joints and these are complimentary, each with their own strengths and weaknesses. Conventional x-rays are cheap and readily available but only show joint damage (erosions) at a relatively late stage in the disease. Isotope bone scanning can detect joint inflammation at a much earlier stage but the findings are non-specific and the technique exposes the patient to a significant dose of radiation. Magnetic resonance imaging (MRI) provides the most detailed images and is the ‘gold standard’ by which all other imaging techniques are judged. It is particularly useful for studying changes in bone and cartilage but the technique is expensive and access, in the NHS, is restricted. MRI produces static images of great detail but is not suited to the examination of moving joints.

Ultrasound is best at imaging soft tissues like tendons, ligaments and joint linings. The technique is ideal for the dynamic assessment of the musculoskeletal system. The clinician is ideally placed to interpret these images in the light of the clinical history and examination. We have found that scanning enhances the rheumatologist’s clinical skills and improves his/her understanding of how rheumatic diseases damage the body tissues. Because it involves no harmful radiation, the technique can be repeated where there is a need to assess the patient’s response to treatment.

Ultrasound is a technique that is heavily dependent on the skill of the operator. Acquiring that skill requires dedication and lots of practice under expert supervision. These requirements have important implications for the training of young rheumatologists but we are convinced that the extra effort will pay dividends in the way that doctors treat patients with arthritis. New technology is constantly improving our ability to image the human body but musculoskeletal ultrasound is assured of a place in these developments because of its special qualities. As one expert has said, “Ultrasound is most valuable when used in a clinical setting, enabling it to become the clinician’s extended finger.”

Ultrasound Fig 1	Ultrasound Fig 2