Introduction

Ultrasound uses pulses of ultrasonic (out of the range of human hearing) sound waves and their echo waves (i.e. reflected waves after the sound waves hit tissue interfaces) to image sections of the human body. Doppler ultrasound employs the ultrasonic sound waves to detect movement. This allows the detection of red blood cell movement in blood vessels and therefore vascularity. Musculoskeletal ultrasound has increasingly been seen to be a promising tool for rheumatologists across the world, often termed the “stethoscope of the joint” Ultrasound use has increased due to improved technology that allows high resolution imaging of the musculoskeletal system with some advantages over other imaging techniques . Specifically ultrasound does not use ionizing radiation, is relatively low cost, can image in multiple planes in real time and is acceptable to patients . The growth of ultrasound has also been due to the growing body of evidence for the assessment of a wide range of rheumatologic diseases. The uptake by clinicians of ultrasound however varies across the world and in part is due to rheumatologists’ attitudes towards the technology, training opportunities, and costs .

Ultrasound utilisation

Ultrasound use is more prevalent in Europe compared to elsewhere in the world but through out Europe the utilisation also varies . In a questionnaire to all the national rheumatology societies of EULAR, it was found that there was in general less than fifty percent of rheumatologists who were performing ultrasound routinely. The variation in use was widespread, from less than 10% in some countries to up to 80% in Germany . The United Kingdom has approximately 33% of rheumatologists performing ultrasound, and this proportion has not changed greatly from when a survey was performed in 1999 .

Outside of Europe there are low rates of ultrasound utilisation. Studies in the United States describe 20% of rheumatologists performing ultrasound, whilst in Canada it has been found to be 7.3% . In Japan it was found that 7.95% of clinicians were performing ultrasound themselves .

Though there is global variability in the current utilisation of ultrasound there is significant interest in learning to use the technology, with up to 75–85% of rheumatologists in some surveys suggesting it should be a routine part of the consultation . When interviewed the major reason for rheumatologists underutilising ultrasound has been the lack of training opportunities. Studies from the United Kingdom, EULAR, The United States and Japan indicate that lack of training opportunities is the principal reason for the lack of utilisation with up to 75% of respondents suggesting this .

Ultrasound utilisation

Ultrasound use is more prevalent in Europe compared to elsewhere in the world but through out Europe the utilisation also varies . In a questionnaire to all the national rheumatology societies of EULAR, it was found that there was in general less than fifty percent of rheumatologists who were performing ultrasound routinely. The variation in use was widespread, from less than 10% in some countries to up to 80% in Germany . The United Kingdom has approximately 33% of rheumatologists performing ultrasound, and this proportion has not changed greatly from when a survey was performed in 1999 .

Outside of Europe there are low rates of ultrasound utilisation. Studies in the United States describe 20% of rheumatologists performing ultrasound, whilst in Canada it has been found to be 7.3% . In Japan it was found that 7.95% of clinicians were performing ultrasound themselves .

Though there is global variability in the current utilisation of ultrasound there is significant interest in learning to use the technology, with up to 75–85% of rheumatologists in some surveys suggesting it should be a routine part of the consultation . When interviewed the major reason for rheumatologists underutilising ultrasound has been the lack of training opportunities. Studies from the United Kingdom, EULAR, The United States and Japan indicate that lack of training opportunities is the principal reason for the lack of utilisation with up to 75% of respondents suggesting this .

Training in ultrasound

The training of a rheumatologist in ultrasound encompasses the imparting of a knowledge base related to the principles of how US operates and important anatomical and pathological features it can detect, as well as learning how to perform technical aspects of the scan by using the US probe and machine . There are a guidelines for the musculoskeletal ultrasound developed by EULAR to allow standardisation of practice . This was added too by the extensive work of Brown and colleagues to develop recommendations for the educational standards for musculoskeletal ultrasonography . Experts in musculoskeletal ultrasound were surveyed in a four stage delphi exercise to determine the important knowledge and skills that a rheumatologic ultrasonographer should have. Brown et al. found that the knowledge and skills required an understanding of a number of ultrasound ultrasound specific areas. This included ultrasound physics, ultrasound equipment, ultrasound artifacts, machine function and operation, probe positioning, image optimisation, planes and systems of examination, dynamic assessment, Colour and power Doppler. It was also recommended that rheumatologists should further study anatomy, pathology and perform ultrasound of all the major joints of the musculoskeletal system. An understanding of the indications and limitations of the technology was also thought to be valuable .

The knowledge base that is required of rheumatologists to learn ultrasound having been established then requires a clinician to have this knowledge imparted to them. Once the knowledge base has been established, clinicians need the opportunity to practice the technique. In general there has been a wide variety of methods for rheumatologists to achieve their training . It has encompassed however to a large degree the attendance at a formal course and subsequently supervised scanning by ultrasound trained rheumatologists, radiologists or musculoskeletal sonographers .

There are now many courses that are available to rheumatologists to learn the fundamentals of sonography. These include the EULAR, BSR, ACR ultrasound courses. They are usually divided into basic, intermediate and advanced courses to cater to the varied degrees of competence and experience. The supervision of the training of rheumatologists in ultrasound is varied however across countries as is the emphasis by national societies. There are national training programmes in many European countries as well as incorporation of ultrasound into the postgraduate rheumatology curriculum in some European countries .

The EULAR group has developed guidelines for the content and conduct of EULAR ultrasound courses . Further to this there is EULAR Ultrasound Teacher course to help standardise the teaching and help increase the availability of courses.

The difficulty in continued supervised scanning has been addressed by other methods including web based training, short intensive training periods and the development of modular based systems , There has also been self taught rheumatologists who have been shown to have very good accuracy .

The training of rheumatologists in ultrasound is a very important aspect given that ultrasound is an operator dependent imaging technique. However, reproducibility between readers for detecting abnormalities has been extensively investigated and is moderate to good in trained rheumatologists .

Once trained competency assessment and certification are issues that are still under development .

Ultrasound equipment

The purchase of ultrasound machine is a significant expense and depends on the needs of the individual or department. The important considerations include the need for portability, image resolution, transducer function, colour/power Doppler. Increasingly newer techniques such as 3d imaging, fusion imaging and elsatography can also be included though it does increase the price. Reducing the cost can also be achieved by opting to programme the system for solely musculoskeletal sonography though in the future vascular studies may also be needed .

The optimum transducer to purchase depends on the clinical need. There is always a trade off in ultrasound between penetration and resolution depending on the frequency; that is the higher the frequency the better the resolution but the poorer the penetration. A high frequency probe (7.5–20 Mhz) is therefore very good for small- superficial joints but a lower frequency probe will be more appropriate for larger, deeper structures . Some probes with a wide range of frequencies may be able to accommodate both of these competing interests.

The use of power and colour Doppler allows visualisation of vascularity. There is very good evidence for the validity of power Doppler in showing vascularity when compared to histological evidence of blood flow. It has further been shown to be useful in the assessment of inflammatory diseases . This is a very important component of the ultrasound machine and with the increasing evidence of its importance it should not be overlooked in the purchase of a machine.

Three dimensional and four dimensional (3D performed in real time) imaging acquire a block of information as compared to a slice that is seen with traditional two dimensional imaging. It is a heavier probe but it does provide potential advantages including increased speed of image acquisition and reliability . Elastography is the ability to use ultrasound to visualise the elastic properties of tissues by collecting ultrasound information before and after tissue compression or after the tissue is insonated with low frequency vibrations. It has been used for liver assessment in particular and is now being tested primarily in the assessment of tendon disease 3d and 4d imaging and elastography are currently techniques that are being evaluated and may not be necessary at this time for the practicing rheumatologist.

Using ultrasound in rheumatologic conditions

Musculoskeletal ultrasound in rheumatology can be used for a number of purposes including education, diagnosis, stratification and monitoring of disease, and for guidance for aspiration and injection.

The basis for education can be for medical student, trainee and patient education. This has not been formally assessed in many studies but is often referred to by clinicians. Ogasawara had shown that the use of ultrasound improved the clinical skills of rheumatologists through the immediate assessment of their clinical skills as compared to ultrasound and then subsequent retesting of their clinical skills . Wright et al. have used ultrasound as part of undergraduate rheumatology teaching and found that the students enjoyed the teaching and had better understanding of musculoskeletal anatomy . Preliminary research has only been done on assessing patient education with ultrasound, though it has been suggested it helps patient understanding if their illness .

Rheumatoid arthritis

Rheumatoid arthritis diagnosis is characterised by swollen and painful joints . The diagnosis of rheumatoid arthritis is often determined by whether the joints are truly swollen and ultrasound can be an important tool in determining this. In some studies ultrasound has been shown to be superior to clinical examination in detecting swollen joints. This is through the detection of hypoechoic areas corresponding to synovitis and also effusions as anechoic areas that are compressible. It can improve sensitivity of clinical examination findings from 0.4 to 0.7 when MRI is used as the gold standard , Ultrasound as a method of demonstrating synovitis has led to its inclusion in the 2010 classification of rheumatoid arthritis .

Beyond detecting swollen joints it can help to diagnose patients based detection of erosions. A number of studies have shown that bone erosions are detected earlier on ultrasound than on conventional radiology. For example Wakefield et al. found that 56 of 100 RA patients had erosive disease compared to 17 RA patients having erosions on radiography .

Power Doppler ultrasound has been established as a method of demonstrating the vascularity of synovium. This has been shown to be a useful method of demonstrating the activity of synovitis and complements the grey scale assessment of joints , Fig. 1 illustrates the changes of synovitis with power Doppler signal and erosions.

Longitudinal view of a metacarpophalangeal joint showing synovitis with power Doppler signal and bone erosions due to rheumatoid arthritis.

Ultrasound has been shown to detect disease in rheumatoid arthritis patients in clinical remission , Further to this ultrasound and in particular power Doppler ultrasound is predictive of a clinical flare .

Ultrasound can be used to monitor disease activity with a number of studies showing improvement in grey scale and power Doppler ultrasound with treatment .

The future development of erosive disease is correlated with power Doppler ultrasound findings. This has been shown in longitudinal studies and importantly was shown to help predict those patients in clinical remission who would develop radiographic progression .

Tendon disease, nodules and neuropathies can also be diagnosed and monitored by ultrasound in rheumatoid arthritis .

The findings that rheumatoid arthritis can be diagnosed, monitored and importantly both clinical flare and progressive erosive disease even whilst patients are in remission has led to the proposed initiative of a new “Treat to Target of Power Doppler Ultrasound”

The practising rheumatologist can therefore consider ultrasound to help the decision making process. It could be used in the diagnostic phase to detect swollen joints, erosions and tendon disease. It can also help to stratify risk of disease progression by detecting ongoing disease in patients in remission or predict clinical flare. It would seem for the practicing rheumatologist not every patient will need ultrasound if the clinician is already going to adjust treatment on clinical grounds but in areas where more information is needed it will certainly aid the decision making process.

Spondyloarthritis

Spondylarthritis can have a number of manifestations that can be assessed by ultrasound to help in the diagnosis and monitoring of disease. The major features that can be assessed include enthesitis, sacroiliitis, dactylitis and synovitis of joints.

Ultrasound of the enthesis the most studied area of the spondyloarthropathies. An abnormal enthesis being described as a loss of the normal fibrillar echogenicity at the tendon insertion, which may have an increase in tendon thickening, calcium depositis, scars, periosteal changes and/or power Doppler signal . It has been shown in a number of studies that there is a high frequency of asymptomatic enthesis with abnormal ultrasound findings . Doppler however can differentiate inflammatory from non-inflammatory diseases . The findings of erosive changes and power Doppler signal is thought to be very specific for the diagnosis of a spondyloarthopathy , Fig. 2 illustrates entheseal inflammation and erosive changes.

Longitudinal view of an Achilles enthesis with tendon thickening, power Doppler signal and bone erosions due to ankylosing spondylitis.

Monitoring of entheseal disease with ultrasound has been shown to change with therapy but the data is currently limited . Prognostic information to this point has not been well established.

Sacroilitis can be diagnosed with ultrasound and it is significantly improved by the administration of a micro-bubble contrast agent to enhance power Doppler signal Monitoring of disease has been demonstrated in limited studies at the sacroiliac joints .

Dactylitis had been found on ultrasound to show a tenosynovitis, synovitis, tendonitis and subcutaneous oedema . Monitoring of dactylitis with ultrasound has not been performed.

Synovitis of larger joints such as the knee can also be assessed in spondyloarthritis and have been shown to respond to therapy

The practicing rheumatologist could therefore use ultrasound in the spondyloarthropathies to help diagnosis, particularly looking for specific features such as the ultrasound features of active entheseal inflammation. Monitoring and prognostic information however are not well established in these conditions, though ongoing research may show value into the future.

Crystal disease

Ultrasound has been shown to useful for the diagnosis of gout through the detection of gout crystals along the surface of cartilage, where it makes the superficial cartilage border hyperechoic (double contour sign). The synovial fluid can also show aggregates of crystals sometimes causing a “snow storm effect”. Tophi can be variable in echogenicity depending on the density of the tophi. Erosions are often deeper than when compared to those seen in RA, and the most obvious site is the medial aspect of the first MTP, though this is a less specific findings. Other less specific features such as bone erosion, joint effusions, synovial hypertrophy and hypervascularity using power Doppler are also seen .

These diagnostic signs can be helpful for diagnosis and guidance for aspiration is another method of using ultrasound to confirm a diagnosis.

There are limited studies on monitoring gout with ultrasound, though reduction in tophus size has been shown with treatment of gout

Calcium pyrophosphate dihydrate arthropathy has characteristic appearances on ultrasonography. Crystal deposition can be identified within articular cartilage, in comparison to along the cartilage border in gout. Focal hyperechoic deposits can be seen within the cartilage. The areas affected are also different to gout especially affecting tendons and also fibrocartilage . Once more ultrasound can aid diagnosis through guidance for aspiration.

There have been no monitoring studies in Calcium pyrophosphate dihydrate disease.

Clinical use of ultrasound in gout and pseudogout can therefore be used for diagnosis and perhaps in the future more studies will help identify monitoring strategies. Guidance for aspiration however is a very practical use of ultrasound in these diseases.

Osteoarthritis

Ultrasound has been shown to be able to evaluate many of the structural changes that occur in joints affected by osteoarthritis . The areas that can be evaluated by ultrasound in osteoarthritis, include cartilage, joint effusions, synovial hypertrophy, joint capsule, bone surface, ligaments, tendons and bursae .

The cartilage can be directly evaluated and is seen as a well defined anechoic structure. Cartilage changes such as blurring of the edges, loss of homegeneity, focal and then diffuse thinning to complete absence can be seen. The thickness of the cartilage can also be assessed in joints with correct positioning of the joint, due to the limited acoustic window that is afforded by ultrasound .

Joint effusions are able to be detected with ultrasound and in particular minimal amounts are able to be distinguished. They can appear anechoic or have some internal echoes based on intra-articular debris . The joint capsule can also appear thickened in osteoarthritis .

Synovitis is seen in osteoarthritis on ultrasound, and may have Doppler flow corresponding to active inflammation. This may be useful to for prediction of more erosive changes .

The bone surface in osteoarthritis can be easily distinguished form the normal hyperechoic continuous bright line . The abnormalities in osteoarthritis that can be appreciated on ultrasound include osteophytes, erosions and bony irregularities , osteophytes appear as irregularities that have a step up bony prominence a the end of normal bony contour in comparison to an erosion that has a step down contour defect .

The ultrasound findings in osteoarthritis allow the rheumatologists the ability to make the diagnosis of osteoarthritis at the bed side and review multiple joints at one time. The detection of effusions is an important finding that is significantly enhanced by ultrasound. Prediction of outcomes and monitoring of osteoarthritis with ultrasound is still being evaluated.

Ultrasound in polymyalgia rheumatica and vasculitis

The diagnosis and monitoring of vasculitis can be assisted by ultrasound. This can be through the use of vascular ultrasound but also by evaluation of end organs. The most work has been in temporal arteritis where it has been shown to be useful as a diagnostic tool. In a meta-analysis ultrasound was found to have a sensitivity of 87% and specificity of 96% compared to a clinical diagnosis .

The particular features that are evaluated on duplex ultrasound include a number of features. Oedema of the vessel wall that appears as a dark, hypoechoic, circumferential wall thickening or “halo”. Stenosis can be detected by increased velocity of blood flow in vessels and by turbulent flow that on colour Doppler ultrasound appears as a mixture of colours and persisting colour signal in diastole. Occlusion of the vessel can also be seen in grey scale with no colour flow signal detectable . These changes can also be seen in peripheral vessels with large vessel vasculitis .

The monitoring of vasculitis with ultrasound can also be performed as the changes in the vessel wall can resolve after 2 weeks of corticosteroid therapy, though histology can still be positive after this time .

The presence of vasculitis in polymylagia rheumatic patients has been demonstrated with ultrasound in up to 15% of patients when both temporal and axillary arteries are examined . Other features of polymylagia rheumatica that are seen on musculoskeletal ultrasound include subdeltoid bursitis, biceps tenosynovitis, glenohumeral synovitis, hip joint synovitis and trochanteric bursitis. Importantly these findings have now been included as part of the classification criteria for polymylagia rheumatica .

The skill of the sonographer is important for diagnosis and monitoring of vasculitis and it has been suggested that at least 30–50 persons without GCA should be examined to be comfortable with the normal appearance of the temporal artery .

In routine practice, most rheumatologists still consider biopsy a very important aspect in the diagnosis and management of giant cell arteritis. Though there is good data for the use of ultrasound, the consequences of a missed diagnosis and the long term immunosuppression that is required for treatment, result in the gold standard proof of a biopsy still being the investigation of choice for many clinicians.

Rheumatologists should consider diagnosis and monitoring of particularly temporal arteritis with ultrasound. Ultrasound has become very important in the assessment of polymylagia rheumatica patients for classification and also for detection of arteritis.

Tendon, ligaments, bursae and muscle

Musculoskeletal ultrasound is an excellent technique for evaluating dynamically the integrity and function of tendons and ligaments. Diagnosis and assessment in particular for soft tissue rheumatic diseases using ultrasound has been a well studied subject, especially for the shoulder.

Tendon damage on ultrasound can be divided into a number of pathologies. Tendinosis which is seen on ultrasound as a heterogeneity of the normal fibrillar structure of the tendon and can also be associated with swelling of the tendon. Partial tears are tears that spread through a tendon but do not go through the whole tendon. Intrasubstance tears are wholly within the tendon and can be an area where the tendon seems to split within it. Full thickness tears are one where the tendon is torn through the whole tendon in at least one area of the tendon. This is different to complete tears where the whole tendon is separated. There can be Doppler flow which suggests neovasculisation and also calcification in tendons . Fig. 3 demonstrates a complete rupture of an Achilles tendon.

Longitudinal view of an Achilles tendon rupture.

Tenosynovitis is seen on ultrasound as an inflammation of the synovial sheath appearing on ultrasound as a concentric anechoic or hypoechoic swelling around the tendon. It can progress to a non compressible thickening of the tendon resulting in entrapment such as in De Quervain’s tenosynovitis . Fig. 4 demonstrates tenosynovitis with power Doppler signal.

longitudinal view of posterior tibial tenosynovitis with swelling of the tendon with tendon sheath swelling and power Doppler signal.

Ligamentous injuries can also be assessed by ultrasound and particularly the dynamic nature of ultrasound again enables stress to be placed on ligaments to further outline injuries. They usually are viewed as thin hyperechoic structures attaching to bones. Ligamentous tears appear similar to tendon tears with thickening and loss of architecture to discontinuity of the ligament progressing to retraction which may also have Doppler flow .

Bursae are often evaluated in rheumatology, for example in the trochanteric region, olecranon, subdeltoid and subacromial, pre, supra and infrapetallae bursae. Theswelling of a bursae are seen on ultrasound as an increase in size of a hypoechoic or anechoic compressible fluid .

Muscle tears and ossification and myositis can be evaluated by ultrasound. Once more the dynamic nature of ultrasound allows muscle tears to become obvious. The changes on ultrasound that can be seen include hyperechoic appearance when there is an acute haemotoma, progressing to an anechoic appearance. If there is scar development or calcification it will be hyperechoic .

Rheumatologists treat multiple soft tissue rheumatic syndromes involving tendons, ligaments, bursae and muscle. Ultrasound is a very useful tool in this situation to aid diagnosis and management. It has been shown to reduce repeated hospital appointments and improve quality of care and should be a routine part of management .

Peripheral nerves

The peripheral nerves are able to be shown to be compressed with typical signs on ultrasound. The signs on ultrasound of nerve compression are a proximal swelling of the nerve and then a thinner nerve at the site of compression. The nerve appears hyopechoic through out as there is oedema of the fascicles and epineurium .

The cross-sectional area of the median nerve has been shown to have a sensitivity of 87% and specificity of 83.3% in a recent meta-analysis . Other nerve entrapment syndromes can also be detected such as the ulnar nerve at the elbow with similar rates of sensitivity 80% and sensitivity of 91% . Lower limb neuropathies such as tarsal tunnel syndrome can be diagnosed with ultrasound with a cause found in 60–80% of patients . Other neuropathies can be diagnosed but do not have the same level of evidence to show sensitivity and specificity.

Morton’s neuromas are able to be diagnosed with ultrasound as a hypoechoic fusiform swelling in the interdigital space . Lateral compression of the metatarsal heads can cause the neuroma to bulge helping to make the diagnosis . The sensitivity of ultrsound is 95–100% with a specificity of 83% in comparison to MRI .

Ultrasound for the diagnosis of compressive neuropathies can be used to supplement nerve conduction studies and is very useful for demonstration of Morton’s neuroma.