Musculoskeletal Ultrasound in Rheumatology - The Federation of ...

Medical Bulletin
VOL.10 NO.2 FEBRUARY 2005
Musculoskeletal Ultrasound in
Rheumatology
Dr Woon-leung Ng FHKAM (Medicine), FRCP (Glasg)
Senior Medical Officer, Department of Medicine and Geriatrics
United Christian Hospital
Dr Woon-leung Ng
In the past decade, there has seen a phenomenal growth in the
research and application of musculoskeletal ultrasound (MSUS)
in the understanding and management of rheumatic diseases. 1
Ultrasound (US) is noninvasive and biologically safe. There
is practically no contraindication for the technique. The
portability of US machines makes them accessible for both
out-patients and in-hospital patients including the critically
ill. Utilisation of medical US is ubiquitous. In fact, one can
hardly think of a clinical specialty involving direct patient
care that does not include US as part of their diagnostic and
therapeutic armamentarium. (Perhaps one notable exception
is psychiatry for which all kinds of “sounds” have to be
treated with a grain of suspicion!)
Musculoskeletal ultrasound is indeed a late comer!
History of musculoskeletal ultrasound
Though the first report of MSUS was published as early as in
1958, it was not until 1972 when Daniel G. McDonald
described the first important clinical application of US to
differentiate Baker’s cysts from thrombophlebitis. 2,3 This
remains an important use of the technique to date. The next
milestone was the demonstration of ultrasonographic features
of congenital dislocation of hip, which led to the first
widespread application of MSUS. 4 Technical difficulties in
producing high resolution images needed for MSUS largely
accounted for its laggard development.
The past two decades have seen revolutionary advances in
imaging resolution, capabilities and cost of MSUS equipment.
Advances in high-speed digital processing and transducer
technology enabled the production of high-quality images
of musculoskeletal structures. Visualisation of synovitis,
tenosynovitis, rheumatoid erosions and demonstration of soft
tissue hyperaemia in rheumatic diseases by ultrasonographic
techniques opened up an unexplored and fascinating realm
for rheumatologists and musculoskeletal specialists.
Advantages of musculoskeletal ultrasound
Apart from the aforementioned advantages, MSUS has
several other exclusive features. US is a truly real-time
imaging modality. It provides the observer with the news as
well as the history about the targeted articular and
periarticular structures. Symptomatic areas can be easily
located and confirmed with the patient during examination.
Rapid side-to-side comparison can be done with ease.
Diagnosis is instantaneous. Large number of joints in different
regions of the body can be imaged swiftly and selectively
within a single examination session.
US provides the best means for dynamic assessment of bone
and tendon movement. Differential changes in various
structures can readily be appreciated during active, resisted,
and passive motion. US has multi-planar imaging capability
currently only rivalled by magnetic resonance imaging (MRI),
albeit more expensive. Its high repeatability and sensitivity
to change offer the potential use in monitoring disease
progression and evaluation of therapeutic efficacy of both
local and systemic treatment. 5
Perhaps the greatest benefit of US in daily clinical practice
lies in the guidance for diagnostic and therapeutic
interventions. MSUS may be used to assist needle positioning
to facilitate invasive rheumatological procedures such as
aspiration of fluid, drainage of abscess, tissue biopsy and local
injection of therapeutic agents. It is particularly useful when
the fluid collections are very small, as in the case of
tenosynovial effusion or when the inflammatory process
occurs in deep-seated or otherwise inaccessible anatomical
targets such as the hip. Sonographic guidance has been
proven to increase the success rate of procedures 6,7 and to
help minimise the risk of damage to adjacent vital structures.
Study has shown that an experienced musculoskeletal
radiologist and a rheumatologist with limited ultrasound
training can achieve high interobserver agreement rates for
identification of synovitis (91%) and bone erosions (87%) by
means of standardised approach. 8
Indications for musculoskeletal ultrasound
MSUS is a versatile technique and the potential applications
are myriad. 9 This review will focus on the more widely
accepted and proven indications.
Effusion
This is perhaps the commonest application of MSUS. US is
superior to clinical examination in distinguishing effusion
from synovial proliferation. 10 Joint, tendon sheath and bursal
effusion can be readily diagnosed on US and confirmed by
guided aspiration (Figure 1).
Figure 1. Effusion (Eff) in
suprapatellar pouch of a
patient with rheumatoid knee
effusion. The tip of the
advancing needle is shown
(arrow). The hyperechoic line
represents the bony surface
of the femur (F)
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VOL.10 NO.2 FEBRUARY 2005
Synovitis
The presence of joint, bursal or tendon sheath effusion is an
excellent indirect surrogate for synovial inflammation. MSUS
also allows visualisation of synovial thickening, proliferation
and villous formation. US is more sensitive than clinical
examination to detect synovitis and to differentiate between
inflammatory and non-inflammatory joint diseases. 11 The
introduction of power Doppler further enhances the ability
to detect smaller degree of synovitis with reported accuracy
close to that of dynamic MRI. 12
Bony erosions
Early detection of bony erosions is pivotal in modern day
management of arthritic conditions, notably rheumatoid
arthritis (RA). MSUS can detect up to seven times more
erosions than plain radiography in early RA. 13
Tendons and ligaments
MSUS has risen to supremacy in the examination of tendon
and ligamentous structures. US is superior to MRI in the
detection of longitudinal split tendon tear and subluxed
tendon and has the advantage of allowing dynamic tendon
assessment. 14 Focal tendonitis and calcific tendonitis can be
detected by US. MSUS is an important tool in diagnosis of
painful shoulder conditions, especially in rotator cuff tears. 15
Enthesitis, inflammation of ligamentous insertion into bones,
is a characteristic feature in spondyloarthropathies which is
better detected by US than clinical examination. 16
Peripheral nerves
In recent years MSUS has become a useful tool in diagnosing
focal nerve compression such as the entrapment neuropathies.
A prototypic example is carpal tunnel syndrome (CTS). Various
US criteria for diagnosing CTS have been proposed 17 and
recently, a local study by Wong et al reported a sensitivity of
89% and a specificity of 83% for sonographic diagnosis of CTS. 18
Interventional ultrasonography
Guidance for intervention (joint aspiration, synovial or soft
tissue biopsy, joint or tendon sheath injection) is a major
application of ultrasonography. US guided procedures can
be performed under direct sonographic visualisation.
Alternatively, the skin surface can be marked after
determining the most appropriate entry point and the depth
of the target area prior to the placement of the needle. 19
Miscellaneous indications
MSUS has a multitude of developing and potential indications.
US measurement of skin thickness is being evaluated as an
objective outcome measure for systemic sclerosis. Differential
diagnosis of skin and soft tissue infections including necrotising
fasciitis 20 can be assisted by US examination and guided
aspiration (Figure 2). Characteristic ultrasonographic features
are present in arteries of patients with Takayasu's and giant
cell arteritis though the role of US in the diagnosis of these
conditions remains to be defined. 21
Figure 2. Ultrasound of the thigh of a
diabetic patient with severe limb pain.
Note the irregularity of the fascia (F),
abnormal fluid collections along the fascia
planes ( * ) and diffuse thickening of the
fascia (F) and subcutaneous tissue (SC).
Necrotising fasciitis was confirmed on
surgical exploration.
Medical Bulletin
Equipment, techniques and training
A detailed description of the technics and techniques of MSUS
is beyond the scope of this review but the key elements are
highlighted below.
Equipment
The appropriate selection of equipment is critical in facilitating
the introduction and training of MSUS. A fundamental issue
in selection of sonographic instruments is to decide whether
the machine is devoted for MSUS or if it is multi-purpose. Other
important considerations include cost, image resolution and
quality, transducer design, equipment size/portability and
other optional features such as colour/power Doppler.
MSUS requires transducers with linear array. High frequency
(7.5 - 20 MHz) transducers have better spatial resolution but
shallower tissue penetration and are best used for
demonstrating small and superficial structures like the hand
joints. Lower frequency (

Medical Bulletin
(>16 MHz) with resolution power lower than 0.1 mm allowing
delineation down to the level of histological details. Though
many problems remain to be solved, the possibility of carrying
out a histosonographic study is a fascinating conception.
Clinically relevant histosonographic pathologies include
minimal cartilage lesions, morphological and structural
tendon changes, and minimal interruptions of bone cortical
profile. 1
MSUS is a booming and maturing technique. New frontiers
including the use of contrast-enhanced ultrasonography and
ultrasonographic analysis of synovial fluid are being explored
and expanded.
Limitations and pitfalls
MSUS is not omnipotent and its usefulness is often limited
by acoustic accessibility, equipment inadequacies and
operator i ne xperi ence. It shoul d b e consi dered
complementary rather than competitive with respect to other
imaging techniques such as conventional radiography and
MRI. Though the procedure itself has no inherent deleterious
effects, harm may result from improper acquisition or
interpretation of imaging findings.
US is the most operator-dependent imaging modality. The
value of the diagnostic information obtained will rely upon
the skill and experience of the examiner. A basic
understanding of the principles of ultrasonography and a
detailed knowledge of normal and pathologic anatomy is
mandatory. Much experience is needed to discern artifacts
and normal variations from pathologic appearances and to
avoid interpretation errors. Learning curve is relatively long.
The cost implication in terms of equipment and human
resources needs to be justified.
Challenges and developments
Despite rising enthusiasm, there is still considerable
variability in the uptake of MSUS by rheumatologists
worldwide. In some European centres, MSUS is a routinely
provided service for proven clinical indications. In Germany
and Italy, MSUS is an integral part of rheumatology training
while in the United States and United Kingdom, it remains
mostly in the terrain of radiologists. 23 There are challenges as
well as potentials for collaboration between radiologists and
rheumatologists in the development of MSUS given their
respective expertise i n i magi ng technol ogy and
musculoskeletal pathology. Much work is needed in
refinement of the technique and cost-effective analysis of
sonographic applications. Outstanding issues of training and
reproducibility are among the essentialities that need to be
addressed.
Conclusion
Musculoskeletal ultrasound provides quick, safe, dynamic
and real-time sequential information unrivalled by other
imaging modalities. A skilled clinician is greatly advantaged
by using US to answer specific question regarding the
characteristics of the underlying pathology, its localisation,
its extent and the evolution of anatomical changes. New
indications and applications of this versatile technique are
being explored and consolidated. In future, musculoskeletal
ultrasound may have the potential to emulate the success of
echocardiography and obstetrical ultrasonography. Maybe
VOL.10 NO.2 FEBRUARY 2005
one day we will find our internists carrying a new gadget in
their al ready l oaded whi te coat pockets - “The
Musculoskeletoscope”.
Imagination is more important than knowledge. Albert
Einstein
References
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