BULLETIN VOL 1 NUMBER 1 - FEBRUARY 1998 Ultrasound of the Wrist Neil Simmons MBBS, DRACR
Sonography of the wrist has become a relatively common procedure over
the past few years. Understanding of the basic principles of musculoskeletal
ultrasound, usually acquired during shoulder ultrasound studies, is being
applied to many different parts of the body, including the wrist. As elsewhere,
knowledge of the relevant anatomy is essential. Normal anatomical variations
are common in the wrist. Ignorance of these will lead to incorrect diagnoses.
An understanding of the basic pathologies can, with a little lateral thinking,
solve most problems. This article will emphasise anatomy, pathology and
scanning tips.
One advantage of
the wrist is that it is relatively small, so that the small area of
the transducer head does not have to be moved far. Most structures lie
close to the surface, so high frequency transducers [7.5 MHz or greater],
with their excellent near field resolution are required. Stand-off pads
are sometimes needed for very superficial structures or to demonstrate
contour deformities of the skin. If pads are not available, are cracked,
or create too much artefact, applying a thick layer of gel and scanning
with very little pressure will give good results. "Heel-toeing" of the
transducer to avoid anisotropic artefact is essential in the many tendons
and nerves which curve in the region of the wrist.
Other forms of
imaging may be essential to extract the greatest amount of information
from a scan. Plain X-rays are still necessary to demonstrate possible
fractures, arthritis, subluxation, soft tissue calcification or foreign
body and bony deformity. Nuclear medicine may highlight focal soft tissue
or bony abnormalities. CT scans demonstrate internal architecture of
bones and are moderately useful at tissue characterisation [usually
lipomas]. Magnetic Resonance is, in some countries, the preferred method
of wrist imaging. Indeed, there is little doubt that the images and
information derived from a well performed MR scan in many cases surpass
ultrasound. In others, however, a diagnosis can be obtained with ultrasound
at half the cost, in half the time. Dynamic scanning of tendon movement,
colour Doppler energy and colour Doppler imaging are all factors which
increase the effectiveness of ultrasound. Ultrasound equipment is more
readily available than MR. New dedicated peripheral MR coils eliminate
some well known problems with MR eg claustrophobia and ferrous material
in the body, but these are still relatively uncommon. The absence of
a Medicare rebate for MR for private patients increases the attractiveness
of a rebateable ultrasound scan. Arthrography of the radiocarpal, midcarpal
and distal radioulnar joints is still useful to demonstrate ligament,
capsule and cartilage tears.
The majority of
ultrasound scans are requested to investigate swellings, pain, sensory
disturbances or restriction of movement. A request such as "diffuse
wrist pain FI" is often associated with a fruitless search for a cause
[1]. Rheumatoid arthritis, however, may present with diffuse synovial
swelling and tenosynovitis. A thorough examination of the anterior [ventral]
and posterior [dorsal] aspects should be undertaken in cases of non-localised
symptoms. Even if the problem seems simple to solve, eg. a swelling
shown to be a ganglion, searching a little further afield often demonstrates
extra pathology. Beware of the "satisfaction syndrome". I find that
the best source of clinical information is sitting opposite me. Most
patients are only too happy to talk about their problems. The thoroughness
of the investigation of the problem is appreciated and most patients
are interested in dynamic scanning of tendons etc. Even a negative result
can be accepted if the sonographer/sonologist has made an obvious effort.
SUMMARY
|
Bulletin
