AJR 2000; 175:637-645
© American Roentgen Ray Society
An Illustrated Tutorial of Musculoskeletal Sonography
Part I, Introduction and General Principles
John Lin1,
David P. Fessell,
John A. Jacobson,
William J. Weadock and
Curtis W. Hayes
1
All authors: Department of Radiology, The University of Michigan Medical
Center, 1500 E. Medical Center Dr., TC 2910, Ann Arbor, MI 48109-0326.
Received December 8, 1999;
accepted after revision February 10, 2000.
Address correspondence to J. Lin.
Introduction
Musculoskeletal sonography is a rapidly evolving technique that is gaining
popularity for the evaluation and treatment of joint and soft-tissue diseases.
Inherent advantages of sonography include accessibility, quick scan time, low
cost, multiplanar capability, and the ability to perform dynamic real-time
imaging with contralateral comparison. Advances in technology with higher
frequency transducers, power Doppler sonography, and extended field-of-view
function have facilitated the progressive development of sonography
[1,2,3].
One notable drawback of sonography is operator-dependency; the quality and
consistency of sonographic studies rely on the expertise of the examiner.
Other limitations include a long learning curve and a physician time-intensive
examination, particularly for beginners. Musculoskeletal sonography is a
widely accepted and available tool in Europe and other parts of the world, in
which it is often the principal technique performed for many clinical
indications. However, in the United States, sonography is relatively underused
because of the wide availability of MR imaging and the small number of
training programs offering instruction and experience in musculoskeletal
sonography. Additionally, physicians, including radiologists, are often
unaware of the potential applications of sonography for the assessment of
joint and soft-tissue disease. Sonography offers a cost-effective alternative
for imaging musculoskeletal disorders in many situations
[1,2,3].
We discuss basic principles, advanced imaging functions, scan artifacts,
and general characteristics of key musculoskeletal structures. Subsequent
articles will feature abnormalities pertaining to specific joints, and the
final installment will focus on musculoskeletal tumors, sonographically guided
interventions, and miscellaneous topics. Our intent is to review current
accepted clinical applications of musculoskeletal sonography and generate
interest in what we believe to be an underused technique. We hope to inspire
physicians to consider musculoskeletal sonography as a viable, and frequently
primary, option in the assessment of joint and soft-tissue disorders.
General Principles
When performing musculoskeletal sonography, the proper equipment is
essential to facilitate optimal image quality and diagnostic examinations. In
general, the structures examined will be superficial; therefore,
high-frequency (
7-12 MHz) linear array transducers are usually the most
appropriate choice. The high resolution attainable allows detailed anatomic
depiction of pertinent structures
[1]. Proper positioning of the
patient is of paramount importance in obtaining high-quality studies.
Different sonographic techniques have been described, with the universal goal
of optimizing the visualization of structures of interest.
Musculoskeletal Structure Characteristics
In this section, we describe the sonographic characteristics of key
musculoskeletal structures.
The evaluation of tendon abnormality is the most common clinical indication
for musculoskeletal sonography. Whether the tendon is in the shoulder, wrist,
or ankle, the sonographic appearance of a normal tendon is fairly uniform. On
sonography, tendons should have a fibrillar pattern of parallel hyperechoic
lines in the longitudinal plane and a hyperechoic round-to-ovoid shape in the
transverse plane [4] (Fig.
1A,1B,1C).
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Fig. 1A. —36-year-old asymptomatic man. Longitudinal (A) and transverse
(B) sonograms reveal normal supraspinatus tendon (white
arrows). Note hyperechoic cortex of humerus (black arrows),
including cortex (arrowheads) of greater tuberosity (GT) in A.
Deltoid muscle (D) is overlying supraspinatus tendon. m = medial, a =
anterior.
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Fig. 1B. —36-year-old asymptomatic man. Longitudinal (A) and transverse
(B) sonograms reveal normal supraspinatus tendon (white
arrows). Note hyperechoic cortex of humerus (black arrows),
including cortex (arrowheads) of greater tuberosity (GT) in A.
Deltoid muscle (D) is overlying supraspinatus tendon. m = medial, a =
anterior.
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Fig. 1C. —36-year-old asymptomatic man. Transverse sonogram reveals normal
peroneus brevis (white arrowheads) and peroneus longus (black
arrowheads) tendons. Note border between peroneus tendons
(arrows) and peroneus brevis muscle (PB). a = anterior, p =
posterior, F = fibula.
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Ligaments have an appearance similar to tendons but are static stabilizers
connecting bone to bone. Ligaments can be differentiated from tendons by
noting their more compact fibrillar, hyperechoic pattern
[1]. Superficial ligaments,
such as the anterior talofibular ligament or elbow ulnar collateral ligament
(Fig. 2), are readily
visualized. Deeper internal ligaments, such as the anterior cruciate ligament,
are more difficult to consistently identify.
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Fig. 2. —30-year-old woman without symptoms. Longitudinal sonogram reveals
normal ulnar collateral ligament (black arrows) of elbow. Note medial
epicondyle (M and white arrows) and proximal ulna (U and
arrowheads). d = distal.
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Normal skeletal muscle shows low- to mid-level echogenicity with
hyperechoic fascial planes [1]
(Fig.
1A,1B,1C).
Partial and complete tears can be characterized on sonography, and the degree
of retraction, if any, can be accurately measured. Dynamic imaging with
contraction of the affected muscle can sometimes better illustrate the
abnormality and provide functional information (Fig.
3A,3B,3C).
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Fig. 3A. —60-year-old man with muscle herniation caused by remote trauma.
Longitudinal sonogram of anterolateral lower extremity, in region of focal
bulge, reveals herniation of anterior tibial muscle (white arrows)
through defect in fascia (black arrows).
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Fig. 3B. —60-year-old man with muscle herniation caused by remote trauma.
Longitudinal split-screen sonogram obtained in same location as A shows
minimal motion of anterior tibial muscle with dynamic imaging between
dorsiflexion (left-sided image) and plantar flexion (right-sided image). Note
muscle herniation (solid arrows), fascia (open arrows), and
small subfascial fluid collection (asterisk).
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Fig. 3C. —60-year-old man with muscle herniation caused by remote trauma.
Longitudinal split-screen sonogram shows comparison of muscle echotexture
between scarred, herniated symptomatic leg (left-sided image) and normal
contralateral asymptomatic leg (right-sided image). Note fascia (open
arrows) and muscle herniation (solid arrows).
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Larger peripheral nerves can also be accurately identified on sonography
[5]. Normal peripheral nerves
typically appear as echogenic fascicular structures and tend to be slightly
less echogenic than tendons or ligaments
[6] (Fig.
4A,4B).
This appearance is somewhat variable depending on the location and orientation
of the nerve but can usually be identified by the nerve distribution.
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Fig. 4A. —32-year-old asymptomatic man. Transverse (A) and longitudinal
(B) sonograms of carpal tunnel of wrist show normal appearance of
median nerve (black arrows) and flexor tendons (white
arrows). r = radial, u = ulnar, p = proximal, d = distal.
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Fig. 4B. —32-year-old asymptomatic man. Transverse (A) and longitudinal
(B) sonograms of carpal tunnel of wrist show normal appearance of
median nerve (black arrows) and flexor tendons (white
arrows). r = radial, u = ulnar, p = proximal, d = distal.
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On sonography, the bone cortex appears as an echogenic surface with
posterior shadowing (Fig.
1A,1B,1C).
Only the superficial surface of the bone can be consistently evaluated on
sonography. Radiographically occult fractures can be detected on sonography,
seen as a "step off" cortical disruption
[1,
7]
(Fig. 5).
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Fig. 5. —36-year-old woman with patellar fracture. Longitudinal sonogram
shows mildly displaced fracture of patella (arrows) that was not
revealed on radiographs of knee. p = proximal, d = distal.
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A thin hypoechoic rim paralleling the echogenic articular cortical surface
represents hyaline cartilage (Figs.
1A,1B,1C
and 6). Ongoing research on
the potential clinical applications of sonography of fibrocartilage is
promising. Sonography may play a more significant role in the assessment of
labral and meniscal lesions as technology continues to improve
[1]
(7 and
8).
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Fig. 6. —80-year-old woman with rotator cuff tear. Transverse sonogram
reveals small full-thickness tear (curved arrows) in distal
supraspinatus tendon. Note hypoechoic hyaline articular cartilage (black
arrowheads) of humeral head. Fluid present within defect of supraspinatus
tear accentuates echogenicity at surface of hyaline cartilage (white
arrowhead). a = anterior, p = posterior.
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Fig. 7. —37-year-old man with shoulder pain. Transverse sonogram of posterior
glenohumeral joint shows normal posterior glenoid labrum (arrows).
Note glenoid (G) and humeral head (H). Pain was caused by torn rotator cuff
tendon (not shown).
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Fig. 8. —18-year-old woman with contralateral hip pain. Longitudinal sonogram
of asymptomatic left hip shows normal anterior acetabular labrum
(arrows). Note acetabulum (A) and femoral head (F).
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Calcifications typically exhibit increased echogenicity with associated
posterior acoustic shadowing (Fig.
9). However, the presence of shadowing depends on the size of the
calcification [8]. When
calcification is present within the substance of a tendon, it commonly
represents calcific tendonitis (Fig.
10A,10B).
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Fig. 9. —27-year-old woman with dermatomyositis. Transverse sonogram of
medial upper arm in region of several small non-tender palpable nodules shows
several subcutaneous echogenic foci (arrows) with distal shadowing
(arrowheads) that represent superficial calcifications.
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Fig. 10A. —21-year-old man with calcific tendonitis of Achilles tendon.
Longitudinal (A) and transverse (B) sonograms of Achilles tendon
at distal insertion reveal extensive calcifications (white arrows)
within tendon, consistent with calcific tendonitis. Note distal shadowing
(arrowheads), and note superoposterior aspect of calcaneus (C and
black arrows) in A. p = proximal, d = distal, m = medial, l =
lateral.
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Fig. 10B. —21-year-old man with calcific tendonitis of Achilles tendon.
Longitudinal (A) and transverse (B) sonograms of Achilles tendon
at distal insertion reveal extensive calcifications (white arrows)
within tendon, consistent with calcific tendonitis. Note distal shadowing
(arrowheads), and note superoposterior aspect of calcaneus (C and
black arrows) in A. p = proximal, d = distal, m = medial, l =
lateral.
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Examination
Although sonography is operator-dependent, the interaction between the
examiner and the patient is invaluable. Additional clinical history about the
precise location and character of symptoms, direct feedback about tenderness
with probe palpation, and positions or movements that elicit or aggravate
symptoms can assist in the accurate interpretation of findings.
The flexibility and dynamic capability of sonography allow a targeted
examination, specific for each individual. Dynamic imaging can readily reveal
certain transient conditions related to specific positions or movements, which
can be absent during static examination
[2] (Fig.
11A,11B,11C).
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Fig. 11A. —50-year-old man with intermittent ulnar nerve subluxation.
Transverse dynamic sonograms of cubital tunnel region reveal transient
dislocation of ulnar nerve (black arrows) out of cubital tunnel
(white arrowheads) with progressive flexion. Note medial epicondyle
(white arrows) and origin of common flexor tendons (black
arrowheads), which appear hypoechoic because of anisotropy artifact (see
Figs. 17 and
18A,18B).
v = volar.
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Fig. 11B. —50-year-old man with intermittent ulnar nerve subluxation.
Transverse dynamic sonograms of cubital tunnel region reveal transient
dislocation of ulnar nerve (black arrows) out of cubital tunnel
(white arrowheads) with progressive flexion. Note medial epicondyle
(white arrows) and origin of common flexor tendons (black
arrowheads), which appear hypoechoic because of anisotropy artifact (see
Figs. 17 and
18A,18B).
v = volar.
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Fig. 11C. —50-year-old man with intermittent ulnar nerve subluxation.
Transverse dynamic sonograms of cubital tunnel region reveal transient
dislocation of ulnar nerve (black arrows) out of cubital tunnel
(white arrowheads) with progressive flexion. Note medial epicondyle
(white arrows) and origin of common flexor tendons (black
arrowheads), which appear hypoechoic because of anisotropy artifact (see
Figs. 17 and
18A,18B).
v = volar.
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Fig. 17. —66-year-old woman with left shoulder pain. Three-dimensional image
of intact long head of biceps tendon with joint effusion extending into
bicipital tendon sheath shows three standard orthogonal planes: axial
(solid arrowhead), coronal (straight arrow), and sagittal
(open arrowhead). Oblique plane (curved arrow) was chosen by
sonographer. Clinical use of this function for musculoskeletal sonography is
under investigation.
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Fig. 18A. —62-year-old man with left shoulder pain. L = lesser tuberosity, G =
greater tuberosity. Standard transverse sonogram of long head of biceps tendon
is poorly visualized because of deep location of biceps tendon caused by large
body habitus of patient. Note bicipital groove (arrowheads).
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Fig. 18B. —62-year-old man with left shoulder pain. L = lesser tuberosity, G =
greater tuberosity. Transverse sonogram with tissue harmonics function reveals
intact long head of biceps tendon (arrows) discretely in bicipital
groove (arrowheads).
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Compression from applying transducer pressure under real-time visualization
can reveal important information about the composition of underlying
structures and allows increased conspicuity or detection of abnormalities that
may be otherwise hidden [2]
(Fig. 12).
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Fig. 12. —64-year-old man with rotator cuff tear. Split-screen image shows
complete full-thickness tear of distal supraspinatus tendon. Manual
compression (COMP) of transducer (right-sided image) reveals volume loss
(solid arrows) and bursal contour deformity (arrowheads)
confirming diagnosis of full-thickness tear. Note echogenic debris (open
arrows) present in tear defect. Secondary sonographic findings of
full-thickness rotator cuff tear will be discussed in part 2, "Upper
Extremity."
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Contralateral comparison is easily performed in the musculoskeletal system;
it distinguishes significant findings from normal variants and occasionally
reveals unsuspected abnormalities, which can be crucial to the treatment of a
patient (Figs. 13 and
14).
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Fig. 13. —48-year-old woman with left Achilles tendinosis. Longitudinal
split-screen image compares abnormal focally thickened left Achilles tendon
(white arrowheads, left-sided image), consistent with tendinosis,
with asymptomatic normal-caliber right Achilles tendon (black
arrowheads, right-sided image).
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Fig. 14. —36-year-old man with right brachial muscle atrophy. Split-screen
image compares severely atrophied right brachial muscle (arrows) at
anterior aspect of elbow with normal appearance of left brachial muscle
(arrowheads). Note capitellum (C) and radial head (R). Contralateral
comparison provides internal control, particularly for difficult or
unsuspected findings.
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Technical Features
Color and power Doppler sonography features show the degree of vascularity
associated with inflammatory processes and solid masses. Power Doppler
sonography can be used to characterize musculoskeletal inflammation in
cellulitis, abscess, synovitis, myositis, and bursitis
[9] (Fig.
15A,15B).
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Fig. 15A. —56-year-old woman with rheumatoid arthritis. Longitudinal sonogram
of radial aspect of left wrist shows hypoechoic periarticular lesions
consistent with synovial hyperplasia and pannus (black arrows). Note
abductor pollicis longus tendon (black arrowheads), distal radius
(white arrows), and scaphoid (white arrowheads). d = distal,
p = proximal.
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The split-screen function that is available on most sonography units can
expand the field of view to approximately double the width or can be used for
side-by-side comparisons (Figs.
13 and
14). The extended
field-of-view function, available on the Sonoline Allegra sonographic unit
(Siemens Medical Systems, Iselin, NJ), can display very large continuous
sections of anatomy, preserving spatial resolution without distorting
structural relationships [10,
11]
(Fig. 16).
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Fig. 16. —68-year-old woman with large hematoma caused by falling.
Longitudinal extended field-of-view sonogram of anterior aspect of right leg
reveals large pretibial hematoma (black arrowheads), which measured
10 cm in length. Extended field-of-view function allows full coverage of this
lesion. Note tibial cortex (arrows). Mirror-image artifact (white
arrowheads) is present. p = proximal, d = distal.
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Recent innovative functions such as three-dimensional imaging
(Fig. 17) and tissue harmonics
(Fig.
18A,18B)
may provide further improvement in the diagnostic effectiveness of sonography.
The role of these functions in the assessment of musculoskeletal disorders is
currently under investigation
[3].
Artifact
Anisotropy is an important artifact that can affect the image and should be
considered when examining any musculoskeletal soft-tissue structure. This
finding is most obvious with tendons and ligaments, caused by the highly
ordered, parallel pattern of collagen fibers that shows the greatest degree of
reflectivity when examined perpendicular to the ultrasound beam. Anisotropy
occurs when the ultrasound beam is not perpendicular to the fibrillar
structure of the tendon, resulting in the absence of specular reflectors and
an artifactual hypoechoic to anechoic appearance
[4] (Figs.
19A,19B
and
20A,20B).
The sonographer should be aware of proper transducer position and may need to
manipulate the heel-toe and fore-aft angulation of the probe to avoid this
artifact [12]. When a tendon
has a curving course, the effects of anisotropy cannot be entirely eliminated.
Each separate portion of the tendon must be examined individually, and the
evaluation of tendon integrity should be primarily determined during real-time
scanning.
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Fig. 19B. —36-year-old asymptomatic man. L = lesser tuberosity, G = greater
tuberosity. Transverse sonogram obtained at same location as A shows
effect of anisotropy with artifactual hypoechogenicity in expected location of
tendon (arrows).
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Fig. 20B. —49-year-old asymptomatic man. Transverse sonogram obtained at same
location as A shows effect of anisotropy with artifactual
hypoechogenicity in expected location of tendon (arrows).
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Top
Introduction
General Principles
