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SOUND JUDGMENT SERIES
Musculoskeletal Sonography
of the Tendon
Kenneth S. Lee, MD
Invited paper
The Sound Judgment Series consists of
invited articles highlighting the clinical
value of using ultrasound first in specific
clinical diagnoses where ultrasound has
shown comparative or superior value. The
series is meant to serve as an educational
tool for medical and sonography students
and clinical practitioners and may help
integrate ultrasound into clinical practice.
Received September 4, 2012, from the Department of Musculoskeletal Radiology, University of
Wisconsin School of Medicine and Public Health,
Madison, Wisconsin USA. Revision requested
September 17, 2012. Revised manuscript accepted
for publication September 28, 2012.
Address correspondence to Kenneth S. Lee,
MD, Department of Musculoskeletal Radiology,
University of Wisconsin School of Medicine and
Public Health, 600 Highland Ave, CSC E3/366,
Madison, WI 53792-0002 USA.
E-mail: [email protected]
Abbreviations
MRI, magnetic resonance imaging
T
endon abnormalities are common musculoskeletal injuries
that comprise 7% of all physician visits in the United States
and up to 50% of all sports-related injuries.1–3 Common
tendon abnormalities include tendinopathy and tendon tears, which
impose a substantial cost to society in the United States and abroad.
According to the American Public Health Association, tendon disorders account for approximately $850 billion per year in health care
costs and indirect lost wage expenditures.4
Accurate and timely diagnosis of musculoskeletal tendon
injuries is critical to ensure proper treatment and thus minimize
societal costs. Magnetic resonance imaging (MRI) has been the
imaging standard for musculoskeletal injuries. However, MRI is
costly and overused.5 Improvements in ultrasound technology have
made sonography a rapidly growing imaging alternative and complementary tool to MRI for the diagnosis of common tendon
injuries.6 Sonography is both portable and cost-effective, with the
potential to save $7 billion in health care costs over the next 15 years
with increased use.5 High-resolution and dynamic assessment
advantages make sonography well suited for tendon evaluation and
should be a first-line complementary diagnostic tool. Currently in
clinical practice, musculoskeletal sonography is widely accepted and
expanding in Europe.7 Most recently, the use of musculoskeletal
sonography is increasing among radiologists and nonradiologists in
the United States, but especially by nonradiology groups.8
Sonographic Appearance of the Tendon
Tendons connect muscle to bone and are, therefore, unique structures that give a characteristic sonographic appearance. The tendon
is made up of bundles of parallel linear fibers that contain, at a basic
level, a relatively high percentage of type I collagen that is arranged
in a cross-linked triple-helix structure.9 The helical structure is stabilized by tightly bound water molecules.10,11
The orientation of the collagen fibers is along the long axis of
the tendon in keeping with the biomechanical strain placed between
muscle and bone.3 On sonography, this pattern is seen as multiple
tightly spaced echogenic parallel lines in a fibrillar pattern (Figure
1A).12 Transverse plane imaging shows multiple echogenic dots
(Figure 1B). The normal tendon is uniform in echo texture and size.
©2012 by the American Institute of Ultrasound in Medicine | J Ultrasound Med 2012; 31:1879–1884 | 0278-4297 | www.aium.org
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Lee—Musculoskeletal Sonography of the Tendon
The ultrasound beam should be perpendicular to the
orientation of the collagen fibers. If the beam is not perpendicular and off as little as 2° in angulation, the expected
sonographic appearance is lost, simulating disease and
increasing the likelihood of a false-positive diagnosis (Figure 2A).13 This artifact is called anisotropy, unique to the
musculoskeletal system. Therefore, great care should be
given in imaging a tendon that is not parallel to the skin
surface and for complex tendon structures that may change
fiber orientation even within a tendon, such as seen in the
rotator cuff (Figure 2B). While evaluating and documenting the tendon in orthogonal planes, the operator will often
gently toggle the transducer or even indent the skin surface with one end of the transducer in what is known as a
“heel-toe” maneuver to optimize tendon visualization by
orienting the ultrasound beam perpendicular to the tendon structure.
Figure 1. Normal sonograms of the tendon in a 32-year-old man. A, Longitudinal grayscale sonogram of the Achilles tendon (arrowheads)
shows the parallel echogenic lines in a fibrillar pattern that is uniform in
size and echo texture. B, Transverse grayscale sonogram of the normal
Achilles tendon shows the tightly spaced network of tendon fibrils in a
normal polka dot appearance in cross section. Star indicates calcaneus.
Advantages of Sonographic Evaluation
Musculoskeletal sonography has come a long way over the
past 30 years due to improved computer and transducer
technology. The earliest sonographic reports of the tendon investigated patients with Achilles tendon rupture in
1984.14 Ultrasound technology advancements such as the
development of linear array probes to decrease anisotropy
and improvements in near-field high-resolution and focusing capabilities have helped propel musculoskeletal sonography as a viable imaging tool.15
The most defining advantage of sonography over MRI
is its real-time imaging capability, which allows for dynamic
evaluation of the tendon using a variety of stress maneuFigure 2. Anisotropy of the normal supraspinatus tendon in a 32-yearold man. A, Longitudinal grayscale sonogram of the normal supraspinatus tendon (arrowheads) of the rotator cuff shows relative
hypoechogenicity (arrow) of the deep tendon fibers as it angles away
from the ultrasound beam to insert onto the footprint, mimicking tendon disease. B, Longitudinal grayscale sonogram of the same normal
supraspinatus tendon without the hypoechogenicity after the transducer
probe was gently adjusted shows normal tendon fibers (arrow).
A
A
B
B
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vers.16,17 For example, in the neutral position, the long head
of the biceps tendon may lie normally in the bicipital groove
(Figure 3), only to dislocate medially once the arm, with
elbow flexed, is externally rotated (Figure 4). In addition to
tendon subluxation, other tendon abnormalities diagnosed
dynamically include tendon snapping, friction between two
structures such as in shoulder impingement,18 and increasing conspicuity of tendon tears while stressing the tendon
or with sonopalpation.17 Real-time dynamic sonographic
evaluation provides this unique diagnostic ability using
controlled movements.
Real-time imaging capability also allows for direct needle visualization during sonographically guided procedures.16,19 Sonography can guide a needle to the target in
any plane that is comfortable for both the patient and
physician, while avoiding major neurovascular structures.
Common sonographically guided procedures include tendon sheath and bursa steroid injections and lavage of calcium deposits seen in calcific tendinitis of the rotator cuff.20
Innovations in sonographically guided therapy of the tendon such as platelet-rich plasma, percutaneous tenotomy,
and sclerotherapy of neovessels to treat tendinopathy are
only made possible because of the real-time capability and
needle visualization under sonography (Figure 5).21,22
Patient and referring provider satisfaction is also high
because sonography can be used to both diagnose and treat
various tendon abnormalities in one setting during a single
appointment, requiring less days off work for the patient
and accompanying family members. The therapeutic
advantage of sonography clearly differentiates this imaging modality from others.
High spatial resolution is another advantage of sonography, made possible by the emergence of high-frequency
(10–12 MHz) linear array transducers.23 High-frequency
imaging can resolve finer detail within a tendon than MRI.
For example, the axial resolution of a 10-MHz probe is
about 150 μm, whereas a typical 1.5-T MRI scanner with
a matrix of 256 × 256 pixels and a 5-mm slice thickness is
about 469 × 469 μm.24,25 This high-resolution advantage of
sonography allows for a sensitive evaluation for tendinopathy and tendon tears.
The power Doppler capability of sonography can give
important information about hyperemia that can be associated with tendinopathy.26 Tendinopathy is an overuse
injury characterized by disorganization of fibers, tendon
weakening, and abnormal tendon thickening from edema
and fibroblast accumulation.27 Hyperemia is increased vascularity that can also be seen with tendinopathy.27 Typical
sonographic findings of tendinopathy include loss of the
normal fibrillar pattern, tendon thickening, and hypoechogenicity. Increased Doppler flow helps increase specificity that the sonographic finding is likely correlated to the
patient’s site of pain (Figure 6).16 Hyperemia can also be
seen in tenosynovitis or bursitis closely associated with the
tendon. Color Doppler imaging is also useful for detecting
blood vessels that can be carefully avoided during sonographically guided procedures.19
Accessibility of ultrasound equipment and lower cost
are other advantages of musculoskeletal sonography.
When a quick diagnosis to initiate early treatment coupled
with increasing concerns of health care costs becomes a
priority, sonography may be the preferred modality.5
Figure 3. Dynamic sonographic evaluation of the long head of the
biceps tendon in a 45-year-old woman. Transverse grayscale sonogram
shows the long head of the biceps tendon (arrow) located within the
bicipital groove.
Figure 4. Dynamic sonographic evaluation of the long head of the
biceps tendon in a 52-year-old woman. Transverse grayscale sonogram
obtained during dynamic real-time evaluation of the long head of the
biceps tendon (arrow) shows the tendon medially dislocating out of the
bicipital groove.
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Figure 5. Sonographically guided needle placement into the supraspinatus tendon (arrowhead) during platelet-rich plasma treatment for
rotator cuff tendinopathy in a 58-year-old man. Long-axis grayscale
sonogram of the supraspinatus tendon shows in-plane needle placement (arrow) with the needle in the tendon and the needle tip placed on
the footprint of the greater tuberosity (asterisk).
A recent Medicare population study found that by the year
2020, the potential annual cost savings to Medicare by
using musculoskeletal sonography instead of MRI, when
appropriate, would be around $736 million.5
Sonography Versus MRI
Although MRI is considered the imaging modality of
choice for many musculoskeletal injuries, musculoskeletal
sonography has been rapidly growing in popularity in the
United States as a complementary or sometimes preferred
imaging tool. This growth is in part due to increasing
evidence-based literature stating that the diagnostic accuracy of musculoskeletal sonography is comparable to that
of MRI. Magnetic resonance imaging has excellent soft tissue contrast and, therefore, is capable of evaluating the
bone marrow and intra-articular structures such as cartilage and labrum that cannot be effectively imaged with
sonography. However, sonography serves as a useful comFigure 6. Longitudinal power Doppler sonogram from a 25-year-old
man with proximal patellar tendinopathy shows hyperemia (red) along
the deep surface of the abnormally thickened and hypoechoic proximal
patellar tendon (arrowheads). Star indicates patella.
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plementary tool that can quickly assess the integrity of
superficial tendon structures as well as real-time dynamic
evaluation for tendon snapping or dislocation.
Many studies have investigated the accuracy of diagnosing tendon injuries using sonography. The best-studied tendon, and the most commonly imaged with
sonography, is the shoulder rotator cuff. Recent metaanalyses that reviewed up to 62 sonographically based
studies of the shoulder found that sonography had sensitivity of 92% to 96% and specificity of 93% to 96% for
full-thickness tears compared to the reference standard
of surgery (Figure 7).28–30 For partial-thickness rotator
cuff tears, the sensitivity and specificity were 67% to
84% and 89% to 94%, respectively. Similarly, a metaanalysis of 67 MRI-based studies showed sensitivity of
92% and specificity of 93% for full-thickness tears compared to surgery and sensitivity of 64% and specificity of
92% for partial-thickness tears.30 When comparing the
accuracy of MRI and sonography for diagnosing rotator
cuff tears, there was no statistically significant difference.
Interestingly, however, patient satisfaction was significantly higher for sonography when receiving both MRI
and sonography of the shoulder.31 Because shoulder
pain is most likely due to rotator cuff tears in the older
population,32 unlike labral tears in the younger population, sonography offers a quick, cost-effective, and accurate assessment of rotator cuff integrity.
Studies have also investigated the accuracy of MRI
and sonography for tendon tears of the ankle. Sonography
has been shown to have sensitivity of 100% and specificity
of 83% for differentiating partial- from full-thickness tears
of the Achilles tendon (Figure 8).33 Magnetic resonance
imaging has shown a similar high level of sensitivity and
specificity. However, for smaller ankle tendons such as the
Figure 7. Full-thickness tear of the supraspinatus tendon in a 62-yearold man. Longitudinal grayscale sonogram of the supraspinatus tendon
shows a large anechoic defect of a full-thickness tear (arrows). Arrowhead indicates articular cartilage of the humeral head.
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Figure 8. Partial-thickness tear of the Achilles tendon in a 56-year-old
woman. Longitudinal grayscale sonogram of the distal Achilles tendon
(arrowheads) shows a hypoechoic defect (arrow) involving the deep
surface of the Achilles tendon near its calcaneal insertion. Asterisk indicates calcaneus.
peroneal tendons, sonography compared to surgery was
more sensitive (100% versus 83%) for detecting tears.34,35
A meta-analysis for detecting gluteal tendon tears
comparing MRI and sonography to surgery was also
recently done.36 The study found that the sensitivity of
MRI for detecting gluteal tendon tears ranged from 33%
to 100%, whereas specificity remained consistently high
(92%–100%) across studies. Sonography was found to be
consistently sensitive (79%–100%) compared to MRI,
suggesting that sonography may be a first-line imaging tool
for evaluating gluteal tendon tears.
Tendinopathy is also a commonly imaged tendon
abnormality. With respect to surgical correlation, sonography may be slightly more sensitive for detecting rotator
cuff tendinopathy but less specific than MRI. However,
Figure 9. Calcific tendinitis of the rotator cuff in a 48-year-old woman with
chronic intermittent shoulder pain. Longitudinal grayscale sonogram of
the supraspinatus tendon (arrowheads) shows a rounded hyperechoic
calcium deposit (arrow) with some posterior acoustic shadowing within
the supraspinatus tendon. Asterisk indicates greater tuberosity.
J Ultrasound Med 2012; 31:1879–1884
sonography is highly sensitive for detecting shoulder calcific tendinitis, whereas MRI is not (Figure 9).20,37
Another comparison study between MRI and sonography for patellar tendinopathy compared with clinical diagnosis showed sonography to be more sensitive than MRI.
Specificity was also higher when power Doppler imaging
was used to detect hyperemia.38 Other studies comparing
the sensitivity and specificity of MRI and sonography for
Achilles tendinopathy and lateral epicondylosis had mixed
results.39,40 These discrepancies in results, however, may
be limitations with regard to operator dependence, equipment differences, and the reference standard used.
Musculoskeletal sonography is well suited for evaluating tendon abnormalities. In most cases, sonography and
MRI have comparable diagnostic accuracy for detecting
tendon tears or tendinopathy. However, the additional
advantages of sonography such as accessibility, low cost,
dynamic capability, and needle guidance make it a viable
first-line imaging modality. Musculoskeletal sonography
should be implemented as a complementary imaging tool
in a growing musculoskeletal imaging practice that wants
to offer integrated expertise across all modalities.
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