Category Archives: MSK




The Sonographic Revolution

For many years the rheumatologist adopted to fight against time to diagnose and follow most of the rheumatic diseases, this fighting continues to occur with no winners until the sonographic revolution has occurred in rheumatology.

Ultrasonography has been shown to be capable of substantially changing the traditional approach to most clinical problems in daily rheumatological practice because of its ability to allow a quick, safe and inexpensive access to otherwise undetectable anatomical information on the early targets of most rheumatic diseases.

Ultrasonography completes the physical examination in a rapid and accurate manner and allows the very early detection of a wide spectrum of pathological findings involving different anatomical structures in the musculoskeletal system.1


Although musculoskeletal ultrasound may be considered as one of the latest developments in ultrasound applications, it was first used, as far back as 1958, in the assessment of the acoustic attenuation of musculoskeletal tissues by K.T Dussik et al.2, 3

Dussik had also been the first to use ultrasound as a medical imaging modality in 1942. 2, 4

Ultrasound developed slowly until 1960 when Donald and colleagues produced the first automatic scanner.2

For the next decade, ultrasound was predominantly limited to the evaluation of abdominal and pelvic diseases.

By 1972 the first B-scan image of a joint was reported in the differentiation of a Baker’s cyst and thrombophlebitis.5

Graf, in 1980, published his landmark paper on the use of ultrasound in the diagnosis of congenital hip joint dislocation.6

In 1988, L. De Flaviis described ultrasound of the hand in rheumatoid patients including erosions, 10 years after Cooperberg described features of synovial thickening and joint effusion in the rheumatoid knee.7, 8

Since this time, particularly in the past decade, there has not only been a rapid development in ultrasound technology, but also widespread use of ultrasound in the investigation of musculoskeletal disorders to the point where it is now firmly established as a key imaging modality.


Ultrasound uses high-frequency sound waves to acquire images for the soft tissues, bones, and nerves of the body.

The ultrasound machine sends an electrical signal to the transducer, which is connected (via a cable) to the monitor and computer processing unit.

This system results in the production of sound waves that are transmitted from the transducer to the soft tissues of the body through acoustic transmission gel.9

The sound waves interact with the tissue interfaces and some reflect back toward the transducer on the surface of the skin.

The ultrasound image is produced from this reflection, which converts sound waves to an electrical current.9

The ultrasound machine then measures the amplitude of the returning electrical signal and records its travel time to determine the depth of the reflected structure.

As the machine generates and records the amplitudes and travel times of the sound beams, it uses the computer software to produce a two-dimensional image of the scanned structures.10

Transducer Selection:

The transducer is an essential element of US equipment, responsible for the generation of a US beam and the detection of returning echoes.

It greatly influences spatial resolution, penetration and signal-to-noise ratio, and in turn its selection affects the quality of the US image.9

Frequency of the Transducer:

To produce an image of optimal quality, it is important to select the proper transducer for the area of interest.

A transducer is described by the range of sound wave frequencies it can produce (MHz).

Higher-frequency transducers produce higher resolution images, but at the expense of beam penetration, because higher-frequency sound is more rapidly absorbed by the tissues.

Lower-frequency transducers are more capable of assessing deeper structures, but they have lower resolution.9

Shape of the Transducer foot plate:

Transducers also can be described as linear or curvilinear.

Linear transducers produce a sound wave that is propagated in a straight line perpendicular to the transducer surface (Fig.1).

Such transducers are best for evaluating linear structures like tendons.

Curvilinear transducers produce an arched beam and are less commonly used, but have some advantages in evaluating deeper structures (Fig. 2) and the small-footprint linear array L shaped transducer (hockey-stick transducer) which is suitable for evaluation of the small joints (Fig. 3).

Commonly used transducers in musculoskeletal ultrasound include the high frequency (20–7 MHz), linear transducer, and the low- to medium frequency (5–2 MHz) curvilinear array transducer.

The examiner should choose the highest-frequency transducer that can adequately image the target structure at the appropriate depth.9

Fig.1: Linear transducers are best for evaluating linear structures like tendons (coated from Jacobson JA, 9).

Fig.2: Curvilinear transducers are used for evaluating deeper structures such as hip, piriformis muscle, and sciatic nerve (coated from Jacobson JA, 9).

Fig.3: The small-footprint linear array transducer is also called a hockey-stick transducer and has higher frequency compared with other transducers. This transducer is used for evaluating small superficial structures such as peripheral nerves (coated from Jacobson JA, 9).


Reducing the width and thickness of the US beam to be limited to the area of interest has definite advantages in terms of contrast and spatial resolution.

In modern linear-array transducers’, focusing is currently not obtained by means of a fixed lens as in the old mechanical sector probes in which degrading of the image quality occurred at a short distance from the focal zone.

Focusing is now produced electronically by activating a series of elements in the array with appropriate delays, so that the trigger pulses to the inner elements are delayed with respect to the pulses to the outer ones.

In this way a curved wave front results from constructive interference bringing the US beam toward a focus. Recently, the introduction and refinement of matrix (1.5D probes) transducers led to further progress.

In these transducers, the single row of long piezoelectric elements found in a conventional probe is replaced by more layers (three to seven) incorporated into a single thin layer to produce parallel rows of short elements.

The slice thickness of the US image is improved by performing dynamic focusing in the elevation plane.

This leads to better spatial and contrast resolution and reduction of partial- volume averaging artifacts.11 A less expensive alternative to 1.5D probes is the use of peculiar acoustic lenses – Hanafy lenses –placed in front of the piezoelectric elements.

The Hanafy lens has nonuniform thickness and resonance properties: it produces a narrow and uniform image slice thickness and, simultaneously, a very broad bandwidth pulse.

The inner portion of the lens is thinner, resonates at higher frequencies and focuses in the near field, whereas its outer portions resonate at lower frequency and are focused in both transmission and reception at the deepest part of the image providing better penetration.12

Fig 4: Hanafy lens (Acuson-Siemens) coated from Claudon et al., 12.

Basic Scanning Techniques:

At first it is important to use enough acoustic transmission gel.

After that the examiner should begin by holding the transducer between the thumb and fingers of their dominant hand, positioning the end of the transducer near the ulnar side of the hand.

It is essential to securely stabilize the transducer on the patient’s body, with either the palm of the imaging hand or the small finger.

After the transducer is properly placed on the patient’s skin, a rectangular image is produced on the monitor.

The top of the image represents the tissues in contact with the transducer; the bottom of the image displays the deeper structures.

The left-to right orientation of the image can be altered using a button on the machine or by rotating the transducer 180 degree (fig 5).9

The image on the screen can be further adjusted and optimized by changing the sound-beam penetration using the depth controls.

Selection of the proper transducer is also critical in evaluating the depth of a structure.

There is an inverse relation between the frequency of the transducer and its depth of penetration, such that higher-frequency transducers are usually best to view superficial structures, whereas lower-frequency transducers are used for deeper structures.10, 13

Fig.5: (A, B) Orientation of the image. The top of the image usually shows the shallow structures and the bottom of the image, the deeper structures. The notch (arrow) of the probe usually represents the left side of the image (asterisk), but an image can be inverted by controls on the machine and it is important to confirm the side of the transducer with the side of the image on the screen. During examinations, t is important to be consistent. Many find it helpful to align the left side of the image with the examiner’s left side, coated from Jacobson JA, 2007.9 

The next step in imaging is adjusting the focal zone of the ultrasound beam.

The number of focal zones should be reduced to span the area of interest.

The zone feature is usually displayed on the side of the image as a series of cursors or symbols.

The depth and length of the focal zone position should match the position of the structure of interest.

The examiner may adjust the gain to either increase or decrease the brightness of the echo image.

A standardized approach to the study of the various anatomical regions is advisable even if the choice of the acoustic window is conditioned by the specific diagnostic need.14

Each anatomical area should be explored on various scan planes so as to obtain all of the necessary information.

An in-depth knowledge of the anatomy of the region examined is required for the musculoskeletal US. 14

Advantages and Disadvantages of Musculoskeletal Ultrasound:

When comparing US with other musculoskeletal imaging techniques (radiography, computed tomography, and magnetic resonance imaging), ultrasound offers numerous advantages.

Perhaps the most important of these is that ultrasound offers a hands-on, dynamic examination, allowing the clinician to image in real-time, while interacting with the patient.15

The clinician can ask the patient for assistance during the examination and may accurately localize painful areas by palpating with the transducer and seeking patient feedback.16

The sonographer can also ask the patient to reproduce the abnormal or painful event while scanning dynamically.

Furthermore, ultrasound is less expensive when compared to CT or MRI, can be repeated, and US can be used to compare the finding in the diseased side with the normal side of the same patient in the same session.

Ultrasound transmits no radiation to the patient or user, and thus may be used in special populations, including pregnant women and those with metal implants or other sources of imaging artifacts. 16

In addition, the enhanced sensitivity for detecting low-velocity flow in small tendon and synovium vessels achieved by recent colour Doppler and power Doppler techniques has led to the incorporation of Doppler US in rheumatology.

US allows an immediate correlation between imaging findings and clinical data, which improves diagnosis and management of patients with a range of rheumatic diseases from inflammatory arthritis, vasculitis or osteoarthritis to soft-tissue diseases.16-20

US has demonstrated more sensitivity than clinical evaluation in assessing joint inflammation.21-26

In addition, ultrasound is a bedside tool for performing accurate and safe musculoskeletal injections.27

On the other hand, the primary disadvantage of ultrasound is that it is operator dependent and there is a steep learning curve. Numerous examinations must be performed to establish a reliable diagnostic algorithm.28

Ultrasonographic Tissue Appearance:

Musculoskeletal ultrasound can be used to identify muscles, tendons, ligaments, nerves, bone surface and vessels, at a resolution of less than0.1 mm.

These structures can be characterized and described by their echogenicity. 29

When there is a large difference in impedance at the interface between tissues the sound beam is strongly reflected, creating a bright echo on the image. This process is described as hyperechoic.

If an image displays no echo and is black, it is referred to as anechoic, and when a weak or low echo is produced, it is termed hypoechoic.

When the echogenicity of a structure appears equal to an adjacent structure, it can be described as isoechoic or of equal echogenicity. 29

In general, when interpreting musculoskeletal ultrasound, a practical order of echogenicity is: bone/ligament/tendon/nerve/muscle.

In addition to their echogenicity, tissues are also described by their echotexture, which refers to their internal echo pattern.

Echotexture varies based on whether a structure is imaged longitudinally or transversely.30, 31

Definitions of Basic ultrasound terminology:

Echotexture refers to the coarseness or non-homogeneity of an object.
Echogenicity refers to the ability of tissue to reflect ultrasound waves back toward the transducer and produce an echo. The higher the echogenicity of tissues, the brighter they appear on ultrasound imaging.
Hyperechoic structures are seen as brighter on conventional US imaging relative to surrounding structures due to higher reflectivity of the US beam.
Isoechoic structures of interest are seen as bright as surrounding structures on conventional US imaging due to similar reflectivity to the US beam.
Hypoechoic structures are seen as darker relative to the surrounding structures on conventional US imaging due to the US beam being reflected to a lesser extent.
Anechoic structures that lack internal reflectors fail to reflect the US beam to the transducer and are seen as homogeneously black on imaging.
Longitudinal structure is imaged along the long axis.
Transverse structure is imaged perpendicular to the long axis.


1. Grassi W., Filippucci E., and Busilacchi P. Musculoskeletal ultrasound Best Practice & Research
Clinical Rheumatology 2004; 18: No. 6, pp. 813–826.
2. Kane D, Grassi W, Sturrock R et al. A brief history of musculoskeletal ultrasound: ‘From bats and
ships to babies and hips.’ Rheumatology 2004;43:931–933.
3. Dussik KT, Fritch DJ, Kyriazidou M et al. Measurements of articular tissues with ultrasound. Am
J Phys Med 1958;37:160–165.
4. Dussik KT. On the possibility of using ultrasound waves as a diagnostic aid. Z Neurol Psychiatr
5. McDonald DG, Leopold GR. Ultrasound B-scanning in the differentiation of Baker’s cyst and
thrombophelebitis. Br J Radiol 1972;45:729–732.
6. Graf R. The diagnosis of congenital hip-joint dislocation by the ultrasonic combound treatment.
Arch Orthop Trauma Surg 1980;97:117–133.
7. De Flaviis L, Scaglione P, Nessi R et al. Ultrasonography of the hand in rheumatoid arthritis. Acta
Radiol 1988;29:457–460.
8. Cooperberg PL, Tsang I, Truelove L et al. Gray scale ultrasound in the evaluation of rheumatoid
arthritis of the knee. Radiology 1978;126:759–763.
9. Jacobson JA. Fundamentals of musculoskeletal ultrasound. Philadelphia: Saunders Elsevier; 2007.
p. 1–38.
10. Smith J, Finnoff JT. Diagnostic and interventional musculoskeletal ultrasound: Part 1.
Fundamentals. PM R 2009;1(1):64–75.
11. Rizzatto G. Evolution of US transducers: 1.5 and 2D arrays. Eur Radiol1999;9:304–306
12. Claudon M, Tranquart F, Evans DH et al. Advances in ultrasound. Eur Radiol 2002;12:7–18
13. Kremkau F. Diagnostic ultrasound. Principles and instruments. 6th edition. Philadelphia: WB
Saunders; 2002. p. 428.
14. Backhaus M, Burmester GR, Gerber T, et al. Guidelines for musculoskeletal ultrasound in
rheumatology. Annals of the Rheumatic Diseases 2001; 60: 641–649.
15. O’Neill J. Introduction to musculoskeletal ultrasound. In: O’Neill J, editor. Musculoskeletal
ultrasound. New York: Springer; 2008. p. 3–17.
16. Grassi W, Cervini C. Ultrasonography in rheumatology: an evolving technique. Ann Rheum Dis
17. Wakefield RJ, Brown AK, O´ Connor PJ, et al. Musculoskeletal ultrasonography: what is it and
should training be compulsory for rheumatologists? Rheumatology 2004;43:821–2.
18. Kane D, Grassi W, Sturrock R, Balint PV. Musculoskeletal ultrasoundda state of the art review in
rheumatology. Part 2:
19. Clinical indications for musculoskeletal ultrasound in rheumatology. Rheumatology 2004;43:829–
20. Schmidt WA, Seifert A, Gromnica-Ihle E, et al. Ultrasound of proximal upper extremity arteries to
increase the diagnostic yield in large-vessel giant cell arteritis. Rheumatology 2008;47:96–101.
21. Backhaus M, Kamradt T, Sandrock D, et al. Arthritis of the finger joints: a comprehensive
approach comparing conventional radiography, scintigraphy, ultrasound, and contrast-enhanced
magnetic resonance imaging. Arthritis Rheum 1999;42:1232–45.
22. Kane D, Balint PV, Sturrock RD. Ultrasonography is superior to clinical examination in the
detection and localization of knee joint effusion in rheumatoid arthritis. J Rheumatol
23. Wakefield RJ, Green MJ, Marzo-Ortega H, et al. Should oligoarthritis be reclassified? Ultrasound
reveals a high prevalence of subclinical disease. Ann Rheum Dis 2004;63:382–5.
24. Karim Z, Wakefield RJ, Quinn M, et al. Validation and reproducibility of ultrasonography in the
detection of synovitis in the knee: a comparison with arthroscopy and clinical examination.
Arthritis Rheum 2004;50:387–94.
25. Szkudlarek M, Narvestad E, Klarlund M, et al. Ultrasonography of the metatarsophalangeal joints
in rheumatoid arthritis: comparison with magnetic resonance imaging, conventional radiography,
and clinical examination. Arthritis Rheum 2004;50:2103–12.
Chapter One Principles of ultrasound
26. Naredo E, Bonilla G, Gamero F, et al. Assessment of inflammatory activity in rheumatoid
arthritis: a comparative study of clinical evaluation with grey scale and power Doppler
ultrasonography. Ann Rheum Dis 2005;64:375–81.
27. Koski JM. Ultrasound-guided injections in rheumatology. J Rheumatol 2000;27:2131–8.
28. Nofsinger C, Konin JD. Diagnostic ultrasound in sports medicine: current concepts and advances.
Sports Med Arthrosc 2009;17(1):25–30.
29. Smith J, Finnoff JT. Diagnostic and interventional musculoskeletal ultrasound: Part 2. Clinical
applications. PM R 2009;1(2):162–77.
30. Lew HL, Chen CP, Wang TG, and Chew KT. Introduction to musculoskeletal diagnostic
ultrasound: Part 1: examination of the upper limb. Am J Phys Med Rehabil. Apr 2007. 86(4):310-
31. Chew KT, Stevens KJ, Wang TG, Fredericson M, and Lew HL. Introduction to musculoskeletal
diagnostic ultrasound: Part 2: examination of the lower limb. Am J Phys Med Rehab. Mar 2008.






Tendons are characterized by their parallel course with respect to the skin surface and by a typical fibrillar echotexture that is clearly detectable in longitudinal scans.

The fibrillar echotexture is generated by parallel running fascicles of collagen fibres, which appear as closely positioned, fine hyperechoic lines with even finer anechoic thin lines in between, corresponding to inter-fascicular ground substance. Fig.6

On tendons with a synovial sheath, a subtle anechoic rim interposed between the sheath and the tendon margin can be detected.1

Fig.6: Tendon longitudinal:
A: sonographic picture,T= tendon, F= fat pad, C= cartilage, I.P=Proximal phalanx, I.MC=
metacarpal head, JS= joint space.
B: Tissue specimen of the same picture, T= tendon, S= subcutaneous fat, B= bone.

Fig.7: Tendon transverse:
A: sonographic picture,T= tendon, B= bone.
B: Tissue specimen of the same picture, T= tendon,B= bone.

In transverse scans, tendons appear as round or oval structures, characterized by numerous closely joined dots that are homogeneously distributed and correspond to the intra-tendinous connective fibers.

The tendon’s sonographic characteristics in healthy subjects are fairly homogeneous and have limited intra- and inter-individual variability.1 Fig.7


They are made up of two components: the muscle fibers, which are long and cylindrical in structure, representing the cellular unit of muscle, and stromal connective tissue.

Individual muscle fibers are grouped together in bundles, which are commonly known as fascicles, and several fascicles join together to form an individual muscle (Fig. 8).

Thin connective tissue strands – the endomysium – separate the individual muscle fibers; a more substantial connective sheath with small vessels and nerve endings, the perimysium (also referred to as fibroadipose septa), envelops individual fascicles; a thick fibrous layer, the epimysium, surrounds the entire muscle. 2,3 , Fig.8.

Fig.8: Muscle fiber: cross-section (coated from van Holsbeeck and Introcaso, 2001).3

The fasciculi can be identified as separate structures on ultrasound.2, 3 They are best identified in the longitudinal plane as hypoechoic cylindrical structures, separated by the hyperechoic intervening connective tissue, the perimysium (fig 9,10).

Individual fibers and the endomysium are not individually discernible. The epimysium, fascia, and intermuscular fat are all thin, linear hyperechoic structures on ultrasound.

During contraction of a muscle, the fibers shorten, causing an apparent increase in muscle bulk. When the muscle is contracted, the fascicles have a thicker and more hypoechoic appearance.3

Fig.9: Muscle longitudinal: A: sonographic picture F = fascia, M = muscle. B: Tissue specimen of the same picture, F = fascia, M = muscle. (coated from van Holsbeeck and Introcaso, 2001).3

Fig.10: Muscle Transverse: A: sonographic picture F = fascia, M = muscle. B: Tissue specimen of the same picture, F = fascia, M = muscle. (coated from van Holsbeeck and Introcaso, 2001).3


Ligaments are fibrous structures appearing similar to tendons. However, they are less compact and are composed of a more diverse pattern of collagen bundles.4

Ligaments are usually well defined and easily visible on ultrasound examination. However, when they occur as a focal thickening of a joint capsule, they may not be distinguishable as distinct structures.

Ligaments display a hyperechoic, linear appearance on ultrasound and are optimally evaluated when they are stretched.5, Fig.11

Similar to tendons, ligaments appear fibrillar during longitudinal scanning and have a broom-end appearance on transverse scans.

However, ligaments can be distinguished from tendons by tracing them back to the bony structures to which they attach.4

Fig.11: Ultrasound image of medial collateral ligament reveals the superficial ligament (arrows) and meniscofemoral ligament (mf) and meniscotibial ligament (mt) attached to the meniscus (asterisk).


A peripheral nerve is a cordlike structure containing a large number of individual nerve fibers.

The nerve fibers are grouped together into bundles known as fascicles Fig.12. The fascicles are enclosed in a connective tissue sheath or membrane known as the epineurium.

Each fascicle is in turn covered by a sheath of connective tissue, the perineurium. The individual nerve fibers within the fascicle are also enclosed by a sheath of connective tissue, the endoneurium.

Extending inward from the epineurium is the interfascicular epineurium, which is thin septae adding further support to the nerve bundles and their vascular supply. 6, 7.

Fig.12: Peripheral nerve: cross section (coated from van Holsbeeck and Introcaso, 2001).3 

Ultrasound, in the longitudinal axis of the nerve, demonstrates a fascicular pattern of uninterrupted hypoechoic bands with intervening linear interrupted hyperechoic bands Fig.13.

The hypoechoic bands represent the fasciculi and the hyperechoic bands the supporting interfascicular epineurium.

The epineurium is hyperechoic and of similar appearance to perineural fat and may not be separable on ultrasound.

In the axial study, the nerve is composed of fasciculi seen as multiple hypoechoic dots, which may be of varying size, intermingled in a hyperechoic background of the supporting connective tissue.2, 8–10

Fig.13: Ultrasound image of median nerve (A= long axis, B= short axis) shows hypoechoic nerve
 fascicles (arrowheads). t = flexor digitorum tendon, p = palmaris longus tendon, R = radius, L = lunate.


Ultrasound provides limited views of bones. It can display vivid anatomic details of the cortical surfaces of the superficial bone.5

Bones appear with well-defined, linear, and smooth hyperechoic borders. This hyperechoic appearance is caused by the high reflectivity of the acoustic interface.

Because nearly the entire sound beam is reflected, ultrasound is unable to image beyond the bone surface or that of other calcified structures, so the image beyond the interface appears black; this is referred to as posterior acoustic shadowing.4

Because of this phenomenon, Ultrasound can provide information only about the superficial portion of bones Fig.14.

Fig.14: US appearance of normal bone: surface echotexture. a Longitudinal 12–5 MHz US image obtained over the diaphysis of the radius demonstrates the bone surface as a continuous straight hyperechoic line (arrows) produced by a strong reflection of sound due to the marked difference in acoustic impedance of the soft tissues and bone. Reverberation artifact (arrowheads) projecting in the shadow beyond the bone can be seen.


Synovial joints are the most common joints examined with ultrasound. They are formed by articulating bone surfaces, fibrous capsules, and ligaments, and other intraarticular structures (ligaments, menisci, labra, and fat pads) 2, Fig.15.

Ultrasound examination of joint surfaces reveals a homogeneously smooth hypoechoic smooth linear band (the hyaline cartilage).11,12

The joint capsule appears as a hyperechoic line merging with the para-articular tissues.2 The deeper subchondral bone is a regular, continuous, bright, hyperechoic line.

Fig (15): Elbow joint anterior longitudinal veiw:
 A: sonographic picture, M= muscle, F= fat pad, CA= cartilage, R=Radius phalanx, H= humerus,
 JS= joint space. B: Tissue specimen of the same picture. (coated from van Holsbeeck and Introcaso, 2001).3


Cartilage can be divided into hyaline cartilage, white fibrocartilage, and elastic or yellow fibrocartilage.

The latter is present in only select regions, e.g., the auricle of the external ear.

Articular hyaline cartilage is of varying thickness, being thicker in points of greater stress and on convex rather than concave surfaces.

It provides a degree of elasticity and shock absorption, as well as helping to dissipate stress across a joint.6,7 On ultrasound, it has a smooth, well-defined surface and border and is uniformly hypoechoic. 3, Fig.17.

Fig.17: Articular hyaline cartilage:
 A: sonographic picture, S= Skin, C= cartilage, B=bone. B: Tissue specimen of the same picture
 (coated from van Holsbeeck and Introcaso, 2001).3


It’s a variable mixture of white fibrous tissue and cartilaginous tissue with a large component of collagen fibrils.

It provides elasticity and flexibility. The menisci of the knee, temporomandibular and sternoclavicular joints, the glenoid and hip labra, and the triangular fibrocartilage of the wrist are composed of fibrocartilage.

On ultrasound, fibrocartilage is hyperechoic with well-delineated borders. Because of its position within joints, it is not always fully accessible to a full ultrasound examination.3, Fig.18

Fig.18: Fibrocartilage. The posterior glenoid labrum (arrow) is demonstrated here as a well-defined, hyperechoic triangular structure between the articulating surfaces of the glenoid (G) and humerus (H).


Normal bursae in healthy subjects are not always easily visualized. They appear as a thin hypoechoic space delimited by echoic borders corresponding to the tissue–fluid interface.

Bursitis is characterized by an increase in the synovial fluid that usually appears as a sharply defined anechoic area.13, Fig.16.

Fig.16: Retrocalcaneal bursa: + bursa , t, Achilles tendon; c, calcaneal bone.



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