Chapter 4
Sonographic and power
Doppler semeiotics
in musculoskeletal disorders
111
4.1 Cartilage
Sonography has great potential for the non-invasive
study of hyaline cartilage, as it can depict micro-
scopic lesions to be demonstrated with a high spa-
tial resolution. The main limit to the sonographic
study of articular cartilage is the relatively limited
dimensions of acoustic windows available for the
visualization of the cartilage surfaces. The most
frequent errors in the study of cartilage, especial-
ly at knee level, are linked to incorrect examina-
tion. The most frequent artifacts come out in supra-
patellar panoramic views, as the cartilage profile
of the femoral trochlea is not perpendicular to the
direction of the US beam. An apparent loss in
sharpness of the chondro-synovial margin of the
cartilage and an apparent reduction or increase of
the cartilage thickness are the main artifacts caused
by incorrect technique [2].
Ultrasonography provides rapid and reliable,
albeit incomplete, information about the charac-
teristics of articular cartilage, without radiation
risk or patient discomfort [3-5].
A wide range of cartilaginous changes can be
detected in patients with osteoarthritis and chron-
ic arthritis. These include: loss of sharpness of the
superficial margin, loss of transparency of the car-
tilaginous layer, cartilage thinning and subchon-
dral bone profile irregularities.
Osteoarthritis
Cartilage involvement in osteoarthritis ranges from
subtle findings to extensive, easily detectable
abnormalities [6-8]. Loss of clarity of the cartilage
and loss of sharpness of the synovial space-carti-
lage interface are clearly evident features even in
the absence of other US signs of cartilage damage.
The integrity of the synovial space-cartilage inter-
face is the main distinguishing feature of healthy
subjects, when compared to patients with
osteoarthritis (Fig. 4.1). Loss of cartilage trans-
parency could reflect pathological changes such as
fibrillation of cartilage and cleft formation.
Blurred and/or irregular margins together with
marked cartilage thinning are the most common
US findings in advanced osteoarthritis (Fig. 4.2 a, b).
Although standard criteria for assessing US
changes in osteoarthritic condylar cartilage are
not yet widely accepted, McCune et al. [7] have
reported four main abnormalities in patients with
knee osteoarthritis that can be regarded as US hall-
marks of the disease at different stages. These
include loss of cartilage transparency, reduced
sharpness of the superficial cartilage margin,
increased intensity of the deep cartilage margin
and cartilage thinning [8-12].
112 Musculoskeletal Sonography
Osteoarthritis.Transverse (a) and longitudinal (b) supra-patellar US scans of the knee.Marked diffuse thinning (arrowheads) of the
cartilage layer of the lateral femoral condyle (f). p = upper pole of the patella
Fig. 4.2 a, b
a b
Osteoarthritis.Transverse (a,b) and longitudinal (c,d) supra-patellar US scans of the knee.a,c Normal cartilage features.b,d Loss of sharp-
ness of the superficial margin and circumscribed thinning (arrows) of the cartilage layer of the medial femoral condyle (f)
Fig. 4.1 a-d
c d
a b
Sonographic and power Doppler semeiotics in MSKD 113Chapter 4
Rheumatoid arthritis
US has much to offer in the study of rheumatoid
arthritis in spite of the relative lack of scientific
reports on the subject. The main drawbacks to
research in this field include the current limited
availability of very high resolution probes togeth-
er with the lack of standardized US criteria for car-
tilage involvement.
In rheumatoid patients, US can visualize pre-
erosive changes, particularly at the level of the
metacarpophalangeal joint, together with loss of
the cartilage layer and irregularities of the sub-
chondral bone (Figs. 4.4, 4.5) [3, 12].
Osteoarthritis.Transverse view of
the femoral trochlea in a patient
with patello-femoral involvement
shows inhomogeneous echo-
genicity and non-uniform thin-
ning of the articular cartilage,with
conspicuously uneven profile of
the osteo-chondral interface
Fig. 4.3
Rheumatoid arthritis. Longitudi-
nal dorsal scan of a metacar-
pophalangeal joint shows prolif-
erative synovitis with early erosive
changes.Complete loss of the car-
tilage layer of the metacarpal head
with initial subchondral involve-
ment (arrowhead).m = metacarpal
head; p = proximal phalanx;
t = extensor tendon
Fig. 4.5
Rheumatoid arthritis. Longitudinal dorsal scan of a metacar-
pophalangeal joint.Severe cartilage damage involving all the
cartilage layer of the metacarpal head. Power Doppler tech-
nique shows active pannus invading the subchondral bone.
m = metacarpal head; p = proximal phalanx
Fig. 4.4
114 Musculoskeletal Sonography
Gout
In patients with long-standing untreated gout,
monosodium urate crystal deposition on the sur-
face of the articular cartilage results in hypere-
choic enhancement of the superficial margin,
which can range from the homogeneous thicken-
ing of the synovial space-cartilage interface, to
areas of focal deposition (Fig. 4.6 a, b).
Due to the deposition of monosodium urate
crystals, reflectivity of the superficial margin is
no longer dependant upon the angle of
insonation, and a panoramic visualization of the
full synovial space-cartilage interface can be eas-
ily ascertained, and the amount of crystal depo-
sition estimated. The adherence of monosodium
urate crystals to the superficial margin of the
articular cartilage can be confirmed by dynamic
assessment using active and passive movement
of the joint.
Chronic gout.Transverse (a) and longitudinal (b) supra-patellar views of the knee demonstrate diffuse urate crystal deposition
(arrowheads) on the cartilage surface of the lateral femoral condyle (f). p = upper pole of the patella
Fig. 4.6 a, b
a b
Pyrophosphate arthropathy.Transverse para-patellar view of
the knee depicts minimal aggregates of pyrophosphate crys-
tals within the femoral cartilage. f = medial femoral condyle;
p = patella
Fig. 4.7
Pyrophosphate arthropathy
In patients with pyrophosphate arthropathy, crys-
tals are detectable within the substance of the hya-
line cartilage (Fig. 4.7) [11-13]. The sparkling reflec-
tivity of pyrophosphate crystals allows for clear
depiction of even minimal aggregates within car-
tilage. Crystal deposition can be focal or diffuse –
leading to the development of a ‘double contour’,
which is created by the permeability of the crystal
layer, allowing US to penetrate and depict the bone
profile beneath.
This is typically seen in the articular cartilage of
the femoral condyles and should not be confused with
meniscal calcification [9].One striking feature of this
deposition pattern is the apparent geometric loca-
tion of the crystal layer within the middle portion of
Sonographic and power Doppler semeiotics in MSKD 115Chapter 4
the articular cartilage,which may help to understand
why cartilage is damaged in pyrophosphate arthropa-
thy, leading to secondary degenerative changes.
Calcific deposits in pyrophosphate arthropathy
appear as hyperechoic rounded or amorphous
shaped areas and their location within the fibrocar-
tilage can be confirmed by dynamic assessment of
the joint during real-time scanning.These aggregates
can be identified in the menisci of the knee and in
the triangular ligament of the wrist. There is close
correlation between the appearance of these crystal
deposits on X-ray and US (Figs. 4.8 a, b, 4.9 a, b).
Pyrophosphate arthropathy. a Longitudinal US scan of the ulnar aspect of the wrist. b X-ray. Calcification of the triangular liga-
ment of the carpus (arrowheads) is evident. t = extensor carpi ulnaris tendon; u = ulna; tr = triquetrum
Fig. 4.8 a, b
a
b
116 Musculoskeletal Sonography
4.2 Synovial cavity
Ultrasound is a highly sensitive technique for the
detection of even minimal fluid collections and it
still represents a particularly useful diagnostic
tool to quantify fluid and to monitor its evolution.
This latest application is considerably helpful in
rheumatological therapy because it constitutes a
valid method of evaluation of efficacy. The con-
siderable sensitivity of the identification of syn-
ovial fluid collection, the highly detailed anatom-
ical depiction and the real time visualization of
tissues make US the ideal imaging technique for
interventional guided procedures, such as arthro-
centesis. Thanks to US, the aspiration of synovial
fluid is even possible even when the joint collec-
tion is minimal.
Pathologic conditions that can be assessed with-
in the synovial cavity with US include hydrarthro-
sis, pneumohydrarthrosis, pyarthrosis, hemarthro-
sis, lipohemarthrosis, bursitis, tenosynovitis and
synovial thickening.
US may occasionally detect the presence of syn-
ovial ganglia, joint mice and synovial calcification.
Intracavitary synovial fluid collection
A collection of fluid within the synovial cavity caus-
es the swelling of the involved joint.
In hydrarthrosis, US shows fluid collection with-
in the cavity, which has an anechoic appearance
with dorsal acoustic enhancement (Fig. 4.10 a, b).
The amount of fluid within the joint is directly
proportional to the severity of the synovial inflam-
mation and to the capability of the capsular wall
to expand. In some cases the anechoic appearance
of the fluid collection can be inhomogeneous
because of the presence of dot-like echoes scattered
within the collection itself [14-16]. This more com-
plicated appearance of the collection may depend
on the presence of a fibrinous component within
the inflammatory exudate, which can be particu-
larly abundant in relapsing collections and can be
Pyrophosphate arthropathy of the
knee joint.a,b US images.c X-ray.
Lateral (a) and medial (b) longi-
tudinal US scans demonstrate the
presence of calcification of both
the menisci (arrowheads).f = femur;
t = tibia
Fig. 4.9 a-c
a b
c
Sonographic and power Doppler semeiotics in MSKD 117Chapter 4
visualized as arranged echogenic and inhomoge-
neous clusters, with a scirrhous conformation.
Pyarthrosis occurs in bacterial arthritis, which
is usually rare in patients with normal immune sys-
tems, while it is common in children, in immuno-
suppressed patients, in diabetics and in patients
on dialysis. In acute infections with joint fluid col-
lection, it is necessary to sample the fluid in order
to prescribe the most appropriate antibiotic ther-
apy. In chronic infections the fluid collection is usu-
ally poor and it is often associated with consider-
able synovial thickening. In infections the fluid is
usually hypoechoic, but it may appear hyperechoic
in more superficial joints. In such cases, the syn-
ovial hyperemia can be well-depicted with the use
of Doppler techniques as a complement to gray
scale US [17, 18]. However, it should be kept in mind
that synovial hyperemia in bacterial arthritis is not
a mandatory finding, because it depends on the
patient’s age, on the duration of the infection and
on the immune status. Therefore, since there is no
certainty in differentiating septic from aseptic
inflammation and it is more suitable to perform a
biopsy when clinical suspicion is high.
Hemarthrosis exhibit a peculiar US pattern that
changes with time similar to hematoma. Hemor-
rhagic fluid collections are in fact homogeneously
echogenic within the first two to three days from
onset, due to the presence of a corpuscular con-
tent. After the third day, the hemarthrosis shows a
progressive reduction in echogenicity due to lytic
enzyme release. Eventually, US shows echogenic
branches, corresponding to fibrinous clots, cross-
ing the anechoic-appearing zone [14, 15].
Occasionally, the post-arthrocentesis follow-up
examination demonstrates the presence of pneu-
mohydrarthrosis. The presence of gas in the joint
cavity produces a highly reflective mist within the
anechoic fluid collection, forming an air-fluid level
that changes together with the patient’s position.
When assessing hydrarthrosis and pneumohy-
drarthrosis, color and power Doppler techniques
do not demonstrate significant vascular changes
[3, 17, 18].
Lipohemarthrosis is easily identified by means
of US and it appears as a dual-phase collection,
showing a fluid-fluid level. The overlying echogenic
fraction corresponds to the lipid content, while the
underlying fraction is hemorrhagic.When lipohe-
marthrosis is found in a post-traumatic limb, the
presence of a joint fracture can be suspected.
Synovial thickening
Hypertrophic or hyperplasic synovial thickening
is a condition found in several long-standing
inflammatory arthropathies and it can be the cause
of bone and cartilage erosion in the joint.
US nowadays can identify inflammatory syn-
ovial thickening more accurately than clinical exam-
ination, especially when small joints such as the
metacarpophalangeal and interphalangeal joints
are affected, commonly observed in chronic pol-
yarthropathies. Synovial thickening is character-
ized by heterogeneous echotexture varying from
hypoechoic to hyperechoic, depending on the
amount of water contained in the synovial tissue
a US scan of medial paracondylar recess.Anechoic reactive fluid collection containing a thin septum (physiological medio-patel-
lar plica, arrowheads). b Axial fat suppression sequence magnetic resonance (MR) scan confirms the presence of mediopatellar
plica (arrowheads), which appear as low signal bundle within the hyperintense articular fluid collection
Fig. 4.10 a, b
a b
118 Musculoskeletal Sonography
(Figs. 4.11, 4.12). In larger joints, such as the knee,
the synovial thickening appears as a succession of
irregularly proliferating branches, mildly echoic,
jutting out from the synovia into the articular cav-
ity; the assessment of synovial pannus is consid-
erably easier when associated with a fluid collec-
tion because it works as a contrast agent [1, 14-16]
(Fig. 4.13).
In pigmented villonodular synovitis, the syn-
ovial hypertrophy is usually overabundant, made
of thick fusiform villi and gross nodules, with a
winding outline surrounded by abundant fluid col-
lection. A similar appearance can be observed in
joints affected by relapsing hemarthrosis in hemo-
philic arthropathies. The continual presence of
hemorragic effusion irritates the synovial mem-
brane and determines the formation of pannus that
starts as a simple thickening and then turns into
villous hypertrophy. The sonographer should always
Longitudinal sonogram of wrist,
dorsal side. Patient affected by
rheumatoid arthritis. In this case,
synovial proliferation (arrowheads)
has a hyperechoic appearance
Fig. 4.12
Longitudinal US scan of supra-patellar recess showing large
amount of anechoic fluid collection with hyperechoic syn-
ovial proliferation (*). TQ = quadricipital tendon; F = femur
Fig. 4.13
Longitudinal sonogram of wrist,
dorsal side in a patient affected
by rheumatoid arthritis. Synovial
proliferation appears hypoechoic
(*). T = extensor tendons
Fig. 4.11
Sonographic and power Doppler semeiotics in MSKD 119Chapter 4
Longitudinal US scan of wrist, dorsal side. Patient affected by
rheumatoid arthritis.a Gray-scale scan and (b) power Doppler
scan.The use of power Doppler allows the amount of synovial
proliferation to be assessed more than MR without contrast
(spin echo T1 (SET1), short T1 inversion recovery (STIR)) (c, d)
or a plain film (e)
Fig. 4.14 a-e
a b
c
e
d
120 Musculoskeletal Sonography
keep in mind that synovial hypertrophy is a non-
specific finding and that the differentiation between
a non-specific synovitis and a synovial tumor can
be very tricky (hemangioma, synovial sarcoma)
[14-16]. A fibrinous exudate can make it difficult
to detect the thickened synovial membrane con-
tour, especially when it is abundant, because it may
simulate the US pattern of synovial hyperplasia. In
these cases, when fluid and hypertrophic synovia
cannot be differentiated it is possible to use dynam-
ic and compressive maneuvers. Such a technique
allows the fluid to be “squeezed out” from the
hypertrophic synovial wall and the differentiation
of the two articular contents [1, 14, 16].
When doubt persists with gray-scale US, power
and color Doppler techniques can be applied to dif-
ferentiate the fluid from the proliferating tissue,
with the presence or absence of vascular signals
[17-20] (Fig. 4.14 a-e).
The role of Doppler techniques for the assess-
ment of synovial vascularization in rheumatoid
arthritis is very important. In rheumatoid arthritis,
the formation of pannus is a crucial event in the
pathogenesis of articular degeneration. Neoangio-
genesis is an important pathological element in
rheumatoid synovitis [21, 22]. Since hypervascu-
larization is proportional to the degree of inflam-
mation of the synovial pannus, it is fundamental
to study and quantify the vascular signals in order
to evaluate the aggressiveness of the pannus itself.
Power Doppler is able to assess the increased vas-
cularization involving synovial hyperplasic tissue
and consequently to give information regarding
the activity of the synovial pannus [1, 18-20] (Fig.
4.15 a, b). Despite attempts at semiquantitative or
quantitative evaluation of the vascularization by
means of dedicated software, the technique is lim-
ited by the poor reproducibility.
Nevertheless, the recent availability of power
Doppler techniques in association with the use
of contrast agents (Contrast-enhanced Power
Doppler – CePD) has allowed a more detailed
analysis of the synovial vascularization. It should
be considered that the information derived from
power Doppler and CePD refer exclusively to the
macrovasculature of synovial pannus. Such lim-
its have now been overcome by the introduction
of new generation contrast agents (SonoVue) that
allow quantitative analysis of the synovial
microvascularization to be performed by means
of gray-scale US (Contrast-enhanced US – CeUS)
[23-25] (Fig. 4.16 a-c).
Patient with rheumatoid arthritis. a The power Doppler scan shows a high degree of hyperperfusion, an expression of hyperac-
tive pannus. b Follow-up during therapy. A significant reduction in flow signal is shown within the pannus (arrows)
Fig. 4.15 a, b
a b
Sonographic and power Doppler semeiotics in MSKD 121Chapter 4
Bursitis
Bursae are anatomical entities located near joints
(non-communicating bursae) or in direct commu-
nication with the joint cavity (communicating bur-
sae). The main function of non-communicating
bursae, located at the insertional areas of the anchor
tendons of several joints, is to reduce the friction
between tendon and bone. Communicating bursae,
on the other hand, when an abundant intra-articu-
lar fluid collection occurs, function by reducing the
joint cavity pressure, by expanding and being filled
with the fluid coming from the cavity.
Bursitis represents the most common bursal
pathology and US is the first choice diagnostic
technique.
Non-communicating bursitis
a. Acute traumatic bursitis: affecting several syn-
ovial bursae, the bursal expansion follows direct
impact or chronic frictional microtrauma. The
most commonly involved bursae are the sub-
acromial-deltoid bursa, the pre-patellar and
deep infra-patellar bursa, the retro-calcaneal
and superficialis bursa of the Achilles tendon
and the trochanteric bursa. In acute forms, an
increase in anechoic fluid within the bursa is
observed (a comparison with the controlateral
limb may be useful), while the synovial wall
keeps its original thickness (Fig. 4.17 a, b). In
chronic forms, the fluid often appears hypoe-
choic and contains hyperechoic spots consis-
tent with microcalcification, and the bursal walls
are thickened [26] (Fig. 4.18 a, b).
b. Hemorrhagic bursitis: usually following a vio-
lent sporting trauma on artificial surfaces and
mainly affect the hands and knees. The hem-
orrhagic effusion may organize and form adhe-
sions or calcifications. Clots and fibrin, appea