Chapter 5
Pathological findings
in rheumatic diseases
157
The ability of US to make an accurate evaluation
of soft tissue involvement in a wide range of dis-
eases of the locomotor system has led to its increas-
ing widespread use in the field of rheumatology
[1-10]. Significant technological progress has been
made over the last few years, generating ever more
sophisticated and reliable ultrasound machinery.
The high resolution is now such that real in vivo
histological examination is now possible. The main
reason for the relative lack of wide diffusion of its
use amongst rheumatologists is that a long training
period is necessary in order to acquire full opera-
tor independence.
Initially, the use of US in rheumatology was
limited to the identification of large collections
of synovial fluid (popliteal cysts, bursitis) [11].
These collections can be easily identified even
with ‘first generation’ US equipment that uses
probes with frequencies between 3.5 and 5 MHz.
These are, however, inappropriate for the study of
superficial soft tissues. With the advent of the ‘sec-
ond generation’ US machines, with 7.5 MHz linear
probes, US can now explore larger joints. Clinical
practice now includes the study of the shoulder,
hip and knee has proven useful in the examina-
tion of large tendons (Achilles, long head of biceps
and patellar tendon).
The potential applications of US in rheuma-
tology have been further increased with the dawn
of the ‘third generation’ US machines, equipped
with very high-frequency probes (> 10 MHz).
These can reach a spatial resolution of less than a
tenth of a millimeter and make it possible to study
the finest details of the smaller joints and hand
tendons which are involved early on in chronic
arthritis.
Osteoarthritis. Supra-patellar transverse scan with knee in
maximal flexion shows loss of the normal clarity of cartilage
layer together with blurring of the superficial margin of the
femoral condylar cartilage. f = femur
Fig. 5.1
5.1 Osteoarthritis
Several sonographic abnormalities may be observed
in patients with osteoarthritis. These include
changes within cartilage, joint cavity widening
resulting from fluid collection with or without syn-
ovial proliferation, and osteophytes [12-14].
Changes within cartilage
Loss of the thin, sharp contour of the superficial
margin of the cartilaginous layer is one of the early
features of osteoarthritis. US is exquisitely sensi-
tive in detecting structural changes within differ-
ent tissues and can reveal fibrillation and cleft for-
mation in osteoarthritis (Fig. 5.1) [15].
158 Musculoskeletal Sonography
Increased echogenicity with patchy or diffuse
loss of clarity may be seen even in patients with-
out any other findings to indicate damage to the
cartilage structure. These changes would seem to
reflect structural alterations such as fibrillation
of cartilage and cleft formation [13]. Particular
attention should be paid to distinguish these early
findings in osteoarthritis from artifacts caused
by inaccurate setting (gain level) or probe posi-
tion [16].
A slight increase in cartilage thickness caused by
inflammatory edema in the early phases of
osteoarthritis has been noted [13]. Variable nar-
rowing of the cartilaginous layer is detectable in
patients at a more advanced stage of the disease.
Cartilage thinning may be focal, or extend along
the entire cartilaginous layer (Fig. 5.2).
US measurement of femoral condyle articu-
lar cartilage thickness could be of practical ben-
efit for an early diagnosis of osteoarthritis. Accu-
rate quantification of cartilage thickness cannot
always be obtained in patients with advanced
osteoarthritis because of poor visualization of
the cartilage-synovial space interface. Complete
cartilage loss can be observed in advanced dis-
ease (Fig. 5.3) [12, 13, 17].
Supra-patellar scanning of weight-bearing areas
can be difficult in patients with advanced
osteoarthritis and/or painful knee, resulting in lim-
ited maximal active flexion [15-18]. Diagnostic
accuracy in the detection and grading of cartilage
abnormalities should be the subject of further
research. The knee and the metacarpophalangeal
joints are the locations in which US can best
demonstrate the various evolutionary phases of
cartilage involvement in osteoarthritis.
The articular cartilage of the metacarpal head
can be evaluated by longitudinal and transverse
dorsal scans, with the metacarpophalangeal joint
held in maximal active flexion. Standard longitu-
dinal dorsal and volar scans may also be useful.
Proximal and distal interphalangeal joints are
generally evaluated by means of longitudinal and
transverse dorsal scans with the finger in a neutral
position. US with high frequency probes allows for
an in-depth study of these joints, even if only a lim-
ited portion of the cartilage can be explored, due to
the acoustic barriers (Fig. 5.4 a, b, c)
Joint effusion
Small to moderate joint effusions are commonly
found in patients with osteoarthritis (Figs. 5.5,
5.6, 5.7). Minimal fluid collections that may be
missed on clinical examination are easily detect-
ed by US. Synovial fluid is usually anechoic. Non-
homogeneous echogenicity of synovial fluid
and/or echogenic spots with or without acoustic
shadowing can be generated by proteinaceous
material, cartilage fragments, crystal aggregates
and calcified loose bodies.
Osteoarthritis.Supra-patellar transverse scan with knee in max-
imal flexion demonstrates focal cartilage thinning (arrowhead)
and marked irregularity of the subchondral bone. f = femur
Fig. 5.2
Osteoarthritis. Supra-patellar transverse scan with knee in
maximal flexion shows complete loss of cartilage. f = femur
Fig. 5.3
Pathological findings in rheumatic diseases 159Chapter 5
Osteoarthritis. Supra-patellar longitudinal US scan showing
widening of the supra-patellar pouch due to synovial fluid (*)
and proliferation (+). f = femur; p = upper pole of the patella;
t = quadriceps tendon
Fig. 5.5
Osteoarthritis. Index finger of the dominant hand. Dorsal lon-
gitudinal views.a Distal interphalangeal joint.b Proximal inter-
phalangeal joint.c Metacarpophalangeal joint.dp = distal pha-
lanx; mp = middle phalanx; pp = proximal phalanx; m = meta-
carpal bone; t = extensor tendon; arrowhead = osteophyte
Fig. 5.4 a-c
a
b
c
Osteoarthritis of the knee. Differ-
ent US features of popliteal cysts.
a Anechoic with floating echogenic
spots. b Areas of synovial prolifer-
ation.c Septa and areas of synovial
proliferation. d Completely filled
by synovial proliferation
Fig. 5.6 a-d
c d
a b
160 Musculoskeletal Sonography
Fine particulate debris floating in the synovial
fluid is generally observed after long-standing or
repeated joint effusions or after intra-articular cor-
ticosteroid administration.
In patients with asymptomatic Heberden’s
nodes, there is usually no detectable joint space
widening. Conversely, symptomatic joint involve-
ment is frequently associated with variable capsu-
lar distension (Fig. 5.8 a, b).
Popliteal cysts are a frequent finding in patients
with knee osteoarthritis (Fig. 5.6 a-d). US pro-
vides structural details about the content of the
cyst, its communication with the joint space and
possible compression of adjacent vascular struc-
tures. Both the size and shape of cysts vary wide-
ly, ranging from small (<1 cm) to giant, multi-loc-
ulated entities.
Synovial proliferation
Synovial proliferation in osteoarthritis may display
US features similar to those observed in patients
with chronic inflammatory arthritis but without
the invasive properties of rheumatoid pannus (Fig.
5.7 a, b). Thickened, edematous synovium is fre-
quently observed in more severe disease and in
patients with recurrent effusions.
Osteophytes
Osteophytes are easily detected as irregularities of the
bone contour. The skyline view of an osteoarthritic
joint is characteristic and correlates with conven-
tional radiographic changes (Fig. 5.9 a, b).
Osteoarthritis of the knee. Later-
al longitudinal views of the supra-
patellar pouch showing different
aspects of synovial proliferation
(arrowheads). f = femur
Fig. 5.7 a, b
a b
Heberden’s nodes. Longitudinal dorsal US scan. a Sympto-
matic joint. Dorsal subluxation of the distal phalanx with
no evidence of joint inflammation. b Symptomatic joint.
Joint effusion (*) and osteophytes (arrowheads). dp = distal
phalanx; mp = middle phalanx; t = extensor tendon; arrow-
head = osteophyte
Fig. 5.8 a, b
a
b
Osteophytes in knee osteoarthritis.a Conventional radiogra-
phy.b Medial longitudinal US scan showing an osteophyte of
the femoral condyle (arrowhead). f = femur; t = tibia
Fig. 5.9 a, b
a b
Pathological findings in rheumatic diseases 161Chapter 5
Erosive osteoarthritis of the distal interphalangeal joint.The arrowhead indicates a bone erosion at the head of the middle pha-
lanx depicted both on longitudinal (a) and transverse (b) dorsal sonograms. dp = distal phalanx; mp = middle phalanx
Fig. 5.10 a, b
a b
Erosive osteoarthritis
Sonographic findings in patients with erosive
osteoarthritis usually combine the aspects of both
osteoarthritis (osteophytes and subluxation of the
articular surfaces) and inflammatory involvement
(joint space widening and intra-articular power
Doppler signal) (Fig. 5.10 a, b) [19, 20].
5.2 Rheumatoid arthritis
US in patients with rheumatoid arthritis demon-
strates a wide range of anomalies [21-31]. It pro-
vides detailed information on the quantity and
characteristics of the fluid collection, the presence
of synovial proliferation and the integrity of artic-
ular cartilage and subchondral bone.
Joint effusion
Distension of the joint capsule and the increase
in volume of synovial fluid are the most common
initial US findings. In these embryonic stages of
the disease the synovitis is prevalently exudative
and the content of the joint space is characterized
by its homogenous anechogenicity (Fig. 5.11).
Early rheumatoid arthritis. Exu-
dative synovitis of the proximal
interphalangeal joint of the dom-
inant hand. Longitudinal volar
scan depicting anechoic joint cav-
ity widening (*).mp = middle pha-
lanx; pp = proximal phalanx;
t = extensor tendon
Fig. 5.11
162 Musculoskeletal Sonography
US makes it possible to document the presence of
even minimal distension of the joint capsule and
of intra and peri-articular synovial fluid collec-
tion (synovial cysts, bursitis).
Synovial proliferation
Proliferation of the synovial membrane appears as
hypoechoic thickening of the ‘internal capsular
wall’ which can be either homogenous or adopt
various conformations (villous, polypoid, or bushy
appearance) (Fig. 5.12).
These appearances can be documented even in
early stages of the disease. Synovial hypertrophy
should be differentiated from the accumulation of
proteinaceous material or leukocytes that are mild-
ly echogenic or finely granular with a cloudy
appearance that changes upon palpation with the
probe over the skin surface. The identification of
synovial proliferation in finger joints together with
the evaluation of pannus perfusion using power
Doppler has heralded the search for pre-erosive
changes in rheumatoid arthritis (Fig. 5.13). High-
ly vascularized synovial pannus can predict radi-
olographic damage in rheumatoid arthritis and
therefore the presence of synovial proliferation rep-
resents an important element in the classification
of early arthritis.
Bone erosions
Over the last few years, several studies in rheuma-
toid arthritis have confirmed that ultrasonography
permits accurate and detailed analysis of the
anatomical changes induced by the inflammatory
process and is more sensitive than conventional X-
rays for the detection of bone erosions [24-26].
Rheumatoid arthritis. Proliferative synovitis of the second
metacarpophalangeal joint of the dominant hand. Longitu-
dinal dorsal scan depicting hyperperfused areas of synovial
hypertrophy invading the cartilage layer of the metacarpal
head (°). pp = proximal phalanx; m = metacarpal bone;
t = extensor tendon
Fig. 5.13
Rheumatoid arthritis.Proliferative
synovitis of the second metacar-
pophalangeal joint of the domi-
nant hand. Longitudinal dorsal
scan detecting very small areas
(less than 1 mm in size) of synovial
proliferation (+). pp = proximal
phalanx; m = metacarpal bone;
t = extensor tendon
Fig. 5.12
This higher sensitivity in the detection of ero-
sions depends both on the high spatial resolution
of the high-frequency transducers and on the pos-
sibility of carrying out multiplanar examination
(Fig. 5.14 a-d).
Bone erosions are viewed on US as an inter-
ruption of the sharp hyperechoic bone profile with
the wall and the floor, in most cases filled by hyper-
perfused synovial pannus.
At the level of the metacarpophalangeal joints,
US can identify a number of erosions much more
frequently than conventional X-ray in patients with
early rheumatoid arthritis [26]. The radial aspect of
the second metacarpal head and the lateral aspect
of the fifth metatarsal head are the anatomical loca-
tions where ‘micro-erosions’ in ‘early arthritis’ can
Pathological findings in rheumatic diseases 163Chapter 5
be recognized [25]. In both areas longitudinal scans
should be integrated with transverse scans both in
order to confirm the findings and to ensure explo-
ration of a greater surface area of the bone profiles
(Figs. 5.14, 5.15).
In patients with rheumatoid arthritis the fifth
metatarsophalangeal joint is an early target for
aggressive synovitis. At this level, US can detect
even minimal erosions which are often missed by
conventional X-ray.
Conventional morphological study should
always be integrated with power Doppler study,
when seeking to confirm synovitis in an active
phase (Fig. 5.16 a-d) [29, 31-35].
Rheumatoid arthritis.Proliferative synovitis of the second metacarpophalangeal
joint of the dominant hand. Dorsal longitudinal (a) and transverse (b) scans
showing clear signs of synovial proliferation and bone erosion of the metacarpal
head (arrowhead). c Intra-articular power Doppler signal. d Conventional radi-
ography. pp = proximal phalanx; m = metacarpal bone
Fig. 5.14 a-d
a b
c
d
164 Musculoskeletal Sonography
Tendon involvement
US is particularly useful in the study of tendon
involvement in early rheumatoid arthritis, which
often accompanies and in some cases precedes evi-
dence of the disease at joint level. The range of ten-
don change in rheumatoid arthritis is wide and
includes distension of the tendon sheath, loss of
‘fibrillar’ echotexture, loss of definition of tendon
margins and the partial or complete loss of tendon
continuity [36].
US is of very important practical value in the
evaluation of finger tendons. Tendon sheath widen-
ing is the hallmark of early tendon involvement in
rheumatoid arthritis and other conditions charac-
terized by synovial inflammation. Several US pat-
terns of tendon sheath widening can be character-
ized by the extent of the widening, amount of syn-
Rheumatoid arthritis.Semi-quan-
titative scoring system for intra-
articular power Doppler signal.
a Grade 0;no intra-articular signal.
b Grade 1;single intra-articular sig-
nal.c Grade 2;confluent intra-artic-
ular signals. d Grade 3; huge
amount of intra-articular signals
Fig. 5.16 a-d
a b
c d
Rheumatoid arthritis.Proliferative synovitis of the second metacarpophalangeal joint of the dominant hand.Lateral (on the radi-
al aspect of the joint) longitudinal (a) and transverse (b) scans showing a large erosion (arrowhead) (maximal distance between
the edges of the erosion:4 mm).c,d Using the same scanning planes,power Doppler revealed hyperperfused pannus within the
bone erosion. e Conventional radiography. pp = proximal phalanx; m = metacarpal bone
Fig. 5.15 a-e
a b
c d e
Pathological findings in rheumatic diseases 165Chapter 5
ovial fluid within the sheath, profile of the tendon
sheath, echogenicity of the sheath content and the
presence of synovial hypertrophy.
The amount of synovial fluid within a widened
tendon sheath may vary considerably, ranging from
minimal homogeneous widening (difficult to detect
if the pressure of the transducer is too high) to dra-
matic, balloon-like distension. There is no direct
relationship between the extent of tendon sheath
widening and clinical symptoms.
The profile of a widened tendon sheath can be
regular or extremely non-homogeneous with sac-
cular or aneurysmal appearance, especially in
chronic tenosynovitis. The appearance of sheath
content is characteristically anechoic in patients
with acute tenosynovitis. Conversely, if synovial
fluid is rich in proteinaceous material or has an
elevated cellular content, a variable degree of soft
echoes can be detected. The use of very high fre-
quency transducers allows for the detection of syn-
ovial hypertrophy which appears as an irregular
thickening of the synovial layer and/or bushy or
villous vegetations (Fig. 5.17 a, b) [22].
Analysis of tendon echotexture is one of the fun-
damental aims of US examination. Circumscribed
abnormalities of the homogenous distribution of
the intratendinous connective fibers are the
unequivocal expression of anatomical damage medi-
ated by the process of chronic inflammation. In the
early phases of inflammation the morphological
picture is that of ‘tendon erosion’ that can precede
a more extended ‘loss of substance’ and evolve into
a partial or complete tendon tear (Fig. 5.18 a-e).
Rheumatoid arthritis. Proliferative tenosynovitis of the tibialis posterior tendon (tp). Transverse (a) and longitudinal (b) scans
showing a tendon sheath filled with pannus (+). ti = tibia
Fig. 5.17 a, b
a b
Rheumatoid arthritis.Wrist pain. Lateral transverse (a, b) and
longitudinal (c,d) scans showing active proliferative tenosyn-
ovitis of the extensor carpi ulnaris tendon (t) with partial ten-
don rupture (arrowheads). e Conventional radiography
Fig. 5.18 a-e
a b
c d
e
166 Musculoskeletal Sonography
Rheumatoid arthritis.Wrist pain.Lateral transverse (a) and lon-
gitudinal (b) scans showing proliferative tenosynovitis of the
extensor carpi ulnaris tendon (t) with pannus (+) invading the
tendon texture (arrowheads). u = ulna; tr = triquetrum
Fig. 5.19 a, b
a
b
Rheumatoid arthritis.Finger flexor tendons.Tenosynovitis and tendon tears.Longitudinal (a) and cross-sectional (b-e) volar scan-
ning of the finger flexor tendons (t) at the level of the metacarpophalangeal joint.Tendon tears appear as small anechoic areas
(less than 1 millimeter) within tendon echotexture (arrowheads)
Fig. 5.20 a-e
b
a
c
d e
Where ‘tendon erosion’ is suspected, this diag-
nosis should always be confirmed by dynamic
investigation and comparison with images taken
on longitudinal and transverse scans. This is in
order to exclude the possibility of artifacts due to
altered inclination of the probe rather than a real
anatomical alteration. It may be difficult to dif-
ferentiate between partial tendon tear and tendon
degeneration. The term ‘intrasubstance abnor-
mality’ or ‘intrasubstance tear’ is often used to
describe irregular areas of very low echogenici-
ty within the tendon. More commonly, partial
tendon tears appear clearest on transverse views,
but the possibility of an artifact should always
be kept in mind and the suspicion of a tendon
tear on a single field of observation must be ver-
ified along contiguous slices with the US beam
held perfectly perpendicular to the tendon (Figs.
5.19, 5.20).
Inadequate transducer positioning is the most
frequent source of false diagnosis of tendon tear.
Complete tendon tear is easily detectable especial-
ly if tendons with synovial sheaths are involved
(empty sheath sign). The edges of the torn tendon
are frequently retracted and curled up.
Power Doppler studies make it possible to doc-
ument hyperemia associated with the phases of
active inflammation, also at the level of the tendon.
Pathological findings in rheumatic diseases