Health&Medicine

1. Artifacts and pitfalls of Knee, Hip and Ankle joints.
Dr/ ABD ALLAH NAZEER. MD.

2. Knee Joint:
Meniscofemoral ligaments extends from the posterior
horn of lateral meniscus to the lateral aspect of medial
femoral condyle. Consists of ligament of Humphrey,
anterior to the posterior cruciate ligament (PLC), and
ligament of Wrisberg, posterior to the PLC and larger
Vahey and colleagues identified meniscofemoral
ligaments in 50% of 109 MR scans. In 39% they causes
appearance of pseudotear in sagittal images. The
interposition of a thin layer of fat between the posterior
horn of the lateral meniscus and ligament
meniscofemoral simulates tear. It is necessary to follow
these normal structures on subsequent images to do not
interpret as meniscal injury

3. Coronal proton-density fast spin-echo (TR 3580 ms, TE 44 ms):
example of Wrisberg meniscofemoral ligament (black arrow heads).

4. b. Transverse ligament
The transverse ligament is identified on MR images of
the knee as a hypointense structure that connects the
anterior horn of the lateral and medial meniscus. It was
detected by Sintzoff and colleagues in 78% of cases.
The space filled by fat between the ligament and the
meniscus can simulate tear in the anterior horn of
lateral meniscus,but can also be seen in medial
meniscus. Following sequential images confirm it is not
a tear, but transverse ligament. Furthermore, isolated
lesions in the anterior horn of the lateral meniscus are
uncommon, detected in 6% of cases.

5. Proton-density fast spin-echo (TR 3580 ms, TE 44 ms)
sequential images confirm it is just the transverse ligament.

7. A and B proton-density fast spin-echo (TR 3580 ms, TE 44 ms). Transverse
ligament simulating tear in the anterior horn of lateral meniscus (white arrow
in A). Ligament transverse showed in axial images (black arrowhead in B).

8. MENISCAL PITFALLS:
-Speckled anterior horn of the lateral meniscus:
it may mimic a meniscal tear of the anterior horn
but it is a normal variant created by the insertion
of fibers of the ACL into the meniscus.
-Transverse intermeniscal ligament: it may mimic
a meniscal tear of the anterior horn of both
menisci.
-Menisco-meniscal and menisco-femoral
ligaments may also simulate a tear of the
posterior horn of the lateral meniscus, but the
continuity of these structures in consecutive
slices on MRI helps to make an accurate
diagnosis.

13. Popliteus tendon
The popliteus tendon and its sheath stands
between the articular capsule and lateral
meniscus to insert in the lateral femoral condyle.
The tendon sheath appears as a structure of high
signal and can be interpreted as a lesion in the
posterior horn of the lateral meniscus, especially
in the presence of joint fluid (Herman and Beltran
775-81;Muglia et al. 161-66).
Anatomical knowledge and following of images
are essential for correct diagnosis.

14. Proton-density fast spin-echo (TR 3180 ms, TE 50 ms) sagittal image shows the popliteus tendon
(short arrow). The direction of the pseudo tear (long arrow) is the same of the tendon.

16. Speckled anterior horn
Frequently is observed a speckled
appearance of the anterior horn of
lateral meniscus, possibly occurs by
the insertion of the anterior cruciate
ligament.
This aspect is found in approximately
56% of cases and should not be
confused with injury

17. Sagittal proton-density fast spin-echo (A) and T1 weight images
(B): speckled anterior horn of lateral meniscus (arrows).

19. Chondrocalcinosis
The presence of meniscal calcification is a form
manifestation of calcium pyrophosphate dihydrate of
the deposition disease.
This calcification may cause high signal in the meniscus
and mimic tear. On the other hand, may obscure a real
lesion. It is recommended radiography correlation.
Meniscal ossicles are uncommon, often incidental,
findings on radiography and cross-sectional imaging of
the knee.
The ossicle should follow bone marrow signal on all
sequences:
T1: hyperintense
T2FS/STIR: hypointense

20. a-d Lateral knee joint of a 44-year-old man with single focal hyaline cartilage
chondrocalcinosis at the medial tibia. (a) Coronal 3D T1-weighted gradient-echo sequence,
(b) coronal reformation of 3D DESS, and a (c) coronal proton density-weighted FSE image
showing a focal hypointensity in the hyaline cartilage (arrows). (d) PA radiograph showing a
corresponding hyperdense calcification in this area (arrow). Calcium-containing crystal can
clearly be depicted on gradient echo sequences (a, b) in comparison to FSE sequence (c)

23. Meniscal flounce
Meniscal flounce is a normal find present in 0.2%
of cases which is associated with ligamentous
laxity. The meniscus has a folded appearance and
it possibly has no clinical significance.
A ring meniscus is a very rare anatomical variant
of the lateral meniscus of the knee. The inner
margin of a ring meniscus on coronal images can
easily be mistaken for a bucket-handle meniscal
tear displaced into the intercondylar space, so it
is usually diagnosed during arthroscopy.

25. Meniscal flounce.

26. Ring meniscus. Coronal intermediate-weighted MR image (TR/TE, 3300/36) shows central triangular low-signal-
intensity structure mimicking bucket-handle tear (arrowhead). Structure has smooth triangular appearance and
remainder of lateral meniscus was normal without evidence of tear or loss of meniscal volume.

27. Oblique meniscomeniscal ligament. Midsagittal fat-suppressed T2-weighted MR image (A) (TR/TE,
3750/68) shows linear low-signal-intensity structure (arrowhead) within intercondylar notch
mimicking displaced meniscal fragment. Axial fat-suppressed T2-weighted MR image

28. Wrisberg rip” and pseudotear.

29. Meniscocapsular recess resembling tear.

30. Fluid-filled popliteus recess mimicking a tear of the posterolateral
meniscus. Coronal FS T2-WI (A) shows a fluid-filled popliteus recess
mimicking a peripheral tear of the posterolateral meniscus (white
arrow). Analysis of the axial (B) and sagittal images (C) as well as
the typical location allows correct diagnosis of a pseudotear.

31. Pseudo jumper knee:
The patellar tendinopathy is associated with sports
activities and is also known as jumper's knee. This
condition presents with pain, swelling and functional
limitation. In studies of MRI appears as striates thickening
and increased signal in the tendon.
However, often there is a high signal and slightly
increased thickness at eighter or both ends in
asymptomatic patients.
Schweitzer and colleagues found focal areas of signal in
74% and intratendon signal was also seen commonly in
the inferior aspect of the tendon (32%).
Therefore, it is important to always relate to clinical
information. Furthermore, increased thickness of tendon
tends to be higher in jumper's knee.

32. Sagittal proton-density fast spin-echo (A) and T1 weight images (B):
observe the small areas of increased signal in A and B (arrows).

33. Pseudo iliotibial band friction
The iliotibial band friction syndrome is a clinical
condition associated with intense physical activity
in which occurs friction of the iliotibial tract over
the lateral femoral condyle.
Joint fluid that accumulates in the lateral recess of
the knee can simulate the iliotibial tract syndrome.
However, in the syndrome fluid accumulates on
both sides of the tract and there are alterations in
the iliotibial tract, such as sign changes and
thickening. Liquid only on the medial side of the
iliotibial tract indicate joint fluid.

34. Coronal proton-density fast spin-echo (TR 2620 ms, TE 40 ms) shows a normal iliotibial tract (arrow) and
fluid in the lateral recess (arrowheads). It should not be mistaken to iliotibial band friction syndrome.

35. Anterior cruciate ligament cyst
Anterior cruciate ligament (ACL) is the most common
site of cystic lesion inside the knee joint The cysts are
most common in males and have an incidence up to
0.44% in MRI studies. Patients usually complain about
painless and restriction of movement. Is important to
mention that trauma may cause local changes that
lead to cyst formation.
These cysts eventually may simulate rupture of the
ACL. Meanwhile, the clinical lesion is different and it
presents with a drumstick appearance on sagittal
images and cystic on coronal or axial images.

36. Mucoid degeneration of the anterior cruciate ligament (ACL). On sagittal T1-WI (A), the
ACL is of intermediate signal intensity and the ligamentous structure has disappeared. On
sagittal FS T2-WI (B), the ACL has a striated pattern with interspersed intact ligamentous
fibers, resembling a celery stalk (white arrow). There is also an intraosseous ganglion cyst
at the tibial insertion of the ACL (black arrowhead). Axial FS T2-WI (C) demonstrates the
intermediate signal of the ACL with interspersed intact ligamentous fibers (black arrow).

37. A bipartite patella in which secondary or accessory ossification
centers of the patella fail to unite with the main osseous body of
the patella is a normal developmental variant seen in 2% of the
population. The most common type is a bipartite fragment
involving the superolateral pole of the patella (75%). A bipartite
patella can be distinguished on MRI from a fracture by the location
of the bipartite segment, presence of well-corticated margins to
the accessory segment, and typical integrity of underlying articular
cartilage of the patella overlying the incompletely united accessory
ossification center. Marrow edema at the interface of the bipartite
segment is suggestive of micromotion at the synchondrosis, and
defects in the normally intact articular cartilage may be features
associated with symptomatic anterior knee pain. The dorsal defect
of the patella is a further variant thought to be related to normal
enchondral ossification involving the superolateral patella, which
is seen in up to 1% of individuals

38. Bipartite patella. Axial fat-suppressed T2-
weighted MR image (TR/TE, 3500/70) shows
osseous fragment (arrowhead) involving
superolateral patella with low-signal-intensity
interface with patella. There is osseous edema
on both sides of interface. Overlying articular
cartilage is intact but shows focal signal change.
Dorsal defect of patella. Axial fat-
suppressed T2-weighted MR image
(TR/TE, 3350/60) shows focal
osseous defect (arrowhead)
involving lateral facet of patella.
Overlying cartilage is intact.

41. DISTAL FEMORAL GROOVES: They are normal notches in the trochlear surface and the medial
and lateral femoral condyles and they should not be mistaken from impaction fractures.

42. Prominent insertion of the medial gastrocnemius onto the posterior aspect of the distal femoral metaphysis:

43. We show an example of a normal cortical spur in the internal tibial metaphysis.

44. FEMORAL PSEUDO-OSTEOCHONDRITIS: It is seen in children and teenagers. It refers to the irregularity
of the ossification of the femoral condyles but, unlike the osteochondritis dissecans, these femoral
condylar irregularities will have intact overlying cartilage and marrow edema is usually absent.

45. BONE MARROW: Hematopoietic bone marrow hyperplasia: low signal on T1WI
and high signal on T2WI in the femoral metaphysis with epiphysis spared. Its
differential diagnosis includes pathological bone marrow infiltration.

47. 45-year-old woman with hematopoietic marrow
involvement of distal femur. A, Proton density
image (TR/TE, 2300/15) shows heterogeneous
marrow signal intensity changes involving distal
femoral diametaphysis (arrowheads). Signal
intensity changes do not cross physeal scar, and
there are areas of interspersed fat within involved
area. Axial fat-suppressed T2-weighted MR image
(TR/TE, 3550/70) shows mild patchy hyperintensity
of distal femoral marrow (arrowheads).

48. Bone marrow reconversion. Sagittal T1-WI (A) and FS T2-WI (B) shows bone
marrow of intermediate signal intensity in the distal femoral diaphysis and
proximal tibia in a middle-aged heavy smoking female patient.

49. Hip
Synovial herniation pits
Femoral fibrocystic changes may
occur anteriorly at the junction of the
head and neck . Recently, it has been
speculated that these fibrocystic
changes are related to repetitive
impingement of the femoral neck
and the anterosuperior acetabulum.

50. Herniation pit.

51. Radial PD WI of the right hip (arthro-MRI). Synovial herniation pit (red circle).

52. Os acetabuli
The origin of bone fragments along the acetabular
rim, called os acetabuli or os acetabulare . It has
been attributed that some acetabula may have
secondary ossification centers, and this should not
be confused to fractures or ossification of the
labrum and/or acetabulum, secondary to the cam
type femoroacetabular impingement syndrome.
Acetabular ossification may also appear after
trauma, rickets, osteomyelitis, and osteochondritis
dissecans .

53. Os acetabuli (arrows).

54. Transverse acetabular ligament
The acetabulum closely covers the femoral head,
with the exception of its anteroinferior aspect,
where there is an absence of bone and cartilage.
This anteroinferior aspect of the acetabulum is
crossed by the transverse acetabular ligament (TAL).
Also, the TAL forms a complete ring around the
acetabulum. The transverse ligament attaches to the
acetabular rim anteriorly and posteriorly and to the
ligamentum teres femoris. The junction between TAL
and the acetabular labrum occurs a normal cleft that
can be mistaken for an acetabular labral tear .

55. Transverse acetabular ligament.

56. Perilabral recess
Similar to the shoulder, the hip joint capsule
attaches to the osseous rim of the
acetabulum, sustained posteriorly by the
ischiofemoral ligament and anteriorly by the
iliofemoral and pubofemoral ligaments.
Between the medial joint capsule and the
acetabular labrum may exist a normal sulcus,
so called perilabral recess .

57. Joint recess.

58. Supra-acetabular fossa
The supra-acetabular fossa is small
cavity in the superior, weight-
bearing region of the acetabulum. It
is usually filled with fibrous tissue,
covered by cartilage and should be
easy distinguishable from an
osteochondral lesion.

59. Superior anterior labrum rupture.

60. Tubular acetabular intraosseous
contrast tracking:
Intraosseous track of contrast material in
MR arthrography may be found in hips at
approximately 15%. These tracks are
linear and blind-ending structures that
originate from the acetabular fossa at or
near its margin with the acetabular
cartilage . This finding is thought to be an
unlikely source of hip pain.

62. 52-yearold woman who underwent bilateral hip imaging for
suspected unilateral acetabular labral tears. Consecutive axial
fat-suppressed 3D fast low angle shot (TR/TE, 48/11; flip angle,
40°) MR arthrographic images in cranial–caudal sequence show
asymptomatic hip. A, Anterior tubular track (A) originates from
margin (arrow) of acetabular fossa close to articular cartilage
(arrowhead). B, Anterior tubular track (A) originates from
margin of acetabular fossa. Posterior tubular track (P) originates
from junction (arrow) of posterior margin of acetabular fossa
and articular cartilage. C, Posterior tubular track (P) originates
from junction of posterior margin of acetabular fossa and
articular cartilage. D, Dilatation of blind end of posterior tubular
track known as clubbing phenomenon (asterisk) is evident

63. Stellate crease
The stellate crease, also improperly called
stellate lesion, is another anatomic variant
and represents a uncovered area within the
acetabular articular surface above the
anterosuperior margin of the acetabulum .
On MR imaging, the stellate crease can
appear irregular and could be mistaken for
an osteochondral lesion.

64. Stellate "lesion".

65. Iliopsoas bursa
The iliopsoas bursa is located subjacent to
the iliopsoas myotendinous junction and a
communication either congenital or acquired
may occur (15% of people). Obviously, a
normal iliopsoas bursa is usually collapsed
and not visible on MR imaging, although
distention with a small amount of fluid may
also be observed in asymptomatic hips. In
MR arthrography, intra-articular contrast
material may be easy seen.

66. Iliopsoas bursa in a patient with synovitis.

67. Accessory iliacus tendon:
The accessory iliacus tendon is a common
anatomy variation, seen in 66% of MR
arthrograms, which may simulate iliopsoas
tendon abnormality. On MR transversal images,
accessory iliacus tendon is represented by a
small tendon paralleling the iliopsoas major
tendon, separated by a fat plane. Therefore,
visualization of liquid instead of fat is prone to
tendinopathy. Also, tendon pathology is
frequently associated with iliopsoas bursitis.

68. Accessory iliac tendon.

69. Ankle:
Pseudodefect of talar dome
Pseudodefect of talar dome is a normal groove in the
posterior aspect of the talus for the passage of the
posterior talofibular ligament and should not be confused
with osteochondral fracture.
This is a very common finding, observed in most MRI
studies. In a series involving 40 patients, the pseudodefect
was found in 96% of cases. In a few cases that had been
examined both ankles, the groove was present in 86%.
It is seen on MRI images as an irregular area of low signal
in the posterior aspect of the talus. This characteristic
location and the absence of other findings make easy to
recognize this pitfall and differentiates it from
osteochondral injury.

70. 7-year-old boy with history of nonspecific nontraumatic
foot and ankle pain. A, Coronal T1-weighted (A), coronal
intermediate-weighted fat-suppressed (B), sagittal STIR
(C), and sagittal T1-weighted (D) MR images show
relatively prominent notch (arrows). Notch is filled by
trace synovial fluid and partially contains articular
cartilage. No subjacent subcortical osteosclerosis, ankle
joint effusion, osteochondral lesions elsewhere in ankle,
or bone marrow edema were present. No loose
osteochondral body or other derangements were
present on radiographs (not shown).

71. 48-year-old woman with nontraumatic nonspecific ankle pain. D, Coronal
intermediate-weighted (A), coronal intermediate-weighted fat-suppressed
(B), sagittal STIR (C), and sagittal T1-weighted (D) MR images show relatively
prominent notch (arrows). Notch is filled by trace synovial fluid. No subjacent
subcortical osteosclerosis, ankle joint effusion, osteochondral lesions elsewhere
in ankle, or bone marrow edema were present. No loose osteochondral body
or other derangements were present on radiographs (not shown).

72. T1-weighted sagittal image: osteochondral fracture. There is a bone defect
of talar dome with low sign intensity (arrow).

73. Appearance variations in ligaments and tendons
Tendons and ligaments usually appear as homogeneous and
hypointense structures on MRI images. This appearance indicates
that there are no injuries and that these structures must be
intact. Nevertheless, they may have a different aspect in some
cases, usually because of fatty tissue between the ligament and
tendon fibers, which does not necessarily indicate injury.
The following ligaments are often seen as a striated structure,
with heterogeneous signal: posterior talofibular, posterior
tibiofibular, talocalcaneal and anterior tibiotalar (deep deltoid).
This appearance should not be confused with injury. Normal
posterior talofibular ligament with irregular and frayed superior
edge was found by Noto and colleagues in 13 of 30 cases.
Similarly, the posterior tibial tendon can easily simulate injury,
since it has multiple insertions, providing a complex image
appearance

74. Normal striated signal intensity pattern in deep deltoid ligament (arrow).

75. Coronal proton-density fast spin-echo (A) and T1 weight images (B)
shows inhomogeneity of posterior talofibular ligament (arrowheads).

76. Accessory bones and sesamoids
First of all is necessary to differentiate sesamoids from accessories
bones, which can be a source of confusion.
Sesamoids are located in the intimacy of the tendon, in places where
they change course and over bony prominences. There is a sesamoid
bone in the peroneus longus tendon proximal to its entrance into the
cuboid sulcus (os peroneum). Another one can be found in the posterior
tibial tendon proximal to its insertion into the navicular tuberosity.
Accessory bones are secondary ossification centers that can be found in
various locations of the foot and ankle. They rarely have clinical
significance. However, the navicular bone (especially type 2) may
eventually present with symptoms, for example. The os trigonum is
found in about 10% of population and also may present with pain (os
trigonum syndrome).
They are commonly found in imaging studies and should not be
confused with fracture. They have regular appearance, rounded shape
and typical location. There is no difficulty to make this differentiation.

77. T1-weighted sagittal image shows an os trigonum (arrow).

78. Axial T1-weighted MR images shows peroneus quartus muscle belly
(white arrow) and its tendon inserting in calcaneal bone (black arrow).

79. T1-weighted sagittal image shows focal low signal intensity irregularly
(arrow) and should not be confused with osteochondral fracture.

80. Accessory muscles
It is not uncommon to find accessory muscles in the ankle. In most cases they
do not have clinical significance and are often incidentally found. In a few
instances may present as a palpable mass, simulating a tumor, or may cause
compression of local structures(64, 68).
The peroneus quartus muscle is found in up to 17-22% of the population. It
originates in the lateral and distal aspect of the fibula, positioned
posteromedial to peroneal tendons, and attachment is variable, including the
calcaneus and cuboid bones and the peroneal tendons.
Be careful not to confuse the peroneus quartus muscle with low-lying
peroneus brevis muscle belly. The insertion site is different for each one.
The peroneus quartus muscle is generally asymptomatic. However,
eventually may associate with dislocation and injury in the peroneal tendons.
The accessory soleus muscle is rarely found and it is usually asymptomatic.
However, there are some cases in the literature that this anomalous muscle
presents as soft tissue mass or with local pain.
Another muscle described in the ankle is the flexor digitorum longus
accessories, encountered in 6% of asymptomatic individuals, but may be
associated with tarsal tunnel syndrome.

81. Axial T1-weighted MR image shows low position of the peroneus brevis muscle (arrow).

82. Accessory soleus with a fleshy insertion. Axial (9a) and sagittal (9b) T1-weighted
MR images of a 43 y/o female with ankle pain. An accessory soleus (arrows) with
a fleshy insertion on the medial calcaneus (red arrowhead) is apparent.

83. Peroneus quartus (peroneal calcaneal variant).
Axial (11a), and sagittal (11b) T1-weighted MR
images show a fleshy accessory peroneus
quartus muscle (arrows) coursing posterior the
peroneal longus (PL) and peroneus brevis (PB)
tendons and inserting onto the retrotrochlear
eminence of the calcaneus (asterisk).

84. Peroneocalcaneus internus (PCI). Sequential axial T2-weighted MR images in a 73 y/o female
patient with heel pain, numbness, and a clinical diagnosis of tarsal tunnel syndrome. At the
distal tibia, the PCI muscle (red) interdigitates with the flexor hallucis longus muscle (blue).
Distally, the PCI tendon (red arrow) is seen lateral to the flexor hallucis longus tendon (blue
arrow). Both tendons are highlighted by tenosynovial fluid (asterisk) posterior to the talus and
sustentaculum tali. The neurovascular bundle is seen medial to these tendons (yellow outline).
The PCI tendon inserts on the medial calcaneus below the sustentaculum tali (red arrowhead).

85. Thank You.