In this presentation we will discuss the role of medical imaging---plain Radiography, Ultrasound,Arthrography, CT and MRI in the evaluation of Developemental dysplasia of hip. Our main focuss will be on Sonographic evaluation.
3. DEVELOPMENTAL DYSPLASIA OF HIP (DDH)
• CONGENITAL DYSPLASIA OF HIP
• Deformity of acetabulum due to disrupted relationship between
femoral head and acetabulum
• DDH is composed of two elements:
• (1) instability and
• (2) abnormal morphology.
• M:F—1:4 - 1:8
4. DDH—Types
• Normal hip
• Lax = subluxable hip
• Concentric dislocatable unstable hip
• Decentered subluxed hip
• Eccentric dislocated hip
5. Ortolani’s sign
• Hold the knees and abduct the hip while
lifting up on the greater trochanter
• A positive test is feeling the dislocated hip
clunk into the acetabulum.
6. Barlow Provocative / dislocation test
• Adduct and push posteriorly on
the hip
• A positive test is feeling the hip
out of the acetabulum
7. Asymmetrical thigh folds
• Indicative of abnormal hips
• Also seen in infants with abnormal hips
• Widened perineum
• Prominent greater trochanter
8. Galleazzi’s / Allis sign
• Allis sign = Galeazzi sign = affected knee is
lower with knees bent in supine position
• In bilateral hip abnormality asymmetry is
not a feature.
13. Shenton's curved line
• Arc formed by inferior surface
of superior pubic ramus(= top
of obturator foramen)+ medial
surface of proximal femoral
metaphysis to level of lesser
trochanter
• Disruption of line (DDx: coxa
valga)
14. Acetabular angle I index
• Slope of acetabular roof=
angle that lies between
Hilgenreiner's line and a line
drawn from most
superolateral ossified edge of
acetabulum to superolateral
margin of triradiate cartilage
15. Center-edge angle of Wiberg
• Angle subtended by one line drawn from the acetabular edge to
center of femoral head+ second line perpendicular to line connecting
centers of femoral heads
• <25° suggests femoral head instability
16. • Fig. 2—Measurement of center-edge angle. A, Drawing shows center-edge
angle (CEA), which is measured by drawing line through center of both
femoral heads on well-centered anteroposterior pelvis radiograph
perpendicular line in femoral head of interest and line through lateral
margin of acetabulum and femoral head. Angle formed between
perpendicular and lateral margin of acetabulum is CEA. B, Anteroposterior
pelvis radiograph in 38-year-old woman shows dysplastic left hip (CEA <
20°).
17.
18.
19. Ultrasound
• Reference standard in an infant before 6 months
• It is a nonionizing, quick, and portable examination
• Both Dynamic and Standard static views.
• American College of Radiology recommends
• Coronal view in the standard planes at rest
• Transverse view of the flexed hip with and without stress.
24. Transverse flexion view
• The hip and knee are flexed 90 and the
ultrasound transducer is placed
perpendicular to the lateral aspect of the
infants hip.
27. Alpha angle
• Angle between straight lateral edge of
ilium and bony acetabular margin
(coronal view); determines sonographic
hip type
28. • Coronal ultrasound of a normal right
hip. Note how the echogenic iliac bone
bisects the femoral head. The alpha
angle in this study is measured to be >
60 degrees.
29. Beta angle
• Angle between straight lateral edge of
ilium and fibrocartilaginous
acetabulum—determines nuances of
sonographic hip type
30. Sonographic Findings
• Screening period: >2 weeks and up to 4-6 months of age
• @ Relationship of femoral head & acetabulum
• Femoral head position at rest in neutral position
• Hip instability under motion + stress maneuvers
• Dislocated(= eccentric) hip can be reduced (Ortolani positive):
• Hypoechoic femoral head not centered over triradiate cartilage
between pubis+ ischium (on transverse view)
31. Sonographic Findings
• Increased amount of soft-tissue echoes ("pulvinar") between femoral
head and acetabulum
• Cartilaginous acetabular labrum interposed between head and
acetabulum (inverted labrum)
• Posterior+ superior dislocation of head against ilium
• Equator sign = <50% of femoral head lies medial to line drawn along
iliac bone (on coronal view): >58% coverage is normal ; 58% to 33%
coverage is indeterminate; <33% coverage is abnormal
32. • Ultrasound images with developmental dysplasia of hip shows α angle
(dashed line) is abnormal, measuring 45° and 43° respectively. Acetabulum is
shallow and femoral head is laterally dislocated. There is pulvinar fat
hypertrophy (arrowhead) and blunting of bony acetabulum (thick solid arrow).
33. Coronal sonogram of the hip with calculation of the d / D ratio.
Coverage of 58% or greater is considered normal
36. Sonographic Findings
• Femoral head
• Disparity in size of directly visualized unossified femoral head
• Disparity in presence+ size of ossific nucleus
37. Sonographic Findings
• Acetabulum
• Delayed ossification of acetabular corner
• Wavy contour of bony acetabulum with only slight curvature
• Abnormally acute alpha angle ( = angle between straight lateral edge
of ilium+ bony acetabular margin)
• a >60° in an infant is normal
• a 55-60° can be normal <4 weeks of age
• a <55° occurs in an immature acetabulum
• 4°-6° interobserver variation!
38. • Coronal ultrasound of the left hip in an infant shows a shallow acetabulum ſt,
fatty pulvinar between the femoral head and deepest acetabulum st, and lateral
subluxation of the femoral head ſt. (Right) Transverse ultrasound confirms the
shallow acetabulum ſt, fatty pulvinar st, and lateral subluxation of the femoral
head ſt. Dynamic investigation is used to demonstrate whether or not the femoral
head is reducible or unstable. Ultrasound is the imaging modality of choice for
DDH in an infant.
ſt.
ſt,
st,
39.
40. DDH—Types
• Normal hip
• Lax = subluxable hip
• Subluxability up to 6 mm is normal in newborns (still under influence
of maternal hormones); decreasing to 3 mm by 2nd day of life
41. DDH—Types
• Concentric dislocatable unstable hip
• = joint laxity allowing non displaced femoral head to become
subluxed I dislocated under stress
• • Barlow positive
• slight increase in femoral anteversion
• mild marginal abnormalities in acetabular cartilage
• early labral eversion
• Prognosis: 60% will become stable after I week; 88% will become
stable by age of 2 months
42. DDH—Types
• Decentered subluxed hip
• femoral head shallow in location
• loss of femoral head sphericity
• increased femoral anteversion
• early labral inversion
• shallow acetabulum
43. DDH—Types
• Eccentric dislocated hip
• femoral head frankly displaced out of acetabulum
• (a) reducible = Ortolani positive
• (b) irreducible= Ortolani negative
• accentuated flattening of femoral head
• shallow acetabulum
• limbus formation(= inward growth+ hypertrophy of labrum)
• "hip click" = usually result of joint capsule and tendon stretching+
snapping (often confused with "hip clunk")
44. Plain Radiograph
• AP pelvic radiograph: >4- 6 months of age (von Rosen view = legs
abducted 45° + thighs internally rotated)
• Not reliable first 3 months of life!
• Proximal + lateral migration of femoral neck:
• eccentric position of proximal femoral epiphysis (position estimated
by a circle drawn with a diameter equivalent to width of femoral
neck)
• Interrupted discontinuous arc of Shenton's line
45. Normal Radiograph
• B, Normal anteroposterior radiograph of hips
in 2-year-old boy shows α angles of right and
left hips are normal for age, measuring 18° and
20°, respectively. Note how contour of
acetabula changes with age. Ossified femoral
epiphyses are symmetric and well seated
within acetabula. Hilgenreiner (long-dashed
line), Perkins (short-dashed line), and Shenton
(dotted line) lines are superimposed. Femoral
epiphysis is appropriately situated in
inferomedial quadrant. Center edge angle is
formed by vertical line through center of
femoral head and line from center to lateral
acetabular roof (solid lines).
46. Normal Acetabular Angle
• Normal anteroposterior
radiograph of hips in 6-month-
old boy shows acetabular angles
in right and left hip (lines) are
normal for age, measuring 22°
and 24°, respectively.
47. • A, Anteroposterior radiograph obtained at 6
months of age shows shallow left acetabulum with
steep roof, compatible with DDH.
• B, Anteroposterior radiograph obtained at 1 year of
age shows interval growth of left femoral
epiphysis; however, it remains smaller relative to
right femoral epiphysis. Left acetabular dysplasia
persists.
48. • A, Initial radiograph shows
superolateral subluxation of right
femoral head, valgus deformity,
and acetabular dysplasia.
• B, Postoperative radiograph after
iliac osteotomy and femoral varus
osteotomy shows interval healing
and improved acetabular roof
coverage of femoral head. Previous
valgus deformity has been
corrected.
49. • Frontal radiograph of the pelvis in a 1-year-old child with a dislocated
right hip. The degree of ossification of the femoral head on the
dislocated side is decreased compared with that of the normally
located left hip. The abnormally located hip articulates with a false
neoacetabulum.
50. Plain Radiograph
• Line drawn along axis of femoral shaft will not pass through upper
edge of acetabulum but intersect the anterior-superior iliac spine
(during Barlow maneuver)
• Apex of metaphysis lateral to edge of acetabulum
• femoral shaft above horizontal line drawn through the Y-
synchondrosis
• Unilateral shortening of vertical distance from femoral ossific nucleus
I femoral metaphysis to Hilgenreiner's line
51. Plain Radiograph
• Femoral ossific nucleus I medial beak of femoral metaphysis outside
inner lower quadrant of coordinates established by Hilgenreiner's +
Perkin's lines
• Acetabular dysplasia= shallow incompletely developed acetabulum:
• Acetabular angle >30° strongly suggests dysplasia
• Development of false acetabulum
• Delayed ossification of femoral epiphysis (usually evident by 4 months
(range, 2nd to 8th months) of life
52. • Frontal radiograph of the pelvis obtained with the legs in the frog-leg
position indicates that the plane of the femoral projection is toward the
triradiate cartilage, suggesting that the hips are reducible.
56. Fluoroscopic image from arthrography in 15-month-
old girl with left developmental dysplasia
of hip shows contrast material within joint. Femoral
head is seated in dysplastic acetabulum.
Arthrography
• performed intraoperatively at the time of
reduction.
• Identify Obstacles to successful reduction,
such as limbus eversion,
• Arthrography during reconstructive
osteotomy helps obtain concentric
reduction of the hip.
57. • Arthrogram of congenital hip dysplasia. (A) Arthrogram of the right hip in the
neutral position in a 1-year-old girl with congenital subluxation of the hip shows
the typical displacement of the hip lateral to, but below the acetabular labrum.
There is accumulation of contrast agent in the stretched capsule (arrow), and the
ligamentum teres is elongated. (B) In the frog-lateral position, the head moves
more deeply into the acetabulum, but subluxation is still present.
58. • Arthrogram of congenital hip dislocation. (A) Anteroposterior radiograph of the right hip in an 8-
year-old girl demonstrates complete superolateral dislocation of the femoral head. Note the
shallow acetabulum. (B) Arthrogram of the hip shows a deformed cartilaginous limbus and
stretching of the ligamentum teres. The femoral head lies superior and lateral to the edge of the
cartilaginous labrum. Note the accumulation of contrast agent in the loose joint capsule.
59. CT Scan
• CT (during cast treatment I attempted closed reduction):
• Sector angle = angle between line drawn from center of femoral head
to acetabular rim+ horizontal axis of pelvis (=reflection of acetabular
support)
• Anterior acetabular sector angle <50°
• Pposterior acetabular sector angle <90°
• Horizontal acetabular sector angle <140
60. • CT of congenital hip dislocation. Axial section through the proximal femora and
hips of a 6-month-old boy shows posterolateral dislocation of the left hip. The
right hip is normal.
61. AASA, PASA & HASA
• Anterior acetabular sector angle is created by drawing lines through
centers of femoral heads and line tangential to anterior lip of
acetabulum. Adequate anterior acetabular coverage is present when
anterior acetabular sector angle is greater than 50°.
• PASA is measured by drawing lines through centers of femoral heads
and line tangential to posterior lip of acetabulum. Adequate posterior
acetabular coverage is present when PASA is greater than 90°.
• HASA is measured by drawing lines from anterior lip of acetabulum
through center of femoral head and posterior lip of acetabulum.
Adequate global acetabular coverage is present when HASA is greater
than 140°.
62. • Drawing shows measurement of anterior acetabular sector angle
(AASA), posterior acetabular sector angle (PASA), and horizontal
acetabular sector angle (HASA). Values are measured on axial CT one
cut above greater trochanters.
63. • Mild right hip dysplasia. AP pelvic
view shows lateral CE angle
measuring less than 20º (lateral CE
angle = 19º, considered diagnostic
of hip dysplasia); and axial CT
image shows deficient anterior,
posterior and global acetabular
coverage with decreased AASA,
PASA and HASA (AASA = 46º , PASA
= 87º ad HASA = 133º).
64. • CT image in 29-year-old woman shows dysplastic hip with deficient
anterior coverage (anterior acetabular sector angle < 50°), deficient
global coverage (HASA < 140°), and borderline deficient posterior
coverage (normal PASA > 90°).
65. • A, Preoperative radiograph showing left
DDH.
• B, Postoperative CT image was obtained to
evaluate relocation of left hip after iliac and
femoral varus osteotomy.
66. • Treatment of congenital hip dysplasia.
(A) Anteroposterior radiograph of the pelvis in
a 1-year-old boy demonstrates the typical
appearance of congenital dislocation of the
left hip. (B) After conservative treatment with
a Pavlik harness at age 2, there is still
subluxation. Note the broken Shenton-
Menard arc. At age 3, after further
conservative treatment by skin traction and
application of a spica cast, there is almost
complete reduction of subluxation, as
demonstrated by contrast arthrography (C).
(D) CT scan, however, demonstrates some
minimal residual lateral displacement of the
femoral head, as evidenced by the medial
accumulation of contrast.
67. Role of MRI
• Reserved for difficult cases
• The major advantage of MRI is the ability to delineate soft-tissue
structures as well as osseous structures without ionizing radiation
• Many MRI studies are ordered in the postoperative period, usually
after reduction and spica cast placement.
68.
69. • Fig. 8—Fat-suppressed equivalent T1-weighted image in normal left
hip in 11-month-old girl with left developmental dysplasia of hip with
structures routinely identified by MRI: A = triradiate cartilage, B =
labrum, C = ilio-psoas tendon, D = un-ossified femoral head, E =
ossified femoral head, F = acetabular cartilage, G = acetabulum. Note
dysplastic right hip with subluxed femoral head (arrow).
70. • 11-month-old girl with hip click (patient B). A, Anteroposterior
radiograph shows lateral dislocation of right hip. Right acetabulum is
steep and shallow. Right femoral head ossification is delayed. B and C,
MRI was performed immediately after right hip arthrogram, closed
reduction, and adductor release. Axial T1-weighted images show interval
reduction of right hip with mild persistent posterior subluxation.
Acetabulum is shallow. Compared with normal left side (solid arrow, C),
right femoral head ossification is delayed (long solid arrow, B). Anterior
labrum is mildly inverted (short solid arrow, B). Significant pulvinar
hypertrophy (dotted arrow, B) was noted. D, Radiograph obtained 6
months after surgery shows interval improvement with mild persistent
subluxation of right hip. However, right acetabulum is still dysplastic with
abnormal acetabular angle. Right acetabular angle measures 34° and left
acetabular angle is 23°.
71. E F G H
• Fig. 9 (continued)—11-month-old girl with hip click (patient B). E and F,
Follow-up MRI was performed to assess whether second operation was
indicated. Axial (E) and coronal (F) fat-suppressed equivalent T1- weighted
images show hypertrophic acetabular cartilage and good morphology of
cartilage portion of right femoral head, overall improved since prior MRI. G
and H, Coronal non–fat-suppressed (G) and fatsuppressed (H) equivalent
T1-weighted images show mild right pulvinar fat hypertrophy (arrow) with
improved position of femoral head relative to acetabulum since prior MRI.
72. • I and J, Coronal T1-weighted images with fat saturation show superimposed bony
acetabular index angle (I) and cartilaginous acetabular index angle (J). Bony
acetabular index measures 39.6°, which is fairly concordant with 34° acetabular
angle measured on radiographs. Hypertrophic acetabular cartilage contributes to
15° cartilaginous acetabular index, which is still abnormal but relatively closer to
normal range (mean cartilaginous acetabular index in 2-year-old is 8.2 ― 1.9 [40])
compared with measured bony acetabular index. This examination served as
guide for further orthopedic management. Compared with radiographs, femoral
head appears more concentrically located in acetabulum. Surgeon subsequently
elected to treat more conservatively.
74. Treatment
• (1) Flexion-abduction-external rotation brace (Pavlik harness) I splint I
spica cast
• (2) Femoral varus osteotomy
• (3) Pelvic (Salter) I acetabular rotation
• (4) Increase in acetabular depth (Pemberton)
• (5) Medialization of femoral head (Chiari)
75. • A, Anteroposterior radiograph shows shallow steep dysplastic left acetabulum (long arrow),
lateral subluxation of left hip, and delayed ossification of left femoral head (short arrow).
Radiopaque objects seen at bottom of image are buttons overlying patient.
• B, Axial T2-weighted image with fat saturation obtained after interval reduction and with spica
cast in place shows mild residual subluxation of left femur and fibrofatty pulvinar hypertrophy
with small effusion. Note signal intensity loss of fibrofatty pulvinar with fat saturation (long
arrow). Anterior labrum is inverted (short arrow). Right hip appears normal with normal-sized
spherical femoral head compared with small and aspherical left femoral head.
• C, Coronal T1-weighted image shows lateral subluxation of left femoral head and fibrofatty
pulvinar hypertrophy (arrow). Note delayed ossification and aspherical shape of left femoral
head.
Acetabular dysplasia (without femoral subluxation I dislocation) can be determined only by imaging!
Ultrasound is the reference standard for evaluating the hip in an infant before 6 months, when capital femoral epiphyseal ossification usually occurs. It is a nonionizing, quick, and portable examination that furthermore offers the advantage of dynamic imaging in addition to standard static views.
The American College of Radiology recommends that a standard ultrasound examination be performed in two orthogonal planes:
a coronal view in the standard plane at rest and a transverse view
of the flexed hip with and without stress. Three anatomic landmarks
—ilial line, triradiate cartilage, and labrum—are used to measure the α and β angles. A standard plane includes a straight iliac line, the femoral head with maximum diameter, the tip of the echogenic acetabular labrum, and the triradiate cartilage. shows the anatomic landmarks in a normal hip. Meticulous scrutiny of the α angle measurement is necessary because false-positive findings can occur if the imaging plane is suboptimal. When reporting the α angle, the largest angle, not the average angle, should be given.
acetabulum has a small bony component+ a large cartilaginous component at birth; acetabulum highly susceptible for modeling within first 6 weeks of age + less susceptible > 16 weeks of age
positive examination result (up to 3 months of age):
• positive Ortolani reduction test = reduction of dislocated femoral head into the acetabulum by lifting the flexed thigh + pushing the greater trochanter anteriorly; may be
associated with audible "clunk"
• positive Barlow dislocation test = posterior displacement of nondislocated proximal femur by progressive adduction with downward pressure (piston maneuver) on flexed hips and knees associated with audible "clunk"
• warning signs on physical examination:
• limited hip abduction on affected side
• shortening of thigh on affected side:
• asymmetric thigh I buttock creases
• Allis sign = Galeazzi sign = affected knee is lower with
knees bent in supine position
• Trendelenburg test= visible drooping+ shortening on
dislocated side with child standing on both feet, then one foot
Location: left7right7bilateral = 117174
Instability often resolves spontaneously by 2 weeks of age!
Examination impractical beyond 4-6 months of age
(1) static evaluation (popularized in Europe by Graf)
(2) dynamic evaluation (popularized in USA by Harcke)
alpha-angle <50° at birth I 50°-59° after 3 months
indicates significant risk for dislocation without
treatment; follow-up at 4-week intervals are
recommended
Incidence: 0.25-0.85% of all newborn infants (213 are firstborns)
Radiography: After the child is 4–5 months old, the ossification of the femoral epiphysis begins to obscure sonographic landmarks and radiography becomes more reliable for detection of DDH. This is the standard tool to diagnose DDH after 6 months. An anteroposterior radiograph of the hips in neutral position is used to assess the morphology of the acetabulum, ossification of the femoral head, and position of the femoral head relative to the acetabulum. In early infancy, a normal acetabulum is relatively steeper and straighter. The morphology of the acetabulum changes with age, with the acetabulum becoming more curved inferiorly along the medial and lateral margins. shows the spectrum of normal hips in anteroposterior radiographs in a 6-month-old child and a 2-year-old child, respectively. In DDH, there is delayed ossification of the femoral head and an abnormally shallow acetabulum, thereby predisposing to subluxation and dislocation. Additionally, late complications, such as osteoarthritis and avascular necrosis, can occur. A frog-leg lateral view is sometimes used to determine whether a subluxed hip reduces. Several lines and angles are used to diagnose and further characterize DDH: The first is the Hilgenreiner line, which
is a line crossing through both tri-radiate cartilages. The second is the acetabular angle, which is formed by the Hilgenreiner line and a line drawn through the acetabular roof. A neonate should normally have an acetabular angle of less than 30°. The acetabular angle should be less than 22°
at and beyond 1 year of age. Acetabular morphology and the degree of femoral head ossification changes with age. The third is the Perkins line, which is a vertical line drawn perpendicular to the Hilgenreiner line and intersecting the lateral rim of the acetabular roof. A normally situated femoral head is in the inferior medial quadrant. The fourth is the Shenton line, which is a C-shaped line drawn along the inferior border of the superior pubic ramus and the inferomedial border of the femoral neck. A normal Shenton line should form a smooth arc. The fifth is the anterior center-edge angle, which is an angle subtended by a craniocaudal line through the center of the ossified femoral head and a line from the center of the femoral head to the lateral margin of the acetabular roof. A center edge angle less than 20° is indicative of dysplasia.
is typically performed intraoperatively by the orthopedic surgeon at the time of reduction. Obstacles to successful reduction, such as limbus eversion, can be identified. Arthrography during reconstructive osteotomy helps obtain concentric reduction of the hip.
Fluoroscopic image from arthrography in 15-month-old girl with left developmental dysplasia
of hip shows contrast material within joint. Femoral head is seated in dysplastic acetabulum.
CT is generally reserved for problem solving in difficult cases and involves a low dose technique, often in the setting of pre or postoperative evaluation
CT had sensitivity of 100% and specificity of 96% for the postoperative non subluxed hip, whereas MRI showed sensitivity of 100% and a specificity of 100%. Compared with MRI, CT requires shorter imaging time and less, if any, postoperative anesthesia. It is also a useful modality for patients with surgical hardware. However, the primary disadvantage of CT is the exposure to ionizing radiation.
CT is generally reserved for problem solving in difficult cases and involves a low-dose technique, often in the setting of prior postoperative evaluation. The CT technique at our institution is weight based (Table 4). CT is more commonly used postoperatively after the patient has been placed in a cast to define the success of reduction. Postoperatively, concentric reduction of the femoral head can be confirmed. Preoperative assessment includes evaluation of bony acetabular morphology and the ossified femoral epiphysis as well as the femoral head position relative to the acetabulum.
In fact, spica cast placement is one of the most common indications for MRI in the setting of DDH. After open reduction, the hip is held in 90° flexion and partial abduction, and the femoral head is held in position by a plaster spica cast. The degree of abduction must be carefully controlled because too little results in redislocation and too much can increase the risk of avascular necrosis. Neither hip should be abducted more than 55–60° [28]. Surgeons have varying thresholds and criteria for ordering MRI after spica casting; however, inability to clinically confirm femoral head reduction or abnormal radiography after casting are common indications
MRI Findings of the Normal Hip Familiarity with the normal appearance of the pediatric hip on MRI is critical to detect pathology. The ossified and unossified femoral heads, cartilage, and ligaments are clearly depicted. The infantile acetabulum can be categorized into three basic components: bony, cartilaginous, and ligamentous or soft tissue. The bony acetabulum is seen on radiography and is composed of the acetabular parts of the ilium, ischium, and pubis, all of which are held together by the triradiate cartilage. The cartilaginous acetabulum consists of the hyaline cartilage at the articular surface, which is U-shaped and is bridged by the transverse acetabular ligament, and the supporting vascularized growth cartilage, which includes the triradiate cartilage. The labrum, trans-verse acetabular ligament, and the ligamentum teres are the primary ligamentous structures. The labrum is of low to intermediate signal intensity and appears as a small triangular structure along the edge of the acetabulum on axial images. The labrum's intrinsic signal intensity typically increases slightly from T1- to T2-weighted images. It is important to evaluate for normal morphology and position of the labrum when evaluating dysplastic hips. The transverse ace-tabular ligament is located inferiorly, where there is a deficiency of cartilaginous acetabulum. The ligamentum teres originates from the transverse ligament and inserts on the femoral head fovea. The iliopsoas tendon is a low-signal-intensity structure that is seen just anteromedial to the anterior labrum on the axial plane. The intraarticular fat pad, or pulvinar, lies in the central portion of the acetabulum and has the highest signal intensity of all the structures in the hip, paralleling that of subcutaneous fat. It is important to assess for pulvinar hypertrophic changes, which can serve as an obstacle to successful reduction. The pulvinar in the affected hip can be compared with the contra lateral side to determine any relative size asymmetry.
The ossified femoral epiphysis appears as a low-signal-intensity structure within the high-signal-intensity unossified hyaline cartilage. Symmetry between the two ossified femoral heads should be noted. When evaluating for concentric femoral head positioning, a line can
be drawn through both triradiate cartilages. After successful reduction, the ossified portion of the femoral epiphyses should lie anterior to this line. The ossified portions of the anterior and posterior columns are low to intermediate in signal intensity, with an interposed band of high-signal-intensity triradiate cartilage. Depending on the degree of acetabular dysplasia, the unossified parts of the anterior
and posterior columns affect acetabular depth. The fibrous joint capsule attaches to the acetabular margin peripheral to the labrum.
At birth, the femoral attachment is near the metaphysis and migrates inferiorly as the hip develops. By 12 months of age, the capsule is partly fused to the femoral neck periosteum and runs up the femoral neck, attaching to the edge of the cartilaginous femoral head. Normal acetabular development is dependent on concentric positioning of the femoral head within the acetabulum.
MRI Findings of Developmental Dysplasia of the Hip When characterizing DDH using MRI, the dysplastic acetabulum should be evaluated for retroversion and degree of femoral head coverage. There may be associated cartilaginous defects or delamination. Delayed ossification of the femoral head can be determined by comparing the ossific nucleus of the femoral head in the affected hip with the contra-lateral side. A major advantage of MRI is the ability to visualize the cartilaginous acetabulum and determine its contribution to femoral head coverage. MRI depicts the unossified acetabular epiphysis in the ilium and underlying labrum, therefore showing greater and more accurate acetabular coverage than that seen on radiography alone.
Recent orthopedic articles have described the utility of bony and cartilaginous acetabular indexes on MRI in the evaluation of DDH. The bony acetabular index can be measured by MRI using an anteroposterior coronal view and is similar to the acetabular index measured on radiography. To obtain the bony acetabular index, the Hilgenreiner line and Perkins line are drawn using the same landmarks as used on radiography. The bony acetabular index line is drawn from the Hilgenreiner line at the lateral part of the triradiate cartilage to the Perkins line at the lateral aspect of the bony acetabulum. The angle subtended by the bony acetabular index line and the Hilgenreiner line is the bony acetabular index angle. The cartilaginous acetabular index is measured by drawing a line from the lateral part of the triradiate cartilage at the Hilgenreiner line to the lateral acetabular cartilaginous margin (the cartilaginous acetabular index line). The cartilaginous acetabular index angle is formed by the cartilaginous acetabular index line and the Hilgenreiner line.