radiological changes in Avascular necrosis of Hip grading of AVN

1. Radiographic appearance
in Avascular Necrosis of
head of femur
Dr. Gaurav Singh
Central institute of orthopaedics
VMMC & Safdarjung Hospital

2. Definition
• Avascular necrosis of femoral head refers to the death of
the osteocytes with subsequent structural changes
leading to femoral head collapse and secondary
osteoarthritis of hip joint

3. Diagnostic modalities
• Routine radiographs
• MRI
• CT scan
• SPECT
• Perfusion scanning
• Bone scan
• Digital subtraction angiography

4. Radiography
• Routine radiographs first step towards diagnosis
• High quality films taken at least two views 90 degrees
apart
• Helpful in assessing flattening of the femoral head and
associated degenerative changes
• Limitations:
1. Sensitivity for detecting early stages of the disease 41%
2. Does not detect ficat arlet stage 0 and 1

5. radiological changes on plain x-ray
• Osteoporosis
• Mottled trabecular pattern
• Sclerosis
• Subchondral fractures (Crescent sign)
• Fragmentation
• Subchondral cysts
• Loss of spherical weight bearing dome
• Partial collapse of head
• Secondary osteoarthritis

6. Sclerosis and subchondral cysts~

7. Conventional radiograph of the right femur in the frog-leg position obtained with the
patient’s thigh abducted and flexed shows subchondral area of hyperlucency (arrows) in
the anterolateral aspect of the proximal femoral head

8. AP radiograph with the lucent crescent sign (white arrow) and the discontinuity where
the subchondral bone has collapsed (black arrowhead)

9. Fragmentation
Radiolucent clefts
seen traversing bone

11. Alternating regions of the sclerosis and lucency within the superior aspect of the left
femoral head (arrows), representing the reparative stage (stage 2). The lucent areas
represent the site of resorption of necrotic marrow and trabecular. The sclerosis
represents apposition of new bone on dead trabeculae.

12. There is a crescent-shaped density (arrow) representing the femoral head surface on an
underlying zone of decreased density underneath the crescent-shaped bone
representing demineralization.

13. Sclerosis
Subchondral cysts

14. Asymmetric joint-space narrowing (arrow), juxta-articular sclerosis, and subchondral cyst
formation

15. Anteroposterior radiographyc view of the pelvis shows flattening of the outer
portion of the right femoral head from avascular necrosis, with adjacent joint space
narrowing, juxta-articular sclerosis, and osteophytes representing degenerative
joint disease (stage IV)

16. Modified Ficat and Arlet Radiographic
Staging
Stage Phases Interpretation
0 Preclinical and
preradiologic
Only suggestive
1 Preradiologic Minimal osteoporosis, blurring of bony
trabeculae
2a Reparative Diffuse osteoporosis, sclerosis and cysts
A linear subcortical lucency beneath the
articular cortex-the crescent sign, Subarticular
cortex may remain attached to the cartilage and
is separated from the underlying femur by soft
tissue-the eggshell sign, joint-space widening.
2b
3 Early collapse of femoral
head
Sequential collapse and loss of sphericity of
head
4 Progressive degenerative
disease
Degenerative joint disease with joint-space
narrowing, marginal osteophyte formation, and
subchondral cyst formation.

17. University of pennsylvania
classification of osteonecrosis
Stage Interpretation
0 Normal/ non diagnostic x ray, bone scan or MRI
1 Normal X ray; abnormal bone scan and/ or MRI
•Mild (15% of femoral head affected)
•Moderate (15-30%)
•Severe (>30%)
2 Cystic and sclerotic changes in femoral head
•Mild (15% of femoral head affected)
•Moderate (15-30%)
•Severe (>30%)
3 Subchondral collapse (crescent sign) without flattening
•Mild (15% of articular surface)
•Moderate (15-30%)
•Severe (>30%)

18. ……contd.
Stage Interpretation
4 Flattening of femoral head
•Mild (15% of surface)
•Moderate (15-30%)
•Severe (>30%)
5 Joint narrowing and/ or acetabular changes
•Mild (average of femoral head involvement as determined by
stage 4 and estimated acetabular involvement)
•Moderate (average of femoral head involvement as
determined by stage 4 and estimated acetabular involvement)
•Severe (average of femoral head involvement as determined
by stage 4 and estimated acetabular involvement)
6 Advanced degenerative changes

19. Marcus radiographic staging of
AVN
Stages Interpretation
Stage 1 Normal or equivalent radiograph, MR
imaging or bone scan
Stage 2 Sclerotic or cystic leison
Stage 3 Crescent sign
Stage 4 Sequential collapse, step off in outline
of subchondral bone
Stage 5 Narrowing of cartilage space with
degenerative changes

20. CT scan
• Evaluate the extent of involvement, such as subchondral
lucencies and sclerosis during the reparative stage
• Osteoporosis is first visible CT scan sign
• Later, the central bony asterisk is distorted, appearing as
clumping and fusion of the peripheral asterisk rays
• Limitation:
1. Insensitive in detecting stage 0 and 1 AVN

21. Axial computed tomograph scan of a patient with avascular necrosis of the
femoral head shows clumping and distortion of the central trabeculae
representing the asterisk sign (arrowhead) and an adjacent low-density region
(arrow) representing the reparative zone.

22. Joint space narrowing, juxta-articular sclerosis, and osteophyte
formation (degenerative joint disease)

23. MRI
• Most sensitive means of diagnosing avascular necrosis
(AVN)
• It helps in accurate staging because images clearly
depict the size of the lesion, and gross estimates of the
stage of disease can be made

24. MRI
• Advantages of MRI:
 Allows sequential evaluation of asymptomatic lesions
that are undetectable on plain radiographs
 Facilitates better response to treatment because AVN is
diagnosed at an earlier stage, and therapeutic measures
are more successful the earlier they are begun.
 May help guide interventional procedures such as core
decompression,
 May demonstrate response of the femoral head to
treatment
 May detect the joint effusions and bone edema
 It demonstrates superior soft-tissue resolution, and has
high spatial and contrast resolution, allowing evaluation
of morphologic features

25. …….MRI
• MRI of both hips (> 50% - bilateral)
• Earliest – band form (low-signal T1 representing
separation of normal and ischemic bone)
• Pathognomonic – double line sign (combination of band
form & high-signal-intensity line T2 representing
hypervascular tissue)
• AS quadrant usually affected, although changes seen in
all areas of head

26. A Coronal T2-weighted fat suppressed image demonstrates a small focus of avascular
necrosis with the double-line sign. The linear high signal intensity inner line (arrow) and
dark peripheral line (arrowhead) is typical

27. MRI
• Coronal plane is the most important imaging plane
• Sagittal images eliminate partial-volume averaging,
which is especially present on axial image
• When the lesion is located anterosuperiorly, off-coronal
images, angled toward the axial plane are preferred
• T1WIs and T2WIs are obtained in the coronal plane, 4-
mm thick, with a 1-mm gap
• Short tau inversion recovery (STIR) images provide
excellent fat suppression and demonstrate areas of bone
marrow edema

28. AVN Classification based on MRI
Class A
• Central osteonecrotic focus signal analogous to fat
• Increased signal on T1WIs
• intermediate to high signal on T2WIs

29. Class B
•The presence of central osteonecrotic focus signal
analogous to that of blood is observed
•Increased signal is demonstrated on both T1WIs and T2WIs

30. Class C
Coronal fat-saturated T2WI - increased signal within the
femoral head and neck (arrow), representing edema

31. Coronal T1WI shows decreased signal within the
femoral head (arrow), representing edema

32. Class D
• The presence of central osteonecrotic focus signal
analogous to that of fibrous tissue
• Decreased signal is demonstrated on both T1WIs and
T2WIs.

33. A T2-weighted coronal image reveals subtle subchondral signal changes within the
right femoral head (arrow) compatible with AVN. An associated stress fracture
(arrowhead) is noted within the femoral neck

34. T1-weighted coronal image demonstrates a
ring-like subchondral area (arrow) present
in the anterior-superior femoral head.
T1-weighted sagittal image confirms the
crescentic subchondral area (arrow) present
at the anterior-superior femoral head.

35. Mitchell’s MRI staging
Class T1 T2 Definition
A Bright Intermediate Fat signal
B Bright Bright Blood signal
C Intermediate Bright Fluid and
edema signal
D Dark Dark Fibrosis
signal

36. SPECT
• Cold spot (photon-deficient region) within the femoral
head is highly specific for avascular necrosis (AVN) and
is the earliest scintigraphic evidence of this disease
• Increased uptake represent revascularization and repair
• The central region of photopenia with surrounding zone
of increased uptake is termed the doughnut sign

37. A small area of intense uptake at the level of RFH.

38. Perfusion and static planar
radionuclide imaging
• Uptake is decreased in the perfusion and static phases,
which represents the early ischemic event
• Uptake is decreased within the femoral head in the
perfusion phase and increased around the cold region in
the static phase which represents the reactive zone

39. Bone scan
Bone scan of a patient with avascular necrosis of the femoral head shows increased
uptake in the superolateral aspect of the right femoral head, indicative of avascular
necrosis but providing little information concerning the structural integrity of the hip

40. Bone scan
Planar bone scan of the pelvis in a patient with bilateral avascular necrosis of the femoral
head shows marked increased uptake of radiopharmaceutical agent in both hips

41. Digital subtraction angiography
• Detects vessel abnormality
• Predict head at risk due to abnormal circulation

42. ARCO
• 1991, committee of nomenclature and staging of the
Association Research Circulation Osseous (ARCO)
endorsed the staging system developed by the
University of Pennsylvania in the 1980s
• 1992, location of leison as described by Japanese
system added
• 1993, stages 3 and 4 combined as well as stages 5 and
6

45. Thank you