Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

Transient Osteoporosis of the Hip vs Osteonecrosis of the Femoral Head

1. Transient Osteoporosis of the Hip

Transient osteoporosis is not osteonecrosis of the femoral head.

Typical Patients

It usually affects:

Pregnant women
Men in the fifth decade of life

Clinical and Radiographic Features

A characteristic feature is that the symptoms are more significant than the X-ray findings.

Plain radiographs may show:

Osteopenia

MRI is much more characteristic.

MRI Findings

MRI shows:

Bone marrow edema
Increased T2 signal intensity

The signal abnormality may involve:

Femoral head
Femoral neck
Sometimes the intertrochanteric region

An important distinction is:

Transient osteoporosis does not show the double-line sign characteristic of osteonecrosis.

Treatment

Transient osteoporosis:

Is not a tumor
Is not osteonecrosis
Does not require surgery

2. Osteonecrosis of the Femoral Head

Osteonecrosis is a fundamentally different condition.

Bilateral Disease

Osteonecrosis may be bilateral in approximately 80% of patients according to the lecture.

Therefore:

Always assess the opposite hip, even if it is asymptomatic.

3. Importance of Early Diagnosis

Early diagnosis may improve the possibility of successful head-preserving treatment.

Examples mentioned include:

Core decompression
Bone grafting

In advanced disease:

Femoral head collapse

can occur.

Once significant collapse has occurred, head-preserving treatment is unlikely to provide a good outcome, and the femoral head may need to be replaced.

4. Imaging of Osteonecrosis

Plain Radiographs

Obtain:

AP view
Frog-leg lateral view

The frog-leg lateral view may demonstrate the characteristic crescent sign associated with subchondral fracture.

However, early osteonecrosis may have normal radiographs.

5. MRI

MRI is the study of choice, particularly when:

Hip pain persists
Radiographs are negative
Osteonecrosis is suspected
Risk factors are present

T1 MRI

A typical finding is:

Well-defined band of low signal intensity
Usually in the superior/anterior portion of the femoral head

This represents the interface between necrotic and reparative bone.

6. The Double-Line Sign

The double-line sign is best appreciated on T2-weighted MRI.

It consists of:

An inner high-signal line
An outer low-signal line

The high-signal component represents hypervascular granulation tissue.

The low-signal peripheral line represents the reactive interface.

This creates the characteristic:

Double-line sign

The double-line sign is an important MRI feature distinguishing osteonecrosis from transient osteoporosis.

7. Size of the Lesion Matters

The size of the osteonecrotic lesion is an important factor in:

Development of symptoms
Disease progression
Prognosis

Better Prognosis

The best prognosis occurs with:

Small lesion
Sclerotic margins

Bone Marrow Edema

The presence of bone marrow edema on MRI is associated with:

Worsening pain
Future disease progression

8. Multifocal Osteonecrosis

Multifocal osteonecrosis refers to disease involving three or more skeletal sites.

Possible sites include:

Hip
Knee
Shoulder
Ankle

The lecture states that multifocal disease occurs in approximately 3% of patients.

Important Clinical Point

If a patient presents with osteonecrosis at a site other than the hip:

MRI of the hip should be considered to look for an asymptomatic femoral-head lesion.

Quick Comparison

Feature	Transient Osteoporosis	Osteonecrosis
Basic pathology	Transient osteoporosis	Bone necrosis
Typical patients	Pregnancy, men in 5th decade	Various risk groups
X-ray	Often normal or osteopenic	May be normal early
MRI	Diffuse bone marrow edema	Characteristic low-signal band
Femoral head/neck edema	Common	May occur
Double-line sign	Absent	Present
Crescent sign	Not characteristic	May indicate subchondral fracture
Bilateral disease	Not emphasized	Common
Early treatment	Non-operative	Head-preserving procedures may be possible
Late collapse	Not expected as osteonecrosis	Femoral-head collapse
Advanced treatment	Usually no surgery	Femoral-head replacement may be required

Exam Pearls

Transient osteoporosis is not osteonecrosis.
Transient osteoporosis often has more symptoms than X-ray abnormalities.
MRI in transient osteoporosis shows bone marrow edema without a double-line sign.
Osteonecrosis may be bilateral, so examine the opposite hip.
MRI is the investigation of choice when radiographs are negative but osteonecrosis is suspected.
Crescent sign = subchondral fracture.
Double-line sign on T2 MRI = osteonecrosis.
Lesion size is an important prognostic factor.
Bone marrow edema is associated with worsening pain and progression.
Early osteonecrosis may be amenable to core decompression or bone grafting; advanced collapse may require femoral-head replacement.

Post Views: 3,160