Background

 

Bilateral hip AVNHip AVN MRI

 

Definition

 

Lack of sufficient blood supply or oxygen leads to cell death, fracture, and collapse of the femoral head

 

Epidemiology

 

20 - 50 years old (average 38)

Male : Female 4:1

 

Etiology 

 

AS IT GRIPS 3Cs

 

Alcohol - > 400 ml / day

Steroids - > 20 mg / day

Idiopathic - 20 - 40% of cases

Trauma - hip fracture / dislocation

 

Gout, Gaucher's, genetics (Factor V Leiden mutation)

Rheumatoid, radiation

Infection, increased lipids, inflammation (arteritis)

Pancreatitis, pregnancy

SLE, Sickle cell, smoking

CRF, chemotherapy, Caisson (decompression sickness)

 

Pathogenesis

 

Cell death caused by blood supply / oxygenation issues

 

Bone resorption by osteoclasts > bone formation osteoblasts

 

Trauma

- most common cause

- Garden III / IV subcapital 16% risk

- intertrochanteric 1% risk

 

Corticosteroids

- second most common cause

- postulated secondary to changes lipid metabolism / fat emboli

- increased risk with higher dose

- high incidence in children with ALL, transplant patients

 

Alcohol

- also postulated secondary to changes lipid metabolism / fat emboli

 

SLE

- independent of steroid use

- thought due to prothrombotic effects

- incidence 6-8%

 

Sickle cell disease

- due to precipitation of hemoglobin S in low oxygen conditions

- incidence 2 - 4%

 

Stages

 

1. Necrosis

2. Inflammation / Revascularisation / Resorption

3. Repair - osteoblasts, new bone on dead trabeculae

4. Remodelling

 

Pathology

 

Starts in Anterior / Superior / Lateral head 

- wedge shaped area

 

Cysts - regions of bone reabsorption

 

Crescent Sign 

- subchondral collapse of the necrotic segment

- separation of subchondral plate from necrotic cancellous bone

 

Collapse

 

Classification

 

Ficat - developed in 1985, no MRI

 

ARCO (Association Research Circulation Osseous)

- combines Ficat, Steinberg and JOA

 

Most important

- stage I/II: pre collapse

- stage III/IV: collapse, THA

 

Stage Ficat ARCO
Stage I Normal xray

Normal xray

Abnormal MRI

Stage II Sclerosis with cysts

Abnormal xray

No flattening

Stage III

Flattening femoral head

Crescent sign

Subchondral fracture

IIIA: <2mm flattening

IIIB: > 2 mm flattening

Stage IV Collapse with osteoarthritis Osteoarthritis

 

Xray

 

Stage II: sclerosis with cystic areas resorption, no collapse

HipAVN Type 2Hip AVN Type 2 APHip AVN Type 2 Lateral

 

Stage III: collapse / flattening femoral head with preserved joint space

Hip AVN Type 3Hip AVN stage 3Hip AVN stage 3

 

Stage IV: Collapse with osteoarthritis

Hip AVN Type IIIHip AVN Type 3Hip AVN Type IV

 

MRI

 

T1

Hip AVN MRI T1AVN T1AVN T1

 

T2

Hip AVN MRI Anterior headHip AVN MRIHip AVN MRI

 

T2 Double Line Sign

 

Two lines virtually diagnostic of AVN

- outer line / low signa intensity

- inner line / high signal intensity / hypervascular granulation tissue

 

Hip AVN MRI T2 Double Line SignHip AVN double line

T2 double line sign

 

Modified Kerboul Combined Necrotic Angle (CNA)

 

Adding the arc of the femoral head necrosis

- mid-sagittal and mid-coronal MRI

- low risk collapse: < 190 degrees

- moderate risk collapse: 190 - 240 degrees

- high risk collapse: > 240 degrees

 

Kerboul angle 1kerboul angle 2KerboulKerboul 1

 

Natural history

 

Kerboul CNA

 

Ha et al JBJS Am 2004

- CNA > 240: 100% collapse

- CNA 190 - 240: 50% collapse

- CNA < 190: 0% collapse

 

AVN T1Large hip AVN

 

Asymptomatic Contralateral Hip

 

Mont et al JBJS Am 2010

- systemic review of asymptomatic contralateral hips

- 59% progressed to symptoms or collapse

- small medial lesions progressed to collapse < 10%

- sickle cell high risk, SLE low risk

 

Nam et al JBJS Am 2008

- 105 asymptomatic contralateral hips

- 59% became symptomatic within 5 years

- 1/21 with < 30% volume of femoral head AVN became symptomatic

- 11/24 with 30 - 50% volume of femoral head AVN became symptomatic

- 50/60 with > 50% volume of femoral head AVN became symptomatic

 

Differential diagnosis

 

Bone marrow edema syndrome

- diffuse edema throughout femoral head

- possible stress / overuse reaction / low Vit D in athletes

- possible early AVN

 

Bone marrow edemaBone marrow edema

 

Subchondral insufficiency fracture

- trauma

- acute line

 

Hip subchondral fracture

 

Transient osteoporosis of the hip

- third-trimester pregnancy

- edema into metaphysis or neck

 

Boneschool page

 

Transient osteoporosis hip

 

 

CT

 

Can diagnose early collapse & flattening

 

Hip AVN CTHip AVN CT

 

Bone Scan

 

Most useful to investigate if head vascular after subcapital fracture