Nontraumatic avascular necrosis of the femoral head

epidemiology

· most common in middle-aged males

· M:F = 4:1

· peak incidence 30-60 yrs

· bilateral in 50-80%

aetiology

· exposure to corticosteroids and alcohol account for 90% of cases

Steroid therapy

· risk increased with

· length of therapy

· size of dose

· overall incidence is 3-25%

· interval between use and onset is 6 months to 3 yrs

· often multiple sites

· often bilateral

· usually progresses to joint failure

Conditions

Post-transplantation

· incidence following renal transplantation was 20%

· now 2% with use of cyclosporin A as steroid dose reduced

· usually develops within 1 yr but may be delayed up to 6 yrs

· involves (in decreasing order)

· femoral head (75% bilateral)

· humeral head

· femoral condyles

· majority have multiple sites

Lymphoma and leukaemia

· seen in survivors of malignant lymphoma and in childhood acute lymphocytic leukaemia

· due to steroids combined with chemotherapy and/or radiotherapy

Rheumatoid arthritis

Asthma

Alcoholism

· most common association

· present in 15-75% of patients

· 5-30% of alcoholics develop AVN

· bilateral in 75%

· may affect other sites

· humeral head, femoral and tibial shafts

· studies show increased risk with as little as 400 ml/wk

· most idiopathic lesions likely to be alcohol-related

Other conditions

· sickle cell disease

· dysbarism

· Gaucher’s disease

· radiation

associated factors

Gout

· 40% of patients with AVN have gout or hyperuricaemia

· mechanism obscure

· no gross deposits of MSU crystals in femoral head

Chronic pancreatitis

· increased incidence

· may be due to

· alcohol intake

· altered lipid metabolism

Lipid metabolism

· abnormalities associated with AVN include

· hypercholesterolaemia

· raised serum triglycerides

· raised beta-lipoproteins

SLE

· seen occasionally in SLE patients untreated with steroids

· probably due to vasculitis

pathology

· area of necrosis is

· wedge-shaped

· subchondral

· anterosuperolateral

· healing response ineffective in 90%

· leads to mechanical failure of joint surface

· result is degenerative changes

clinical

History

· present with aching pain in groin or thigh

· may radiate to buttocks or knee

· usually gradual onset

· occasionally sudden

· initally mechanical

Examination

· ROM limited by pain

· esp. internal rotation and abduction

staging

Ficat and Arlet

STAGE	SYMPTOMS	X-RAY	BONE SCAN	MRI
0	none	normal	normal	norrmal
1	minimal	normal	decreased uptake	positive
2	mild	patchy sclerosis	increased uptake	positive
3	moderate	flattening crescent s	increased uptake	positive
4	severe	acetabular changes	increased uptake	positive

Ficat and Arlet

Stage 1

· onset of ischaemia

· preclinical stage

· x-rays normal

· MRI (+/- bone scan) changes

Stage 2

· onset of pain

· early x-ray changes

· cystic and sclerotic areas

Stage 3

· onset of structural changes

· classical x-ray changes

· crescent sign

· flattening

Stage 4

· onset of degenerative changes

Modifications

Hungerford and Lennox

· added stage 0

Steinberg

· divided stage III into

· with collapse

· without collapse

· quantified extent of involvement of femoral head

· mild (< 15%)

· moderate (15-30%)

· severe (>30%)

Japanese Investigation Committee

· incorporated radiographic location

· A - medial

· B - central

· C- lateral

Investigations

Plain films

· AP and frog-leg lateral

· initial changes

· mottling

· sclerotic line at junction between dead and living bone

· later changes

· crescent sign

· segmental collapse

· end-stage cha nges

· osteoarthritis

· until osteoarthritis develops, joint space maintained

Bone scan

· pathognomonic finding is

· cold-in-hot

· increased uptake surrounding photopaenic area

· absent or decreased uptake seen due to avascularity

· not always seen

· increased uptake seen due to repair

· non-specific

· cold areas may be due to metastatic deposits

· hot areas may be due to any cause of increased bone vascularity or formation

· most useful to detect avascularity following acute femoral neck fracture or hip dislocation

CT scan

· not routinely performed

· high exposure to radiation

· usually unecessary to make diagnosis

· can be used to assess extent of

· subchondral fracture

· flattening and collapse of articular surface

MRI

· most sensitive and specific investigation

Changes

Normal

· on T1 image

· normal medullary cavity emits strong signal (white) from hydrogen-rich fatty marrow

· normal cortex and subchondral plate emit weak signal (black)

Necrosis

· T1 shows low-signal line

· corresponds to sclerotic line on x-ray

· takes weeks to develop

· area cupped by low-signal band shows varying amount of decreased signal signifying dead bone

· T2 shows characeristic double line

· outer low-signal line related to thickened trabeculae

· inner high-signal line related to granulation tissue

Advantages

· able to identify necrosis in high-risk patients in pre-radiological state

· accurately reveals site and extent of bone death

· can show revascularisation and response to treatment

· allows sequential evaluation of asymptomatic lesions

Functional exploration

· three-phase invasive investigation developed by Ficat

· no longer routinely used if MRI available

Intraosseous pressure

· intertrochanteric cannula inserted

· bone marrow pressure measured

· abnormal if

· baseline pressure > 30 mm Hg

· pressure > 30 mm Hg 5 min after injection of 5 ml isotonic saline

· oxygen saturation of blood from cannula > 85%

Intramedullary venogram

· 10 ml contrast injection

· abnormal if

· injection difficult and painful

· diaphyseal stasis or reflux seen at 15 min

Biopsy

· trephine from greater trochanter to within 5 mm of articular cartilage

· abnormal if shows

· empty lacunae involving multiple adjacent trabeculae