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Avascular Necrosis of Femoral Head - Draft

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Overview

Avascular necrosis (AVN), also known as osteonecrosis, is a condition where bone tissue dies due to an interruption in blood supply. The femoral head is particularly vulnerable due to its unique vascular anatomy.

Key Points

High-risk groups include patients with corticosteroid use, alcohol abuse, trauma, sickle cell disease, and certain autoimmune or coagulation disorders.
Early diagnosis is critical to prevent joint collapse and the need for surgical intervention.

Epidemiology

Mean age of presentation in the UK is 58.3 years, with a prevalence of two per 100 000 patients. On average, AVNFH occurs earlier in life than typical osteoarthritis. It is more common in men and the highest prevalence is in men aged 25 to 44 and women aged 55 to 75. In the UK it is the third most common indication for total hip replacement in people under 50.(1)

Risk Factors

Trauma: e.g., femoral neck fractures, dislocation.
Non-traumatic:
- Corticosteroid use (most common non-traumatic cause)
- Alcohol abuse
- Sickle cell disease
- Systemic lupus erythematosus
- Chronic renal failure
- Coagulopathies or antiphospholipid syndrome
- Decompression sickness (e.g., divers)
- HIV infection or treatment-related

Clinical Features

Pain:
- Insidious onset of groin pain (most common)
- May radiate to thigh or buttock
- Exacerbated by weight-bearing
Limited range of motion: Especially internal rotation and abduction.
Bilateral involvement: Can occur in up to 50% of non-traumatic cases.

Who to Refer

An urgent referral should be made if AVN is suspected or confirmed.

Consider rheumatology/haematology input if autoimmune or haematological cause suspected.

Red Flags

Immediate assessment should be arranged (contact orthopaedic team on call or send to ED) if:

Rapidly worsening hip pain
Inability to weight bear
X-ray evidence of collapse or advanced AVN

Before Referral

Initial Assessment

History and risk factor review
Physical examination:
- Antalgic gait
- Reduced ROM
- Positive Patrick (FABER) test

Investigations

If immediate referral is not indicated then consider the following investigations in primary care:

X-ray - although may be normal in early disease.
MRI (gold standard for early diagnosis) - high sensitivity in detecting bone marrow oedema and early necrosis.
Bloods (not diagnostic but may help in assessing underlying causes - FBC, CRP, Lipid profile, autoimmune screen, coagulation screen.

Referral

Consider immediate (same-day) referral if there are red flags.

If no red flags then refer to the Musculoskeletal Interface (MSKI) Service

Resources

(1) Avascular necrosis of the hip | The BMJ

(2) Differential diagnosis | Greater trochanteric pain syndrome | CKS | NICE

(3) Avascular Necrosis Femoral Head - Physiopedia

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