Avascular necrosis

Question 1

Which sites are most susceptible to avascular necrosis?

Answer 1

Femoral head
Femoral condyles
Head of humerus
Proximal poles of scaphoid and talus

Question 2

Describe how ischaemia can occur in avascular necrosis

Answer 2

Severance of local blood supply
Venous stasis and retrograde arteriolar stoppage
Intravascular thrombosis
Compression of capillaries and vascular sinusoids by marrow swelling

Question 3

List the common causes of traumatic osteonecrosis

Answer 3

Fracture and dislocation of hip: retinacular arteries supplying femoral head +/- ligamentum teres
Fractures of scaphoid or talus

Impact injuries and osteoarticular fractures of any convex articular surfaces ➔ osteochondrosis (small segments of osteonecrosis)

Question 4

Name 5 causes of non-traumatic osteonecrosis

Answer 4

Osteomyelitis
Septic arthritis
Perthe's disease
Cortisone
Alcohol abuse
Sickle-cell disease
Gaucher's disease
Caisson disease
Ionising radiation

Question 5

Define Perthe’s disease

Answer 5

Childhood avascular necrosis of hip ➔ collapse and flattening of the femoral head

Question 6

Describe the clinical features of osteonecrosis

Answer 6

Patients tend to present when lesion is advanced.
Usual complaint is pain: near joint with stiffness
Local tenderness and nearby joint swelling
Restricted movement

Question 7

What x-ray changes are seen with osteonecrosis?

Answer 7

Subarticular segment of increased bone density: due to reactive new bone formation
Fracturing and collapse of necrotic segment
Normal joint space: differentiates from OA

Question 8

How is osteonecrosis investigated?

Answer 8

MRI scan shows early signs

X-ray changes tend to occur after several months

Question 9

Outline the staging of osteonecrosis of hip

Answer 9

ARCO staging of osteonecrosis

0. Biopsy shows osteonecrosis. Asymptomatic with normal clinical investigations
1. X-ray normal, MRI shows osteonecrosis
2. X-ray and/or MRI show necrosis, but no distortion of bone shape or fracture
3. X-ray shows early abnormality, but femoral head still spherical
4. Signs of flattening or collapse of femoral head
5. As above + loss of joint space
6. As above + destruction of articular surface

Question 10

What is crescent sign of avascular necrosis?

Answer 10

Subchondral lucency of femoral head: indicates imminent articular collapse

Question 11

How is osteonecrosis treated?

Answer 11

Treat any underlying causes where possible
Stage 1 and 2: weight relief, splint, surgical decompression (if venous stasis or marrow oedema)
Stage 3: realignment osteotomy: transfers stress to an undamaged area
Stage 4-6: treatment similar to OA

Question 12

What is the treatment for stage 4-6 osteonecrosis?

Answer 12

Treatment similar to OA

Education, advice, assisted devices, strengthening exercises, weight loss

Paracetomal and/or topical NSAIDs (knee/hand)
Oral NSAIDs
Intra-articular corticosteroids: temporary
Codeine: last resort

Arthroplasty: shoulder, hip, knee
Arthrodesis (fusion): ankle, wrist

Question 13

Define sickle-cell disease

Answer 13

An autosomal recessive disorder affecting red blood cells, which predominantly affects African or Afro-Caribbean ethnicity). Characteristically features HbS which becomes distorted and sickle-shaped (esp in hypoxia).

This can result in anaemia and sickle cell crisis (vaso-occlusion).

Question 14

Which organism commonly causes acute osteomyelitis in patients with sickle-cell disease?

Answer 14

Salmonella

Question 15

Define Caisson disease (Decompression sickness)

Answer 15

Rapid decompression of blood and tissues supersaturated with nitrogen causes release of gas bubbles. This causes local tissue damage and generalised embolic phenomena.

Symptoms: pain near joints (the bends), breathing difficulties, vertigo

Question 16

Define Gaucher’s disease

Answer 16

Autosomal recessive disorder of enzyme deficiency resulting in abnormal accumulation of the lipid glucocerebroside. Effects mainly seen in liver, spleen, and bone marrow.

Accumulation causes increased medullary cell volume and capillary compression ➔ bone complications including osteonecrosis.

Question 17

Define osteochondritis

Answer 17

A group of conditions featuring compression, fragmentation, or separation of a small segment of bone with involvement of the attached articular surface.

Osteocondritis dissecans is an example, which may cause locking or giving way of knee or ankle if the segment becomes impinged in the joint.