hip AVN

Question 1

what is AVN?

Answer 1

osteonecrosis of the bone secondary to a disruption of the blood supply lead to cell death

Question 2

what are the causes of AVN of the hip?

Answer 2

• can be broken up into: large vessel, small vessel and systemic

Large vessel
* fracture dislocation

small vessel
* thomboemboli
* fat emboli
* caisson’s disease - nitrogenous emboli
* smoking

systemic
* sickel cell anaemia
* vasculitis
* alcoholic liver disease
* exogenous - drugs/ etoh

Question 3

what are the typical sites affected by osteonecrosis?

Answer 3

• femoral head
• medial femoral condyle
• humeral head
• capitellum (panner’s disease)
• lunate ( kienbock’s)
• talus
• navicular (kohler’s)
• metatarsal head (freiberg’s)

Question 4

what is the pathogenesis of osteonecrosis

Answer 4

Three theories:
* intraosseous HTN - bone comp syndrome
* microvascular abnormalities - more prone to avn
* fat embolism

3 phases
1. necrosis - loss of blood supply
2. repair - creeping substitution - new woven bone laid down and resorption of necrotic bone- longer with cortical bone
3. structural - - new bone not as strong leading to subchondral bone collapse - this leads to degeneration

Question 5

what investigations can you perform?

Answer 5

• xray - may not detect earlier changes
• MRI scan - gold standard

Question 6

how can you classify hip AVN?

Answer 6

ficat classifcation system
* 0 - silent - no clinical symptoms or radiology - histological diagnosis - if suspected due to other hip involvement
* 1 - preradiographic - groin pain with mri changes but no xray changes
* 2a - precollapse - osteopenia and sclerosis of femoral head
* 2b - crescent sign - subchondral fracture
* 3 - collapse - flattening and collapse of head. pain, limited rom and limp
* 4 - osteoarthritis - secondary degeneration with deformed head

Question 7

how does the ficat classification change management?

Answer 7

• pre-collapse = joint preservation
• collapse = salvage

Question 8

what are the treatment options for AVN of the hip?

Answer 8

joint preservation vs salvage procedures

**joint preservation **
* conservative - protective WB and weight loss
* medical - bisphosphonates, thrombolytic and lipid lowering agents
* surgical:
1. core decompression
2. core decompression and tantulum rods
3. strut bone graft - fibula non-vascularised
4. femoral osteotomies - valgus or varus - move necrotic area from WB zone

**Salvage procedures

• THR - uncemented CoP for young and hybrid for older patients
• arthrodesis - theoretical option

Question 9

how does core decompression work?

Answer 9

• relieves intraosseous pressure
• increases vascularity
• stimulates healing
• 84% of ficat 1 hips treated with decompression survive - meta-analysis - mont
• 2/3rds hips do well

Question 10

what is the purpose of adding tantulum rods?

Answer 10

• acts as a structural graft without the need for bone graft
• porous material - allows ingrowth
• core decompression - necrotic bone removed and rod inserted