What is the most common site for avascular necrosis?
Avascular necrosis is more common after chronic abuse of what?
Why does chronic alcoholism predispose for AVN?
- Alcohol metabolism increases NADH:NAD
- Raised NADH contributes to fatty liver disease
- It can also cause AVN in the femoral head
As well as chronic alcoholism, what else may cause AVN?
Disruption to blood supply
(often after fractures)
Fractures of which bone are often missed, yet is a common location for AVN?
(after falling on an outstretched hand)
On sectioning a bone in AVN what is seen
a) Large wedge shaped area of discolouration
b) Trabeculae without osteocytes in the lacunae
What is the term given to describe the miscopscopic appearance of attempted bone healing in AVN?
Osteochondritis tends to occur in which age group?
Children and adolescents
Why is osteochondritis proposed to affect children and adolescents more frequently?
- Increased physical activity
- Increased body weight
What is the pathogenesis for osteochondritis?
- Recurrent impact or traction injuries cause bleeding and oedema in the bone
- This causes capillary compression
- Bone necrosis ensues
- Compression, fragmentation or separation of the bone follows which can cause flattening or incongruence of a joint or a pothole on the surface
- Pain and progression to arthritis are common
What are common sites for osteochondritis?
- 2nd metatarsal head (Freiburg's disease)
- Navicular bone (Kohler's disease)
- Lunate of the carpus (Kienbock's disease)
- Capitellum of the elbow (Panner's disease)
- Vertebral compression (Scheuermann's disease)
- Perthes disease
Where does traction osteochondritis occur?
At apophysis (a bony tubercle where a tendon attaches)
Name the traction osteochondritis occuring at the tibial tubercle
What is Sever's disease?
A traction osteochondritis at the calcaneus
(N.b. Not Severus' disease)
What is osetochondritis dissecans?
Fragmentation with separation of bone and cartilage within a joint
Name 3 areas prone to osteochondritis dissecans
- Lateral part of medial femoral condyle in the knee
- Anteromedial talar dome
- Superomedial femoral head
- Humeral capitellum
What are the key symptoms of oseochondritis dissecans?
How is a damaged joint from osteochondritis repaired?
How is osteochondritis dissecans repaired?
- Large or unstable segments of bone are pinned for repair
- Small segments of bone are removed arthroscopically
What is avascular necrosis?
Ischaemic necrosis of bone occuring mostly in adults
Which sites are particularly prone to AVN?
- Femoral head
- Femoral condyles
- Head of humerus
- Proximal pole of the scaphoid
- Proximal part of talus
What are the risk factors for developing AVN?
- Subsequent to trauma or fracture
- Steroid use
- Sickle cell disease
- Antiphospholipid deficiency in SLE
- Decompression sickness
Why are alcoholism and steroid use risk factors for AVN?
- They alter fat metabolism
- This results in mobilisation of fat in circulation
- The capillary system can struggle to maintain normal flow with increased fat content of blood
- This promotes coagulation in prone areas of bone
- Increased fat content also compresses venous outflow causing stasis and ischaemia
What is the disease name given to decompression sickness?
What is Caisson's disease
AVN is caused due to nitrogen bubbles forming in the circulation after rapid depressurisation after deep diving
Why does secondary OA often follow on from AVN?
- Patchy sclerosis and subschondral collapse can occur
- This causes irregularity in any articular surface
How can AVN be imaged best?
(early cases can only be seen this way)
If the articular surface has not yet collapse in a patient with AVN, what is the treatment?
Drilling under fluoroscopy to decompress bone
This prevents further necrosis and aids healing
If the articular surface has collapsed in a patient with AVN, what is the treatment?
(especially in the knee, hip or shoulder)
Fusion may be considered for bones in the wrist or ankle