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"[526] AVASCULAR NECROSIS (AVN)"

December 23, 2020 Edit this post

“ EPONYMOUS NAMES FOR AVASCULAR NECROSIS Hip (Perthe disease) Medial tibial condyle (Blount disease) Metatarsal head (Freiberg infarction) L...

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EPONYMOUS NAMES FOR AVASCULAR NECROSIS
  • Hip (Perthe disease)
  • Medial tibial condyle (Blount disease) Metatarsal head (Freiberg infarction) Lunate (Kienbock malacia)
  • Navicular (Kohler disease)
  • Capitellum (Panner disease) 
  • Scaphoid (Preiser disease) 
  • Vertebral body (Kummel disease)
Interruption of blood supply causes the cell death of the bone constituents, mostly due to an arterial problem (it can also be due to venous insufficiency). It can affect any bone, but the hip is most commonly affected. It affects the epiphysis (if it affects the diaphysis or metaphysis, it is known as bone infarction). 
Causes include trauma, haematological conditions (systemic lupus erythematosus [SLE], Gaucher disease or sickle cell anaemia), Cushing syndrome, steroid use, alcoholism, pancreatitis, pregnancy, Caisson disease, etc. Patients taking steroids and transplant recipients are especially at risk.
PLAIN FILM 

•  Focal radiolucencies
•  Sclerosis
•  Bone collapse
•  Loss of joint space

MRI

•  Most sensitive for diagnosis.
•  Low signal on T1 and intermediate signal on T2 (reflects adipocyte death).
•  Surrounding high signal on T2/STIR indicates oedema (suggesting an acute event).
•  Oedema localises to the subchondral surface with increased severity, with an irregular rim of low T1 signal.
•  ‘Double line’ sign (paired rims of low and high signal on T2 demonstrating the interface of viable/dying bone marrow).


BONE SCAN

•  80%-85% sensitive.
•  Early disease is demonstrated by a focus of reduced tracer uptake.
•  In late disease, there is a focus of reduced uptake surrounded by a ring of increased uptake (‘doughnut sign’) due to capillary revascularisation and bone synthesis.

Kohler disease. Foot x-ray demonstrating sclerosis and flattening of the navicular in keeping with avascular necrosis (Kohler disease).
 Avascular necrosis. Pelvic x-ray demonstrating bony sclerosis with irregularity and flattening of the left femoral head. Note the pelvic clips, anastomosis and femoral line in keeping with renal failure/transplant with steroids, therefore being the likely cause of the avascular necrosis.

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