Dr. Ebraheim’s educational animated video describes the condition of avascular necrosis.
Avascular necrosis or osteonecrosis is the death of a segment of bone due to disruption of the blood supply. Causes of avascular necrosis are numerous. There are different ways that could interrupt the blood supply.
1-Trauma: avascular necrosis may occur due to trauma as described in the previous video. These are examples of how trauma associated with dislocation or fracture of the femoral neck may interrupt the blood supply of the hip. Hip dislocation, femoral neck fracture due to mechanical disruption of the blood vessels.
2-Occlusion of the arterial blood supply: avascular necrosis may occur due to occlusion of the arterial blood supply by fat embolism, nitrogen bubbles in the blood stream (Caisson disease) or with sickle cell disease. Avascular necrosis may also occur due to fat embolism. To explain sickle cell anemia, under low oxygen levels, the cells become sickle shaped and unable to pass through the vessels. Results in diminished blood flow leading to AVN. Patient with sickle cell disease and asymptomatic AVN diagnosed by MRI will have a higher incidence of progression to collapse of the AVN and pain (75%). Deterioration of the AVN will be rapid and can be bilateral. Screen the other hip now and periodically. Also, watch the humeral head for AVN.
3-Obstruction of the venous outflow: leads to increased interosseous pressure.
4-Injury or pressure on the blood vessel wall:
Gaucher's disease: increased fat cell size may prevent the arterial inflow and lead to ischemia.
Marrow disease such as lymphoma and leukemia may also cause AVN.
Radiation, vasculitis, and cytotoxins.
5-AVN may be associated with hypercoagulable states such as decreased anticoagulants, protein S and protein C. increased procoagulants.
Most common causes:
•Trauma
•Steroid use
•Alcohol
•Idiopathic (no cause)
•Metabolic and genetic factors
•Systemic lupus erythematosus (SLE)
•Renal failure
•Organ transplant
•Hemophilia
All of these conditions may cause loss of the vascular supply, marrow necrosis, and osteocyte death.
Important conditions related to AVN:
Steroid use: high doses for 2-3 weeks or low doses for long durations can cause AVN. There is a direct connection between the dose and duration of steroid use in the development of AVN. Joint injection is not proven to cause AVN.
HIV: avascular necrosis of the femoral head is a complication in HIV infected patients. The increased incidence of AVN may be caused by an increased prevalence of predisposing factors of osteonecrosis, including protease inhibitors, hyperlipidemia, corticosteroid use, alcohol and intravenous drug use. Protease inhibitors play a role in the development of osteonecrosis through a tendency to cause hyperlipidemia.
Causes of AVN mnemonic
A S E P T I C
•ALCOHOLISM/ AIDS
•SICKLE CELL DISEASE/ SLE
•ERLENMYER FLASK (Gaucher’s)
•PANCREATITIS/PREGNANCY
•TRAUMA
•IDIOPATHIC/INFECTION
•CAISSON’S (the bends)
AVN is death of a segment of bone. The anterosuperior segment of the femoral head is the area usually affected.
Resorption of some of the dead bone is bone by osteoclasts. Dead trabecular bone is resorbed, ready to be remodeled. Osteoclasts resorb some of the dead bone. Osteoblasts lay down new woven bone. The process is repeated and the bone becomes weak. At this weakest stage the AVN will result in collapse. Remodeling is not enough to support the bone. Progressive collapse due to bone death, resorption, remodeling, and microfracture. AVN ends by final collapse, joint changes, and arthritis.
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Background music provided as a free download from RU-vid Audio Library.
Song Title: Every Step
6 сен 2024
