Avascular necrosis of the hip

Let’s talk about avascular necrosis of the femoral head in sickle cell disease.

Avascular necrosis (AVN) is one of the most common causes of chronic pain in sickle cell disease. We define it as bone death due to compromised blood supply.

The hip joint is at the forefront in this condition as it is the most commonly affected site of the body.

Necrosis of the head of the femur occurs when the sickled red blood cells occlude the only nutrient capillaries. It is not surprising that to understand that the distal portions of the bone near the joint are the areas with the maximal hypoxia, with almost no collateral circulation. So, when occlusion occurs, there is always no other way the affected bone part can get access to oxygen as well as other nutrients.

Risk factors include the sickle cell genotype, age, frequency of painful episodes, α-gene deletion, and the level of haemoglobin.

AVN affects about 10% of the people with sickle cell disease. About 50% of those with HbSS is affected by the age of 33. Having HbSS-α-thalassemia puts such people at the highest risk of developing avascular necrosis at a younger age.

Typically, a patient with AVN of the femoral head reports a chronic severe pain that is worse on walking, relieved by resting, associated with a limited range of motion in the affected hip when they try to bear weight on it.

Related article: Chronic complications of sickle cell disease: Universal definitions.

Up to 80% of the cases, avascular necrosis of the femoral head is bilateral, so examining both hip joints is paramount.

Management of avascular necrosis highly depends on the stage of the disease. There are four stages of avascular necrosis as adapted by the comprehensive sickle cell centre investigators based on radiographic findings, as portrayed in the figures below.

Avascular necrosis of the hip
Fig. 1: Stages of AVN of the hip.
source: European Society of Radiology
Classification of avascular necrosis of the femoral head
Fig. 2: Association Research Circulation Osseous Classification of AVN of the femoral head. source: Research Gate

Now that we’ve attained a brief understanding of what avascular necrosis of the femoral head is; let’s look at what the expert panel noted as the recommendations regarding its management.

  1. Evaluate all children and adults with sickle cell disease and intermittent or chronic hip pain for avascular necrosis by history, physical exam, radiography, and MRI as needed.
  2. Treat avascular necrosis with analgesics and consult physical therapy and orthopaedics for assessment and follow-up.
  3. Refer symptomatic patients with advanced stages of avascular necrosis to an orthopaedic surgeon and sickle cell disease specialist for evaluation and possible hip arthroplasty.

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