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Hip avascular necrosis is one of the common causes of musculoskeletal disability. It results from decreased blood supply to the head of femur which leads to death of the bone tissue.

Introduction to Hip avascular necrosis

There may be tiny breaks in the bone and in the advanced state the head of femur may collapse leaving the hip joint non-functional. The patients with hip avascular necrosis may be asymptomatic to begin with, but the condition gradually progresses leading to destruction of joint which may require total hip replacement. Hip avascular necrosis alone account for almost 10% of the nearly 500,000 total hip replacement surgeries performed in the USA every year. It is a challenging situation as far as diagnosis and treatment is concerned.
 

Causes of hip avascular necrosis

Fundamental cause of avascular necrosis is decreased blood supply to the bone. It may result from many conditions such as trauma, narrowing of blood vessels and pressure inside the bone.

Trauma to hip joint or the neck of femur can damage the vessels around and the blood supply decreases. When the blood supply is not sufficient for prolonged period the bone tissue dies and their normal structural integrity is broken.
 

Hip avascular necrosis risk factors

Prolonged uses of corticosteroid and alcohol consumption are the major risk factors. Besides there are many other risk factors as following:

  • Diabetes
  • HIV
  • Lupus
  • Sickle cell anemia
  • Dialysis
  • Decompression sickness (Caisson disease)
  • Hemoglobinopathies
  • Gaucher disease
  • Irradiation
  • Hemophilia
  • Hypercoagulable

How it develops?

There is no single agreed theory which could explain the mechanism of its development. It most likely results from thrombosis or embolization in the bone. It means small debris get accumulated in the affected area and block the blood flow. Another theory postulates that vasculitis, radiation necrosis, or the release of vasoactive substances result into structural derangement and vasculopathy. Another explanation is increased intraocious pressure due to enlargement of intramedullary fat cells or osteocytes lead to necrotic changes. It is generally agreed that more many factors contribute to decreased blood supply, necrosis and collapse of head of femur. All the factors responsible for hip avascular necrosis may be located in two anatomical locations viz. intravascular and extravascular. It may affect a small area in the bone and may remain unnoticed and on the other extreme it may destroy the whole of the joint.
 

Symptoms of hip avascular necrosis

 

Pain and restricted movement are two main symptoms of hip avascular necrosis. The pain may remain confined to the joint or it may radiate to groin, thigh or knee. As the condition progresses there may be limp while walking and stiffness. It may also remain asymptomatic, especially in the early stages of the disease. In the advanced stage pain may be present even at rest and the patient may not be able to walk on the affected limb.
 

Diagnosis of hip avascular necrosis

In the diagnosis of hip avascular necrosis history and physical examination are the first step. In the cases suggestive of avascular necrosis, a thorough evaluation of patient profile, including occupation, habits, presence of one or more risk factor is required. X-ray and MRI play an important role and bone scan may also be used but MRI has proved to be superior to bone scan. X-ray may be normal in the early stage but in later stage it shows bone changes clearly. MRI is more sensitive and can detect the disease in its early stage.
 

Complications hip avascular necrosis

The condition continues to deteriorate if left untreated. The bone becomes week and fragile which may eventually collapse. The symptoms worsen with time. It further restricts movement because of associated pain and structural damage. Within two to five years the condition becomes very severe and disability sets in.
 

Treatment of hip avascular necrosis

The treatment for hip avascular necrosis is generally aimed at prevention of further loss and restores function as much as possible. The extent of bone damage determines the treatment. In the early stages patient may benefit from conservative treatment but surgical intervention is main stay of treatment in the latter stage. In general conservative treatment has poor prognosis.
 

Conservative treatment

Rest and reduced weight bearing help in prevention of further damage and exercise improve joint movement.
 

Medications

Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin or ibuprofen (Advil, Motrin), are useful for pain and swelling which are almost always associated the condition.

Bisphosphonates such as alendronate (Fosamax) which are generally prescribed for osteoporosis may slow the progression of the disease.
 

Read More: Hip Dysplasia - An Overview

Surgical treatment of hip avascular necrosis

Core decompression or bone marrow decompression:

It is a widely used technique in which the inner layer of the bone is removed. This technique is more effective when the involvement of femoral head is less than 30%. In this operation one or more than one holes are made through the neck of femur to reach to the area of poor blood supply. Thus it reduces pressure from within the bone and thus relieves pain and discomfort and allows space for new blood vessels to grow in the affected area.

Other surgical procedures are bone transplant or bone grafting, osteotomy or reshaping of bone and joint transplant.

Bone grafting

In bone grafting healthy bone from other part of the body are prepared and placed in the affected area. It replaces the dead bone and allows the area to heal. Bone grafting may be done alone or in combination with core decompression.

Osteotomy

In osteotomy the bone is reshaped in such a way that reduces the stress on the affected area.

Joint replacement

In the advances stage when the head of femur is compressed and or other procedures are not useful, joint replacement may be useful. In this procedure diseased parts are completely removed and an artificial joint structure replaces the femoral head and the socket.

Rehabilitation

Surgical intervention alone is not sufficient. The patient needs to work out with physical therapist to achieve maximum functional recovery. It is advisable to use a walker or crutches and avoid all the weight bearing on the joint. After hip joint replacement surgeries in addition to the usual physical therapy patient also need to learn to adjust to the artificial joint. 

  • emedicine.medscape.com/article/386808-overview
  • www.mayoclinic.com/health/avascular-necrosis/ds00650
  • www.upmc.com/Services/sportsmedicine/injuries/hip/Pages/avascular-necrosis.aspx
  • www.eorthopod.com/content/avascular-necrosis-hip