Introduction

Avascular necrosis of the femoral head is a pathological process resulting from interruption of the blood supply to the bone. It is due to traumatic or non-traumatic factors that compromise the circulation of the femoral head. This lack of circulation may be cephalic extraosseous (retinacular arteries) in post-traumatic necrosis, or due to intracephalic vascular processes in idiopathic necrosis. Ischemia in the femoral head results in death of the bone marrow and osteocytes and ending in collapse of the necrotic segment.

It is very important to separate pathogenesis with respect to the etiology of this disease. The understanding of the pathogenesis is very necessary to decide the type of treatment to be used.

To date, there are four theories on the subject:

Bone infarction theory: this is the most accepted theory in the pathogenesis of the disease, some define it as the "coronary disease of the femoral head". In a wide variety of circumstances the blood supply to the anterolateral segment of the femoral head is affected which causes cell death and necrosis. This occlusive episode occurs in a short period of time like myocardial infarction.

1. Theory of fat embolism: many authors now raise the importance of fat embolism in pathogenesis. This is confirmed by the presence of fatty microemboli in the blood vessels of the femoral head and the association between non-traumatic avascular necrosis and lipid metabolism diseases.

2. Theory of the accumulation of stress cells: this is a theory of multifactorial origin. Since avascular necrosis of the femoral head can be associated with other diseases such as chronic renal insufficiency, alcoholism, organ transplantation, haemoglobinopathies, rheumatological diseases such as systemic lupus erythematosus, metabolic-hormonal abnormalities, neoplastic diseases, among others, all have as a common denominator the formation of diseased cells.

3. Theory of progressive ischemia: this theory is based on the increase in intraosseous pressure, which causes a progressive decrease in the light from the blood vessels inside the femoral head, especially the venous sinusoids, increasing peripheral resistance.

The treatment of osteonecrosis of the femoral head is a major problem today. No single or combined method has been shown to prevent the progression of this disease. The natural history of osteonecrosis of the femoral head consists of the presence of sclerosis and osteochondral fractures, which leads to the production of collapse and osteoarthritis of the hip.

The conservative treatment of this disease has a very poor result when compared to surgery, which even so its results are not entirely favorable in all cases. Conservative treatment modalities include suspension of support, pharmacological treatment, hyperbaric oxygenation and electrical stimulation.

The varieties of surgical treatment are applied for the initial stages as well as for the more advanced ones. In the initial stage techniques such as perforation or trepanation of the femoral head are indicated, once collapse occurs other techniques are indicated such as osteotomies of the proximal metaphysis of the femur, Merle technique D´ Aubigne, hemiarthroplasty with cup or prosthesis and total hip arthroplasty.