Avascular Necrosis (AVN) also known as aseptic necrosis or osteonecrosis is a disease of impaired blood flow to bone especially around joint. It commonly affects young people in 3rd to 5th decade. The commonest site of affection is the femoral head. It is a progressive disease which if left untreated leads to complete deterioration of the hip joint. The disease is an end condition that results from multiple causes. The list of causes is long and include alcohol abuse, systemic steroid use, sickle cell anemia, Gout, renal osteodystrophy, Gaucher’s disease and conditions associated with release of a blood clotting factor thromboplastin, like pregnancy, inflammatory bowel disease and malignant tumors. However, in many a cases, the cause cannot be determined; these patients are then labeled as suffering from idiopathic Osteonecrosis (AVN). These patients are most likely to be suffering from an unknown blood clotting disorder.
The pathology of the disease lies in blocking of microcirculation of the femoral head either due to a clot in the vessels or due to raised pressure in the head which causes extrinsic compression of the vessels.
Symptoms: A prompt diagnosis helps in early treatment and may lead to favourable outcome. Thus a high index of suspicion by treating physician is necessary, especially if you have one of the risk factors associated with the disease. The most common complaint is a deep pain in the groin. On examination, your doctor may not find any significant clinical sign and thus the history may be only clue towards the diagnosis. In advanced stages of the disease however, there may be pain on internally rotating the hip, click sounds or restriction of the movements of the hip joint.
Diagnostic Tests:
Radiographs: X Rays are the first step in diagnosis of this condition. They are usually taken in two different planes – Anteroposterior and a frog lateral position. The doctor may be able to see some cysts, sclerosis, or collapse of the head depending on the stage of your disease.
Magnetic Resonance Imaging (MRI): It is the most sensitive and specific test for diagnosing the condition. It is necessary not only to make a diagnosis, but to assess the extent of involvement and evaluate the progression and response to treatment. It is very important to get an MRI done when one hip shows changes of this disease on X rays, as the disease is often bilateral. The detection of the disease in opposite hips in early stage is mandatory as most treatment are successful in the early stages.
Treatment:
A number of classification systems have been developed and they are useful in determining the appropriate treatment. The most common system used is called as ‘Ficat and Arlet’ which has four stages, stage IV being the most advanced stage. The treatment is divided in two groups – one in which the femoral head can be preserved and the other where the femoral head needs to be replaced with an artificial joint. Usually in the early stages the femoral head can be preserved (salvaged) but in late stages the replacement of the joint is the only solution.
Head preserving Methods:
Core Decompression: Core decompression of the head is currently the most common surgical procedure performed in early stage of the disease. It involves creating a tract(s) in the femoral head using a single large drill or multiple small drills. The creation of the tract is believed to relieve the pressure inside the femoral head and increase the blood flow to the area. The procedure needs to be done with help of image intensifier machine that takes the radiograph inside the operation theater. It is necessary so as to ensure that tract made reaches the segment which is dead or is devoid of the blood supply. It is a relatively a small procedure when compared with other procedure and if done well, it has shown to stop progression in 60 -100% cases in stages I and II.
Bone Grafting: In this procedure bone is taken from iliac crest (bone forming pelvis) and placed in the area where the bone is dead. The resulting procedure results not only in decompression or removal of the dead bone but by replacing it with bone from other part of the body, new bone formation is promoted and some degree of structural support is provided.
Vascularised Fibular Grafting: Fibula is one of the two bones of your leg. About two third of this bone can be safely removed as the other bone tibia is the main weight bearing bone. In this procedure this bone is taken with its blood vessels and inserted in the area where there is dead bone. The vessels are then joined (anastomosed) to blood vessels present locally. This helps to improve the blood supply to the region and to the bone graft.
Osteotomies: Osteotomy refers to cutting the bone. In this surgery, the alignment of the bones forming are changed, this helps to reduce the weight bearing stress in the affected region. This surgery however has reported success from very few centres which are doing this procedure routinely.
Head Replacing Measures: There are currently two basic surgery options available, a total hip replacement or a hip resurfacing.
Resurfacing: Resurfacing involves removal and replacement of femoral head with a hollow metal hemisphere which fits into the acetabulum cup. This technique preserves the femoral bone, maintains normal femoral loading and stresses.
Advantages of Hip Resurfacing
- Femoral head is preserved.
- Femoral canal is preserved and no associated femoral bone loss with future revision. Also, the risk of microfracture of femur with uncemented stem implantation is eliminated.
- Larger size of implant "ball" reduces the risk of dislocation significantly.
- Stress is transferred in a natural way along the femoral canal and through the head and neck of the femur. With the standard THR, some patients experience thigh pain as the bone has to respond and reform to less natural stress loading.
- Use of metal rather than plastic reduces osteolysis and associated early loosening risk.
- Use of metal has low wear rate with expected long implant lifetime.
Special Requirements/Risks of Resurfacing Patients
- Solid bone in femoral head to hold resurfacing component. A few cysts or slight AVN collapse may be acceptable.
- Healthy kidneys to process any bloodborne metal ions from debris products.
- Lack of long-term track record. Current device has only been used for about 10 years. Despite known low wear rate, longevity and longterm effects of wear debris are unknown
Total Hip replacement: A total hip replacement, THR, has been the gold standard for many years. It is major surgery that often results in a long post-op recovery and often limits your activities depending on the type of hip device that has been used in the surgery. A total hip replacement means that the top portion of your femur bone will be removed, the remaining bone will be drilled and a device with a long stem will be placed into the bone. The stem is secured with bone cement or secured with a press-fit augmented by a surface coating on the prosthesis which encourages either bone ingrowth (osseointegration) or induces bone growth up to the prosthesis (osseoinduction) which further improves the quality of the press-fit. A cup will be placed in the acetabulum of the hip to provide a pivoting surface for the ball of the femur device.
A THR is expected to last between ten and fifteen years. About 1% per annum fails in the first ten years for a variety of reasons, but 90% can expect to reach ten years. Thereafter, the failure rate increases sharply so that by fifteen years 75% will have failed, usually because of a combination of wear and loosening from the bone.
The three main complications of hip replacement surgery are dislocation, thrombosis and infection. Dislocation occurs when the ball comes out of the socket. It can occur if the components are incorrectly aligned, if either of the components or the bones can touch (impinge) or if there is a muscle imbalance about the hip. It is corrected by manipulation. The risk of dislocation is less than 1%. Thrombosis is a high-risk complication, but the risk is greatly reduced by the appropriate measures. Infection is potentially a very serious complication in a THR. Many special precautions are taken during joint replacement surgery to reduce the risk. The risk is again less than 1%.
Newer methods (yet not conclusively Proven)
Drugs: Most of the medical management revolves around increasing the blood flow to the head by giving antiplatelet agents or vaso dilators. A new group of drugs called as biphosphonates (Alendronate) has shown to prevent progressive bone resorption and bone collapse by certain centres. None of these studies have however shown any reversal in the progression of disease by these drugs.
Stem Cell and Bone morphogenic proteins: With all the hype surrounding the stem cell, there is still hope with this new technology which is set revolutionize treatment of most medical disorders. The stem cell from a persons own body are now routinely being used to increase the new bone formation in early stages of the disease. When this is combined with a newer molecule called as Bone morphogenic protein, the results have been shown to be even better. While implanting the stem cell from ones own body is not very expensive, Bone morphogenic protein (BMP) is a very expensive molecule that needs to be imported. When cost however is not an issue the combination of core decompression, stem cells and BMP may be the best option to prevent the disease progression in stage I and II of the disease.
Alternative Medicine: While it is a commonly seen that people prefer alternative medicine when told that there is no cure for a particular disease, there is non conclusive evidence from any of these medical branch that has conclusively shown a cure or reversal of this disease. At the most the patients experience symptomatic relief for few years, however, unfortunately often this results in the golden period during which smaller surgical intervention that can arrest progression getting lost and often the patient has to undergo a head replacement surgery.