AVNS

`Avascular Necrosis

Introduction
Avascular necrosis is a disease resulting from the temporary or permanent loss of the blood supply to the bones. Without blood, the bone tissue dies and causes the bone to collapse. If the process involves the bones near a joint, it often leads to collapse of the joint surface. This disease also is known as osteonecrosis, aseptic necrosis, and ischemic bone necrosis.
Avascular necrosis usually affects people between 30 and 50 years of age; about 10,000 to 20,000 people develop avascular necrosis each year.
A etiology and pathogenesis
Sites which are peculiarly vulnerable to ischemic necrosis are the femoral head, the femoral condyles, the head of the humerus, the capitulum, and the proximal parts of the scaphoid and talus.
These subarticular regions lies at the most distant parts of the bones vascular territory and they are largely enclosed by cartiage giving restricted access to local blood vessels. The subcondral trabeculae are further compromised in that they are sustained largely by the system of end arterioles with limited collateral connections.
Another factor which needs to be taken into account is that the vascular sinusoids which nourish the marrow and the bone cells unlike arterial capillaries have no adventitial layer and there patency is determined by the volume and pressure of the surrounding marrow tissue which itself is encased in unyielding bone. The system functions essentially as a closed compartment within which one element can expand only at the expense of the others. Local changes such as decreased blood flow, hemorrhage or marrow swelling can therefore rapidly spiral to a vicious cycle of ischemia, reactive oedema or inflammation, marrow swelling, increased intraosseous pressure and further ischemia.
The process described above can be initiated in at least four different ways ( 1 ) severance of local blood supply ( 2 ) venous stasis and retrograde arteriolar stoppage ( 3 ) intravascular thrombosis ( 4 ) compression of capillaries and sinusoids by marrow swelling. Ischemia in the majority of cases is due to a combination of several of these factors.

Causes

Traumatic osteonecrosis
In traumatic osteonecrosis the vascular anatomy is particularly important. In fractures and dislocations of the hip the retinacular vessels supplying the femoral head are easily torn. If in addition, there is damage to or thrombosis of the ligamentum teres osteonecrosis is inevitable. Displaced fractures of the femoral neck are complicated by osteonecrosis in over 20% of cases. Undisplaced fractures or lesser injuries also some times result in subchondral necrosis, this may be due to thrombosis of intra-osseous capillaries or sinusoidal occlusion due to marrow oedema.
Other injuries which are prone to osteonecrosis are fractures of scaphoid and talus. Significantly it is always the proximal fragment which suffers. This is because the principle vessels enter the bones near their distal ends and take an intra-osseous course from distal to proximal.

Non-traumatic osteonecrosis

1- Infection e.g Osteomeylitis and septic arthritis.
2- Haemoglobinopathy e.g Sickle cell disease
3- Storage disorders e.g Gauchers disease.
4- Coagulation disorders e.g Familial thrombophilia, Hypofibrinolysis, Hypolipoproteinaemia.
5- Other such as perthes disease, cortisone administration, alcohol abuse, SLE, anaphylactic shock and ionizing radiation.

Steroid Medications

Corticosteroids such as prednisone are commonly used to treat diseases in which there is inflammation, such as systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, and vasculitis.

Alcohol Use

causes of nontraumatic avascular necrosis. In people who drink an excessive amount of alcohol, fatty substances may Excessive alcohol use and corticosteroid use are two of the most common block blood vessels, causing a decreased blood supply to the bones that results in avascular necrosis.
Sickle cell disease
It is a genetic disorder in which the red cells contain abnormal haemoglobin ( Hbs ). In deoxagenated blood there is increase aggregation of the haemoglobin molecules and distortion of the red cells which become some what sickle shape. At first this is reversible when he blood is oxegenated. Eventually the red cell membrane becomes damage and the cells permanently deformed.
Clinical features
Children during the first 2 years of life may present with swelling of the hands and feet, x-ray at first seems normal, but later there is suggestive features such as marrow densities and periosteal new bone formation. In older children atypical features is recurrent episodes of sever pain associated with fever. These crises which may affect almost any part of the body are thought to be due to infarcts.
Osteonecrosis of femoral head is common both in children and young adult which some times mistaken for Perthes disease.
Gauchers disease
In this familial disorder lack of specific enzyme result in the abnormal storahe of glucocerebroside in the macrophage of the reticuloendothelial system. The effects are seen chiefly in the liver, spleen and bone marrow where the large polyhedral cell ( Gaucher cells ) accumulate. Bone complications are common and osteonecrosis is the worst. The hip is the most commonly affected but lesions also appear in the distal femur, talus and and the head of the humerus.
Radiation necrosis
Ionization radiation if sufficiently intense or prolonged may cause bone death. This is due to the combined effects of damage to small blood vessels, marrow cells and bone cells. Such changes which are dose related often occurred in the past when low energy radiation was in use. Nowadays with megavoltage apparatus technique long term bone damage is much less likely. Areas affected are mainly the shoulder and ribs ( after external irradiation for breast cancer, the sacrum, pelvis and hip ( after irradiation of pelvic lesions and the jaws ( after treatment of tumours around the head and neck.

Symptoms of avascular necrosis

In the early stages of avascular necrosis, patients may not have any symptoms. As the disease progresses, however, most patients experience joint pain--at first, only when putting weight on the affected joint, and then even when resting. Pain usually develops gradually and may be mild or severe. If avascular necrosis progresses and the bone and surrounding joint surface collapse, pain may develop or increase dramatically. Pain may be severe enough to limit the patient's range of motion in the affected joint. The period of time between the first symptoms and loss of joint function is different for each patient, ranging from several months to more than a year.
Diagnosis


After performing a complete physical examination and asking about the patient's medical history , the doctor may use one or more imaging techniques to diagnose avascular necrosis. As with many other diseases, early diagnosis increases the chances of treatment success.
It is likely that the doctor first will recommend a radiograph, commonly called an x ray. X rays can help identify many causes of joint pain, such as a fracture or arthritis. If the x ray is normal, the patient may need to have more tests. Research studies have shown that magnetic resonance imaging, or MRI, is the most sensitive method for diagnosing avascular necrosis in the early stages.

X Ray

An x ray is a common tool that the doctor may use to help diagnose the cause of joint pain. It is a simple way to produce pictures of bones. The x ray of a person with early avascular necrosis is likely to be normal because x rays are not sensitive enough to detect the bone changes in the early stages of the disease. X rays can show bone damage in the later stages, and once the diagnosis is made, they are often used to monitor the course of the condition.

Magnetic Resonance Imaging (MRI)

MRI is quickly becoming a common method for diagnosing avascular necrosis. Unlike x rays, bone scans, and CT (computed/computerized tomography) scans, MRI detects chemical changes in the bone marrow and can show avascular necrosis in its earliest stages. MRI provides the doctor with a picture of the area affected and the bone rebuilding process. In addition, MRI may show diseased areas that are not yet causing any symptoms.
Bone Scan
Also known as bone scintigraphy, bone scans are used most commonly in patients who have normal x rays. A harmless radioactive dye is injected into the affected bone and a picture of the bone is taken with a special camera. The picture shows how the dye travels through the bone and where normal bone formation is occurring. A single bone scan finds all areas in the body that are affected, thus reducing the need to expose the patient to more radiation. Bone scans do not detect avascular necrosis at the earliest stages.

Computed/Computerized Tomography

A CT scan is an imaging technique that provides the doctor with a three-dimensional picture of the bone. It also shows "slices" of the bone, making the picture much clearer than x rays and bone scans. Some doctors disagree about the usefulness of this test to diagnose avascular necrosis. Although a diagnosis usually can be made without a CT scan, the technique may be useful in determining the extent of bone damage.
Biopsy
A biopsy is a surgical procedure in which tissue from the affected bone is removed and studied. Although a biopsy is a conclusive way to diagnose avascular necrosis, it is rarely used because it requires surgery.
Treatment

Appropriate treatment for avascular necrosis is necessary to keep joints from breaking down. If untreated, most patients will experience severe pain and limitation in movement within 2 years.
Several treatments are available that can help prevent further bone and joint damage and reduce pain. To determine the most appropriate treatment, the doctor considers the following aspects of a patient's disease:
The age of the patient
The stage of the disease--early or late
The location and amount of bone affected--a small or large area
The underlying cause of avascular necrosis--with an ongoing cause such as corticosteroid or alcohol use, treatment may not work unless use of the substance is stopped.
The goal in treating avascular necrosis is to improve the patient's use of the affected joint, stop further damage to the bone, and ensure bone and joint survival. To reach these goals, the doctor may use one or more of the following treatments.
Conservative Treatment
Medicines--to reduce fatty substances (lipids) that increase with corticosteroid treatment or to reduce blood clotting in the presence of clotting disorders. Nonsteroidal anti-inflammatory drugs may also be prescribed to reduce pain.
Reduced weight bearing--If avascular necrosis is diagnosed early, the doctor may begin treatment by having the patient remove weight from the affected joint. The doctor may recommend limiting activities or using crutches. In some cases, reduced weight bearing can slow the damage caused by avascular necrosis and permit natural healing. When combined with medication to reduce pain, reduced weight bearing can be an effective way to avoid or delay surgery for some patients.
Range-of-motion exercises--may be prescribed to maintain or improve joint range of motion.
Electrical stimulation--to induce bone growth.
Surgical Treatment
Core decompression--This surgical procedure removes the inner layer of bone, which reduces pressure within the bone, increases blood flow to the bone, and allows more blood vessels to form. Core decompression works best in people who are in the earliest stages of avascular necrosis, often before the collapse of the joint. This procedure sometimes can reduce pain and slow the progression of bone and joint destruction in these patients.
Osteotomy--This surgical procedure reshapes the bone to reduce stress on the affected area. There is a lengthy recovery period, and the patient's activities are very limited for 3 to 12 months after an osteotomy. This procedure is most effective for patients with advanced avascular necrosis and those with a large area of affected bone.
Bone graft--A bone graft may be used to support a joint after core decompression. Bone grafting is surgery that transplants healthy bone from one part of the patient, such as the leg, to the diseased area. Commonly, grafts (called vascular grafts) that include an artery and veins are used to increase the blood supply to the affected area. There is a lengthy recovery period after a bone graft, usually from 6 to 12 months. This procedure is complex and its effectiveness is not yet proven.
Arthroplasty/total joint replacement--Total joint replacement is the treatment of choice in late-stage avascular necrosis and when the joint is destroyed. In this surgery, the diseased joint is replaced with artificial parts. It may be recommended for people who are not good candidates for other treatments, such as patients who do not do well with repeated attempts to preserve the joint. Various types of replacements are available, and people should discuss specific needs with their doctor.


Complications
The natural history of AVN involves subchondral necrosis, subchondral fracture and collapse of bone, deformity of the articular surface, and osteoarthritis.
In later stages, sclerosis and total destruction of the joint may occur.
.Nonunion of fracture and secondary muscle wasting are potential complications.
Prognosis
Prognosis depends on the disease stage at the time of diagnosis and on any underlying conditions.
More than 50% of patients require surgical treatment within 3 years of diagnosis.
Half of patients with subchondral collapse of the femoral head develop AVN in the contralateral hip.
Poor prognostic factors include the following:

Age older than 50 years

Advanced disease (stage 3 or worse) at the time of diagnosis
Necrosis of more than one third of the weight-bearing area of the femoral head on MRI
Lateral involvement of femoral head (compared to medial lesions)
Nonmodifiable risk factors such as cumulative dose of corticosteroids (corticosteroid-induced AVN)