Avascular Necrosis of the Hip

What is avascular necrosis of the hip?

The term “osteonecrosis” means the death of bone tissue caused by interruption of its blood supply. The femoral head — the spherical “ball” of the hip joint — is particularly vulnerable to this condition, because its blood supply depends on a relatively “fragile” network of vessels.

When the blood supply is interrupted, the bone cells of the femoral head die and the bone progressively weakens. As the necrotic bone loses its strength, the spherical surface of the head is at risk of “collapsing” — that is, of losing its normal shape. Once this collapse occurs, the joint no longer functions smoothly and a rapid course towards severe arthritis begins.

Causes and risk factors

Avascular necrosis of the hip may be primary (with no clear cause) or, more often, associated with certain risk factors:

• Long-term corticosteroid therapy
• Excessive alcohol intake
• Trauma to the area (e.g. femoral neck fractures or hip dislocation, which disrupt the blood supply)
• Certain blood disorders and metabolic disorders
• Decompression sickness (divers’ disease)
• Certain systemic diseases

Avascular necrosis often affects younger patients (30–50 years of age) and, in a considerable number of cases, may be bilateral. The presence of a risk factor does not mean that the disease will definitely develop, while in a proportion of patients no clear cause is identified.

Clinical picture – Symptoms

The main symptom is pain, which:

• Is felt in the groin and may radiate to the thigh or the buttock.
• Often appears without any previous injury.
• Worsens with weight-bearing and walking.
• May also occur at rest or at night, in more advanced stages.

In the early stages, symptoms may be mild or intermittent. As the disease progresses, and especially after collapse of the head, the pain becomes severe and constant, with marked restriction of movement.

Diagnosis and stages

Early diagnosis is decisive for the prognosis. Radiographs (X-rays) may be normal in the very early stages, which is why MRI is the investigation of choice: it reveals the necrosis very early, before radiographic changes or collapse appear, and assesses the extent of the lesion.

The disease is staged according to its progression: from the early stages (necrosis without collapse of the head, where the joint retains its shape) to the advanced stages (collapse of the femoral head and development of arthritis). The stage largely determines the treatment approach — the earlier the diagnosis, the more joint-preserving options there are.

How avascular necrosis progresses

Understanding the progression explains why time is so critical. The process begins with the interruption of the blood supply to a segment of the femoral head. In this phase the bone begins to die, but the spherical surface of the head remains intact — symptoms may be mild.

As the necrotic bone weakens, it loses its ability to withstand load. At this critical point, the spherical surface is at risk of “collapsing” — of losing its normal shape. Once collapse occurs, the damage becomes irreversible: the smooth surface is permanently lost and a rapid course towards severe arthritis begins. It is precisely this sequence — necrosis, weakening, collapse, arthritis — that makes early diagnosis so valuable.

Bilateral involvement and follow-up

A particular feature of avascular necrosis — especially when it is associated with systemic risk factors, such as corticosteroid therapy — is that it can affect both hips. For this reason, when avascular necrosis is diagnosed in one hip, the other is often examined as well, even if it is asymptomatic, since early detection allows timely treatment.

Regular follow-up — with clinical reassessment and imaging — is important for assessing the progression of the disease and for making timely treatment decisions, especially in younger patients, in whom saving the joint is a priority.

Treatment

Treatment is tailored to the stage, the extent of the necrosis, and the age and general condition of the patient.

Joint-preserving techniques (early stages)

In the early stages, before collapse of the head, the aim is to save the natural joint. The main technique is core decompression (drilling): the creation of one or more channels into the necrotic area, in order to decompress it, relieve pain and stimulate restoration of the blood supply. This method can halt the progression of the disease in appropriately selected, early cases. It is accompanied by protected weight-bearing on the affected leg and medication.

Total hip replacement (advanced stages)

When the femoral head has already collapsed and arthritis has developed, the indicated solution is total hip replacement. Dr. Tsarouhas uses the modern, minimally invasive ASI method (Anterior Supine Intermuscular), which offers faster recovery and a lower risk of dislocation — a particularly important advantage for the often younger patients with avascular necrosis.

Why early diagnosis matters

Avascular necrosis of the hip is a condition in which time is of decisive importance. In the early stages, before the femoral head collapses, joint-preserving techniques (such as core decompression) can halt the progression and protect the natural joint. Once the head has collapsed, however, the damage becomes irreversible and hip replacement remains the only solution.

For this reason, sudden, unexplained groin pain in a younger patient — especially one with risk factors, such as corticosteroid therapy — should not be ignored, but investigated promptly with MRI.

Cost of treatment

The cost depends on the stage and the type of treatment (core decompression or hip replacement), the materials, the hospital and the class of room, as well as the insurance cover. In most cases, private insurance policies and insurance funds cover a significant part of the expense.

Precise information is given on an individual basis, after the clinical assessment. The practice is at your disposal for any relevant information.

More on the factors that determine the cost and on cover by insurance funds: Cost of surgery.

The role of rehabilitation

Rehabilitation after treatment for avascular necrosis depends on the type of treatment. After core decompression, weight-bearing is initially reduced, to give the bone time to recover. After hip replacement with the ASI method, rehabilitation is rapid, thanks to the preservation of the muscles.

In every case, the physiotherapy programme focuses on maintaining range of motion, strengthening the muscles and gradually restoring gait. Treating the underlying risk factors — where present — is just as important as the local treatment, since it can influence the course of the disease and also protect the other hip.

When pain should be investigated

Avascular necrosis of the hip is one of the conditions in which early investigation of pain makes an enormous difference. Particularly in younger patients with risk factors — such as long-term corticosteroid therapy or excessive alcohol intake — persistent or sudden groin pain should not be ignored.

Since radiographs may be normal in the early stages, MRI is the appropriate tool for early detection. It is diagnosis before collapse of the femoral head that opens the way to joint-preserving techniques — which is why time matters so much.

Frequently asked questions

What causes avascular necrosis of the hip?

It is caused by interruption of the blood supply to the femoral head. It may be primary or associated with factors such as long-term corticosteroid therapy, excessive alcohol intake or trauma.

Which patients does it affect?

It often affects younger patients (30–50 years of age) and in a considerable number of cases may be bilateral.

How is it diagnosed?

MRI is the investigation of choice, as it reveals the necrosis very early, when radiographs are still normal.

Can hip replacement be avoided?

In the early stages, before collapse of the head, core decompression (drilling) can halt the progression and save the natural joint. Once the head has collapsed, hip replacement becomes the indicated solution.

What is core decompression?

It is a joint-preserving technique in which channels are created in the necrotic area to decompress it and stimulate the blood supply. It is used in the early stages.

Is the cost covered by insurance?

In most cases, private insurance policies and insurance funds cover part or all of the expense. The practice can give you detailed information.

Is avascular necrosis the same as arthritis?

No. In arthritis the problem starts with wear of the cartilage, whereas in avascular necrosis it starts with interruption of the blood supply to the bone beneath the cartilage. The distinction is important, as it affects treatment.