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Osteonecrosis

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Osteonecrosis

WHAT IS IT?

Necrosis is the death of any type of cell in an organism.

The femoral head is vascularised by some low-calibre vessels running into its neck. Circumstances decreasing the flow may lead to osteonecrosis or avascular necrosis (death of the bone). This situation may be provisional or permanent. In general, this situation tends to result in a collapse of the femoral head and arthrosis in the secondary hip.

CAUSES

The main cause of osteonecrosis is trauma injury (femoral head fractures, hip dislocations or surgical trauma injury such as that which may occur after hip arthroscopy).

Alcoholism, excessive use of steroids, hypertension, vasculitis, thrombosis, decompression sickness, vascular compression, rheumatic diseases, Sickle-cell anaemia or Gaucher disease are conditions which may also lead to avascular necrosis.

In a number of cases the cause may remain unknown and an aetiological diagnosis may not be made. In different studies it has been found that in 50% of cases it may be bilateral.

SYMPTOMS

In the early stages of necrosis, symptoms do not appear and only in the event of conducting an additional test, generally an MRI, for other reasons can this be diagnosed.

Once the bone necrosis is more advanced the symptoms, which are similar to those relating to hip arthrosis, tend to appear:

  • Groin and thigh pains
  • Stiffness and restricted mobility
  • Limping and muscular atrophy

These symptoms may all appear all of a sudden (as in the case of a heart attack) or gradually, as the area of the necrosis increases and there are greater changes to the articular cartilage.

DIAGNOSIS

Despite the fact that in the early stages of the evolution of the illness there are normally no symptoms and the diagnosis tends to be by chance or accidental, the most common case is to suspect its presence in patients reporting the clinical conditions outlined in the previous section.

Many of these patients are young adults. An age group which in theory is less frequently affected by arthrosis yet where there may be a risk history including cortico-steroid treatment and physical examination consistent with inter-articular hip-based pathologies.

When it is suspected that this is the pathology, the first diagnosis test could be a simple X-ray. Depending on the development stage of the osteonecrosis the X-ray may be completely normal, with slight changes in the involvement of the joint or even clear signs of arthrosis.

Magnetic Resonance Imaging is the most effective medical testing technique to diagnose osteonecrosis as even in stages with no symptoms or when these are detected using conventional radiology, MRI enables the pathology to be located and quantified. Furthermore, MRI is used to classify and calibrate the severity of the osteonecrosis.

TREATMENT

In early stages of the disease, where there has been no collapse (cartilage sinking down into the area of the necrotic bone) the patient may be observed and monitored regularly.

Symptomatic pain treatment may be performed using analgesic or non-steroidal anti-inflammatory medication. Modifying aggressive activity patterns and unloading physical exercise are part of the conservative treatment options.

In the event of diagnosing the exact cause of the osteonecrosis, specific treatments such as vasodilators, anti-coagulants, lipid reducers and even alendronate may be applied.

The natural history of the disease is unknown meaning that it is not clear whether surgical treatment should be offered to asymptomatic patients.

In cases where there are symptoms with mechanical characteristics, the probabilities of the osteonecrosis advancing increase exponentially. If this is not treated, in most cases the result will be the collapse of the femoral head.

From a surgical perspective, the chances of success, which is interpreted as the prevention or delay of the emergence of arthrotic changes, will depend on the condition of the femoral head at the time the diagnosis is performed. Here, the collapse is used as the cut-off point. When the collapse has already occurred, the success rate with any type of non-prosthetic surgical treatment sharply decreases.

Before the collapse occurs different techniques may be used to preserve the joint. The most popular is perforation of the necrotic area with or without a graft. This aims to reduce the intra-osseous pressure on the leading head and thus alleviate the pain.

Other techniques involve grafting the necrotic area in order to replace a dead bone with low load resistance with a live resistant bone. There are different techniques to perform this graft: from the trochanter, from a keyhole in the head through the cartilage. The Arthroscopic Surgery Unit has outlined and published a technique to clean the necrotic area and perform the graft using arthroscopic surgery without dislocating the hip. 

The use of osteotomy (cutting the bone) to reposition the femoral head such that the area bearing the load is a healthy area with no necrosis has also been described.

The outcome of the aforementioned surgery may vary according to many different factors such as patient type, body weight, the local area or the size of the necrotic area.

In the Arthroscopic Surgery Unit different techniques are applied, even on an arthroscopic basis, where in addition to the surgery itself a biological source with potential to repair is added through plasma rich in growth factors PRGF®-Endoret®. The aforementioned action aims to enhance the injured environment and to maximise the reparative capacity. All this is achieved due to the important anti-angiogenic (encouraging the formation of new blood flow) role of the growth factors.

When the collapse has already taken place and in cases where despite non-prosthetic surgical treatment having been performed or where following a positive outcome of the former, this has developed into a hip arthrosis, the only alternative is to replace the joint with a hip prosthesis.

There are different types and models of prostheses. One important prosthesis is the Surface Prosthesis which comprises a large metal head, inserted over the femoral head to avoid bone wear, and a socket part, which is inserted into the socket using pressure. A prosthesis which uses less bone for when it is subsequently replaced can be inserted in younger patients.

There are also conventional full prostheses which comprise one acetubular and another femoral implant, known as a rod, which is inserted into the femoral canal once it has been prepared. Both implants can be cemented (using biological polymethylmethacrylate cement) or non-cemented. Screws may be used to fasten the implants.

In recent years, small or short-rod prostheses have often been inserted.  These implants bring together a concept of anchoring similar to that of conventional femoral rods (nails) yet in a closer area (nearer to the neck) in an aim to save femoral bone for an eventual later change.


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