Avascular necrosis also called osteonecrosis, refers to a painful condition which results from lack of blood supply to bone tissue gradually leading to bone death, collapse of the bone, collapse of articular cartilage covering the bone and finally to disabling arthritis.
Blood flow to the bone may be adversely affected from damage to the blood vessels due to an injury, blockage by air or fat embolism in the blood vessels or by inflammation of the walls of the blood vessels. Injury to the bone is the main cause of avascular necrosis. Other possible causes include use of corticosteroid medications, excessive consumption of alcohol, and excess pressure inside the bone.
Though it can affect any bone, the ends of the thigh bone (femoral heads) are most commonly involved. Avascular necrosis does not show any symptoms in the initial stages of the disease but as it progresses, patients complain of pain and stiffness in the affected joint. Pain may be mild but can become worse at night or following physical activity. Sometimes pain may be so severe that range of motion of the joint will be restricted.
The patients of avascular necrosis are mostly young men below 50 years of age (average age-36 years). In USA, 15,000 new patients of avascular necrosis are added every year. If left untreated 80% of femoral heads of these patients will collapse in 1 to 5 years and lead to severe arthritis of the affected joint. Early treatments are associated with better outcomes of treatment procedures.
Non-surgical treatment involves the use of anti-inflammatory medications to relieve pain, blood thinning agents to reduce blood clots affecting blood flow, and cholesterol lowering agents to reduce fat deposition. The doctor may advise to restrict activities and to use crutches to reduce weight bearing. Range of motion exercises may also be recommended. Stimulation with pulsed electromagnetic fields (PEMFs) or electrical current has been shown to be useful for enhancing bone repair and for exerting a chondroprotective effect on articular cartilage in the early stages of the disease and may also be recommended.
Non-surgical treatments usually relieve pain and delay the time until joint replacement becomes necessary. However, surgical treatment options are most successful especially when avascular necrosis is diagnosed in the very early stages prior to femoral head collapse.
There are several surgical treatment options available to treat avascular necrosis. These include the following:
Core decompression: It is the most commonly performed procedure for osteonecrosis in the last three decades. Core decompression is a minimally invasive procedure. It is safe and has low complication rates. Core decompression delays the need for total hip arthroplasty and does not change the anatomy to compromise THA. However, outcome of core decompression is better when avascular necrosis is in the initial stage that when the lesions are small and bone is in the pre-collapse stage. During core decompression, one large hole or several smaller holes are drilled into the inner core of the bone to reduce pressure inside the bone (intraosseous). This also reduces the edema and increases the blood flow by creating channels for new blood vessels to nourish the affected areas of the bone providing significant pain relief.
Core decompression may also be combined with the following additional treatments to improve the outcome and preserve the joint longer. These procedures may include:
Non-vascularized grafts: Non-vascularized grafts may include autograft, allograft or demineralized bone matrix which is transplanted into a hole created in the affected bone. Although the uses of non-vascularized grafts have shown improved outcome scores, it is associated with extensive dissection and problems due to the use of an allograft or autograft. Moreover, only few results are available with studies being done only in small populations on the use of non-vascularized grafts in combination with core decompression.
Vascularized bone grafts: Vascularized bone grafts involve a segment of bone which is taken from another bone such as fibula or iliac crest bone along with its blood supply (an artery and vein). Like non-vascularized grafts, vascularized bone graft is also transplanted into a hole created in the affected bone by core decompression.
The disadvantages associated with vascularized bone grafts for avascular necrosis of femoral head may include donor site morbidity such as numbness, weakness and ankle pain. Heterotrophic ossification and trochanteric tenderness may also occur. Moreover, it may make THA more difficult.
Other treatments that may be used with core decompression may include cementation, tantalum rods and adjuvant therapy such as electrical or electromagnetic stimulation.
Usually, reconstruction and repair of the necrotic lesion is incomplete after core decompression. The dead bone may be replaced by living bone but osteogenic potential for repair is low in osteonecrosis patient. The biology of osteonecrosis reveals that it is not the necrosis per se but the resorptive component of the repair process that leads to collapse of the affected bone. Thus, the treatment should also involve procedures that promote bone and cartilage regeneration.
Doctor improves the outcome of core decompression by combining it with administration of concentrated bone marrow cells and demineralized bone matrix directly in the affected area of the femoral head and by administration of parathyroid injection.
The bone marrow can be aspirated under general anesthesia, from the iliac crest. The bone marrow cells are then concentrated to increase the number and concentration of progenitor cells and injected into the necrotic lesions in the femoral head using a small trephine guided by images from the fluoroscope. This is followed by injection of demineralized bone matrix into the same area. Injection of parathyroid hormone (PTH) is also given as it is known to play an important role in bone and cartilage healing. PTH accelerates the healing process by replacement of woven bone to lamellar bone and by increasing new cortical shell formation. The same treatment methodology has also been successfully used and is found to be very effective in improving core decompression outcome even in knee and talus osteonecrosis.
Osteotomy: This procedure is done in the early stages of the disease and when only a small portion of bone is affected. It involves reshaping of the bone to decrease the stress placed over the affected bone.
Total joint replacement or arthroplasty: This is considered as a last resort when the disease has progressed to an advanced stage. The diseased joint will be replaced using artificial components. Avascular necrosis accounts for 10% of all total hip replacement and half of patients undergoing THA for osteonecrosis are younger than 40 years.
Avascular necrosis if diagnosed and treated promptly offers a favorable outcome. The amount of unaffected bone greatly influences the treatment options and outcome.