This series will focus on breaking down and understanding each of the complications that might develop from sickle cell, so that you can know how to prevent it, and how to catch it early.
What is Avascular Necrosis?
Avascular Necrosis (AVN), government name osteonecrosis, is defined as death of the bone due to reduced or limited blood supply to the bone tissue. The necrosis (or death), leads to a thick scar tissue developing, which then prohibits any further healing of the bone, leading to joint pain and loss of function.
The joints most often affected by AVN (in decreasing order of incidence) are the hip, knee, shoulder, ankle/foot (talus), wrist and elbow. This is because these sites are more prone to have less collateral (smaller veins) that can provide circulation to the affected area, and usually only have a single large blood vessel that delivers circulation. Sickled cells find it quite easy to clump up this one blood vessel, and the risk for AVN is developed.
Risk Factors: AVN occurs in individuals of all ethnicities; although those with sickle cell diseases are more prone to this complication. It is more common in men than women (ratio of 8:1), and develops most often in middle age. With SCD, patients develop AVN from age 12, and once you have developed it, there is an increased chance for getting AVN in the future. Alcohol use puts you at risk for AVN. Also, patients who are on dialysis, have lupus, or who routinely use steroids (like in the treatment of acute chest syndrome, and pulmonary hypertension, are at an increased risk of getting AVN). More than 50% of patients diagnosed with AVN require surgery 3 years after.
What Causes AVN in Sickle Cell?: When in crises, sickled cells float around clumping up in various parts of the body. This leads to tissue starvation and pain. The bone is a living structure, and requires blood circulation to provide oxygen and energy to all the cells. The arteries and veins are responsible for providing this nutrition. In the bone structure, there is usually only one vein and one artery that delivers blood to a certain area, and once this is clogged up by sickled cells, there are no alternate routes. This leads to death of the bone. Osteoblasts and osteocytes come in to curtail the spread of infection, and a thick scar tissue is developed on the blackened, dead area. This means that no healing or repair can be done once the sickle cells leave and circulation is restored. As a result, that part of affected bone is PERMANENTLY dead, and is unable to function normally.
How do you know if you have AVN? The main sign of AVN is pain in the bone that is there regardless of whether or not you are in crises. Usually this pain is in the joint between the hip and thigh bone, and can be felt when walking. There might be tenderness in other surrounding areas. You might find yourself unable to have a normal range of motion in the affected side. You might find yourself unable to bend over and tie your shoes. In some people, AVN is so advanced that you might have a slight limp or clicking in movement. In addition, if the bone compresses the nerve, there might be some numbness, tingling or lack of sensation in the affected extremity.
AVN of the hip shows up on an X-ray as a blackened area. However, unless your doctor suspects AVN he won’t routinely order this X-ray for you. You have to ask for it. In other parts of the body, the AVN might be so microscopic that it won’t show up on an X-Ray. CT scans or Bone scans are also used, but are not sensitive enough tests. This is why it’s important to ask for an MRI of the affected area. Although MRIs are expensive and there is an increased risk of radiation, they are the most effective with diagnosing AVN.
How do you treat it? There are 7 stagesof AVN and the treatment plan is based on what stage of AVN you are in, whether it is symptomatic, and the severity of symptoms.
Joint/Hip Replacement:Since AVN affects the joints or hip, the dead section is completely removed and a metallic joint is placed in that works just like the dead bone should. Doctors tend not to be aggressive in suggesting Joint Replacement until AVN is in its advanced stages. This is because once you have a hip or joint replacement, you have to have another surgery every 10 years to replace the hardware. And you know every time you go under the knife, there is a risk of complications like infection and hardware rejection.
Core Decompression:The orthopedic surgeon will drill a hole into the affected bone that takes a chunk of the dead necrotic area out. This leads to less pressure on the bone. The thought is that this will then allow the bone to regenerate on its own, since the scar tissue has been removed and blood circulation has been restored. This often works in intermediate stages, promotes healing and provides relief from the pain. It is 35-95% successful in treating AVN patients, especially those in pre-collapse.
Osteotomy: This procedure involves rotating one of the joints, so that the joint is no longer resting on a dead, painful area. It is not as effective as core decompression, and as a result is rarely suggested.
Bone Graft: This involves melding a new piece of bone gleaned from a healthier part of the body, and grafting it unto the dead area, thereby promoting circulation and healing. Bone graft is often done with core decompression and in small areas, is about 70-91% effective in mild to moderate AVN. This option is great because there is a possibility for complete bone healing, especially in the femoral head. In addition, there is a reduced risk of infection from hardware placed during joint replacement. However, the recovery time is longer than with joint replacement and there is less complete pain relief.
Pain Management: In mild AVN, the conservative treatment is pain management through NSAIDs like Motrin, Aleve or other pain-killers and analgesics. If the pain is under control, then you can engage in flexibility and joint exercises which might help to promote circulation to the bone.
Alternative Remedies: To prevent and treat AVN at home, it is recommended to:
Engage in activities and increase circulation in the bone like low impact exercises, walking, yoga, swimming
Take supplements that promote bone growth like calcium, vitamin D, and carao
Reference: Toffieri, J.K. & Gilliland, W. Avascular Necrosis: eMedicine Rheumatology. Published December 19, 2009. http://emedicine.medscape.com/article/333364-overview