Did you know that our bones, just like our organs, are living and growing tissue? Just like all living tissue, our bones rely on blood vessels to circulate blood throughout the body to keep them alive. Most living tissue has blood vessels that come from many different directions. If one blood vessel is damaged it may not cause any complications, due to there being a backup blood supply from the circulatory system coming from elsewhere. However, certain joints within the body only contain a few blood vessels that transports a certain amount of blood. One of these joints with limited blood supply is the hip, and osteonecrosis is a serious concern related to diminished blood supply.
The hip joint is called a ball-and-socket joint. It is the second largest weight-bearing joint after the knee, and one of our most flexible joints in the human body. The socket of the hip is called the acetabulum and forms a deep cup that surrounds the ball of the upper thigh bone (femur). On the end of the femur, and the acetabulum, this ball of the femur and pelvis forms what is called the femoral head.
The surface of the femoral head (ball) and the inside of the acetabulum (socket) are covered with thick cartilage within the joints, called articular cartilage. This material allows the joints to slide against one another without causing bone on bone friction and damage.
All of the blood supply within the hip joint comes from the neck of the femur, called the femoral neck, a thin area of bone that connects the ball to the shaft. If this blood supply within the hip becomes limited or damaged, there is no backup, like in some other areas of the body. This damage to the blood supply, causes bone death, mostly the ball portion of the femur. Once this occurs, the bone is no longer able to maintain itself.
What is Osteonecrosis of the Hip?
As we grow, our bones are always changing. To maintain bone strength, bone cells are constantly repairing the wear and tear and force put on the body, which affects the tissue of the bone. If this repairing stage and process stops, bones can begin to weaken, for example, just like rust can affect metal. Eventually, just like a rusty bridge, the structure of our bones begins to collapse.
When this blood supply is damaged within the hip, the result is a condition called avascular necrosis (AVN) of the hip. AVN is formally known as osteonecrosis (ON), which translates to its literal meaning, “death of bone” (osteo = bone, necrosis = death). Avascular Necrosis or osteonecrosis are the terms used to describe the process that occurs, where the blood flow to an area of bone is compromised, causing parts of your bone to die, most commonly occurring in the shoulder and hip. There are four stages of osteonecrosis which depict the severity of bone death. Depending on the stage, there are many different treatment options available.
This condition causes little breaks or fractures within the hip bone, often leading to the bone to eventually collapse and die, due to a decrease in the blood supply to the affected area, in this case the hip. When osteonecrosis occurs in the hip joint, pressure builds up in the top of the femoral head (the ball portion), causing the articular surface of the hip to flatten and collapse. Due to this low blood supply and collapse of the femoral head, the ball (femoral head), no longer fits inside the socket (acetabulum). Due to the ball and socket not fitting together like a puzzle piece, or a piece of well-oiled machinery, the joint begins to wear itself out as it is trying to hold all this weight and overcompensate. This leads to hip fractures, conditions such as osteoarthritis, and severe chronic pain.
Ultimately, of individuals who are diagnosed with AVN, there is a collapse rate of 67 percent in patients who don’t have symptoms (asymptomatic), and 85 percent in those patients who experience symptoms (symptomatic).
Osteonecrosis frequently appears comorbid, meaning in addition or relation to another disease, such as rheumatoid arthritis. Symptoms are not always present; therefore, it is important to see your orthopedic surgeon immediately, as an early diagnosis can save your life, and avoid severe complications, and even death.
Causes of Osteonecrosis
There are many causes of osteonecrosis. Anything that causes damage to the blood supply going to the hip can cause this condition.
Injury to the hip itself can damage the blood vessels, and therefore, the blood supply. Dislocation of the hip socket or fracturing the femoral neck (the area connecting the ball of the hip joint) can also damage and tear the blood vessels.
People who smoke and drink excessively can experience damage to the blood vessels, making them constrict or narrow. This limits blood supply to the hip, which is dangerous, as this part of the body already has such a small supply of backup blood. Some medications such as corticosteroids (cortisone) can also cause AVN, and conditions such as gout, cancer such as leukemia, blood clots, and sickle cell disease. It usually takes several months for AVN to show up, and it can even become a problem for up to two years following this type of injury.
Symptoms of Osteonecrosis
Symptoms usually begin slowly. In fact, in its earliest stage there are usually no symptoms present. Other people may notice that you are limping before you feel any pain. Once symptoms begin they come and go. If the condition is left untreated, progressive bone damage will often occur. Surgery is usually required to correct the bone damage. The primary symptom of osteonecrosis is limited range of motion, and pain in muscles and joints. If symptoms do occur, they are similar to arthritis, and include:
· Pain, often in the groin or buttock
· Stiffness of the hip joint
· Chronic pain
· Lack of sleep
· Limited mobility
The diagnosis of AVN begins with the doctor learning about your medical history and doing a physical examination. Your doctor will want to know about your occupation, what other medical problems you may have, and what medications you take. You will be asked whether you drink alcohol or smoke, as these are common causes of osteonecrosis. During the physical examination, it will be determined how much stiffness you have in your hip and whether your mobility is compromised. Once this is done, X-rays or further diagnostic testing will most likely be done to rule things out, so an accurate diagnosis can be made, and proper treatment can be administered as soon as possible.
X-rays will usually show if osteonecrosis is present in the hip joint. However, as mentioned before, if the condition is in its very early stages, symptoms may not be present, and results may not show up on the X-rays, even though you are experiencing symptoms and having pain. However, in advanced stages of AVN, the hip joint will be very arthritic, and it may be hard for your orthopedist to tell whether the main problem is AVN or osteoarthritis of the hip.
Therefore, if the X-rays fail to show AVN, your doctor will order further testing, such as a bone scan. A bone scan involves injectinginto your blood stream. Later, a large camera is used to take a picture of the bone around the hip joint. If there is no blood supply around the femoral head (ball of the hip), the picture will show a blank spot where the femoral head should be outlined on the film. Multiple pictures of the hip bones are taken by the scanner. The images look like slices of the bones. This technology helps to very accurately show any signs and small areas of damage to the blood supply of the hip, even shortly after the damage has occurred.
After reviewing the images of the bone scan and X-rays, your doctor will devise the most appropriate treatment approach for you, whether that may be non-surgical or surgical, depending on the severity of your case. In other words, based on the findings, the condition will be classified as either mild, moderate, or severe.
Treatment for Osteonecrosis
Once it has been determined by your orthopedic surgeon that you have a diagnosis of osteonecrosis, treatment choice is determined by how far along your condition is, and the severity of your symptoms. Other factors that guide treatment decisions include your age, activity level, and overall health. For example, patients with this condition usually have other serious health concerns, so they may be treated with non-operative care. No medical treatments will restore the blood supply to the femoral head and reverse AVN.
If AVN is caught early, keeping weight off the hip will most likely be suggested, and the doctor will often prescribe a walker or crutches, and show how to use them. This is to help the fractured hip heal, and to protect it, to prevent further damage. Patients may also be shown stretches and exercises, to help with strength, stiffness, and avoid more loss of range of motion in the hip. Anti-inflammatory medicine is often prescribed as a way to ease pain. If these methods fail, surgery will most likely be the next logical step.
Those with osteonecrosis account for approximately ten percent of all total hip arthroplasties performed in the United States. If your femoral head has not begun to collapse, your surgeon may suggest an operation to try to increase the blood supply to this part of the hip (the ball). Several operations have been designed to do just this, commonly a total hip arthroplasty, known as a total hip replacement. This procedure involves replacing the damaged articular cartilage and bone with artificial implants made of plastic, metal, or ceramic. Total hip replacement for those with hip osteonecrosis has been successful in relieving pain and restoring function and mobility for 90 to 95 percent of patients.