What is Femoral Head Avascular Necrosis?
Avascular necrosis of the femoral head refers to a condition where the upper end of the thigh bone, otherwise known as the femur, loses its blood supply and the bone tissue starts to deteriorate as a result. This condition is usually observed in 10,000 to 20,000 new cases each year in the United States. Both injuries such as fractures or dislocations, and non-traumatic reasons like chronic steroid use or alcohol use, blood clotting disorders, or birth defects can lead to this problem. It’s a debilitating illness that needs health care professionals to detect its signs vigilantly.
Focusing on the anatomy, the majority of the blood reaching the top of the femur comes from the main branches of the profunda femoris artery, which in turn is a subdivision of the femoral artery. Many small arteries branch out from these main branches, providing the necessary blood to the femur’s head. Another artery, the foveal artery which resides inside the ligament connecting the femur’s head to the hip socket, also supplies blood, but is more important in children. Two backup arteries offer extra blood support, though not as much.
The superior and inferior gluteal arteries, starting from the internal iliac artery which is the main artery of the pelvis, also contribute to the blood supply. The hip socket – called the acetabulum – where the femur connects, receives blood from the obturator artery and the superior gluteal artery.
Therefore when the blood supply to the femur’s head gets disrupted, the lack of oxygen and nutrients can cause the bone cells to die leading to necrosis or the death of the bone tissue. If this blood supply isn’t restored soon enough, the bone surface can collapse over time ending in degenerative arthritis, a condition where the cartilage that normally cushions the joints breaks down and causes pain and swelling.
What Causes Femoral Head Avascular Necrosis?
There are many different causes for a particular bone condition known as avascular necrosis or osteonecrosis. This happens when the blood supply to the bone is cut off, leading to the death of the bone tissue.
One of the main causes is physical injury, such as a fracture to the neck of the thigh bone, or the dislocation of the ball and socket joint of the hip. When such injuries happen, the blood flow to the head of the thigh bone can stop, causing avascular necrosis. For instance, between 15% and 50% of the time, osteonecrosis will follow a fracture of the neck of the thigh bone and it will result in 10% to 25% of hip dislocations.
Another major cause of this condition is the long-term use of steroids and excessive drinking. These two factors are responsible for more than 80% of non-injury related cases. Steroid use is the second most common cause of this condition, right after injury. Although it’s known that steroid use can lead to osteonecrosis, it’s not quite clear how that happens. Most likely it’s a combination of things like fat build-up, high cholesterol, and issues with the bone marrow, all of which can cut off the blood supply to the bone. Drinking too much alcohol can cause osteonecrosis in a similar way, but again the exact process is not completely understood.
Osteonecrosis can often be caused by sickle cell disease. This is because the abnormally shaped red blood cells can block blood flow, leading to bone death, with the head of the thigh bone being the most commonly affected site. Autoimmune and chronic inflammatory disorders, such as lupus, are also associated with osteonecrosis of the femoral head. The risk is particularly high with long-term steroid treatment, although it can also happen without steroid use.
There are also rarer causes of this condition. For instance, a disease called Legg-Calve-Perthes can lead to avascular necrosis in children. This is when the blood supply to the head of the thigh bone is cut off, causing bone death. It can lead to deformity, higher risk of developing arthritis, and potential loss of movement. This disease progresses in four stages:
1. Initial/necrosis – this is when the blood supply gets cut off and bone death starts.
2. Fragmentation – at this stage, the body starts to remove the dead bone and replace it with new bone, which is weaker and prone to breaking and collapsing.
3. Reossification – stronger, healthy bone starts to grow back at this point.
4. Healed/Remodeling – the bone growth is complete, but the final shape of the bone (which can be normal or abnormal) depends on the amount of damage done during the fragmentation stage.
Blood vessel disease caused by diabetes and direct damage from toxic substances can also lead to osteonecrosis of the femoral head.
Risk Factors and Frequency for Femoral Head Avascular Necrosis
Avascular necrosis of the femoral head, a condition affecting the hip, is seen in about 20,000 to 30,000 new cases each year in the United States. It’s a significant factor contributing to 10% of the total hip replacements done annually, roughly 250,000. This rate is similar to those seen in German-speaking countries and Japan. While the disease can affect anyone, it’s seen more frequently in patients with sickle cell disease, typically more common in people of African descent. The condition is also more common in men than women, with an estimated 3 to 5 men affected for every woman. The average age when people receive treatment is between 33 and 38 years old.
- Avascular necrosis of the femoral head happens in 20,000 to 30,000 new cases each year in the U.S.
- The condition is responsible for 10% of around 250,000 total hip replacements done each year.
- The rate is comparable to those seen in German-speaking countries and Japan.
- The disease can affect anyone, but it’s seen more in patients with sickle cell disease, commonly more prevalent in people of African descent.
- More men than women experience this condition, with a ratio of 3 to 5 men for every woman.
- People usually get treatment when they are 33 to 38 years old.
Signs and Symptoms of Femoral Head Avascular Necrosis
Early in the development of the disease, patients may not show any symptoms. However, as the condition progresses, they typically experience hip pain that can spread to the groin and thigh. Activities like walking and climbing stairs can worsen the pain, which usually gets better with rest. This discomfort can persist even when the patient isn’t moving. Physical exam signs that suggest osteonecrosis of the femoral head include limited range of motion, pain when the leg is moved away from the body or rotated inward, and tenderness when the hip area is touched.
- Hip pain that can radiate to the groin or thigh
- Pain that worsens with activities like walking and climbing stairs
- Pain that gets better with rest but may linger even without movement
- Limited range of motion in the hip
- Pain when the leg is moved away from the body or rotated inward
- Tenderness when touching the hip region
Testing for Femoral Head Avascular Necrosis
Identifying the condition early can greatly improve the results of treatment. Doctors make a diagnosis by assessing symptoms and using appropriate imaging techniques. These techniques could involve x-rays, bone scans, and MRI scans. They use these images alongside a patient’s symptoms to guide the treatment process.
X-rays are usually taken from two angles – an anterior-posterior view and a side view (referred to as the ‘frog-leg lateral’). X-rays may reveal a particular feature called ‘crescent sign’, indicating a collapse of the bone under the cartilage. Another possible sign is the ‘donut sign’, seen when using Technetium-99m in bone scans, where there is a ring of increased bone activity surrounding a less active center, showing where healthy bone meets dead bone.
The best imaging test for diagnosing this condition is MRI. It’s better than x-rays or bone scans when it comes to detecting the disease early. An MRI allows doctors to observe changes in bone marrow or locate and assess the size of necrotic (dead) bone areas. It can also show the extent of damage to the acetabular cartilage (the cartilage in the hip socket), depth of collapse, and more, which is incredibly helpful in evaluating a patient’s condition and planning their care.
Once doctors have the right images, they can classify the degree of bone death. The Steinberg staging system is most commonly used for this. It identifies seven stages, each stage tells us more about the current state of the femoral head (hip bone).
Doctors might conduct additional lab tests to rule out other reasons for hip pain and to check for additional health issues in patients who may have this disease. These tests might include a complete blood count, lipid panel, and checks for specific proteins and antibodies associated with inflammation and autoimmune processes. Tests for sickle cell disease may also be conducted, as this is one condition that can lead to bone death in the femoral head and cause hip pain even without it.
A biopsy (taking a small tissue sample) is usually not needed, as diagnosis can typically be made based on the images and symptoms. If a biopsy is conducted, the key findings would be the death of bone tissues and marrow cells, with no specific signs of inflammation, cancer cells, or infection. Similarly, angiography (imaging of blood vessels) is not routinely performed, although it can provide useful information about the blood vessels and contribute to research and understanding of the disease.
Treatment Options for Femoral Head Avascular Necrosis
For conditions like avascular necrosis of the femoral head (a condition where the bone in the hip joint dies due to lack of blood supply), treatment options vary from non-invasive to surgical methods. The exact treatment depends on many factors such as the patient’s age, level of pain, location and severity of the disease, other health conditions, and whether the joint surface has caved in or not. It’s best to start treatment before the joint surface collapses. This condition can lead to fractures in the bone layer under the cartilage of a joint (subchondral fractures) within 2 to 3 years if not addressed.
Treatment decisions should be based on the stage of the disease and mainly on whether there is a collapse or not. Generally, non-invasive treatments or procedures to relieve pressure from the bone can benefit patients with small to medium-sized lesions that have not collapsed. For larger lesions, bone grafting (transferring bone tissue from one part of the body to another) or bone reshaping (osteotomies) can be effective. If there’s a collapse in the hip joint or if it has spread to the cup-shaped socket that the hip joint moves in (acetabulum), joint replacement (arthroplasty) might be required.
Conservative treatment includes a variety of non-invasive measures. These may include physical therapy, limited weight-bearing, stopping alcohol intake, discontinuing steroidal therapy, pain relievers, and targeted drugs. As avascular necrosis of the femoral head varies in its progression to more severe stages, and evidence is scarce, there’s no agreed-upon way to manage the condition without surgery. Small lesions without symptoms may heal on their own, but most do grow and need treatment. Various medications including blood thinners, cholesterol-lowering drugs, and bone-strengthening drugs have been used in an attempt to restore blood supply to the hip bone. However, currently, there is no strong consensus on the effectiveness of one medication over another. Pain relief injections directly into the joint are generally not recommended as they provide temporary relief and may worsen the condition.
For those who need a more invasive approach, there are several surgical options. These can be categorized as joint-saving procedures or joint-replacing procedures. The joint-saving techniques include relieving pressure from the bone, bone grafts, use of biologics and/or regenerative therapies, and bone reshaping; reconstruction involves joint replacement.
Relieving pressure from the bone is the surgical removal of affected tissue from inside the hip bone to reduce pressure and increase blood flow. This is the most common intervention during pre-collapse stages. Regenerative therapies, where the patient’s own cells are used to repair and regenerate the damaged tissue, have been used alongside this procedure and suggest improved outcomes with a lower rate of disease progression. This method has shown good results for small to medium-sized lesions before collapse but isn’t used when the hip bone has collapsed.
Bone grafting is an alternative for larger lesions without early collapse. The bone for the graft can be taken from another part of the patient’s own body, and it can be done with or without including its blood supply. The graft taken with its blood supply can bring new blood supply that can improve blood flow in the bone and potentially revitalize the dead zone. Bone reshaping is removing parts of bone to change the load distribution of the joint towards the uninvolved, healthy bone. The dead region of the hip bone can be moved away from weight-bearing regions, theoretically allowing healing or delaying the progression of the disease.
If the damage is extensive, the collapse has occurred, and/or there is involvement of the socket in the hip joint; then a joint replacement might be required. This involves the removal of the ‘ball and socket’ of the hip and replacement with an artificial joint. Although it had mixed success rates in the past, improvements in the artificial joint materials with low wear rates have significantly improved the outcome of hip replacement in this condition over the last twenty years.
What else can Femoral Head Avascular Necrosis be?
The symptoms of avascular necrosis, a disease that impacts the head of the femur (thigh bone), can be very similar to symptoms of other health conditions. Hence, it is vital to perform a differential diagnosis to identify the exact condition.
Two such conditions that could be mistaken for avascular necrosis are bone marrow edema syndrome (BMES) and subchondral fractures. BMES, also known as transient osteoporosis, generally occurs as a reaction to injury, increased physical activity, or osteoarthritis. Dating its onset may be rapid and sometimes without any trauma, but it usually resolves within a year. An MRI scan typically shows extensive bone marrow edema, which is a key feature of this disease.
Subchondral fractures, on the other hand, generally happen after minor trauma in older people, particularly in the context of osteoporosis which leads to subchondral insufficiency – a weakening in the layer of bone beneath the cartilage.
Other potential conditions that may need to be ruled out include:
- Complex regional pain syndrome
- Inflammatory synovitis
- Neoplastic bone conditions (abnormal growths in the bone)
- Osteomyelitis (bone infection)
- Osteoarthritis (joint disease)
- Osteoporosis (loss of bone density)
- Soft tissue trauma
What to expect with Femoral Head Avascular Necrosis
The outlook for femoral head osteonecrosis, a condition where the bone in the hip joint dies due to lack of blood supply, depends on various factors. One of the most important of these is the stage in which the condition is diagnosed. The sooner it is caught, the more effective preventive measures can be, leading to a better outlook.
However, certain elements may predict a worse outcome. These include diagnosis at a late stage, the condition affecting the lateral (outer) part of the ‘head’ of the thigh bone instead of the medial (inner) part, a situation where more than a third of the weight-bearing part of the femoral head is involved (as seen on an MRI scan), and being over the age of 50.
Even if one or more of these factors are present, it’s important to remember that the exact outcome can differ from person to person. It’s best determined by a qualified doctor who can thoroughly assess the patient’s condition.
Possible Complications When Diagnosed with Femoral Head Avascular Necrosis
Possible complications include increased severity of joint pain over time, limited movement, and arthritis. These issues can lead to severe disability for patients.
Possible Complications:
- Worsening of joint pain
- Limited range of motion
- Development of arthritis
- Significant disability
Preventing Femoral Head Avascular Necrosis
If you’re experiencing pain in your hip, thighs, or buttocks, it’s crucial to seek medical help. Some individuals may be more prone to a certain medical condition known as avascular necrosis of the femoral head, which involves reduced blood flow to a part of the hip joint. Sometimes, this condition may not show symptoms early on, which is why proper screening is essential.
People who fall into the higher-risk category include those consuming long-term medication like steroids or bisphosphonates, excessive alcohol drinkers, those undergoing chemotherapy or radiation treatment for cancer, individuals with blood disorders (hemoglobinopathies), and those who have had an injury to the hip or surrounding area. If you fall into any of these categories, make sure to discuss this with your healthcare provider as regular screenings could detect issues early on, improving treatment outcomes.
