Avascular Necrosis of the Hip
Avascular necrosis (AVN), also known as osteonecrosis, is the death of bone tissue caused by a disruption of blood flow within a bone. The condition usually affects the ends of bones where they terminate in a joint. Though AVN can occur in the ankle, elbow, shoulder, and jaw, it most commonly affects the hip joint.
There are an estimated 20,000 to 30,000 new AVN diagnoses in the United States each year. The condition can occur in people of any age, but it is most commonly diagnosed in people between ages 30 and 65. For some patients, AVN is asymptomatic and is discovered incidentally. AVN of the hip can cause pain, which can be debilitating, in and around the hip joint. In the vast majority of cases, the condition worsens over time, and without treatment, the affected bone in the hip joint collapses over a few months or years.
Once the joint has collapsed, the most effective treatment is total hip replacement surgery. In the U.S., AVN is the underlying cause of around 10% of all total hip replacement procedures. While hip replacement surgery usually has excellent outcomes, the prosthetic materials can wear down over time, requiring follow-up surgery. There are also risks of surgical complications, infection around the implants, and hardware failure.
Fortunately, treatments have been developed for early-stage AVN of the hip that can help prevent the collapse of the joint and the need for hip replacement surgery. Core decompression with stem cell therapy is one such treatment. It uses the patient’s stem cells to help the AVN-damaged bone repair itself, with the aim of halting progression of the disease to prevent joint collapse.
“At Yale, we are developing new 3D-navigated treatments to prevent collapse of the hip,” says Yale Medicine orthopaedic surgeon Daniel Wiznia, MD, who co-leads the Yale Medicine Avascular Necrosis & Osteonecrosis Program. “If AVN is treated before the hip collapses, there is a lower risk for needing a hip replacement. Our 3D minimally invasive treatment targets the focus on the lesion, and allows most patients to bear weight after surgery and return to their daily activities.”
What is avascular necrosis?
Bone is a living, changing tissue made of different types of cells, proteins, and minerals. Specialized bone cells continually reabsorb old and damaged bone and replace it with new bone. Bones need a steady supply of oxygen- and nutrient-rich blood to stay healthy.
Avascular necrosis occurs when the blood supply within a bone in a joint is interrupted and, as a result, not enough blood (and the oxygen and nutrients it carries) reaches the affected part of a bone. This results in necrosis, or death, of bone tissue.
What is avascular necrosis of the hip?
The hip is what’s known as a “ball and socket” joint. The “ball” is the head of the femur (thighbone), which has a rounded, ball-like shape. The “socket” is the acetabulum, a cup-shaped part of the pelvis. The rounded head of the femur (known as the femoral head) fits inside the cup-shaped acetabulum. When the hip flexes and moves, the femoral head rotates within the acetabulum.
When AVN occurs in the hip joint, it affects the femoral head. Blood supply to the femoral head gets disrupted, leading to the death of bone tissue.
In most cases, AVN is a progressive condition. As the condition worsens over time, the affected bone tissue degenerates. Without effective treatment, the femoral head can collapse. When this happens, the femoral head loses its rounded shape and no longer rotates smoothly within the acetabulum when the hip moves. This can lead to a form of arthritis known as osteoarthritis. When AVN has reached this advanced stage, total hip replacement surgery is necessary to restore hip function.
Early-stage AVN of the hip may not cause any symptoms, but as the condition progresses, people typically experience pain in the hip, groin, thigh, knee, and/or buttocks. The pain usually sets in gradually over time. Range of motion of the affected hip may also be limited.
What causes avascular necrosis of the hip?
AVN of the hip occurs when the blood supply to the femoral head is interrupted, leading to death of bone tissue. There are two general types of AVN of the hip: traumatic and nontraumatic.
Traumatic AVN of the hip. AVN can occur when trauma interrupts blood flow to the femoral head. For instance, it may develop after a hip fracture, dislocation, or previous hip surgery. Traumatic AVN of the hip is not as common as nontraumatic AVN.
Nontraumatic AVN of the hip. Several nontraumatic risk factors have been associated with AVN of the hip, in particular, the prolonged use of corticosteroids and excessive alcohol use. Together, these two factors account for over 80% of nontraumatic AVN of the hip cases. Other risk factors include, but are not limited to, the following:
- Sickle cell disease
- Systemic lupus erythematosus (SLE)
- Gaucher disease
- Previous radiation therapy
- Previous chemotherapy
- Decompression sickness
- HIV infection
- Chronic liver disease
- Organ transplantation
- Certain blood clotting disorders, including thrombophilia (in which your blood clots too easily)
- Hyperlipidemia (abnormally high levels of lipids in the blood)
In many cases, the cause of AVN of the hip is unknown.
How is avascular necrosis of the hip diagnosed?
To diagnose AVN of the hip, doctors will review your medical history, perform a physical exam, and order one or more tests.
Your doctor may begin to make a diagnosis by asking you about your symptoms, including when they began and whether they have gotten worse over time. They will also review your medical history to see if you have any risk factors for AVN, such as a previous hip injury, corticosteroid use, and whether you have a medical condition associated with AVN of the hip. During the physical exam, your doctor will closely examine your hip and move it around to check whether certain positions cause pain.
Imaging tests such as X-rays and magnetic resonance imaging (MRI) scans of the hip are necessary to confirm a diagnosis.
Your doctor may also order blood work to help determine the underlying cause of AVN.
If you are diagnosed with AVN of the hip, your doctor will determine the stage of the condition. Knowing whether the condition is in its early or late stages helps doctors select the best treatment for each patient.
How is avascular necrosis of the hip typically treated?
The choice of treatment for AVN of the hip depends on several factors, including the patient’s age and overall health, symptoms, and whether the femoral head has collapsed.
Non-surgical treatment options may be used to treat early-stage AVN. Although these treatment options can help improve symptoms, they usually do not stop the progression of AVN. Non-surgical treatments may include:
- Physical therapy to strengthen hip muscles and improve range of motion
- Pain medication, such as nonsteroidal anti-inflammatory drugs (NSAIDs), to relieve pain
- Use of crutches, canes, and walkers to lessen the amount of weight placed on the affected hip
Patients may also be advised to discontinue or reduce the use of corticosteroids and to reduce or stop smoking and alcohol use.
- Hyperbaric oxygen (HBO) therapy. Another nonsurgical treatment known as HBO therapy is a safe and effective option for patients with early-stage hip AVN. During HBO therapy, the patient sits or lies inside a sealed hyperbaric chamber in which the atmospheric pressure is higher than at sea level. While inside the chamber, the patient breathes 100% oxygen. Each treatment session usually lasts 90 minutes, and they are repeated five times a week for a total of 30 or more sessions.
Breathing 100% oxygen at higher-than-normal atmospheric pressure allows more oxygen to dissolve in the blood than in normal conditions. This enables the blood to deliver more oxygen to tissues around the body, including to areas of bone affected by AVN that have a reduced blood supply. Studies have found that HBO therapy effectively and safely reduces the swelling of areas of bone affected by AVN, helping to alleviate pain caused by the condition. The treatment also helps in bone healing and regeneration—and in preventing collapse of the femoral head—in part by improving blood flow within the bone and boosting the function of cells involved in removing damaged bone and growing new bone. HBO has also been shown to mobilize stem cells from the bone marrow.
HBO therapy may be used in conjunction with a surgical procedure called core decompression with stem cell placement (more details below) to prevent progression of the condition and collapse of the hip joint.
Surgical treatment options aim to improve symptoms, prevent or slow the condition’s progression, and restore the hip joint’s function.
- Core decompression, a minimally invasive surgery, involves drilling into the part of the femoral head affected by AVN. Used to treat early-stage AVN, it helps relieve pressure within the bone, restore blood flow, and reduce pain. The goal of core decompression is to stop the progression of AVN, though around 20% to 35% of people who undergo core decompression eventually need a total hip replacement.
Core decompression can be combined with stem cell therapy (see below for more details). In this procedure, the hole (or holes) drilled in the femoral head are filled with the patient’s stem cells to help regenerate new bone.
- Bone grafting is a procedure in which synthetic bone material or healthy bone from elsewhere in the patient’s body—or from a donor—is transplanted to the area of the femur head affected by AVN to stimulate new bone growth. Bone grafts may also be inserted into the hole (or holes) drilled for a core decompression procedure.
- Osteotomy is a procedure in which a surgeon cuts into the femur and repositions it so the patient’s body weight is distributed to parts of the bone that are healthy and capable of bearing weight.
- Total hip replacement may be done if the femoral head has collapsed, there is substantial damage to the hip joint, or the acetabulum is damaged. While other surgical treatments seek to preserve the patient’s own hip joint, in a total hip replacement, the bones that make up the joint are removed and replaced with manmade components.
What are stem cells, and how are they used to treat avascular necrosis?
Stem cells can develop into different types of cells that perform specialized functions in the body. There are two main types of stem cells:
- Embryonic stem cells are present in embryos and can develop into any cell type in the body.
- Adult, or somatic, stem cells are found in organs and tissues (such as the bone marrow) and play an important role in helping the body repair itself.
Adult stem cells are used in the treatment of AVN. Stem cells are collected from the patient’s bone marrow and transplanted to the sections of the femoral head that have been damaged by AVN. The stem cells then develop into bone cells that remove the damaged bone and replace it with new, healthy bone.
What is involved in a stem cell implantation procedure to treat avascular necrosis of the hip?
At the start of the procedure, the surgeon uses a needle to harvest, or collect, bone marrow from the iliac crest, which is part of the pelvis. The needle is inserted into the bone, and using a syringe, the surgeon extracts bone marrow and places it in tubes. The tubes are put into a centrifuge, which spins them to separate stem cells from other components in the bone marrow.
Next, the surgeon performs a core decompression procedure. In a technique that was developed by Dr. Wiznia and is unique to Yale School of Medicine, an intraoperative computed tomography (CT) scan of the hip joint is taken, which provides the surgeon with a three-dimensional model of the hip joint, allowing them to see which areas of the femoral head are affected by AVN.
Through two small incisions—each about a centimeter long—in the skin over the hip joint, the surgeon mounts a computer to the femur to guide the core decompression in 3D. Next, the surgeon uses a computer-navigated drill to remove dead bone from the head of the femur. The surgeon then injects the patient’s stem cells into these channels, along with a bone graft. At the end of the procedure, the incisions are then stitched closed.
In most cases, core decompression with stem cell injection is an outpatient procedure, meaning patients can usually go home the same day as the surgery. However, some patients with pain control concerns will stay overnight in the hospital.
People can put weight on the operated hip, but they may need to use crutches or a walker for the first two weeks following the procedure. Pain medications may be used to reduce pain for the first weeks after the surgery, and medication is prescribed to reduce the risk of blood clots.
People can usually return to their regular activities within two weeks of the procedure, though they should see their doctor for regular follow-up appointments to monitor their hip.
As with any surgical procedure, core decompression surgery with stem cell therapy comes with a risk for complications. Complications are rare but may include infection, bleeding, pain where the bone marrow was collected, and, less frequently, bone fractures, blood clots, and damage to articular cartilage.
What is the outlook for people with avascular necrosis of the hip?
The outlook for people with AVN of the hip varies depending on a number of factors, including the cause of the condition, how advanced the condition was when it was first treated, which part of the femoral head is affected, and the patient’s age and general health. Typically, outcomes are best for healthy people who receive treatment at an early stage of AVN.
In some cases, when AVN affects only a small section of the femoral head, the condition resolves on its own without treatment. However, because AVN is usually progressive, most people will eventually need to have surgery.
Total hip replacement surgery is usually required for people with advanced AVN in which the femoral head has collapsed. Outcomes are generally good, though hip replacement recipients typically need to avoid high-impact exercise and may eventually need further surgery to replace components of the prosthesis. Prosthetic hips usually last for 15 to 20 years.
Some treatments for early-stage AVN, including bone grafting and osteotomy, can successfully prevent or slow the progression of the condition for some people, but they are not commonly used. Core decompression, the most commonly used treatment for early-stage AVN of the hip, effectively relieves pain for the majority of patients and, in many cases, can prevent the condition’s progression. Around 25% to 30% of people who undergo this procedure, however, ultimately need total hip replacement surgery.
A number of studies have found that core decompression surgery with stem cell injection typically offers improved outcomes compared to core decompression alone. Patients report less hip pain and improved hip function, and the procedure helps slow the progression of AVN, thereby reducing the chances of femoral head collapse and the need for total hip replacement surgery.
What makes Yale unique in its approach to treating avascular necrosis of the hip?
“At Yale, we have an integrated program that incorporates patients into a hyperbaric oxygen treatment plan,” says chief of Yale Physical Medicine & Rehabilitation Rummana Aslam, MBBS, who is also co-lead of the Yale Avascular Necrosis & Osteonecrosis Program. “HBO improves oxygen delivery to cells with reduced blood flow, preventing further necrosis and stimulating the growth of new blood vessels. It enhances bone remodeling and repair as well as bone tissue renovation. The therapy also provides significant pain relief.”