Avascular necrosis (AVN) of the hip is a condition where bone cells in the top of the thighbone die because their blood supply gets cut off. Between 10,000 and 20,000 new cases are diagnosed each year in the United States, with an estimated 600,000 people living with the condition. It most commonly strikes adults between the ages of 30 and 50, and without treatment, the bone gradually weakens, collapses, and leads to severe arthritis.
How Blood Loss Causes Bone Death
The ball-shaped top of your thighbone (the femoral head) fits snugly into your hip socket and bears your full body weight with every step. This bone depends on a small network of blood vessels, primarily branches of the femoral artery, that wrap around the outside of the bone and feed inward through tiny vessels called retinacular vessels. Unlike most bones in your body, the femoral head has very limited backup blood supply. If those vessels get blocked or damaged, the bone cells starved of oxygen begin to die.
Once bone cells die, the body can’t repair the area fast enough to keep up with normal wear. Tiny fractures accumulate in the dead zone. Over months or years, the weakened bone surface eventually caves in, changing the shape of the femoral head from a smooth sphere into something flattened and irregular. That misshapen bone grinds against the hip socket cartilage, destroying it and producing the kind of painful arthritis that often ends in hip replacement.
Common Causes and Risk Factors
The two biggest non-traumatic risk factors are corticosteroid use and heavy alcohol consumption. Together, they account for the majority of cases that aren’t caused by an injury.
Corticosteroids (drugs like prednisone, often prescribed for autoimmune conditions, asthma flares, or organ transplants) cause fat cells inside the bone to swell in both size and number. This increased pressure inside the bone damages the walls of tiny blood vessels, triggering clotting and cutting off circulation. The risk climbs with dose and duration. Daily doses of prednisone at 30 to 40 mg or more for at least a month significantly raise the odds, and a cumulative dose of roughly 1,000 mg given over a short window is enough to put someone at increased risk. For every additional 10 mg per day of oral steroids during the first six months of therapy, the risk of AVN rises by about 4.6%. Even short, high-dose bursts can cause it, and rare cases have been linked to inhaled and topical steroid preparations used over many years.
Alcohol damages bone cells through a similar mechanism, increasing fat deposits inside them and pushing the bone’s stem cells to produce more fat tissue instead of new bone. Other established risk factors include sickle cell disease (where misshapen red blood cells physically block small vessels), hip fractures or dislocations that tear the blood supply directly, radiation therapy, and certain clotting disorders. In about 20% of cases, no clear cause is found.
What AVN of the Hip Feels Like
Early AVN is often silent. Some people have no symptoms at all when bone death first begins. As the condition progresses, pain typically shows up in the groin, though it can also be felt in the thigh or buttock. At first, you may only notice it when walking, climbing stairs, or putting weight on the affected leg. As more bone weakens, the pain becomes constant and can wake you at night or bother you even while lying down. Range of motion gradually shrinks, making it harder to rotate the hip or spread the leg outward.
The timeline from first bone death to collapse varies widely. Some people progress over a few months, others over several years. The speed depends on the size and location of the dead zone, whether the cause is still active (for example, ongoing steroid use), and whether both hips are involved. About 17% of cases affect more than one joint.
How AVN Is Diagnosed
Standard X-rays are poor at catching AVN early. Their sensitivity for detecting the initial stages is only about 41%, and they miss the disease entirely before visible bone changes appear. By the time AVN shows up clearly on an X-ray, the bone has often already started to collapse.
MRI is the gold standard. It can detect AVN with greater than 90% sensitivity and specificity even in the earliest stage, before any structural damage has occurred. In fact, the earliest stage of AVN is defined as the point where X-rays still look normal but MRI already shows abnormal signals in the bone. If your doctor suspects AVN based on your symptoms and risk factors, an MRI is the test that confirms or rules it out.
Staging: How Severity Is Measured
Doctors classify AVN into stages that guide treatment decisions. The general progression works like this:
- Stage I: Bone death has begun, but the femoral head shape is still normal. MRI shows the problem; X-rays do not.
- Stage II: X-rays now show changes in the bone (patchy density, cysts), but the round shape of the femoral head is still intact. No collapse has occurred yet.
- Stage III: The surface of the femoral head has started to flatten or crack. This is the “crescent sign” on X-ray, indicating subchondral fracture.
- Stage IV: The femoral head has collapsed enough to damage the hip socket cartilage, producing full-blown arthritis.
Stage matters enormously for outcomes. Treatments that work well in Stage I often fail in Stage II or III, making early detection critical.
Non-Surgical Treatment
For early-stage AVN, medications that slow bone breakdown can delay or prevent collapse. A class of drugs called bisphosphonates, commonly used for osteoporosis, has shown real promise. In a large, long-term study, oral bisphosphonate therapy allowed about 75% of affected hips to avoid surgery entirely. A combination approach using both oral and intravenous forms pushed that number to nearly 87%. Even with treatment, the 3-year collapse rate was about 10% for Stage I hips and 46 to 53% for Stage II hips, roughly half the collapse rate seen in untreated patients.
Reducing or eliminating the underlying cause also matters. If steroids triggered the problem, doctors work to lower the dose as much as the underlying condition allows. Limiting weight on the affected hip with crutches can reduce mechanical stress on weakened bone, though protected weight-bearing alone doesn’t reliably prevent progression.
Surgical Options
Core Decompression
This is the most common surgery for early AVN. A surgeon drills one or more channels into the femoral head to relieve pressure inside the bone and encourage new blood vessel growth. It works best when done before collapse. In Stage I disease, success rates are around 92 to 96%. By Stage II, success drops to roughly 42 to 46%. By Stage III, it falls below 8%. Hips with a single area of dead bone do far better (67% success) than those with multiple affected zones (14% success).
Bone Grafting
For younger patients who want to delay hip replacement, surgeons can transplant a piece of bone from the lower leg, complete with its own blood vessel, into the femoral head. The blood vessel is connected to a local artery so the graft has a living blood supply from day one. Long-term data on this procedure are encouraging: 93% of grafted hips survived at 10 years, and 83% survived at 20 years. Even hips that already had some collapse before surgery showed a 92% graft survival rate at 10 years.
Recovery from this surgery is demanding. You’ll be in a wheelchair for the first week, then on crutches with minimal weight-bearing for about 10 weeks, followed by partial weight-bearing until the six-month mark. There’s also rehabilitation for the donor site on your lower leg, including exercises to prevent stiffness in the big toe.
Total Hip Replacement
When the femoral head has already collapsed and arthritis has set in, hip replacement is typically the final step. Modern hip replacements are highly effective at relieving pain and restoring mobility. However, patients with AVN historically experience higher failure rates than those getting hip replacements for ordinary arthritis, roughly four times higher in long-term studies. Because AVN often affects younger, more active patients, the replaced joint faces more years of use and a greater chance of eventually needing a second surgery.
Living With AVN
If you’ve been diagnosed early, the goal is to preserve your natural hip as long as possible. That means following up with regular imaging to track whether the dead zone is stable or progressing, staying consistent with any prescribed medications, and being strategic about physical activity. Low-impact exercise like swimming and cycling keeps the hip mobile and muscles strong without hammering the weakened bone the way running or jumping would.
If both hips are affected, which happens in a significant number of cases, treatment decisions become more complex because recovery from surgery on one side overlaps with managing the other. Honest conversations with your orthopedic surgeon about your age, activity level, and how much bone damage has already occurred will shape whether you pursue joint-preserving procedures or move toward replacement.