Avascular necrosis of the femoral head is the death of bone tissue in the ball-shaped top of the thighbone, caused by a loss of blood supply. Without adequate blood flow, bone cells die, the internal structure weakens, and the smooth, rounded surface of the femoral head can eventually collapse, destroying the hip joint. The condition disproportionately strikes younger adults, which makes it especially frustrating: people in their thirties and forties can find themselves facing a hip replacement decades earlier than most.
Why the Femoral Head Is So Vulnerable
Most bones in the body have a rich, redundant network of blood vessels feeding them from multiple directions. The femoral head is different. It sits inside a sealed joint capsule, and its blood supply runs through a small number of arteries that travel along the femoral neck before entering the bone. The medial femoral circumflex artery (MFCA) is the dominant vessel, supplying roughly 82% of the femoral head’s blood, with the lateral femoral circumflex artery contributing the remaining 18%.1PubMed. The relative contribution of the medial and lateral femoral circumflex arteries to the vascularity of the head and neck of the femur: a quantitative MRI-based assessment This heavy reliance on one main vessel creates a bottleneck. Any disruption along the MFCA’s path can starve the femoral head of oxygen and nutrients.
Making matters worse, the blood vessels that reach the femoral head are housed within the closed chamber of the femoral head itself, surrounded tightly by marrow cells. If pressure inside that compartment rises for any reason, it can compress the tiny blood vessels, restrict flow, and trigger a chain of ischemia and cell death.2Journal of Translational Autoimmunity. Steroid-induced osteonecrosis This anatomical quirk is why surgeons who operate near the hip must be acutely aware of the vascular “danger zones” around the femoral neck.3PubMed Central. The origin of the medial femoral circumflex artery, lateral femoral circumflex artery and obturator artery
The Most Common Causes
Anything that chokes off blood flow to the femoral head can cause avascular necrosis. The triggers fall into two broad camps: traumatic and non-traumatic.
Trauma
A hip dislocation or a fracture of the femoral neck can physically tear or kink the arteries supplying the femoral head. In one study comparing patients with isolated posterior hip dislocations against those with fracture-dislocations, the avascular necrosis rate was about 5% in the dislocation-only group but jumped to roughly 35% when a fracture accompanied the dislocation. Delays in getting the hip back into place also mattered: the longer the joint stayed out, the higher the rate of bone death.4PubMed. Avascular necrosis of the femoral head after traumatic posterior hip dislocation with and without acetabular fracture Timing of reduction is one of the clearest modifiable factors in traumatic cases.
Corticosteroids
Steroid medications are the single most common non-traumatic cause. The exact chain of events at the molecular level is still being worked out, but the broad strokes are well recognized: corticosteroids promote fat cell growth inside the bone marrow, increase fat levels in the blood, damage the lining of small blood vessels, and tip the body’s clotting balance toward forming small clots.5PubMed Central. Glucocorticoid-induced avascular bone necrosis: diagnosis and management The expanding fat cells raise pressure inside the femoral head, squeezing the already-vulnerable blood supply until flow drops below the level needed to keep bone alive.6Journal of Translational Autoimmunity. Steroid-induced osteonecrosis High-dose or long-course steroid use carries the greatest risk, but the threshold dose that triggers necrosis varies from person to person, which makes prevention tricky.
Alcohol
Chronic heavy drinking is the other major non-traumatic culprit. Alcohol damages bone health through several overlapping routes: it disrupts fat metabolism, triggers chronic inflammation, impairs new bone formation, reduces arterial blood flow, and promotes intravascular clotting. Both the duration and the dose of alcohol exposure matter.7PubMed Central. Osteonecrosis Related to Steroid and Alcohol Use—An Update on Pathogenesis
Sickle Cell Disease
People with sickle cell disease carry an unusually high risk. The abnormally shaped red blood cells can clump together and block the small vessels feeding the femoral head. Estimates suggest that between 20% and 50% of sickle cell patients develop avascular necrosis of the femoral head over their lifetime, making it the most common bone complication of the disease.8PubMed. Aseptic osteonecrosis of the femoral head in patients with sickle cell anemia In one large cohort, the overall prevalence of avascular necrosis was about 20%, with the hip being the most frequently affected joint.9Clinical Epidemiology and Global Health. Osteonecrosis of the femoral and Humoral heads in sickle disease patients: Risk factor, Comorbiditis
How It Is Diagnosed
A major frustration with avascular necrosis is that it often stays invisible on standard X-rays until significant damage has already occurred. The sensitivity of plain X-rays for detecting early-stage disease is only about 41%, and there can be a delay of one to five years between the onset of symptoms and the appearance of anything abnormal on a standard hip film.10PubMed Central. Imaging of Avascular Necrosis of Femoral Head: Familiar Methods and Newer Trends By the time an X-ray shows a crescent sign or flattening, the window for joint-preserving treatment may have narrowed considerably.
MRI changed the landscape. It can detect the earliest stages of disease with better than 90% sensitivity and specificity, picking up bone marrow edema and subtle signal changes long before structural collapse begins.11PubMed Central. Imaging of Avascular Necrosis of Femoral Head: Familiar Methods and Newer Trends If you have unexplained hip or groin pain and a risk factor like steroid use or sickle cell disease, an MRI is far more likely to catch the problem early than an X-ray alone.
Predicting Whether the Femoral Head Will Collapse
Not every case of avascular necrosis ends in catastrophic collapse. The size and location of the dead zone inside the femoral head are the strongest predictors. One widely used approach measures the “combined necrotic angle” on MRI, which estimates how much of the femoral head is involved. In a study using this method, none of the hips with a combined necrotic angle of 190 degrees or less collapsed over three years, while all of the hips with an angle of 240 degrees or more did.12PubMed. Prediction of collapse in femoral head osteonecrosis: a modified Kerboul method with use of magnetic resonance images The hips between those two numbers had about a 50-50 chance. This kind of measurement helps doctors and patients decide how aggressively to treat, and whether joint-preserving surgery is worth trying or a hip replacement should be planned sooner rather than later.
That said, no staging system is perfect. Studies comparing the commonly used Ficat and ARCO classification systems found poor agreement between different doctors reading the same images, with reliability scores (kappa values) hovering around 0.3 to 0.4, which is considered poor.13PubMed Central. Avascular necrosis of the femoral head: inter- and intraobserver variations of Ficat and ARCO classifications Multiple classification systems are in use worldwide, and there is still no universal consensus on which one is best.14Hip & Pelvis. Updating Osteonecrosis of the Femoral Head This lack of agreement complicates comparisons between research studies and sometimes leads to different treatment recommendations depending on the system a surgeon uses.
Joint-Preserving Treatments
When avascular necrosis is caught before the femoral head collapses, there is a realistic chance of saving the natural hip. The goal of all early interventions is the same: restore blood flow, relieve pressure, and give the bone a chance to repair itself.
Core Decompression
The most established joint-preserving surgery is core decompression, in which a surgeon drills one or more channels into the femoral head to reduce the built-up pressure and encourage new blood vessel growth. It works best when the necrotic area is small. When the combined necrotic angle exceeds about 250 degrees, the failure rate climbs steeply, with disease progression and eventual hip replacement becoming far more likely.15PubMed. Modified Kerboul Angle Predicts Outcome of Core Decompression With or Without Additional Cell Therapy
Adding Stem Cells to Core Decompression
A growing body of evidence supports combining core decompression with bone marrow stem cell transplantation. A meta-analysis of multiple studies found that adding stem cells led to better pain relief, lower collapse rates in the medium term, and a lower rate of conversion to total hip replacement compared with core decompression alone.16PubMed Central. Stem cell therapy combined with core decompression versus core decompression alone in the treatment of avascular necrosis of the femoral head: a systematic review and meta-analysis The benefit was clearest when the stem cells were combined with some form of mechanical support inside the drill channel and when follow-up was under five years. Beyond five years, the advantage over core decompression alone became less clear, which raises the question of whether stem cells delay collapse or truly prevent it.17PubMed Central. Stem cell therapy combined with core decompression versus core decompression alone in the treatment of avascular necrosis of the femoral head: a systematic review and meta-analysis
Vascularized Fibular Grafting
For larger necrotic areas or patients who need structural support, surgeons sometimes transplant a piece of the fibula (the smaller bone in the lower leg) along with its blood supply into the femoral head. This provides both a scaffold of living bone and a new blood source. Systematic reviews have found vascularized fibular grafts to be superior to non-vascularized grafts and to core decompression in terms of clinical outcomes and prevention of femoral head collapse.18PubMed. Treatment of avascular necrosis of the femoral head utilising free vascularised fibular graft: a systematic review Patients treated with vascularized grafts had better hip function scores and less pain at early follow-up than those who received non-vascularized grafts.19Acta Orthopaedica et Traumatologica Turcica. Comparison of early results of vascularized and non-vascularized fibular grafting in the treatment of osteonecrosis of the femoral head The surgery is technically demanding, though, and not all centres offer it.
When Hip Replacement Becomes the Answer
Once the femoral head has collapsed and the joint surface is destroyed, joint-preserving options are off the table. Total hip arthroplasty is the definitive treatment at that point. In young patients with osteonecrosis, a large study with a mean follow-up of 14 years found that 10-year implant survival was 86% and 20-year implant survival was 66%.20PubMed. Outcomes after total hip arthroplasty in young patients with osteonecrosis of the hip Those numbers are good but not perfect, meaning a person who gets a hip replacement in their thirties has a realistic chance of needing at least one revision surgery in their lifetime. This is one of the driving forces behind the push to diagnose avascular necrosis earlier and pursue joint-preserving treatments when possible.
Genetic Susceptibility
Why do some people on high-dose steroids develop avascular necrosis while others taking the same regimen do not? Part of the answer appears to be genetic. Researchers have identified several gene variants that affect clotting, fat metabolism, and blood vessel function, all of which influence susceptibility to bone death. A meta-analysis found a significant link between a polymorphism in the PAI-1 gene, which regulates clot breakdown, and the risk of osteonecrosis of the femoral head. People carrying the 4G/4G version of this gene had roughly double the odds of developing the condition compared with those carrying the 5G/5G version.21PubMed. Association between PAI-1 4G/5G Polymorphisms and osteonecrosis of femoral head: a meta-analysis
Not every candidate gene has panned out, though. A pooled analysis of twelve studies looking at a common variant in the MTHFR gene, which is involved in folate metabolism and has been implicated in clotting disorders, found no overall association with osteonecrosis risk, even when results were broken down by ethnicity.22PubMed Central. Genetic Association between Methylenetetrahydrofolate Reductase Gene Polymorphism and Risk of Osteonecrosis of the Femoral Head The genetics research overall points toward a condition where multiple mechanisms, including abnormal clotting, suppressed new blood vessel growth, and shifted bone remodeling, converge, and your particular genetic makeup determines how many of those pathways are activated at once.
The Mental Health Side
Living with avascular necrosis, especially before definitive treatment, can take a significant psychological toll. A study of patients younger than 60 who developed avascular necrosis after femoral neck fractures found that depression was the single strongest independent predictor of quality of life, outweighing the physical variables.23PubMed. Effect of depression on femoral head avascular necrosis from femoral neck fracture in patients younger than 60 years This finding is worth knowing because depression is treatable, and addressing it can meaningfully change how someone experiences the condition, even before the hip itself is fixed.
Interestingly, mild or moderate osteonecrosis does not always translate into severe functional impairment. In a cohort of young adults with osteonecrosis secondary to hip dysplasia, patients with lower-grade disease reported hip function and physical function scores that were essentially the same as patients without osteonecrosis. It was only at the most advanced grades that a significant dip in physical examination scores appeared.24PubMed Central. Patient-reported outcomes in young adults with osteonecrosis secondary to developmental dysplasia of the hip – a longitudinal and cross-sectional evaluation This can be both reassuring and a trap: because early-stage disease may cause only modest symptoms, patients and doctors sometimes underestimate its urgency until collapse is imminent.
How Children Differ from Adults
In children, avascular necrosis of the femoral head goes by a different name: Legg-Calvé-Perthes disease. The underlying process, bone cells dying due to interrupted blood supply, is essentially the same in children and adults.25Injury. The physiopathology of avascular necrosis of the femoral head: an update The critical difference is that children still have growth cartilage in their femoral head. This cartilage has regenerative potential, so a child’s femoral head can regrow lost height and reshape itself over time, something an adult femoral head cannot do. In adults, once the rounded surface of the femoral head collapses, the deformity is permanent. This is why the same pathology tends to carry a more favorable long-term prognosis in younger children and a worse one in older children whose growth potential is diminishing, making late-onset Legg-Calvé-Perthes disease behave more like adult avascular necrosis.26Journal of Pediatric Orthopaedics. Transtrochanteric Rotational Osteotomy for Late-Onset Legg-Calve-Perthes Disease
Dysbaric Osteonecrosis in Divers and Compressed-Air Workers
An occupational cause that most people have never heard of is dysbaric osteonecrosis, which affects divers and workers who spend time in high-pressure environments like underwater tunnels or caissons. The suspected mechanism involves nitrogen bubbles forming in the fatty marrow of long bones during rapid decompression, which reduces blood flow and sets off necrosis.27Clinical Journal of Sport Medicine. Dysbaric Osteonecrosis: A Literature Review of Pathophysiology, Clinical Presentation, and Management Risk factors include frequent dives, deep dives, inadequate decompression, and advancing age.28PubMed Central. Dysbaric osteonecrosis in diving fisherman: a case report
A tricky aspect of dysbaric osteonecrosis is that it can be silent for years. Patients may present with no symptoms at all, or they may gradually develop joint pain, stiffness, and reduced mobility in the hip or shoulder.29PubMed Central. Dysbaric Osteonecrosis in Divers: A Narrative Review With a Systematic Literature Search of Pathophysiology, Prevalence, Clinical Features, and Screening Radiographic findings include bone cysts, areas of increased density, and the characteristic crescent sign seen in other forms of avascular necrosis. Professional divers in many countries are screened periodically with imaging, though the optimal screening protocol remains debated.
Experimental Scaffolds and the Future of Repair
One of the more exciting frontiers in treating avascular necrosis involves three-dimensional scaffolds designed to be implanted directly into the necrotic region. These engineered structures serve a dual purpose: they physically support the weakened bone and they deliver biological agents that promote new bone growth and blood vessel formation. In animal models, scaffolds loaded with a compound called icariin, derived from a traditional Chinese herb, promoted new bone volume, increased the number of trabeculae (the tiny struts inside bone), and stimulated the growth of new blood vessels in the defect area.30Materials & Design. Icariin-based bone scaffold for treating steroid-induced necrosis of femoral head by restoring angiogenesis and promoting osteogenesis Other groups have tested 3D-printed titanium rods loaded with the same compound, confirming that the combination of structural support and drug delivery fostered bone regeneration and integration with surrounding tissue in animal experiments.31Acta Biomaterialia. Icariin-loaded 3D-printed porous Ti6Al4V reconstruction rods for the treatment of necrotic femoral heads
These approaches are still preclinical, meaning they have not yet been proven in large human trials. But the concept is appealing: instead of simply drilling a hole and hoping biology does the rest, you insert a scaffold that actively recruits bone-forming cells and blood vessels into the dead zone. If the technology makes the jump to routine clinical use, it could extend the reach of joint-preserving surgery to patients with larger necrotic lesions who currently have few options besides waiting for collapse and then getting a replacement hip.