What Causes the Hip Bone to Die

What happens inside the bone when its blood supply is cut off?

Bone is living tissue, and it depends on a steady blood supply the same way any other tissue does. When that supply to a segment of the femoral head — the ball at the top of the thighbone — is interrupted, whether by a blocked vessel, a physical injury, or pressure building up inside the bone, the cells in that area die. Avascular necrosis, also called osteonecrosis, is the general name for this process. In the hip it is the femoral head that is affected first, because it depends on a narrow, easily disrupted set of blood vessels feeding it. Pain usually shows up later, once the dead area weakens and the bone around it tries to repair itself.

Avascular necrosis is a blood-supply problem, not a wear-and-tear one — that single distinction explains almost everything else about how it behaves differently from arthritis.

Long-term corticosteroid use

Sustained corticosteroid treatment is among the most common causes of avascular necrosis, whether the steroid was prescribed for an inflammatory condition, an organ transplant, or another chronic illness. The mechanism isn't fully settled, but the leading explanation involves fat deposits building up inside blood vessels and bone marrow, narrowing the vessels that feed the femoral head and raising the pressure inside it. Most people who take steroids never develop osteonecrosis — the risk tracks with how long and how intensively the treatment runs, and climbs further in people who also drink heavily or are being treated for lupus.

This risk is tied to sustained systemic treatment — pills or infusions taken over weeks to months — rather than to an occasional local corticosteroid injection into a joint or tendon, which is a separate exposure with its own cortisone injection limits worth understanding on its own terms.

Heavy alcohol use

Regular heavy alcohol use is the other major driver of avascular necrosis, and it appears to act through a pathway similar to steroids: fat can accumulate in the vessels that supply bone, and alcohol may also directly affect the cells that build new bone. The risk rises with how much and how long someone drinks. When heavy drinking and steroid treatment occur together, the two risks appear to compound rather than simply add, which is one reason clinicians ask about both when evaluating a new case.

Trauma: hip fracture and dislocation

A hip fracture or dislocation can physically tear the blood vessels supplying the femoral head, making mechanical injury one of the most direct causes of avascular necrosis. The risk is highest after a displaced fracture of the femoral neck or a traumatic dislocation of the hip, injuries that can shear across the exact vessels the head depends on. Because the vessel damage happens at the moment of injury, the resulting bone death can take months to become visible on imaging or to cause symptoms — one reason clinicians who treat these injuries keep watching the hip long after the fracture itself has healed.

Rarer causes: sickle cell disease, decompression sickness, and other contributors

Beyond steroids, alcohol, and trauma, a shorter list of other conditions can interrupt blood flow to the femoral head. Sickle cell disease distorts red blood cells so they clog small vessels, including the ones feeding bone. Decompression sickness — the condition divers and aviators can develop from rapid pressure changes — can force gas bubbles into the bloodstream that block those same vessels.

• Radiation treatment near the hip can damage the small vessels supplying the bone.
• Clotting disorders can make blood more likely to block the femoral head's narrow vessels.
• Chronic kidney disease is associated with higher rates of osteonecrosis.
• Lupus and other autoimmune conditions raise risk on their own, independent of the steroids often used to treat them.

In a younger, active adult, hip pain can also come from an unrelated structural problem: femoroacetabular impingement, where the ball and socket pinch against each other during certain movements. It's worth ruling out separately from osteonecrosis, including whether hip arthroscopy for FAI or physical therapy is the more fitting path once impingement itself is confirmed.

When no cause is found: idiopathic osteonecrosis

Not every case of avascular necrosis has an identifiable trigger. When a thorough evaluation turns up none of the usual risk factors, the condition is labeled idiopathic, meaning the cause is unknown rather than absent. This doesn't change how the hip is monitored or treated, but clinicians will typically still screen for underlying contributors — clotting disorders and lipid abnormalities among them — since a treatable driver, if one exists, is worth finding early.

How this differs from hip osteoarthritis

Avascular necrosis is sometimes confused with hip osteoarthritis, but the two arise from different mechanisms. Osteoarthritis is a gradual, degenerative disease in which joint cartilage breaks down over years, and it is most common with age, particularly after age 50 1Ref 1National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) (2023).Osteoarthritis.That osteoarthritis is a degenerative joint disease driven by cartilage breakdown that is more common with age, the mechanism distinguishing it from vascular-driven osteonecrosis.2Ref 2American Academy of Orthopaedic Surgeons (OrthoInfo) (2024).Osteoarthritis of the Hip.That hip osteoarthritis causes progressive groin/hip pain and stiffness and is initially managed nonsurgically.. Avascular necrosis instead follows a specific vascular insult — steroids, alcohol, trauma, or one of the rarer causes above — and can develop in much younger adults, sometimes advancing over months rather than years. Nonsurgical measures are usually tried first for an arthritic hip 3Ref 3American Academy of Orthopaedic Surgeons (AAOS) (2023).Management of Osteoarthritis of the Hip — Clinical Practice Guideline.That nonsurgical measures such as exercise and activity modification are recommended first-line for hip osteoarthritis before surgical options are considered., and more than 58 million US adults live with some form of arthritis 4Ref 4Theis KA, Murphy LB, Guglielmo D, et al. (CDC/MMWR) (2021).Prevalence of Arthritis and Arthritis-Attributable Activity Limitation — United States, 2016-2018.The US prevalence estimate of about 58.5 million adults with doctor-diagnosed arthritis, used to give scale for how much more common arthritis is than osteonecrosis. — a very different scale from osteonecrosis, which is comparatively uncommon. The distinction matters because early evaluation tends to be more urgent here than the gradual 'wait and see' approach that often works reasonably for arthritis.

If avascular necrosis is confirmed, it helps to read next about what avascular necrosis hip symptoms look like as the condition progresses, and what avascular necrosis hip treatment surgery involves once a stage has been established.