Hip pain in a person in their thirties or forties is often attributed to muscular strain, a back problem, or simply overuse. Sometimes it is. But there is one diagnosis in this age group that is missed often enough, and matters enough, to be worth knowing about: avascular necrosis of the femoral head.

What avascular necrosis is

The ball of the hip joint depends on a relatively fragile blood supply. When that supply is interrupted, a segment of bone under the joint surface loses its viability. The bone becomes structurally weak, and if the process continues the surface collapses and the joint degenerates.

The critical point for patients is that there is a window before collapse. Once the femoral head has collapsed, the options narrow substantially.

Who is at risk

Recognised associations include prolonged or high dose corticosteroid use, significant alcohol intake, previous hip trauma or fracture, sickle cell disease and certain clotting disorders. A proportion of cases have no identifiable cause.

Steroid exposure is the association patients most often overlook, because the course may have been months or years earlier and for an unrelated condition.

How it presents

The typical complaint is deep groin pain, sometimes felt in the buttock or referred to the front of the thigh and knee. It is worse on weight bearing, and often worse on rotating the hip, which patients notice when getting out of a car or turning in bed.

Pain referred to the knee from a hip problem is a classic trap. A patient with knee pain and a normal knee examination should always have the hip examined.

Stiffness is common, particularly loss of internal rotation, and often precedes severe pain.

Why early imaging matters

In early disease the X-ray is frequently normal. This is the single most important thing to understand: a normal hip X-ray does not exclude avascular necrosis.

MRI is the investigation that detects it early, before any collapse and often before the X-ray changes. In a patient with unexplained groin pain and a risk factor, an MRI is a reasonable early step rather than a last resort.

What treatment depends on

Treatment is determined largely by the stage. Before collapse, joint preserving options such as core decompression, with or without biological augmentation, aim to relieve pressure and support healing in a head that still has an intact surface.

Once the head has collapsed and the joint surface is damaged, joint preserving surgery becomes far less reliable, and total hip replacement is generally what restores function. Modern implants perform well in younger patients, though the conversation about long term revision is an honest part of that decision.

Both hips are often involved

Avascular necrosis is bilateral in a substantial proportion of patients, and the second hip is frequently asymptomatic when the first is diagnosed. Imaging both hips at diagnosis is reasonable, because an asymptomatic pre-collapse hip is exactly the one where early intervention has the most to offer.

A detailed guide on avascular necrosis in younger patients is available here: https://www.mayurajcc.com/hip-guides/hip-replacement-avn-young-patients

When to seek assessment

Get a hip assessment if you have groin pain lasting more than a few weeks that is worse on weight bearing, particularly if you have a history of steroid use, significant alcohol intake, sickle cell disease or previous hip injury. Ask specifically whether an MRI is indicated if the X-ray is normal and the pain persists.