What it is.
The femoral head depends on a relatively fragile blood supply that runs up the neck of the femur. If that supply is interrupted, an area of bone within the head dies. The dead bone does not hurt in itself, and for a period the joint continues to work normally.
The problem comes later. As the body attempts to repair the dead segment, the bone beneath the cartilage temporarily weakens. If the weakened area is large enough and it is carrying load, the surface collapses. Once the ball is no longer round, the cartilage on both sides of the joint wears rapidly, and the hip becomes arthritic.
So avascular necrosis is best understood as a race between repair and collapse. Almost everything about treatment depends on which side of that event you are on.
Causes.
Recognised associations include corticosteroid use, particularly at higher doses or over longer periods, significant alcohol intake, previous hip fracture or dislocation, sickle cell disease, chemotherapy and radiotherapy, systemic lupus erythematosus, and decompression sickness in divers. A meaningful proportion of cases have no identifiable cause.
It affects both hips in a substantial proportion of cases, so the other hip is imaged even when it is not yet painful.
Symptoms.
Groin pain, often of relatively sudden onset compared with the slow build of osteoarthritis, and typically in someone younger than the usual arthritis patient. Pain on weight bearing and night pain are common. A characteristic pattern is pain that seems out of proportion to a radiograph that looks close to normal.
How it is diagnosed.
MRI is the key investigation. It shows avascular necrosis months to years before anything appears on a plain X-ray. A normal radiograph does not exclude the diagnosis, and if the clinical picture fits, the correct next step is an MRI rather than reassurance.
Staging systems describe the progression: changes visible on MRI only, then changes on X-ray with the head still round, then collapse of the surface, then arthritis of the whole joint. The presence or absence of collapse is the decisive line.
Treatment.
Before collapse. Risk factors are addressed where they can be. Options include protected weight bearing and core decompression, in which channels are drilled into the dead segment to relieve pressure and encourage revascularisation, sometimes with graft or biological augmentation. Results are best in small lesions caught early. This is joint-preserving surgery and is performed by surgeons who specialise in it.
After collapse. Once the femoral head has lost its shape, preservation is no longer realistic and total hip replacement is the operation that reliably relieves pain. Modern results in this group are good, though these patients are often younger, which means a longer lifetime exposure to the implant.
Where this practice fits.
Professor Rodda's practice is focused on hip and knee replacement. He does not perform joint-preserving surgery such as arthroscopy or osteotomy. If your condition is at a stage where preservation surgery is the right option, you will be told that and referred to a colleague who does it, within Sunshine Coast Orthopaedic Group or elsewhere. Where the joint has reached the point that replacement is the reasonable option, that is the work done here.
Common questions.
My X-ray was normal but my hip hurts. Could it be avascular necrosis?
It could. Avascular necrosis is visible on MRI months to years before it shows on a plain X-ray. If the history fits, particularly with corticosteroid use or significant alcohol intake, an MRI is the appropriate next investigation.
Will it definitely collapse?
No. Small lesions, particularly those away from the weight-bearing surface, may never collapse. Large lesions involving the weight-bearing portion are much more likely to. Size and location on MRI are the main predictors.
Does stopping steroids or alcohol reverse it?
It does not reverse bone that has already died, but removing the cause is important because it reduces the risk of further lesions and of the other hip being affected.
Should I stay off it?
Protected weight bearing is sometimes advised but on its own it has not been shown to prevent collapse reliably. It is one part of management rather than a treatment in itself.
Is hip replacement different for avascular necrosis?
The operation is much the same, but the patients are often younger, so the conversation about implant longevity and the likelihood of eventual revision carries more weight. Bone quality can also be affected by the underlying cause.
References.
- Mont MA, Salem HS, Piuzzi NS, et al. Nontraumatic osteonecrosis of the femoral head: where do we stand today? A 5-year update. J Bone Joint Surg Am. 2020;102(12):1084-1099.
- Zalavras CG, Lieberman JR. Osteonecrosis of the femoral head: evaluation and treatment. J Am Acad Orthop Surg. 2014;22(7):455-464.
This page provides general information about a medical condition and a surgical procedure. It is not individual medical advice and does not replace consultation with a qualified practitioner. Outcomes vary between individuals and all surgery carries risk. A referral is needed for a consultation with Professor Daevyd Rodda; without one, you can start with the practice nurse practitioner, who can provide it.