Avascular Necrosis of the Hip (Osteonecrosis)
Patient information — Dr Christopher Spelman, Orthopaedic Surgeon
Overview
Avascular necrosis (AVN), also called osteonecrosis, is a condition in which the blood supply to the ball of the hip (the femoral head) is disrupted, causing an area of bone to die. While the bone remains supported it may cause few symptoms, but once the dead segment weakens it can fracture just beneath the joint surface and collapse, so that the femoral head loses its round shape and the joint becomes arthritic. AVN often affects younger adults (frequently in their 30s to 50s) and is bilateral – affecting both hips – in a large proportion of people, which makes early diagnosis and joint-preserving treatment particularly important.
Causes
AVN results from anything that interrupts the fragile blood supply to the femoral head. Common causes and associations include:
● Corticosteroid medication (particularly high-dose or prolonged) and significant alcohol intake – the two most common non-traumatic causes
● Previous hip injury – a fracture of the femoral neck or a hip dislocation can directly damage the blood supply
● Blood and marrow disorders such as sickle cell disease and Gaucher disease; decompression (“the bends”) in divers; some autoimmune conditions and their treatments; and radiotherapy or chemotherapy
● In a large number of people no cause is found (idiopathic)
Symptoms and diagnosis
AVN typically causes groin pain that worsens with weight-bearing, though it can be silent in the early stages. Because X-rays are often normal early, MRI – the most sensitive test – is used to make the diagnosis before any collapse, and to check the other hip. The condition is staged (commonly using the ARCO system) according to how far it has progressed: the earliest stages have a normal-shaped head; a “crescent sign” indicates a fracture just beneath the surface (impending collapse); later stages show collapse of the head and then arthritis of the whole joint. Staging is central to choosing treatment, because the aim before collapse is to save the hip, whereas after collapse the joint usually needs to be replaced.
Treatment
Treatment depends on the stage and on the size and location of the dead segment.
Before the femoral head collapses (early stages)
The aim is to preserve the hip. Options include protected weight-bearing and treating the underlying cause; core decompression – drilling one or more small channels into the femoral head to relieve pressure and stimulate new blood vessels, increasingly combined with bone marrow (stem cell) or growth-factor (biologic) augmentation; a vascularised fibular graft – transplanting a segment of the patient’s own fibula bone with its blood vessels into the femoral head to provide both structural support and a new blood supply; and, in selected cases, an osteotomy to rotate the dead area away from the main weight-bearing zone. Medications such as bisphosphonates have been tried but the evidence for them is limited.
After collapse (later stages)
Once the femoral head has collapsed and the joint is arthritic, a total hip replacement is the most reliable option and works well, including in younger patients.
What the evidence shows
Core decompression works best when performed early, before collapse and for smaller lesions, with success rates of around 60–80% at five to ten years in early disease. Success falls as the stage advances – roughly 78% for stage I, 62% for stage II and 41% for stage III in one analysis. For larger or slightly more advanced pre-collapse lesions, vascularised fibular grafting has been shown to give better results than core decompression alone and can substantially delay – or avoid – the need for hip replacement. Once collapse has occurred, joint preservation is much less likely to succeed and replacement is generally required. This is why early MRI diagnosis and prompt treatment are so important.
Complications
The main risk is progression of the disease – the femoral head can collapse despite treatment, leading to arthritis and the need for hip replacement. Core decompression carries a small risk of fracture, infection and bleeding. A vascularised fibular graft is a bigger operation and can cause donor-site symptoms at the lower leg (temporary weakness, altered sensation, or great-toe stiffness). Where hip replacement is required, it carries the usual risks of that operation, though results in AVN are generally good.
Summary
AVN of the hip is a serious condition that can lead to joint collapse, particularly in younger patients, and often affects both hips. Diagnosing it early on MRI opens the door to joint-preserving treatment such as core decompression (with biologics) or a vascularised fibular graft, while established collapse usually needs a hip replacement. Dr Spelman will stage the condition carefully and discuss the most appropriate treatment for your hip and stage.