Avascular Necrosis of the Femoral Head
Article by Shane Armfield
What is Avascular Necrosis of the Femoral Head?
Avascular Necrosis (or Osteonecrosis) is a condition affecting the upper part of the leg - specifically the femoral head. Essentially, the femoral head or ball of your hip joint receives less and less blood supply. Since bone is living tissue, when this blood supply is reduced enough the bone dies. Once the bone dies, the femoral head collapses and if severe enough, the hip joint itself collapses.
Avascular Necrosis mainly affects those aged between 20-50 years old. In general, the healthier you are, the less risk you have of developing avascular necrosis. It usually comes about secondary to an underlying health issue or previous injury.
What Causes Avascular Necrosis of the Femoral Head?
Avascular Necrosis arises either as a result of traumatic or nontraumatic means. Sustaining a dislocated hip - where your femoral head becomes dislodged from its joint, can result in a traumatic onset of avascular necrosis. It has been argued that up to 20% of people who dislocate their hip, develop avascular necrosis of the femoral head.
Nontraumatic avascular necrosis can arise from an array of issues, most notably excessive alcohol use, chronic corticosteroid use and blood clots/any damage to the arteries supplying the femur.
The pathophysiology behind the association of chronic corticosteroid and alcohol use with avascular necrosis isn’t fully understood but it is proposed that the overuse of the aforementioned substances interferes with the breakdown of fatty substances. Consequently, the fatty substances build up and collect within the blood vessels, inevitably making them narrower. As expected, the narrower the blood vessels are, the less blood flow can travel through them and reach the femoral head. Again, once this blood supply is reduced enough, the bone begins to undergo necrosis (die).
Other known causes are the following diseases:
What are the Symptoms of Avascular Necrosis?
Avascular Necrosis requires time for its onset. It is relatively asymptomatic to begin, but as it progresses, the pain becomes more pronounced. Pain limited hip range of motion is the ultimate symptom both passively and actively which can refer pain down the length of the leg. Generally, the pain will arise when pressure is placed on the bone which unfortunately includes walking around!
Avascular Necrosis can often mask itself as other conditions in the early phase given its general pain presentation within the hip. Therefore, it is paramount for your health practitioner to record a detailed history of your presentation and perform a thorough examination to identify if avascular necrosis is your true cause of pain.
How is Avascular Necrosis Diagnosed?
Avascular Necrosis can often mask itself as other conditions. Once other causes are excluded and avascular necrosis is looking like the culprit, the gold standard for diagnosis is imaging of the hip. Although MRI has proven to be the most accurate in diagnosis, researchers and radiographers have proposed a classification system based off plain x-rays known as the Ficat system:
Other scans are less useful and are more specific to certain stages of the injury such as a bone scan or CT scan. The MRI can be used as a diagnostic tool
and also as a means to monitor the remodelling/healing.
Avascular Necrosis Treatment
Conservative treatment with physiotherapy has proven to be relatively ineffective for avascular necrosis. Although the aim of conservative treatment is to decrease the weight bearing load through the head of the femur (usually by implementing crutches), research has shown that the condition still progresses in 1-2 years. Without definitive treatment, 70% to 80% of all avascular necrosis of the femoral head cases will progress and inevitably undergo surgery.
Irrespective of what surgery is undertaken, the primary goal is always to preserve the natural femoral head as opposed to replacing it.
There have been proposed nonoperative treatments that can be implemented before the condition progresses and the femoral head collapses as seen in the picture on the first page. They are, however, still in the early stages of research and development. The use of various electromagnetic, acoustic stimulation or pharmaceutical modalities has been trialled with varying success. One of the most well known and successful treatments, if the condition is identified early enough, is the core decompression - i.e. decrease the pressure inside the femoral head. This is achieved through drilling holes into the femoral head to create channels for new blood vessels to nourish the affected areas of the hip or the channels are filled with healthy bone from another part of the body. This has proven to be successful, especially in those with early stages avascular necrosis based on preoperative and postoperative MRI studies.
As evident, there is a multitude of different approaches that can be taken to manage avascular necrosis. Ultimately, an orthopaedic opinion is paramount to ensure the condition is treated as effectively as possible. The decision as to which treatment to select will depend on the stage the avascular necrosis in combination with the clinical evaluation of the patient.
If you have any concerns or questions regarding Avascular Necrosis of the Femoral Head, please seek the advice of your doctor, hip surgeon or physiotherapist.
Related Hip Injuries
Hip Joint Pain
Lateral Hip Pain
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