Osteonecrosis also known as Avascular Necrosis or AVN is a musculoskeletal condition characterised by death of bone. This usually affects the weight-bearing joints of the human body and the most commonly affected joint is the hip joint. Avascular necrosis (AVN) of the femoral head (top-most part of the thigh bone that articulates with the socket to form the hip joint) is a debilitating condition where the bone tissue in the head of the femur (thigh bone) dies due to a lack of blood supply. This can lead to the collapse of the femoral head, resulting in pain, arthritis, and limited mobility. If left untreated, eventually approximately 80% of the affected hips will develop painful arthritis with significant limitation of daily activities. Understanding Avascular Necrosis is crucial for early diagnosis and effective treatment.
Etiology: What causes Avascular Necrosis?
AVN occurs when blood flow to the femoral head is compromised. Various factors can contribute to this reduced blood supply, including:
1. Trauma: A fracture or dislocation of the hip can damage nearby blood vessels, leading to AVN. Hip injuries are the most common direct cause of AVN.
2. Corticosteroid Use: Prolonged use of corticosteroids for other medical diseases like rheumatoid arthritis or certain skin conditions is a common risk factor. These drugs can affect the body’s ability to repair bone and alter blood flow to the femoral head.
3. Alcoholism: Excessive alcohol consumption can increase fat deposits in blood vessels, reducing blood flow to the bone.
4. Blood Disorders: Conditions like sickle cell anemia can obstruct blood vessels, leading to AVN.
5. Idiopathic: In some cases, the cause is unknown, termed idiopathic AVN.
Irrespective of the underlying cause, the future course of the disease depends upon the percentage of the femoral head with reduced blood supply which eventually dies. This dead bone leads to compromise of the structural integrity of the entire bone with resultant collapse of the spherical shaped femoral head.
AVN and COVID-19: A Growing Concern
There is emerging evidence linking COVID-19 to an increased risk of AVN. The virus can cause endothelial damage and microthrombosis, leading to disrupted blood flow in various parts of the body, including the femoral head. It’s crucial to monitor COVID-19 patients, especially those with prolonged symptoms, for signs of Avascular Necrosis.
Symptoms and Signs: What to look out for?
Early symptoms of AVN can be subtle and often misdiagnosed as other hip conditions. Key signs and symptoms include:
– Pain in the Groin, Thigh, or Buttock: The pain usually starts gradually and worsens with weight-bearing activities.
– Reduced Range of Motion: As the condition progresses, patients may experience stiffness in the hip joint, making it difficult to move.
– Limping: As pain increases, patients often develop a limp to reduce pressure on the affected hip.
– Night Pain: Some patients report increased pain at night, which can disrupt sleep.
Investigations: How is AVN Diagnosed?
Timely diagnosis of AVN is crucial to prevent further damage to the femoral head. Common diagnostic tools include:
1. X-rays: X-rays are often the first imaging test done, but AVN might not be visible in the early stages.
2. MRI: Magnetic Resonance Imaging (MRI) is more sensitive and can detect AVN in its early stages, even before symptoms appear.
3. CT Scan: Computed Tomography (CT) can provide detailed images of bone structure and is useful in advanced cases to assess the extent of bone collapse.
4. Bone Scan: A bone scan can detect changes in bone metabolism, which can indicate Avascular Necrosis.
Treatment Options: Managing Avascular Necrosis of the Femoral Head
Treatment of AVN depends on the stage of the disease, age of the patient and the severity of symptoms. There are several staging systems that can be used to classify the stage of the disease but the most commonly used system by both orthopedic surgeons and radiologists is the Ficat and Arlet classification.
| FICAT & ARLET CLASSIFICATION | |
| STAGE | FINDING |
| I | Normal appearance of X-ray |
| II | Cysts (cavities) or sclerotic changes |
| III | Crescent sign (subchondral fracture) |
| IV | Flattening of the head with arthritis |
Non-Surgical Treatments
1. Medications: Pain relievers like NSAIDs (Nonsteroidal Anti-Inflammatory Drugs) can help manage symptoms. Bisphosphonates are also used to slow bone damage by reducing bone turnover. Other types of medications that may sometimes be used include lipid-lowering agents and blood thinners (anti-coagulants).
2. Physical Therapy: Exercises aimed at maintaining joint mobility and strengthening muscles can be beneficial. However, activities that put pressure on the hip health should be avoided.
Surgical Treatments
These can be divided into joint-preserving treatments and joint-replacing treatments.
Joint preserving treatment options include:-
1. Core Decompression: In the early stages, core decompression, a minimally invasive procedure that involves drilling into the femoral head to reduce pressure and create channels for new blood vessels, can be effective.
2. Bone grafting: This can be combined with core decompression. It can be non-vascularised bone grafting (where the necrotic bone is removed and replaced with bone graft to act as mechanical support) or vascularised bone grafting (where the bone graft along with a vascular pedicle or intact blood vessel is used to replace the dead bone)
3. Osteotomy: Here the shape of the proximal femur is modified by an inter-trochanteric osteotomy that aims to remove the diseased part of the femoral head from the weight-bearing region of the joint.
4. Arthrodiastasis: The hip joint is distracted which means that the articulating surfaces are held apart from each other so as to allow the diseased part to heal.
The majority of procedures apart from core decompression and to a lesser extent bone grafting are not commonly used now due to less than predictable results.
Joint Replacement procedures: Depending upon the type of implants, the available options are
1. Bipolar hemiarthroplasty: Only the femoral head is replaced but the socket (or acetabulum) is unchanged. One major problem is the increased wear of the acetabulum with complications like protrusion and osteolysis being common.
2. Limited resurfacing of the femur: The Femur head prosthesis is matched with the native acetabulum. Clinical results are mixed similar to bipolar hemiarthroplasty.
3. Total Hip Replacement: Both the femoral head and acetabulum are replaced with a prosthetic joint. Modern implant designs and improvements in biomaterials have greatly improved the longevity of THR implants.
Newer Advances
Advancements in the treatment of AVN include:
– Stem Cell Therapy: Early studies suggest that stem cells can regenerate bone tissue in the femoral head.
– 3D Printing: Custom 3D-printed implants are being explored for use in hip replacement surgeries, providing a more personalized fit.
– Regenerative Medicine: The use of growth factors and other regenerative techniques is an area of ongoing research.
Conclusion
Avascular necrosis of the femoral head is a serious condition that requires timely diagnosis and treatment. While early-stage Avascular Necrosis may respond to conservative treatments, advanced cases often necessitate surgical intervention. When treated appropriately these patients who are often physiologically young can regain their previous lifestyle.
For more detailed information, you can visit the following authoritative sources:
– [American Academy of Orthopaedic Surgeons (AAOS)]
– [National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)]
– [Mayo Clinic]
*Disclaimer: This document is for information purposes only and does not substitute professional medical advice. Always consult with a healthcare provider for an accurate diagnosis and treatment plan.
