Avascular necrosis (AVN), also known as osteonecrosis, is a condition where bone tissue dies because it loses its blood supply. Bones need a steady flow of blood to stay healthy, as blood carries oxygen and nutrients essential for bone cells to survive. When this blood flow is interrupted or severely reduced, the bone cells begin to die, leading to a cascade of problems within the bone and the joint it supports.
The process begins when the blood vessels supplying a particular bone area become blocked or damaged. This can happen due to various reasons such as trauma (like fractures or dislocations), prolonged use of high-dose steroids, excessive alcohol consumption, certain medical conditions, or even unknown causes. Without blood, the bone tissue undergoes ischemia (lack of oxygen), which causes the bone cells to die—a process called necrosis.
The most commonly affected site is the **femoral head**, which is the ball part of the hip joint. The hip is particularly vulnerable because the blood supply to the femoral head is somewhat limited and can be easily disrupted. When AVN affects the femoral head, it can cause pain in the groin, thigh, or buttock area, often worsening with activity. This pain sometimes mimics other conditions like sciatica, which can lead to misdiagnosis.
As the bone tissue dies, the structural integrity of the bone weakens. Tiny fractures, called microfractures, begin to form inside the dead bone. Over time, these fractures can enlarge and cause the bone to collapse. When the femoral head collapses, it loses its smooth, rounded shape, which is essential for smooth joint movement. This deformation leads to joint surface irregularities, causing pain, stiffness, and loss of function.
The damage to the joint is not limited to the bone alone. Since the bone supports the cartilage that cushions the joint, the collapse of the bone disrupts the cartilage surface. This leads to cartilage breakdown and eventually to arthritis in the joint. The joint becomes painful, swollen, and stiff, severely limiting movement and quality of life.
The progression of AVN can be slow or rapid, depending on the cause and severity of blood supply interruption. Early stages might cause mild discomfort or no symptoms at all, making it difficult to detect without imaging studies like MRI, which is very sensitive in identifying early bone changes before collapse occurs.
Treatment aims to preserve the bone and joint for as long as possible. Early on, reducing weight-bearing on the affected joint and using medications to control pain and inflammation can help. In some cases, surgical procedures like core decompression are performed to relieve pressure inside the bone and encourage new blood vessel growth. In advanced cases where the bone has collapsed and arthritis has developed, joint replacement surgery may be necessary to restore function and relieve pain.
In summary, avascular necrosis is a serious condition caused by loss of blood supply to bone tissue, leading to bone death, structural collapse, and joint damage. It primarily affects the hip but can occur in other bones. The damage to the joint results from the collapse of dead bone and subsequent cartilage breakdown, causing pain, stiffness, and impaired movement. Early diagnosis and treatment are crucial to prevent severe joint destruction and maintain mobility.