Understanding Knee Osteonecrosis: Causes, Symptoms, and Treatment Options

Knee osteonecrosis, also referred to as avascular necrosis, is a debilitating condition resulting from a disrupted blood supply to a portion of the bone in the femur (thighbone) or tibia (shinbone). Since healthy bone tissue relies on a consistent blood flow for nourishment and repair, the interruption can lead to the deterioration of the knee joint and the development of severe arthritis. Early diagnosis of knee osteonecrosis allows for less invasive treatment options, such as pain management through medications and reducing stress on the affected knee. However, in more advanced cases, surgical intervention is often necessary to halt further bone damage and restore joint function effectively.

Anatomy

The knee is the largest and most robust joint in the human body. It consists of three key bones: the lower end of the femur (thighbone), the upper end of the tibia (shinbone), and the patella (kneecap). The areas where these bones meet are coated with articular cartilage, a smooth and resilient tissue that cushions the bones and allows seamless movement of the leg by reducing friction. Knee osteonecrosis is most commonly observed on the inside portion of the knee, known as the medial femoral condyle. However, it can also occur on the outer portion (lateral femoral condyle) or on the flat surface at the top of the shinbone, referred to as the tibial plateau.  

Osteonecrosis of the knee occurs most often in the medial femoral condyle, a segment of bone located at the lower end of the femur (thighbone).

 

Cause

Osteonecrosis arises when the blood supply to a specific section of bone is interrupted. Without sufficient blood flow, the affected bone tissue dies and begins to collapse. Consequently, the articular cartilage that overlays the bone deteriorates as well, often leading to severe arthritis and impaired joint function. While osteonecrosis of the knee can develop in individuals of any age, it is more prevalent in people over 60. Women are notably at higher risk, being three times more likely to experience this condition compared to men.

Risk Factors

The exact cause of reduced blood supply to the knee is not always clear, but several factors have been identified that increase the likelihood of developing osteonecrosis:

• Injury: Trauma to the knee, such as a stress fracture or dislocation, can damage blood vessels and impair blood flow to the bone, increasing the risk of osteonecrosis.
• Oral Corticosteroid Medications: Long-term use of oral steroids, commonly prescribed for conditions like asthma and rheumatoid arthritis, is linked to osteonecrosis. Although the exact mechanism is unclear, research indicates that steroid-induced osteonecrosis often affects multiple joints throughout the body.
• Medical Conditions: Certain health conditions, including obesity, sickle cell anemia, and lupus, are associated with a higher risk of knee osteonecrosis. Additionally, individuals undergoing treatment for HIV may experience osteonecrosis due to the effects of antiretroviral medications.
• Transplants: Organ transplant recipients, particularly those who have undergone kidney transplantation, are more prone to developing osteonecrosis.
• Excessive Alcohol Consumption: Chronic alcohol abuse can lead to fatty deposits in blood vessels and increased cortisone levels, both of which reduce blood flow to the bone and contribute to osteonecrosis.

If osteonecrosis is not detected and treated promptly, it can progress to severe osteoarthritis, significantly impairing joint function.

Symptoms

Osteonecrosis progresses through several stages, each with distinct symptoms:

• Early Stage: The initial sign is often a sudden onset of pain on the inside of the knee, which may be triggered by a specific activity or a minor injury.
• Progressive Stage: As the condition worsens, standing, bearing weight, and moving the affected knee become increasingly painful.

Additional symptoms may include:

• Swelling over the front and inner side of the knee
• Tenderness around the knee joint
• Reduced range of motion in the knee

The disease progression can take months to over a year. Early diagnosis is crucial, as studies indicate that prompt treatment leads to more favorable outcomes and may slow or prevent further joint damage.  

The four stages of osteonecrosis of the knee. The disease can progress from a normal, healthy knee (Stage 1) to the collapse of the bone and severe osteoarthritis (Stage 4).

 

Doctor Examination

During a medical evaluation for knee osteonecrosis, your doctor will review your overall health and medical history, followed by a detailed discussion of your symptoms. The physical examination will focus on identifying key signs of the condition, including:

• Joint Swelling, Warmth, or Redness: Indicators of inflammation or underlying joint issues.
• Tenderness: Sensitivity in specific areas around the knee.
• Range of Motion: Assessment of both passive (assisted) and active (self-directed) movement to evaluate joint flexibility and stiffness.
• Joint Instability: Examination to detect any instability or weakness in the knee joint.
• Pain Under Weight-Bearing Conditions: Observation of discomfort when pressure or weight is applied to the knee.
• Muscle, Tendon, and Ligament Health: Checking for any injuries or abnormalities in the surrounding soft tissues.

 

During the exam, your doctor will look for areas of tenderness about your knee.

 

Imaging Studies

Imaging techniques play a crucial role in confirming a diagnosis of osteonecrosis.

• X-rays: X-rays create detailed images of dense structures like bones. These are often used to identify changes in bone structure that occur during the later stages of osteonecrosis. However, in the early stages of the condition, X-ray results typically appear normal, which may necessitate additional imaging for accurate diagnosis.

Advanced imaging methods, such as MRI or CT scans, may also be considered to detect early signs of osteonecrosis and assess the extent of bone damage. Early detection through imaging can significantly impact treatment outcomes.