Spontaneous Osteonecrosis of the Knee

What is Spontaneous Osteonecrosis of the Knee?

Spontaneous osteonecrosis of the knee is a painful condition that suddenly causes knee pain and difficulty in moving. It mainly affects the inside part of the femur bone near the knee (the medial femoral condyle). This condition was first identified in 1968 and is marked by its quick progression and that it is not caused by an injury. Doctors still don’t fully understand why this condition occurs. If not treated, it can lead to the bone under the cartilage collapsing, and osteoarthritis, which would require surgery.

Diagnosis and treatment can be difficult because the symptoms come on quietly and indeterminately. It’s important to understand the knee’s anatomy as it mainly affects the medial femoral condyle. This part of the knee supports a lot of weight and stress and therefore might be more prone to developing the condition. Involvement of the lateral femoral condyle (outside part of the femur near the knee) and tibial plateau (top of the lower leg bone) is less common.

The usual course of this condition begins with sudden symptoms not caused by an injury, followed by quick worsening of the joint. A unique feature of this condition is distinctive crescent-shaped areas of bone death (osteonecrosis lesions). Progression is influenced by things like the size and position of the lesion and the patient’s overall health. How fast it spreads and the pattern of the spread can vary. Some patients may experience slow progression while others may face quick joint destruction. In some cases, the symptoms will improve on their own over time. However, in many patients, the disease worsens over time, often resulting in severe knee pain, swelling, difficulty moving, and the possible worsening of the joint.

Early stages are marked by severe pain and swelling, leading to a narrowing of the joint space and the development of osteoarthritic changes. In more advanced cases, the dead bone may collapse, leading to severe osteoarthritis that would require joint replacement surgery.

What Causes Spontaneous Osteonecrosis of the Knee?

We aren’t completely sure what causes a condition known as spontaneous osteonecrosis of the knee; it appears to have many possible causes and its symptoms can be quite vague. This makes it challenging to diagnose and treat. Some explanations have been given, but it most often happens in older people which could suggest it’s linked to aging. What seem to be the main reasons for the disease are fractures in weak bones, blockages in the veins, and local injury.

Spontaneous osteonecrosis of the knee differs from other types of the disease because it starts gradually and there is no clear cause. Unlike other types, it doesn’t usually happen with known risk factors like prolonged use of steroids or excessive alcohol consumption, suggesting that this disease is likely to be confined to the knee. Earlier ideas suggested that it was caused by the reduction of blood flow to the bone, leading to the bone death. But, recent analysis has suggested that fractures in the bone located just below the cartilage of a joint cause the disease, leading to localized bone death.

These small breaks in the bone are believed to start a series of events, including an intense build-up of fluid in the bone marrow, increased pressure inside the bone, and reduced blood supply. All of this ultimately results in the collapse of the plate below the cartilage of the joint and subsequent bone death. Biomechanical aspects like changes in how weight and forces are distributed across the joint and adjustments in bone alignment tend to worsen the stress on these bones, especially in people who already have abnormalities in the joint line or those who partake in activities that put extra pressure on the knee.

In a 2019 study by Hussain et al, they examined the proposed causes of spontaneous osteonecrosis of the knee and came across a strong link between meniscal tears (tears in the knee cartilage) and the disease. Half to all of the patients with this disease had these tears, with the severity of the tears associated with how severe and large the osteonecrosis was. This finding suggested that the disruption of certain areas of knee cartilage increased the pressure between two bones in the knee, changed knee biomechanics, and resulted in the characteristic signs of the disease. We still need more evidence to pinpoint the exact cause of this disease, because it’s still controversial.

Risk Factors and Frequency for Spontaneous Osteonecrosis of the Knee

Spontaneous osteonecrosis of the knee is a condition that mainly affects middle-aged and older people, particularly women who are 60 or older. This could indicate a link with osteoporosis after menopause. While it’s not a common knee issue, its true occurrence could be understated as it might go unnoticed in patients suffering from severe osteoarthritis. Nevertheless, because of the significant effect it has on people’s lives, it needs more attention and research.

• Spontaneous osteonecrosis of the knee often affects middle-aged to older individuals.
• It’s more common in women who are 60 or older, which suggests a possible link with post-menopause osteoporosis.
• While it’s not a frequent occurrence among knee problems, it’s believed that the actual numbers could be higher since it might go unnoticed in severe osteoarthritis patients.
• Despite its rare occurrence, it has a significant impact on people’s lives, highlighting the need for more research and focus.

Studies show a higher number of spontaneous osteonecrosis of the knee cases in Western populations. This might be due to differences in lifestyle, access to healthcare, and diagnostic practices. The common occurrence of this issue in older adults, particularly postmenopausal women aged 60 or older, strengthens the theory that age-related bone density loss and osteoporosis play a role in its development. Other risk factors could include age, gender, bone health, and possibly even genetic predisposition.

Signs and Symptoms of Spontaneous Osteonecrosis of the Knee

Spontaneous osteonecrosis of the knee is a condition that typically starts with sudden, one-sided knee pain. This pain seems severe compared to any triggering event and is often located on the inner side of the knee. It becomes worse during weight-bearing activities. The exact moment when the pain started can sometimes be pinpointed by the patient, and they may report mild or no injury at all. This can make diagnosing the condition difficult. In some cases, symptoms may develop more slowly, and the pain and swelling gradually get worse. This can seem like it’s due to other age-related joint diseases, which requires a thorough examination and ruling out other possible causes.

When examining the knee, tenderness may be found at the joint line, especially over the inner, upper part of the shin bone. There might be minor knee fluid build-up and a reduced range of motion due to the pain. Crepitus, or a cracking sound, might also be present, indicating damage underneath the joint surface. It’s crucial to check the knee’s alignment and stability, as any deformities can affect the progression of the disease.

• Sudden, severe, one-sided knee pain
• Pain is typically on the inner side of the knee
• Activities that put weight on the knee worsen the pain
• Patients may notice exact moment when the pain started
• Pain might start after mild or no injury
• Symptoms may develop slowly over time, similar to age-related joint diseases
• Tenderness at the joint line during physical examination
• Minor knee fluid build-up
• Reduced range of motion due to pain
• Possible cracking sound (crepitus), indicating damage underneath the joint surface
• Knee alignment and stability are essential to evaluate

Testing for Spontaneous Osteonecrosis of the Knee

If a medical professional suspects you may have a condition called spontaneous osteonecrosis of the knee, a condition causing bone death in the knee, diagnostic tests will be carried out. Their decision is primarily based on your symptoms and the results of a specialized imaging scan known as a magnetic resonance imaging scan (MRI). In order to rule out other possible causes of knee pain, these examinations are crucial.

Initially, your doctor will likely perform basic X-rays of your knee joint. These X-rays can reveal certain signs of the disease in the later stages, such as subchondral sclerosis, which is a hardening of the bone below the cartilage surface. Other indications might include bones in the knee collapsing or the space in the joint narrowing, and flattening of the involved bones of the knee, or condyles. However, in the early stages of spontaneous osteonecrosis of the knee, x-rays often appear normal.

The MRI is considered the best method for detecting this condition due to its capacity to effectively reveal bone edema, a condition where excess fluid accumulates in the bone affecting its functioning. The MRI may reveal a number of key findings such as swelling in the bone marrow, lines of fracture below the cartilage surface of the bone, and specific areas of bone death along with the sinking of the epiphyseal, or end part of a long bone. MRI images are separated into two different types: T1-weighted images and T2-weighted images. T1-type images often display a snaking, low-signal area, which represents the bone decay surrounded by inflamed bone marrow. T2-type images, on the other hand, provide a clearer view of the swelling. MRI’s sensitivity plays a crucial role in evaluating the condition’s extent, leading to better-devised treatment plans.

Apart from imaging studies, your doctor might also want to look into potential other causes of knee pain such as infections or inflammatory arthritis by conducting some laboratory tests. These can include tests for a complete blood picture to check your overall health, erythrocyte sedimentation rate to detect inflammation in the body, and C-reactive protein levels, a protein produced by the liver whose levels rise in response to inflammation.

Treatment Options for Spontaneous Osteonecrosis of the Knee

Spontaneous osteonecrosis of the knee (a condition affecting the bone and cartilage in the knee) can be managed based on the severity of the disease, the symptoms a patient is experiencing, and their overall health. Smaller instances of damage may improve with non-surgical treatments. However, more severe cases can often require surgery. If the disease hasn’t yet caused the joint in the knee to collapse, treatments can attempt to preserve the joint. If joint collapse has already happened, a treatment called total joint arthroplasty can replace the joint. Early stages of the disease may be treated without surgery, but if the disease becomes worse, surgery may be required.

Non-surgical treatments usually apply to smaller instances of damage. Treatments can include pain relief through nonsteroidal anti-inflammatory drugs (NSAIDs, medicines that reduce inflammation) and analgesics (pain relievers). Another important management strategy is to limit the amount of weight and stress put on the knee. This could involve the use of canes or crutches to take the weight off the knee and prevent further damage. Physical therapy is also beneficial as it provides exercises to improve knee movement and muscle strength, helping to relieve stress from the knee. Bisphosphonates, a type of drug used to strengthen bone, may also be used to prevent joint collapse and delay the need for surgery. Despite these treatments, if a patient sees no improvement after 3 months, they might need to consider surgical options.

Surgical treatments might be necessary for larger instances of damage or ones that have already caused the knee joint to collapse. These can include arthroscopy (a procedure to assess the knee and deal with any related issues), core decompression (a procedure to encourage blood vessel formation and relieve pressure inside the knee), and osteochondral grafting (a technique that uses patients own cartilage or donor cartilage to restore the knee joint).

There are different types of surgeries that can be chosen based on the severity and specifics of each patient’s condition. For example, ‘high tibial osteotomies’ might be recommended for younger, active patients to promote healing. ‘Unicompartmental knee arthroplasty’ could be suitable for cases where only one part of the knee is damaged. ‘Total knee arthroplasty’ may be needed for extensive knee damage or inflammatory conditions affecting multiple parts of the knee.

The choice of treatment for spontaneous osteonecrosis of the knee should involve the patient and a team of health professionals. The goal is to align the treatment with the patient’s lifestyle and expectations, aiming for pain relief, functionality, and quality of life.

What else can Spontaneous Osteonecrosis of the Knee be?

In the process of diagnosing spontaneous osteonecrosis of the knee (a disease leading to the death of bone tissue), there are several conditions that might show similar symptoms and should be considered. These include:

• Degenerative arthritis: This is mostly common in older patients.
• Inflammatory conditions, like rheumatoid arthritis: These need to be eliminated with lab tests and medical evaluations.
• Other types of osteonecrosis: These could be linked to steroid use or alcoholism. They display different symptoms and may affect a larger area of the knee.

Identifying the correct condition is vital for providing the most effective treatment. Here are some of the conditions doctors may check for:

• Osteoarthritis: This is frequent among older patients and involves more gradual joint decay.
• Meniscal tear: It looks a lot like spontaneous osteonecrosis in terms of symptoms but usually stems from trauma or a twisting injury.
• Septic arthritis: This should be considered if there’s joint swelling, or the person is unable to move the knee or put weight on it. It needs immediate attention to avoid causing further joint damage.
• Inflammatory arthritis: Diseases like rheumatoid arthritis are often distinguishable through lab tests and clinical evaluation.
• Osteochondritis dissecans: Mostly seen in younger patients, it is characterized by localized bone and cartilage necrosis.
• Transient osteoporosis: It comes with sudden joint pain and bone marrow edema but without necrosis and it primarily affects the hip.
• Shifting bone marrow edema syndrome: It is marked by shifting bone marrow edema which often affects multiple joints over time.
• Bony contusion or hidden fractures: These often follow incidents of severe trauma.
• Secondary osteonecrosis: It generally affects both knee joints and extends to the end of the thigh bone. It is closely linked to certain risk factors like corticosteroid use, heavy alcohol consumption, sickle cell disease, and Gaucher disease.
• Post-arthroscopic necrosis: This happens after knee surgery and involves localized necrosis, but it is usually associated with existing knee issues. Its link to a surgical procedure helps distinguish it from spontaneous osteonecrosis of the knee.

What to expect with Spontaneous Osteonecrosis of the Knee

The potential outcome and treatment of spontaneous osteonecrosis of the knee, a condition where bone tissue in the knee dies due to restricted blood flow, greatly depends on the size of the affected area. Larger affected areas may fuel the disease to progress requiring surgery.

If it’s caught early, there’s a high chance of complete recovery and preserving knee function, especially with non-surgical treatments. But if left untreated or in advanced stages, serious problems like joint collapse and significant loss of knee function may occur.

Younger patients and those with fewer serious health conditions generally have better results. They are more likely to respond positively to non-surgical treatments and recover more effectively from surgical treatments. However, if more than 40% of the joint surface is affected by the disease, there is a high chance that the patient may develop osteoarthritis after around 15 years.

Surgical treatments, like Total Knee Arthroplasty (TKA), can be successful in treating advanced stages of the disease, with most patients experiencing pain relief and improved knee function. But this might not be the best option for younger patients or those with active lifestyles, because joint replacements may limit certain activities.

The disease stage at diagnosis also greatly affects the outcome. This is often measured by the Koshino classification:

1. Stage 1: The x-ray might look normal, but an MRI could reveal bone marrow swelling. At this stage, non-surgical treatments often have a good outcome since the swelling can improve without the disease progressing.
2. Stage 2: The x-ray shows a harder area in the region just below the cartilage indicating early bone changes. While non-surgical treatment can still be effective, there’s an increased risk of the disease progressing compared to Stage 1.
3. Stage 3: The x-ray shows a crescent sign signifying a collapse in the region just below the cartilage. At this stage, the bone’s structural integrity may be compromised, leading to increased risks of joint degeneration and arthritis.
4. Stage 4: The x-ray shows advanced joint destruction and osteoarthritis changes, which implies poor prognosis for preserving the joint. As a result, surgical intervention like TKA often becomes necessary.

Possible Complications When Diagnosed with Spontaneous Osteonecrosis of the Knee

Spontaneous osteonecrosis of the knee is a condition that gets worse over time if left untreated. The complications from this disease typically come from two sources; the worsening of the disease and the risks that come with surgery. People with this condition may find it difficult to remain active, and they have a high chance of developing osteoarthritis in the affected knee. As the disease advances, it can cause ongoing pain, decrease mobility, and reduce the quality of life. Surgical complications include infection, blood clots, and failed implants. Surgery meant to clear out the joint carries risks of joint stiffness and continued pain.

Potential Risks:

• Progressive osteoarthritis: One frequent complication is the knee condition progressing to osteoarthritis, which can lead to joint stiffness, reduced motion, and ongoing pain
• Joint collapse: In advanced stages, the knee condition could cause the collapse of the area right beneath the cartilage, which significantly worsens symptoms and inhibits function.
• Increased risk of fractures: The weakened bone structure in the area of the disease may increase the chance of bone fractures.
• Impaired mobility: As the condition gets worse, patients might experience severe limitations in mobility, affecting their quality of life.
• Persistent pain: Ongoing pain is a common problem even after treatment.
• Limited efficacy of surgery and core decompression: Neither of these two treatments may provide long-lasting relief, especially in the late stages.
• Risk of infections: Both surgery and core decompression have a risk of infection at the surgical site or inside the joint.
• Blood clots: both treatments also carry a risk of deep vein thrombosis and pulmonary embolism.
• Worsening symptoms: There are cases when the symptoms may worsen after surgery, particularly if the procedure does not sufficiently treat the original disease.
• Scarring and stiffness: Surgery may cause scarring within the joint, which can result in stiffness and limited motion.
• Infections, Blood clots, and Implant loosening or failure: These are all risks specific to total knee replacement and partial knee replacement surgeries.
• Periprosthetic fractures: Fractures may occur around the implant site, particularly in patients with osteoporosis or weakened bone structure.
• Nerve and vascular injury: Rare but severe complications include damage to the nerves or blood vessels around the knee.

Preventing Spontaneous Osteonecrosis of the Knee

To prevent spontaneous osteonecrosis of the knee (a condition where poor blood supply causes the knee’s bone to die), it’s important that patients understand the various risk factors and early signs. This condition is especially common in older individuals and women who have gone through menopause.

Maintaining good bone health is essential to prevent osteonecrosis. This can be done by having an adequate intake of calcium and vitamin D, doing regular weight-bearing exercises (exercises where your feet and legs carry your weight), and avoiding smoking and drinking a lot of alcohol. These practices can lower the risk of bone loss (osteoporosis) and spontaneous osteonecrosis of the knee.

Patients should also be familiar with early signs of this condition, which include sudden knee pain without any history of injury, especially in adults over 50. Knowing these signs can lead to quicker medical help, diagnosis, treatment, and potentially slow disease progression.

Understanding the benefits and risks of the different treatments options, such as non-surgical (conservative) and surgical methods, allows patients to be involved in making choices about their care. If diagnosed with spontaneous osteonecrosis of the knee, patients need guidance on how to modify their activity. This means avoiding activities causing knee pain and doing gentle exercises to preserve joint movement and muscle strength. It’s also important to manage weight to lessen pressure on the knee joints.