Blood supply to every organ and tissue in the body is very vital for optimal functioning. Loss of blood supply to any body part or organ leads to a gradual death (necrosis) of that part or organ and can be very dangerous. Loss of blood supply to the brain results in stroke; loss of blood supply to the heart results in a heart attack; loss of blood supply to a bone tissue leads to bone death (osteonecrosis).
Knee osteonecrosis means knee bone death. It occurs mostly in older people, with women being more affected than men. Three types of osteonecrosis affect the knee: spontaneous osteonecrosis of the knee (SONK), secondary, and post-arthroscopic.
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Anatomy of the knee
The knee is one of the two major hinge joints in the body, with the elbow being the other. It is responsible for movement and very vital for weight-bearing. The joint at the knee is the largest and most complex joint in the body. It is made up of three bones the lower end of the femur (thigh bone), the upper end of the tibia (shin bone), and the patella (kneecap). Knee osteonecrosis commonly occurs in the medial femoral condyle (inside of the knee), however, the lateral femoral epicondyle (outside of the knee) or tibial plateau (the flat top of the tibia) may also be likely areas of occurrence.
The knee is vulnerable to injury; according to the database from the National Institutes of Health, it is the most commonly injured joint by adolescent athletes. Among older people, it is prone to knee osteonecrosis, which if not given medical attention early, can progress to osteoarthritis.
The most common form of knee osteonecrosis is spontaneous osteonecrosis of the knee, SONK. It is mostly observed in people who are over age 50. On the other hand, secondary osteonecrosis has been observed to be more common in the younger population and it is linked to some medical conditions like sickle cell disease (SCD), consumption of alcohol, corticosteroids, and tobacco, and myeloproliferative disorders. The last form, post-arthroscopic osteonecrosis, is a rare type. Reports show that it affected 4% of patients who had arthroscopic knee surgery, particularly meniscectomy.
Causes of knee osteonecrosis
When there is a lack of blood supply to bone tissues, it leads to the death of bone cells, which results in an eventual collapse of the bone. This is the case in osteonecrosis. Knee osteonecrosis can result in a collapse of the articular cartilage covering the bone ends, and this can lead to arthritis.
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The cause of the lack of blood supply is still unknown, but studies have linked the following risk factors to the development of knee osteonecrosis:
- Knee injury
Aside from pain and swelling, knee injuries like dislocation or fracture can also result in damaged blood vessels. Dislocation involves bone ends; fracture involves any bone part; either way, both injuries can affect the blood vessels supplying the bone, thereby, reducing the flow of blood to the dislocated/fractured bone. This is why immediate medical attention is needed. Sometimes, an x-ray or MRI scan may be done to have a deeper view of the bone.
- Oral corticosteroid medications
It is not exactly known why oral steroid medications cause osteonecrosis, but research shows that there is a connection between them. This is disturbing because many diseases such as asthma and rheumatoid arthritis are treated with these medications.
- Medical conditions
Some medical conditions such as obesity, SCD, and lupus are associated with the secondary form of knee osteonecrosis. HIV patients are also diagnosed with it this is because the medications for HIV treatment are also linked to the disease.
- Excessive consumption of alcohol
Alcohol causes weight gain because it stops the body from burning fat. Drinking too much alcohol increases the buildup of fat in the body, and this can consequently lead to deposits of fat tissues that can block blood vessels and obstruct blood flow to the vessels.
Studies show that osteonecrosis can occur after organ transplants, especially kidney transplants.
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Symptoms of knee osteonecrosis
The most common symptom associated with osteonecrosis of the knee is pain on the inside of the knee. The pain can be triggered by a specific activity or a minor injury and can become intense at night.
Other symptoms include: swelling over the front and inside of the knee, increased sensitivity to touch in the area, and limited movement of the knee due to pain.
Diagnosis of knee osteonecrosis
A good diagnosis of knee osteonecrosis begins with a thorough history taking.
Here, your doctor will talk about your medical history, ask you to describe your symptoms and then proceed to examine your knee.
While examining your knee, your doctor looks out for swelling within your joints, tenderness, redness, and joint instability.
You may be asked to move your knee to observe the range of motion at your knee joint.
Your doctor also looks out for any sign of injury to the muscles, ligaments, and tendons around your knee.
After a physical examination of your knee, your doctor then goes on to confirm the diagnosis by taking an imaging study of your knee either with an X-ray study, magnetic resonance imaging (MRI) scan, or a bone scan. An imaging study is vital as it helps to take a deeper look at your bones and other aspects of your knee joint to identify the stage of knee osteonecrosis you have.
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Staging of knee osteonecrosis
There are four stages to knee osteonecrosis development:
Stage I: At this stage, the patient experiences symptoms that become intense and last for six to eight weeks. To be sure of the diagnosis, the doctor uses a positive bone scan, not just x-rays to get a better view of the knee. At this point, surgery is not required for treatment, instead, the doctor administers medication for pain relief and other methods that focuses on reduced weight-bearing.
Stage II: From Stage I to this stage takes several months. At this stage, x-rays can confirm the diagnosis, because the medial femoral condyle which is normally rounded now becomes flattened and can be visible with x-rays. Other forms of imaging studies such as MRI, CT, or bone scan can also confirm the diagnosis.
Stage III: From Stage I to this stage takes about three to six months, x-rays alone can confirm the diagnosis. The articular cartilage that covers the bones starts to come off the bone since the bone itself is gradually dying. Surgical procedures may be required to treat the patient at this point.
Stage IV: At this stage, the disease becomes very critical as the articular cartilage is now destroyed and the joint space becomes narrow; severe osteoarthritis develops; joint replacement surgery becomes necessary.
Prognosis of knee osteonecrosis
When knee osteonecrosis is diagnosed early (at stage I), a simple pain relief medication may be all that is needed to treat it. The doctor may also advise lower mobility of the affected knee. At advanced stages, surgery may be done to prevent increased damage to the whole joint.
Treatment of knee osteonecrosis
The treatment option for knee osteonecrosis depends on some factors which include the stage of the disease, the portion of bone that is affected, and the cause of the disease. Based on these factors, treatment can be non-surgical or surgical.
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Non-surgical treatment option
If the disease is at an early stage and only a small area of the knee is affected, surgery may not be necessary. The doctor may suggest any of the following non-surgical treatment procedures:
- Use of medications:
The doctor may prescribe some nonsteroidal inflammatory drugs (NSAIDs) like ibuprofen and naproxen to relieve the pain and swelling in the knee. If the patient is a young person, the doctor may suggest bisphosphonates for treatment.
- Reduced weight bearing:
For some patients, just simply taking weight off their knees may be all that is needed to slow the damage and allow for healing. The patient may need to start using crutches for some time to reduce the weight on their knees.
The patient may be asked to engage in certain physical activities that aid in strengthening the thigh muscles and allow for a range of movement in the affected joint. To avoid stress on the joint, water exercise may also be recommended for the patient.
- Modification in certain activities:
The doctor may advise the patient to stop certain activities that lead to pain.
Surgical treatment options
Your doctor may recommend surgery if there seems to be no improvement after the non-surgical treatment options, or if the portion of the bone affected is quite large. Some surgical procedures that may be recommended include:
- Total knee replacement:
Your doctor may opt for this procedure if the disease has progressed to stage IV, where the bone has been destroyed. The procedure involves a replacement of the destroyed bones and cartilages with metal or plastic joint surfaces to restore the knee function.
In this procedure, the surgeon removes a portion of either the tibia or femur or will insert a wedge of bone graft/synthetic bone to help take the weight off the damaged portion of the knee. This is vital because taking weight off the affected area of the joint will relieve the patient of pain and promote healing.
Other surgical procedures your doctor may recommend osteochondral bone (bone and cartilage) grafting, core compression, arthroscopic debridement and microfracture, and autologous chondrocyte implantation (ACI).
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As much as knee osteonecrosis is likely to occur in people who are over age 50, it can be avoided and effectively treated when we are armed with the knowledge of what it is and how to diagnose and easily manage it.