Articular cartilage is a firm rubbery protein material covering the end of a bone. It acts as a cushion or shock absorber between the bones. When articular cartilage breaks down, this cushion is lost, and the bones will grind together. This causes the development of symptoms such as pain, swelling, bone spur formation and decreased motion. Osteoarthritis commonly affects weight bearing joints such as the knee, but it may affect any joint.
Osteoarthritis of the knee (OA Knee) is one of the five leading causes of disability among elderly men and women. The risk for disability from OA Knee is as great as that from cardiovascular disease. Here are some frequently asked questions about OA Knee. OA Knee usually occurs in knees that have experienced trauma, infection or injury. A smooth, slippery, fibrous connective tissue called articular cartilage acts as a protective cushion between bones. Arthritis develops as the cartilage begins to deteriorate or is lost. As the articular cartilage is lost, the joint space between the bones narrows. This is an early symptom of OA Knee and is easily seen on X-rays. As the disease progresses, the cartilage thins, becoming grooved and fragmented. The surrounding bones react by becoming thicker. They start to grow outward and form spurs. The synovium (a membrane that produces a thick fluid that helps nourish the cartilage and keep it slippery) becomes inflamed and thickened. It may produce extra fluid, often known as "water on the knee," that causes additional swelling.
Over a period of years, the joint slowly changes. In severe cases, when the articular cartilage is gone, the thickened bone ends rub against each other and wear away. This results in a deformity of the joint. Normal activity becomes painful and difficult. Several factors may increase the risk of developing osteoarthritis of the knee.
- Heredity: There is some evidence that genetic mutations may make an individual more likely to develop OA.
- Weight: Weight increases pressure on joints such as the knee
- Age: The ability of cartilage to heal itself decreases as people age.
- Gender: Women who are older than 50 years of age are more likely to develop OA Knee than men.
- Trauma: Previous injury to the knee, including sports injuries, can lead to OA Knee.
- Repetitive stress injuries: These are usually associated with certain occupations, particularly those that involve kneeling or squatting, walking more than two miles a day, or lifting at least 55 pounds regularly. In addition, occupations such as assembly line worker, computer keyboard operator, performing artist, shipyard or dock worker, miner and carpet or floor layer have shown higher incidence of OA Knee.
- High impact sports: Elite players in soccer, long-distance running and tennis have an increased risk of developing OA Knee.
- Other illnesses: Repeated episodes of gout or septic arthritis, metabolic disorders and some congenital conditions can also increase your risk of developing OA Knee.
- Other risk factors are being investigated, including the impact of vitamins C and D, poor posture or bone alignment, poor aerobic fitness and muscle weakness.
OA Knee can be diagnosed in two ways: patient-reported symptoms such as pain or disability or actual physical signs, such as the changes in the joint seen on X-rays. In most cases, both pathology and patient-reported symptoms are present. An evaluation of OA Knee includes a complete history and physical examination. The examination should cover:
- The involved limb
- The spine
- The blood and nervous system
- The joints on either side of the knee, particularly the hip joint, which can also cause knee pain
Initial treatment is generally directed at pain management. OA Knee pain may have different causes, depending on the individual and the stage of the disease. Thus, treatment is tailored to the individual.
A wide range of treatment options is available. You and your doctor should decide together on the course of treatment that's right for you. In general, treatment options fall into five major groups:
- Health and behavior modifications, such as patient education, physical therapy, exercise, weight loss, and bracing
- Drug therapies, including simple pain relievers such as aspirin or nonsteroidal anti-inflammatory drugs, COX-2 specific inhibitors, opiates and stronger drugs for patients who do not respond to other drugs or treatments, and glucosamine and/or chondroitin sulfate
- Intra-articular treatments, including corticosteroid injections or injections of hyaluronic acid (viscosupplementation)
- Surgery, including arthroscopy, osteotomy, and arthroplasty (joint replacement)
- Experimental/alternative treatments such as acupuncture, magnetic pulse therapy, vitamin regimes and topical pain relievers
Osteonecrosis of the knee
Knee pain has many causes. A relatively common cause of knee pain in older women occurs when a segment of bone loses its blood supply and begins to die. This condition is called osteonecrosis, which literally means "bone death."
In the knee, the knobby portion of the thighbone on the inside of the knee (the medial femoral condyle) is most often affected. However, osteonecrosis of the knee may also occur on the outside of the knee (the lateral femoral condyle) or on the flat top of the lower leg bone (tibial plateau). The exact cause of the disease is not yet known. One theory is that a stress fracture, combined with a specific activity or trauma, results in an altered blood supply to the bone. Another theory supposes that a build-up of fluid within the bone puts pressure on blood vessels and diminishes circulation. More than 3 times as many women as men are affected; most are over 60 years of age.
Osteonecrosis of the knee is also associated with certain conditions and treatments, such as obesity, sickle cell anemia, lupus, kidney transplants, and steroid therapy. Steroid-induced osteonecrosis frequently affects multiple joints and is usually seen in young patients. Regardless of the cause, if the disease is not identified and treated early, it can develop into severe osteoarthritis.
Signs and symptoms
- Sudden pain on the inside of the knee, perhaps triggered by a specific activity or minor injury
- Increased pain at night and with activity
- Swelling over the front and inside of the knee
- Heightened sensitivity to touch in the area
- Limited motion due to pain
Osteonecrosis of the knee develops through four stages, which can be identified by symptoms and X-rays.
Stage I: Symptoms are most intense in the earliest stage. Symptoms may continue for 6 to 8 weeks and then subside. Because X-rays are normal, a positive magnetic resonance is needed to make the diagnosis. Treatment at this point is nonoperative and conservative, focusing on pain relief and protected weight-bearing, and in some cases core decompression (see later).
Stage II: It may take several months for the disease to progress to Stage II. At this point, X-rays will show that the rounded edge of the thighbone is starting to flatten out. An MRI or bone scan can be used to diagnose the disease. A CT scan may also be used to measure the affected area of bone area.
Stage III: By the time the disease reaches stage III (3 to 6 months after onset), it is clearly visible on X-rays and no other diagnostic tests are needed. The articular cartilage covering the bone begins to loosen as the bone itself begins to die. Operative treatments may be considered at this point.
Stage IV: At this point, the bone begins to collapse. The articular cartilage is destroyed, the joint space narrows, and bone spurs may form. Severe osteoarthritis results and joint replacement surgery may be necessary.
In the early stages of the disease, treatment is nonoperative. If the affected area is small, this treatment may be all that is needed. Options include:
- Medications to reduce the pain
- A brace to relieve pressure on the joint surface
- A conditioning program with exercises to increase the strengthen of the muscles in your thighs
- Activity modifications to reduce knee pain
If more than half of the bone surface is affected, you may need surgical treatment. Several different procedures may be used to treat osteonecrosis of the knee. Among the surgical options are:
- Arthroscopic cleansing (debridement) of the joint
- Drilling to reduce pressure on the bone surface (core decompression)
- Procedures to shift weight-bearing away from the affected area
- Replacement of one or both joint surfaces
Clinical: Clinical presentation is summarized in the following table.
Table 1. Clinical Presentation of SPONK and Secondary Osteonecrosis
||Typically >55 y
|Associated risk factors
||Corticosteroids, alcohol, SLE, sickle-cell disease, caisson disease, Gaucher disease, fat emboli, thrombi formation
|Other joint involvement
||Approximately 80% bilateral
||One (usually medial femoral condyle or either tibial plateau)
||Epiphyseal to the subchondral surface
||Diaphyseal, metaphyseal, epiphyseal
||Commonly sudden onset of pain and increased pain with weightbearing, stair climbing, and at night
||Usually long-standing insidious pain; patient may have symptoms and signs of an underlying disorder, such as SLE
||Pain localized to affected area; small synovitis or effusion may occur; ligaments are stable; range of motion may be limited by pain or effusion
||Pain is difficult to localize; ligaments are stable; range of motion is grossly intact but may be limited by pain