What causes knee arthritis?
The knee joint is made up of the end of the femur and the top of the tibia. It is supported by ligaments both inside and outside the joint. The knee joint moves like a hinge. The menisci are small ‘shock-absorbing’ pads inside in the knee joint. A healthy knee joint is lined by a specialised, smooth, low-friction (articular) cartilage which allows the joint to move smoothly and freely. Knee arthritis occurs when this specialised cartilage degenerates or wears out, and the underlying bone becomes exposed.
There are two main causes for the specialised cartilage in the knee joint to degenerate:
- Osteoarthritis is the most common cause of knee arthritis. Osteoarthritis may run in families, determined by genetics, however it may also occur as a result of injury, trauma or previous surgery. Removal of a meniscus leads to knee osteoarthritis in the long term. An impaired blood supply to the knee joint may cause collapse of a small area.
- Inflammatory arthritis is an immune disorder that leads to inflammation in the (synovial) lining of the knee joint. Common causes are auto-immune disorders such as rheumatoid arthritis. The synovial lining becomes inflamed and thickened with the production of various damaging molecules in the joint. This in turn leads to damage of the specialised articular cartilage. Rheumatologists treat inflammatory arthritis with medications that target the damaging molecules.
What are the symptoms of knee arthritis?
- The most common locations for pain from knee arthritis are at the inside and outside aspects of the knee. Some patients have a dull pain at the front of the knee, particularly when walking up and down stairs or when seated for longer periods. Pain at the back of the knee may be due to a Baker’s cyst, a symptom of knee arthritis. Pain in the knee may sometimes actually be due to referred pain from hip arthritis.
- Knee arthritis can cause a reduced range of motion at the knee joint. This is usually something that develops slowly over time and may be worse in the morning or with inactivity.
- The inflammation and accumulation of joint fluid in the knee joint will make it feel swollen and warm to touch.
- Knee arthritis may lead to a limp and the need to use a walking stick or walking frame for balance.
- Knee arthritis may lead to a change in alignment of the leg. The leg may appear “bowed-legged” or “knock-kneed”.
- The knee may feel unstable to stand or walk on. The knee may give way without any warning.
- If there is a loose body or torn cartilage in the knee it may become locked in one position.
- Functional limitations. There may be every day functional limitations. This may be a reduction in exercise or walking distance over time. More specifically, it may be uncomfortable to walk up and down stairs, to crouch down or to get down to put on shoes or socks.
How is knee arthritis diagnosed?
Knee arthritis is best diagnosed by your treating doctor. A combination of your history, physical examination and an x-ray is usually enough to determine whether the knee joint is arthritic. The knee joint will usually have a painful limitation in range of motion. There may be points around the knee that are particularly tender to touch. An x-ray may show the space in the knee joint to be narrowed with bony deformity. Rarely, an MRI may be needed to determine if the articular cartilage in the knee joint is damaged. A meniscus tear can also be diagnosed with an MRI. Blood tests are used to diagnose the different inflammatory causes of knee arthritis.
What are the non-surgical treatments for knee arthritis?
There are a multitude of suggested treatments for osteoarthritis, but be careful, not all treatments are supported by the best medical evidence.
The treatments for osteoarthritis with strong supporting evidence in the medical literature include:
- Exercise – referral to a physiotherapist or exercise physiologist may be beneficial.
- Weight loss – for those patients with a body mass index (BMI) greater than 25, a weight loss target of 5-10% of body weight is recommended. Referral to a dietician or upper gastrointestinal surgeon may be beneficial.
Other treatments, that may help, where the medical evidence is less clear, include:
- Cognitive behavioural therapy
- Stationary cycling
- Yoga
- Aquatic exercises (hydrotherapy)
- Massage therapy
- Manual therapy such as stretching
- Heat therapy
- Aids such as walking sticks and frames
- Transcutanous electrical nerve stimulation (TENS)
- Oral anti-inflammatory medications (NSAIDs)
- Corticosteroid injections
Interventions with evidence against use for hip or knee arthritis treatment include opioid medications, viscosupplementation injections, stem cell therapy, glucosamine, chondroitin and omega-3 fatty acid supplements.
What are the surgical options for knee arthritis?
Not all arthritic knees require a total knee replacement. Surgical treatments for knee arthritis can be considered to fall into two broad categories:
- Knee joint preservation. The main goal of joint preservation is to maintain the specialised articular cartilage in the knee for as long as possible, whilst also improving pain relief and mechanical symptoms.
- Knee arthroscopy is a key-hole procedure performed through two small incisions at the front of the knee. A small camera is passed into the knee joint so that the surfaces and contents of the knee can be examined in great detail. This is a suitable procedure for patients with minimal arthritis in the knee, who may have mechanical symptoms arising from a meniscus tear, a loose body or flap of cartilage, or cruciate ligament reconstruction. Knee arthroscopy is not recommended for patients with advanced knee arthritis.
- If pain from knee arthritis is related to the overall alignment of the leg (bow-legged or knock-kneed), the leg may be realigned by cutting the femur or tibia and the forces redirected through the healthy part of the joint. This approach is particularly suitable for young and active patients who are not yet ready for a joint replacement procedure.
- Knee joint replacement procedures involve replacing part of the knee joint surface (partial knee replacement) or the entire joint (total knee replacement) with an artificial joint (prosthesis). The knee joint can be considered to be made of three different compartments; the medial, the lateral and patellofemoral compartments. These compartments are replaced all together or individually. A total knee replacement is a more extensive procedure than a partial knee replacement with a longer recovery period involved.
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