Total Knee Replacement
Total knee replacement is one of the treatment options for knee arthritis. Read below to learn more about knee arthritis and whether you would benefit from knee replacement surgery.
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What is 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?
- Pain. 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.
- Stiffness. 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.
- Swelling. The inflammation and accumulation of joint fluid in the knee joint will make it feel swollen and warm to touch.
- Limp. Knee arthritis may lead to a limp and the need to use a walking stick or walking frame for balance.
- Deformity. Knee arthritis may lead to a change in alignment of the leg. The leg may appear “bowed-legged” or “knock-kneed”.
- Instability. The knee may feel unstable to stand or walk on. The knee may give way without any warning.
- Locking. 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
- 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
- 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.
- Osteotomy. 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 articularly 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.
What is a total knee replacement?
- Severe pain
- Reduced mobility and independence
- Difficulty performing job due to pain and stiffness
- Inability to enjoy recreational activities due to pain and stiffness
- Pain at night that interrupts sleep
What is a partial knee replacement?
Partial knee replacement is a surgical procedure that replaces only part of the knee joint with an artificial surface (prosthesis).
61,005 partial knee replacements have been performed in Australia since 1999. Partial knee replacements may be suitable for patients with arthritis limited to only one compartment of the knee joint. This is most commonly the medial or lateral compartment of the knee joint.
The procedure preserves the remaining healthy compartments and ligaments of the knee joint. When compared to total knee replacement, partial knee replacement involves a smaller incision and approach, less pain after surgery, a more natural feeling knee joint and faster rehabilitation.
What is patient specific instrumentation (PSI)?
Patient specific instrumentation is a technique sometimes used for total knee replacement that utilises pre-operative x-ray and MRI to plan a total knee replacement before manufacturing 3D models and patient specific instruments.
The 3D model takes into account a patient’s unique size and deformity to plan the position of prosthesis.
How does computer-assisted and robotic-assisted surgery work?
What is a knee replacement made of and how is it fixed in place?
Total knee replacement prostheses are most commonly made of metal alloys, usually titanium or cobalt-chromium based.
Some implants are made of ceramics or ceramic/metal mixtures. The spacer between the femoral and tibial component, and patella resurfacing component, is made of ultra-high molecular weight polyethylene.
The components may be fixed to the femur and tibia with or without bone cement. Cement fixation, particularly on the tibial side of the joint, is known to have a reduced rate of revision.
How long will the total knee replacement last?
In 2019, the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) reported the overall revision rate of primary total knee replacement for osteoarthritis as 8.6% at 18 years after surgery.
Age is a major factor in determining how long a total knee replacement will last. Patients that are under the age of 55 have more than 3 times the rate of revision after 6 months and more than 6 times after 10 years, compared to patients aged over 75. Males have a higher rate of revision than females.
How long does it take to recover after a knee replacement?
Whilst every patient has a different starting point prior to knee replacement, patients recover better when they are well informed and have undergone a period a physiotherapy with strength and conditioning prior to surgery. Patients are encouraged to walk almost immediately following surgery under the supervision of a physiotherapist. It takes approximately 2 weeks for the skin wound to be well healed and it may be wet after that.
Recovery after a total knee replacement is much longer when compared to total hip replacement. The range of motion of the knee joint before surgery largely determines the range of motion after total knee replacement. So, if you had a stiff knee before you are likely to have a stiff knee after knee replacement. Most knee replacement patients will have returned to driving a car by 6 weeks.
The primary goals of a total knee replacement are long term pain relief and the maintenance of independent mobility. There will be a steady improvement over the first 3 to 4 months. It is not unusual to still require some simple pain relief at this time. The knee replacement may remain swollen and warmer than the other side for up to 12 months after surgery. This is normal. The knee replacement is made of metal and plastic components and you may hear or feel them click from time to time.
This can also be normal. If the clicking becomes painful, this however needs to be evaluated. Overall recovery for a total knee replacement can be up to 18 months.
Over 85% of patients have good pain relief after total knee replacement and are satisfied with the long-term result. A small percentage, approximately 5%, may have a vague discomfort in replaced knee that cannot be explained. Most patients are able to achieve improvements in mobility and quality of life, returning to activities such as golf, bowls, tennis, swimming and cycling. Total knee replacements are not intended for patients that engage in higher intensity activities such as contact sports, basketball and squash.
What are the main risks of knee replacement surgery?
Deep venous thrombosis (DVT). A blood clot may form in the leg after surgery. This has the potential to propagate or break off, travelling to lung. This is potentially life threatening. Medications can be used to reduce the risk of DVT. Other things that you can do to prevent clots include remaining well hydrated, wearing TED stockings and mechanical calf pumps immediately after the operation. Also, moving around and walking early after surgery will lower your risk of DVT.
Infection. Infection can be either superficial or deep down at the knee prosthesis. This may occur soon after surgery or even many years down the track. The knee replacement may need to be removed while being treated with antibiotics. Infection is the complication that orthopaedic surgeons fear the most. On average the risk of deep infection is 1%. This means that 1 in 100 patients may develop an infection. We do everything we can to prevent this. This includes antiseptic body wash before the operation, antibiotics during and after the operation, and meticulous wound care after the operation. All joint replacements are performed in a laminar air flow operating theatre under sterile conditions.
Fracture. The bone supporting the knee prosthesis may fracture both during or after surgery. Small fractures may heal on their own. Larger, unstable fractures may require further operations.
Loosening. The femoral or tibial component may become loose over time. This is rare with modern day techniques and prostheses. Further revision surgery may be required for this.
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Dr Matthew Broadhead
BSc(Med) MBBS(Hons) ChM PhD FRACS FAOrthA
Consulting in Coffs Harbour, Nambucca, South West Rocks and Yamba.