What is Knee Replacement Surgery?
Knee replacement surgery, or knee arthroplasty, offers pain relief and improved movement to those suffering from advanced arthritis of the knee or a weakened knee joint.
The knee joint is made up of the lower end of your thigh bone (femur) and the upper end of your shin bone (tibia). These normally glide over each other easily because they are covered by smooth cartilage. In most cases, the cartilage is worn away and the surface of the knee becomes pitted, eroded, and uneven. This causes pain, stiffness, instability, and a change in body alignment.
A new knee joint will usually reduce the pain, improve mobility and help the patient become more active. However, the new knee won’t be able to bend quite as far as a normal knee joint.
Artificial knee parts are almost always made of metal and plastic. A knee replacement can last for up to 20 years.
A knee replacement surgery may be needed if:
- Knees are stiff and swollen
- There is pain throughout the day, even at rest
- Walking, getting up, or climbing stairs is difficult and painful
- Medication and therapy do not offer enough relief
The most common reason for knee replacement surgery is osteoarthritis. Other conditions that cause knee damage include:
- rheumatoid arthritis
- disorders that cause unusual bone growth (bone dysplasias)
- death of bone in the knee joint following blood supply problems (avascular necrosis)
- knee injury
- knee deformity with pain and loss of cartilage
Types of Knee Replacement Surgery
There are two main types of knee replacement surgery:
- Total Knee Replacement (TKR) is the most common type of surgery. It involves removing the damaged bone and cartilage and replacing the knee joint with implants (prosthesis) to restore the natural motion and function of the knee. The surgeon will replace the lower end of the thigh bone (femur) and the upper end of the shinbone (tibia) with artificial parts. He/she may also replace the under surface of the kneecap (patella) with a plastic button. However, this is often not needed.
- Partial (or Unicompartmental) knee replacement. In this procedure, the surgeon will replace the ends of the bones on one side of the knee only. He/she may recommend this if the damage to the knee is only on one side (usually the inside of the knee). It may be possible for the surgeon to do a partial knee replacement through a smaller cut (incision) than is needed for a total knee replacement.
For a total knee replacement, it is probably less likely that the patient will need a further knee operation than if he/she has a partial knee replacement. However, medical complications are more likely after a total knee replacement. The surgeon will discuss with the patient which type of surgery is best under present circumstances. This will depend on a number of factors including the condition of the knee and the patient’s general health.
Alternatives to Knee Replacement
The surgeon will usually only recommend surgery if non-surgical treatments no longer help to reduce the pain or improve mobility. Non-surgical treatments might include physiotherapy and exercise, medication or using physical aids like a walking stick. If the patient is overweight, it is encouraged for him/her to lose weight as this will reduce the strain on the knee. Corticosteroid injections can ease symptoms for a few months, but this is not a cure for arthritis.
Alternative surgical procedures include:
- Arthroscopy (if the arthritis isn’t too severe) – this is keyhole surgery where the surgeon clears out bits of debris inside the knee.
- Microfracture – using keyhole surgery, the surgeon makes small holes in the surface layer of the bone to encourage new cartilage to grow.
- Osteotomy (where the leg bones are cut and re-set) – this is sometimes used if the patient is younger, to allow the surgeon to delay knee replacement surgery.
Damaged cartilage and bone are removed from the knee joint. Man-made pieces are then placed in the knee. These pieces may be placed in the following places in the knee joint:
- Lower end of the thigh bone. This bone is called the femur. The replacement part is usually made of metal.
- Upper end of the shin bone, which is the large bone in your lower leg. This bone is called the tibia. The replacement part is usually made from metal and a strong plastic.
- Back side of your kneecap. Your kneecap is called the patella. The replacement part is usually made from a strong plastic.
One of these 2 types of anesthesia will be used:
- General anesthesia – This means the patient will be asleep and unable to feel pain.
- Regional (spinal or epidural) anesthesia. Injection in the back to make the patient numb below the waist. Patient will also get medicine to make him/her sleepy.
After administering the anesthesia, the surgeon will make a cut over the knee to open it up. This cut is often 8 to 10 inches long. Then the surgeon will:
- Move the kneecap (patella) out of the way, then cut the ends of the thigh bone and shin (lower leg) bone to fit the replacement part.
- Cut the underside of the kneecap to prepare it for the new pieces that will be attached there.
- Fasten the 2 parts of the prosthesis to the bones. One part will be attached to the end of the thigh bone and the other part will be attached to the shin bone. The pieces can be attached using bone cement or screws.
- Attach the underside of the kneecap. A special bone cement is used to attach this part.
- Repair the muscles and tendons around the new joint and close the surgical cut.
The surgery takes about 2 hours.
Most artificial knees have both metal and plastic parts. Some surgeons now use different materials, including metal on metal, ceramic on ceramic, or ceramic on plastic.
The procedure for a partial knee replacement surgery is similar to the above. The difference lies in the degree of replacement and repair.
MAKOplasty (Robotic partial knee replacement)
MAKOplasty is a surgical procedure for partial knee arthroplasty using a RIO Robotic Arm Interactive Orthopedic System.
It enables surgeons to plan partial knee replacement procedures by using three-dimensional computer imaging based on a CT scan. This allows them to determine optimal implant size, position, and alignment for each individual patient, and to map out accurately the areas of bone they want to remove.
During surgery, the robotic arm system provides visual, auditory, and tactile control to help assure that surgeons cut away only the bone planned to be resected prior to surgery. The procedure is said to take the guesswork out of surgery, resulting in accurate and reproducible results.
It usually takes around six to 12 weeks to make a full recovery from knee replacement surgery. However, this varies between individuals. The knee will continue to improve for two years after the surgery as scar tissue heals and muscles get stronger through exercise.
Patient may need some kind of pain relief for up to 12 weeks after surgery. Some patients have discomfort for up to six months. Patient may be asked to wear compression stockings for several weeks at home. There may be swelling which can last for three to six months.
Build up daily activities gradually. The patient should be able to move around the home and manage stairs carefully. However, some routine daily activities may be difficult for a few weeks. May need to use a walking stick or crutches for up to six weeks.
Physiotherapy exercises are a crucial part of recovery, it’s essential to continue to do them for at least two months. After three months, the patient can try kneeling using a soft cushion. Kneeling isn’t harmful. However, some patients find that kneeling never becomes comfortable after knee replacement surgery.
For working patients, they should be able to return to work after about eight weeks but this will depend on the type of work. If it’s a physically demanding job, it may take up to 12 weeks before the patient is ready. It may help to have a phased return, where the patient gradually build up to his/her usual work activities. Need to ask the surgeon for recommendations according to specific circumstances.
Most patients can drive after about six weeks following a total knee replacement, and about three weeks after a partial knee replacement. However, need to be sure that the patient can control the vehicle and make an emergency stop – depending on the surgeon’s assessment.
About Knee Implants
Metal components replace the lower end of the thigh bone (femur) and the upper end of the shinbone (tibia). The metal is typically either titanium or a cobalt/chromium-based alloy. Between the metal components lies a plastic tray, or cushion, made of ultra high-density polyethylene. Some designs of implants don’t have a metal component at the top of the tibia. With these, the surgeon attaches a plastic part directly to the bone. If the surgeon replaces the under surface of the kneecap (patella), he/she will use another plastic component there.
Sometimes the plastic cushion is attached firmly to the metal part underneath – this is called a fixed bearing implant. The metal part at the end of the femur then rolls on this fixed cushion as the patient moves. An alternative design is a mobile bearing implant where the plastic cushion can rotate a little against the metal part lying under it. This allows the patient a small amount of rotation in the new knee joint.
The surgeon will usually fix the knee implant in place using a fast-setting bone cement (polymethylmethacrylate). However, some implants have special textured surfaces which allow new bone to grow into them to hold them in place without the need for cement. These are called cementless implants.
A complete artificial knee weighs about 500–600 grams (18–21 ounces).
What should I do next?
The type of knee implant to use will depend on many factors including age, weight, level of activity and health. Ask your Orthopaedic surgeon to explain options and discuss what is best in specific circumstances. To get Dr. HC Chang’s opinion on your condition, contact us today. Visit our FAQ on total knee replacement for more information.