Total Knee Replacement Surgery
During knee replacement surgery , Dr Pandher will resurface the damaged cartilage of your knee with an artificial device (implant). There are various types of implants available for the procedure ranging from total knee replacement surgery
(cruciate retaining, posterior stabilised, high flex, Mobile bearing) to partial knee replacement surgery
. Although replacing the total knee joint is the most common procedure, some people can benefit from just a partial knee replacement.Implants are made of metal alloys, ceramic material, or polyethylene parts, and can be joined to your bone with bone cement. Your surgeon will discuss with you the type of implant that best meets your needs.
The most common cause of chronic knee pain and disability is arthritis. Although there are many types of arthritis, most knee pain is caused by just three types: osteoarthritis, inflammatory arthritis, and post-traumatic arthritis.
This is an age-related "wear and tear" type of arthritis. It usually occurs in people 50 years of age and older, but may occur in younger people, too. The cartilage that cushions the bones of the knee softens and wears away. The bones then rub against one another, causing knee pain and stiffness.
There are various causes of inflammatory arthritis, most common of these is rheumatoid arthritis. In inflammatory the synovial membrane that surrounds the joint becomes inflamed and thickened. This chronic inflammation can damage the cartilage and eventually cause cartilage loss, pain, and stiffness.
This can follow a serious knee injury. Fractures of the bones surrounding the knee or tears of the knee ligaments may damage the articular cartilage over time, causing knee pain and limiting knee function.
Are you the right candidate for knee replacement?
The decision to have total knee replacement surgery should be a cooperative one between you and your knee replacement orthopaedic surgeon. You must clarify all concerns before taking decision to under go knife. Your final outcome and functional recovery expectations should be same as that of your doctor. However, one should not get swayed by myths and rumours spread about joint replacement surgery. Patients often raise concerns like being more disabled after joint replacement. This is unlikely if the procedure is chosen after complete work up and you have chosen the right surgeon for your surgery.
When Surgery Is Recommended
There are several reasons why your doctor may recommend total knee replacement surgery. People who benefit from total knee replacement often have some of the following findings:
- Severe knee pain or stiffness that limits your everyday activities, including walking, climbing stairs, and getting in and out of chairs. You may find it hard to walk more than a few blocks without significant pain and you may need to use a cane or walker.
- Moderate or severe knee pain while resting, either day or night.
- Chronic knee inflammation and swelling that does not improve with rest or medications Knee deformity — a bowing in or out of your knee.
- Failure to substantially improve with other treatments such as anti-inflammatory medications, physical therapy, or other surgeries like high tibial osteotomy or arthroscopic debridement.
The knee joint is where the lower end of your femur (thighbone) meets the upper end of your tibia (shinbone). Patella (knee-cap) sits in front of the joint to provide adequate lever mechanism for functioning of quadriceps muscle.
Types of Designs
For simplicity, the knee is considered a "hinge" joint because of its ability to bend and straighten like a hinged door. In reality, the knee is much more complex because the bone surfaces actually roll and glide as the knee bends. The first implant designs used the hinge concept and included a connecting hinge between the parts. Newer implant designs recognize the complexity of the joint and more closely mimic the motion of a normal knee. Some designs preserve the patient's own ligaments, while others substitute for them.
Several manufacturers make knee implants and there are more than 150 knee replacement designs on the market today. Common types of knee replacement implants include Cruciate retaining (subtypes- ultra-congruent, deep dish), posterior stabilised, and medial pivot. Another concept includes development of "gender specific" implants since a number of studies indicate that the shape and proportions of a woman's knee differ from those of a man's knee. As a result, several manufacturers have developed components for the end of the thighbone which more closely match the average woman's knee. However, there are no studies to show that "gender specific" implants last longer or provide better function than standard implants.
The Right Implant for You
The brand and design used by your doctor or hospital depends on many factors, including your needs (based on your age, weight, activity level, and health), your doctor's experience and familiarity with the device, and the cost and performance record of the implant. You should discuss these issues with your doctor.
Components of knee replacement prosthesis
Routinely two bone surfaces may be replaced in a total knee replacement:
The lower ends of the femur and proximal end of tibia. Knee cap or patella rarely needs to resurfaced, this finding is well supported by scientific evidence in medical literature.
The metal femoral component curves around the end of the femur (thighbone). It is grooved so the kneecap can move up and down smoothly against the bone as the knee bends and straightens. The tibial component is typically a flat metal platform with a cushion of strong, durable plastic, called polyethylene. Some designs do not have the metal portion and attach the polyethylene directly to the bone. For additional stability, the metal portion of the component may have a stem that inserts into the center of the tibia bone
If the back surface of the patella (Knee-cap) is resurfaced, a dome-shaped piece of polyethylene that duplicates the shape of the patella is fixed to it with bone cement.
The metal parts of the implant are routinely made of titanium or cobalt-chromium based alloys, though most recently ceramic implants for femoral component are also available in market. The plastic parts are made of ultra high molecular weight polyethylene. All together, the components weigh between 15 and 20 ounces, depending on the size selected Material Criteria
- The construction materials used must meet several criteria:
- They must be biocompatible; that is, they can be placed in the body without creating a rejection response.
- They must be able to duplicate the knee structures they are intended to replace; for example, they are strong enough to take weightbearing loads, flexible enough to bear stress without breaking, and able to move smoothly against each other as required.
- They must be able to retain their strength and shape for a long time.
Two types of fixation are used to hold knee implants in place.
Cemented and Cementless Implants
- Cemented fixation uses a fast-curing bone cement (polymethylmethacrylate). Cementless fixation relies on new bone growing into the surface of the implant for fixation.
- Cementless implants are made of a material that attracts new bone growth. Most are textured or coated so that the new bone actually grows into the surface of the implant.
There is also hybrid fixation. In hybrid fixation for total knee replacement, the femoral component is inserted without cement, and the tibial and patellar components are inserted with cement. Your surgeon will evaluate your situation carefully before making any decisions about components and fixation. Do not hesitate to ask what type of fixation will be used in your situation and why that choice is appropriate for you.
The longevity and performance of a knee replacement depends on several factors, including your activity level, weight, and general health. Just as wear in the natural joint contributed to the need for a replacement, wear in the implant may eventually require a second surgery (called a joint revision). Revision surgery may require special components. Typically they will have longer stems which fit into the femur and tibia. They may also have attached metal pieces called augments which substitute for missing bone. Revision components often have a cam in the center of the knee similar to a posterior stabilized component. In revision components, though, the cam is larger to give the knee more stability. In cases where the knee is very unstable and a large amount of bone is missing, it may be necessary to join the femur and tibia with a metal "hinge" in the centre. Such implants are rarely required for primary knee surgery when patient presents with severe bone loss or ligament laxity due to advanced degeneration or traumatic damage.