Partial Knee Replacement
The knee is the largest joint in the human body and proper function and health of the knees is required to perform most everyday activities. The knee is made up of the lower end of the femur (thighbone), the patella (kneecap), and the upper end of the tibia (shinbone). Articular cartilage, which is a smooth substance that protects the bones and allows them to move freely, covers the ends of the three bones. Between the femur and the tibia are C-shaped cushioning wedges known as the menisci that act as "shock absorbers". Large ligaments (tough bands of tissues) help hold the femur and the tibia together in order to stabilize the joint by preventing excessive movement. The remaining surfaces of the knee joint are covered by the synovial membrane, which is a thin lining that releases fluid that lubricates the cartilage, reducing the friction within the knee joint. All of these components work together to facilitate proper function of the knee.
If the knee experiences severe damage due to arthritis or traumatic injuries, performing simple, day-to-day activities can become very difficult. An individual might even start to feel pain while sitting or lying down. If non-operative treatments such as medications, bracing, injection, and the use of assistive walking devices such as walkers or crutches are no longer helpful, a partial knee replacement might be an effective option to relive pain and restore normal motion provided certain criteria are met.
Partial knee replacement also known as unicompartment knee replacement, a "uni", or a partial knee resurfacing, involves removing damaged cartilage of the knee and covering the surfaces of the bones with prosthetic implants generally made of metal alloys and high-grade plastics or polymers. Unlike a total knee replacement which removes all of cartilage, a partial knee replacement removes cartilage from a particular region. The purpose of having a partial knee replacement is to relieve pain. This surgery can also re-align the knee and help restore function, allowing for a "normal" range of motion. Partial or uni knee replacement surgery is typically performed on individuals with advanced osteoarthritis that is limited to just one part of the knee. A partial knee replacement is known to feel more "natural" than a total knee replacement since the healthy part of the bone, ligaments, and cartilage are kept. Additionally, a partial knee replacement is associated with a quicker recovery, less post-operative pain, and less blood loss as compared to a total knee replacement. On the other hand, the disadvantage of a uni or partial knee replacement is the potential need for more surgery in the future.
Individuals who opt for partial knee replacement surgery typically experience the following symptoms:
- Chronic inflammation, stiffness, and pain that limit day-to-day activities such as walking, climbing stairs, or getting in and out of chairs
- Severe pain that interferes with sleep or rest
- Mild knee deformity such as the knee bowing inward or outward that is potentially causing pain
- Ineffective non-operative treatment such as medication, physical therapy, etc.
Unlike total knee replacement surgery, partial knee replacement candidates have a stricter criteria concerning, age, weight, level of activity, the integrity of the other components of the knee, as well as the severity of the arthritis affecting their day-to-day activities.
Arthritis of the knee can be diagnosed with a patient history, physical examination, as well as imaging studies. The physician may examine the knee for the symptoms mentioned above along with assessing the motion, stability, strength, and overall alignment. The physician may obtain X-rays or an MRI scan to determine the extent of damage and deformity in the knee. The physician will educate you on the benefits from this surgery as well as what to expect post-operatively.
Although there are many types of arthritis that cause pain, the most common that often lead to a total knee replacement are the following:
- Osteoarthritis - Osteoarthritis is the most common form of arthritis and occurs when the protective cartilage on the ends of your bones wears down over time. It's often called a degenerative joint disease where the cartilage experiences a significant amount of wear and tear over a long period of time, generally occurring in individuals over the age of 50.
- Rheumatoid Arthritis (RA) - Rheumatoid arthritis is quite possibly the most serious form of arthritis as it is a major crippling disorder. Unlike osteoarthritis, rheumatoid arthritis affects the synovial membrane (lining of the joints), causing a painful swelling, resulting in joint deformity and bone erosion. Rheumatoid arthritis is three to four times more likely to occur in women and may affect various systems of the body such as eyes, heart, lungs, skin, and the nervous system.
- Post-Traumatic Arthritis - Traumatic arthritis is caused by a single major injury or repeated trauma to the articular cartilage. Injuries to the knee such as a fracture or sprain can cause major damage to the articular cartilage, which can lead to arthritic changes in the joint over time.
A partial or uni knee replacement primarily replaces the affected surface of the bones and cartilage as opposed to the bones themselves. Generally, the operative process takes anywhere between one to two hours to complete and occurs in the following order:
- Exposure and Evaluation of the Knee - The first step in unicompartmental knee replacement is to view the arthritic part as well as all other portions of the knee. On occasion, the physician may find more advanced arthritis than expected in the portions of the knee thought to be normal. In these instances, the physician may elect to convert to a total knee replacement.
- Bone Preparation - During this step, the damaged cartilage along with a thin layer of the underlying bone is removed from the end of the femur and the tibia.
- Positioning of the Implants - The cartilage and bone removed from the previous step is then replaced with a femoral component and a tibial component to recreate the surface of the joint. Depending on the integrity of the bones and the physician's preference, these components may be cemented or "press-fit" into the bone.
- Inserting a Spacer - In order to create a smooth, gliding surface, a medical-grade plastic spacer is inserted between the femoral and tibial component.
After partial knee replacement surgery, there will be some pain, but the medical team will provide the proper medication to make the patient as comfortable as possible. Walking and knee movement will being soon after the surgery where a physical therapist will provide instructions on the specific exercises to strengthen the leg and restore knee movement to allow for walking and other activities post operatively. A majority of the recovery process will occur at home where proper care must be taken in terms of wound care, diet, and activity as prescribed by the physician and physical therapist. Patients who have undergone total knee replacement surgery generally resume most activities four to six weeks post operatively. Each patient is unique, so the recovery period will vary depending on the level of activity the individual hopes to resume; this should be discussed with the physician as well as the physical therapist.
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