Unicompartmental Knee Replacement (PKR)
A Unicompartmental Knee Replacement, also known as ‘Partial’ Knee Replacement or PKR is a surgery that replaces part of an arthritic knee joint with artificial metal or plastic replacement parts called the ‘prostheses’.
During knee replacement surgery, damaged bone and cartilage is resurfaced with metal and plastic components. In unicompartmental knee replacement (also called “partial” knee replacement) only a portion of the knee is resurfaced. This procedure is an alternative to total knee replacement for patients whose disease is limited to just one area of the knee.
Because a partial knee replacement is done through a smaller incision, patients usually spend less time in the hospital and return to normal activities sooner than total knee replacement patients.
The procedure is usually recommended for older patients who suffer from pain and loss of function from arthritis and have failed results from other conservative methods of therapy.
The typical knee replacement replaces parts the femur (thigh bone) or tibia (shin bone) with plastic inserted between them and usually the patella (knee cap).
Other causes include
- Trauma (fracture)
- Increased stress e.g., overuse, overweight, etc.
- Connective tissue disorders
- Inactive lifestyle e.g., Obesity, as additional weight puts extra force through your joints which can lead to arthritis over a period of time
- Inflammation e.g., Rheumatoid arthritis
In an Arthritic Knee
- The cartilage lining is thinner than normal or completely absent. The degree of cartilage damage and inflammation varies with the type and stage of arthritis.
- The capsule of the arthritic knee is swollen
- The joint space is narrowed and irregular in outline; this can be seen in an X-ray image.
- Bone spurs or excessive bone can also build up around the edges of the joint
The combinations of these factors make the arthritic knee stiff and limit activities due to pain or fatigue.
The diagnosis of osteoarthritis is made on history, physical examination & X-rays.
There is no blood test to diagnose Osteoarthritis (wear & tear arthritis).
The decision to proceed with PKR surgery is a cooperative one between you, your surgeon, family and your local doctor.
The benefits following surgery are relief of symptoms of arthritis. These include
- Severe pain that limits your everyday activities including walking, shopping, visiting friends, getting in and out of chair, gardening, etc.
- Pain waking you at night
- Deformity- either bowleg or knock knees
Prior to surgery you will usually have tried some conservative treatments such as simple analgesics, weight loss, anti-inflammatory medications, injections, modification of your activities, canes, or physical therapy.
Once these have failed it is time to consider surgery. Most patients who have PKR are between 55 to 80 years, but each patient is assessed individually.
- Your surgeon will send you for routine blood tests and any other investigations required prior to your surgery
- You will be asked to undertake a general medical check-up with a physician
- You should have any other medical, surgical or dental problems attended to prior to your surgery
- Make arrangements for help around the house prior to surgery
- Discontinue blood thinners and aspirin or anti-inflammatory medications 5 days prior to surgery as they can cause bleeding
- Discontinue any naturopathic or herbal medications 10 days before surgery
- • Stop smoking 1 month prior to surgery (This is required).
- You will be admitted to the hospital, usually on the day of your surgery
- You will meet the nurses and answer some questions for the hospital records
- You will meet your Anesthetist, who will ask you a few questions
- The operation site will be clipped and cleaned
Each knee is individual and knee replacements take this into account by having different sizes for your knee. If there is more than the usual amount of bone loss, sometimes extra pieces of metal or bone are added.
Surgery is performed under sterile conditions in the operating room under spinal or general anesthesia. You will be on your back and a tourniquet applied to your upper thigh to reduce blood loss. Surgery takes approximately two hours.
The surgeon cuts down to the bone to expose the bones of the knee joint.
The damaged portions of the knee are then cut at the appropriate angles using specialized jigs. Trial components are then inserted to check the accuracy of these cuts and determine the thickness of plastic required to place in between these two components. The patella (knee cap) will be resurfaced.
The real components are then inserted with cement and the knee is again checked to make sure things are working properly. The knee is then carefully closed and drains usually inserted, and the knee dressed and bandaged.
In anticipation of your surgery please review the links below for some helpful exercises to improve your surgical outcome.
- Activities After a Knee Replacement
- Knee Arthroscopy Exercise Guide
- Knee Replacement Exercise Guide
- Cincinnati Sports Medicine’s
When you wake, you will be in the recovery room with intravenous drips in your arm and a number of other monitors to check your vital observations.
Once stable, you will be taken to the surgical floor. Most patients will walk the same day of surgery. Physical Therapy will be continued throughout the hospital stay.
To avoid lung congestion, it is important to breathe deeply and cough up any phlegm you may have. You will also have a device called an Incentive Spirometer to assist with deep breathing.
Your Orthopaedic Surgeon will use one or more measures to minimize blood clots in your legs, such as inflatable leg coverings and possibly compression stockings. Most patients will be started on Aspirin 81 mg take twice daily for 6 weeks after surgery to prevent blood clots. Some patients may be required to use another blood thinner if they are at a higher risk for blood clots.
A lot of the long term results of knee replacements depend on how much work you put into it following your operation.
Usually, you will remain in the hospital for 1-2 nights. You will need physical therapy on your knee following surgery.
You will be discharged on a walker or crutches for 10-14 days, and usually progress to a cane for 10 days.
Sutures are removed at 14 days and you will go home with a waterproof bandage.
Bending your knee is variable, but by 2 weeks should bend to 90 degrees. The goal is to obtain 115-120 degrees of movement.
You may shower with your waterproof bandage. You can drive at about 3-4 weeks, once you have regained control of your leg. You should be walking reasonably comfortably by 6 weeks.
When you go home you need to take special precautions around the house to make sure it is safe. You may need rails in your bathroom or to modify your sleeping arrangements, especially if they are up a lot of stairs.
You will usually have a 1 week, 2 week and 4-6 week, 3 month check up with your surgeon who will assess your progress.
After you are released, you should continue to see your surgeon every 2-3 years for the lifetime of your knee replacement to check your knee and take X-rays. This is important as sometimes your knee can feel excellent, but there can be a problem only recognized on X-ray.
You are always at risk of infections especially with any dental work or other surgical procedures where germs (bacteria) can get into the blood stream and find their way to your knee.
If you ever have any unexplained pain, swelling or redness or if you feel generally poor, you should see your doctor as soon as possible.
- As with any major surgery, there are potential risks involved. The decision to proceed with the surgery is made because the advantages of surgery outweigh the potential disadvantages
- It is important that you are informed of these risks before the surgery takes place
Complications can be medical (general) or local complications specific to the Knee
Medical complications include those of the anesthetic and your general well-being. Almost any medical condition can occur so this list is not complete. Complications include:
- Allergic reactions to medications
- Blood loss requiring transfusion with its low risk of disease transmission
- Heart attacks, strokes, kidney failure, pneumonia, bladder infections Complications from nerve blocks such as infection or nerve damage Serious medical problems can lead to ongoing health concerns, prolonged hospitalization or rarely death
Infection can occur with any operation. In the knee this can be superficial or deep. Infection rates vary. If it occurs, it can be treated with antibiotics but may require further surgery. Very rarely your new knee may need to be removed to eradicate infection.
Blood Clots (Deep Venous Thrombosis)
These can form in the calf muscles and can travel to the lung (Pulmonary embolism). These can occasionally be serious and even life threatening. If you get calf pain or shortness of breath at any stage, you should notify your doctor.
Stiffness in the Knee
Ideally your knee should bend beyond 100 degrees but on occasion, the knee may not bend as well as expected. Sometimes manipulations are required. This means going to the operating room where the knee is bent for you and under anesthetic.
The plastic liner eventually wears out over time, usually 15 to 20 years and may need to be changed.
Wound Irritation or Breakdown
The operation will always cut some skin nerves, so you will inevitably have some numbness around the wound, especially around the lateral (outside) region of your knee. This does not affect the function of your joint. You can also get some aching around the scar. Vitamin E cream and massaging can help reduce this.
Occasionally, you can get reactions to the sutures or a wound breakdown that may require antibiotics or rarely, further surgery.
The knee may look different than it was because it is put into the correct alignment to allow proper function.
Leg length inequality
This is also due to the fact that a corrected knee is straighter and is unavoidable.
An extremely rare condition where the ends of the knee joint lose contact with each other or the plastic insert can lose contact with the tibia (shinbone) or the femur (thigh bone).
Patella (knee cap) can dislocate. This means it moves out of place and it can break or loosen.
There are a number of ligaments surrounding the knee. These ligaments can be torn during surgery or break or stretch out any time afterwards. Surgery may be required to correct this problem.
Damage to Nerves and Blood Vessels
Rarely these can be damaged at the time of surgery. If recognized they are repaired, but a second operation may be required. Nerve damage can cause a loss of feeling or movement below the knee and can be permanent.
Fractures or breaks in the bone can occur during surgery or afterwards if you fall. To repair these, you may require surgery.
Discuss your concerns thoroughly with your Orthopaedic Surgeon prior to surgery.
Surgery is not a pleasant prospect for anyone, but for some people with arthritis, it could mean the difference between leading a normal life or putting up with a debilitating condition. Surgery can be regarded as part of your treatment plan—it may help to restore function to your damaged joints as well as relieve pain.
PKR is one of the most successful operations available today. It is an excellent procedure to improve the quality of life, take away pain and improve function. In general 90-95% of knee replacements survive 15 years, depending on age and activity level.
Surgery is only offered once non-operative treatment has failed. It is an important decision to make and ultimately it is an informed decision between you, your surgeon, family and medical practitioner.
Although most people are extremely happy with their new knee, complications can occur and you must be aware of these prior to making a decision. If you are undecided, it is best to wait until you are sure this is the procedure for you.
Other Procedures Performed