Partial Knee Replacement

It is thought that up to 30% of patients requiring a knee replacement are suitable for a partial knee replacement. A partial knee replacement preserves the native anatomy and ligaments in the unaffected compartments. Partial knee replacements are associated with a faster recovery and a lower risk of post-operative complications. Some studies also suggest superior function after a partial knee replacement compared to a total knee replacement.

A total knee replacement is more suitable for patients with widespread knee pain, rheumatoid arthritis, osteonecrosis of the knee, and osteoarthritis affecting multiple compartments. In addition, a total knee replacement is associated with less early implant failures and increased overall survivorship compared to a partial knee replacement. In a total knee replacement, all compartments (medial, lateral, and patellofemoral) are addressed; this eliminates the potential of arthritis progression in the unaffected compartments.

Dr. Chang is currently performing partial knee replacements using conventional instrumentation. Robotic-assisted partial knee replacement is not yet available in Canada for the robotic system used at Humber River Hospital. There is optimism that robotic-assisted partial knee replacement will arrive in Canada within the next few years.

Non-operative measures should be attempted prior to consideration of knee replacement. These measures are often helpful in the early stages of arthritis.

Pain medication: Tylenol is typically recommended as the first-line pain medication. Some patients with liver disease may not be able to tolerate regular Tylenol. Anti-inflammatory medications are also helpful but are not suitable for all patients. Patients with cardiac disease, high blood pressure, kidney disease, and/or stomach ulcers may not be able to take regular anti-inflammatory medications. Regular opioid medications are not recommended due to risk of addiction and development of chronic pain. Patients should consult with their family doctor prior to starting any new medication.

Physiotherapy: Physiotherapy exercises to improve strength to your core, buttocks, quadriceps, hamstrings, and abductors are often helpful for reducing symptoms in early arthritis.

Injections: Local knee injections can be helpful in the early stages of arthritis. They are less effective in end-stage disease. Consult your surgeon to determine if an injection would be indicated for you.

Bracing: Some patients with specific patterns of arthritis may benefit from bracing in order to “offload” the affected knee compartment. Consult your surgeon to determine if a custom knee brace would be indicated for you.

Weight loss: Weight loss helps reduce the pain associated with arthritis by taking pressure off your knee joint. It is appreciated that regular exercise can be challenging due to persistent and severe knee pain. Your family doctor can often help with diet resources.

Walking aids: A cane or walker may help improve your comfort, stability, and confidence with walking.

The decision to proceed with a partial knee replacement is an individual one. It is important to have a formal discussion with your surgeon to determine if you are a good candidate for a knee replacement.

A partial knee replacement can be considered in a patient with end-stage arthritis and knee pain that restricts walking ability and other day-to-day activities that impact quality of life. Your knee pain should be localized to the affected knee compartment. In addition, patients should have good baseline health and have attempted non-operative measures (see above).

In a partial knee replacement, the distal femur (bottom part of the thigh bone) and the proximal tibia (top part of the shin bone) are replaced with an artificial joint (prosthesis). However, only one side (either the medial compartment or lateral compartment) is replaced.

The femoral component is made out of metal (typically a cobalt-chromium alloy). The tibial component is made out of a metal baseplate (typically a cobalt-chromium alloy) and plastic liner (typically polyethylene).

Many countries, including Canada, mandate data collection on certain medical devices such as joint replacements; these are called national joint registries. Recent evidence derived from pooled joint registry data from multiple countries estimate survivorship of a partial knee replacement is 76.5% at 15 years, 71.6% at 20 years, and 69.8%% at 25 years. It is important to remember that these are estimates of survivorship. There is optimism that the newer generation of implants used today will last longer than what is reported today in the literature.

The majority of partial knee replacements done by Dr. Chang are performed as day surgery. After surgery you will be assessed by a physiotherapist to ensure that you can walk and climb the stairs safely. You will be given a prescription for pain medication and blood thinners prior to discharge.

Your first post-operative appointment will be approximately 2-weeks after surgery in the fracture clinic to check your wound and review your progress.

The second follow-up appointment will be approximately 6 weeks after surgery. A clinical review and x-ray will be performed at that time.

It is typical to require a walker or crutches for the first 1-3 weeks after surgery. It is often advisable to transition to a cane after you have stopped using a walker. Most patients are comfortable with normal day-to-day activities 6 weeks after surgery.

The average recovery time varies by patient but usually is 3-6 months. However, it can take up to 12-18 months after surgery to regain full strength.

All patients recover differently after surgery. The decision on when to return to work is variable and depends on you and your type of job. As a guide, most people with “desk” type jobs can resume work 4-6 weeks after surgery. People with more “physical” type jobs can resume work 12-16 weeks after surgery.

In general, you can drive once you regain full power and function in your leg to safely perform an emergency brake. In addition, you must have finished taking any opioid medication. This typically takes a minimum of 6 weeks after surgery.

One of the goals of a partial knee replacement is to allow you to return to all the recreational activities that you enjoy. Many patients return to walking, hiking, cycling, skiing, skating, golf, tennis, and working out. Regular high impact activities, such as running and jumping, are generally not advised as they may lead to earlier implant failure. Kneeling can be uncomfortable for patients after a knee replacement but there are no specific restrictions against kneeling.

Travel should be delayed for 6 weeks after surgery. Long distance travel and flying increases the risk of developing a blood clot early in the post-operative period.

If flying is essential prior to 6 weeks, it is recommended that you get up and move every hour on the plane. You will also require a prescription blood thinner.

You do not require any antibiotics before a routine dental procedure.

The Canadian Orthopaedic Association (COA), Canadian Dental Association (CDA), and the Association of Medical Microbiology and Infectious Disease (AMMI) have reviewed the best available research and have provided clear guidance on this.

The risk of a (deep) prosthetic joint infection is approximately 1% following primary (first-time) knee replacements and up to 5-10% of revision (re-do) knee replacements. You will receive a dose of IV antibiotics before and after surgery to decrease the risk of infection. Prolonged antibiotics after surgery have not been shown to provide additional benefit and are usually not required.

Symptoms of a prosthetic joint infection include swelling, redness, wound drainage and increasing pain. Patients can also experience systemic symptoms such as a fever. Please contact your surgeon and/or go to the emergency department if you believe you are developing an infection.

Deep prosthetic joint infections may require IV antibiotics and multiple operations in order to eradicate the infection. Some or all of the components may need to be removed or exchanged.

Superficial skin infections are more common and can be usually treated with a course of oral antibiotics.

In a partial knee replacement, only one compartment (usually the medial compartment) is replaced. There is a possibility of subsequently developing arthritis in the other compartments that were not replaced during the partial knee replacement. This is one of the reasons that partial knee replacements are associated with a higher revision (re-do) rate compared to total knee replacements. If you develop arthritis in other compartments, you may require a conversion to a total knee replacement.

Knee stiffness can be a problem after a partial knee replacement. It is normal for your knee to be stiff and painful immediately after surgery. However, it is very important to work on your knee range of motion after surgery to prevent permanent stiffness. Expected range of motion after a partial knee replacement is approximately from 0 (completely straight) to 125 degrees.

If you develop permanent stiffness, you may require surgery to manipulate the knee and break up the scar tissue (manipulation under anaesthesia). In some cases, a revision (re-do) operation may be necessary to improve flexibility.

Instability is another potential complication of a knee replacement. Symptoms include the feeling of your knee “wobbling” or “giving way” while walking. Some patients also describe “lack of confidence” in their knee, particularly when going downstairs.

Instability can often be improved with physiotherapy to strengthen the quadriceps and hamstring muscles that support the knee. In some cases, patients may require bracing or revision (re-do) surgery to convert the partial knee replacement to a total knee replacement.

Your extensor mechanism attaches your quadriceps muscle to the proximal tibia and allows you to straighten you knee when bent. It is made up of the patella tendon, patella, and quadriceps tendon and is essential for adequate function of your knee.

An extensor mechanism injury is a very rare complication of a partial knee replacement. Treatment depends on severity but may involve immobilization in a knee brace or reconstructive surgery.

Most patients undergoing a partial knee replacement develop numbness around the incision and directly outside (lateral) to it. This numbness tends to resolve slowly over time but may become permanent in some patients. Importantly, this has not be shown to affect the function or strength of your knee.

The most common indications for revision (re-do) surgery are infection, instability, stiffness, progression of arthritis, periprosthetic fracture, and loosening of the components. Implants can “wear” out and loosen over time and may require revision surgery to replace the old components or conversion to a total knee replacement.

Conversion of a partial knee replacement to a total knee replacement is associated with increased risk of complications and prolonged recovery compared to a primary (first-time) total knee replacement. However, patients typically do well after revision surgery.

A deep vein thrombosis (DVT) is a blood clot that can develop in the leg veins after surgery. DVTs that occur above the knee can be dangerous as they can dislodge and form a blood clot in the lungs called a pulmonary embolism (PE). This is a rare but serious condition which can be life threatening.

All patients receive medication to reduce the risk of a blood clot after surgery. The type of medication varies depending on the individual risk factors of each patient. If you have had a blood clot in the past it is important to inform your surgeon prior to surgery.

Damage to major nerves, such as the common peroneal nerve, is extremely rare following surgery. It is more common in patients with a severe knock knee (valgus) and flexion deformity (flexion contracture). This can lead to a partial paralysis such as a “foot drop” where there is inability to lift the front part of the foot. Recovery can be prolonged and incomplete.

Major blood vessel damage is also extremely rare but can necessitate emergency blood transfusion and vascular repair in some cases.