Unicompartmental Knee Replacement FAQs

A unicompartmental knee replacement can last anywhere from 5 years to upwards of 15 years. There are a number of factors that determine this including the level of activity that the patient undergoes as well as the possibility of the arthritis extending into the compartments of the knee that were not replaced. The same is true for total knee arthroplasty and although unicompartmental knee arthroplasty patients can go onto require total knee arthroplasties, if selected appropriately then knee replacements can last a decade or even longer.

The procedure for replacing a single compartment in the knee takes slightly less time than the procedure for replacing the knee in its entirety. Although similar instruments and surgical steps are used and undertaken, because we are only replacing a single compartment within the knee, there are fewer surgical steps and so the surgery takes slightly less time than a standard knee replacement.

A total knee replacement would take anywhere from 45 minutes to an hour-and-a-half depending on the specific patient, their anatomy and the severity of their osteoarthritis whereas the unicompartmental knee arthroplasty generally will take between half an hour to an hour in total surgical time.

Given that unicompartmental knee replacements are less invasive than total knee replacement, it will take the patient slightly less time to recover from as compared to a total knee arthroplasty. We generally expect patient who undergoes a total knee arthroplasty to have recovered the majority of their recovery within 3 months of the surgery; however, usually by 6 weeks after the unicompartmental knee arthroplasty, patients are up walking and their pain levels are diminished significantly and they are close to their baseline level.

Please see the previous dictation for the question how does unicompartmental knee replacement surgery take.

Although the patient will likely experience pain from several hours after the surgery, once their spinal anesthetic is worn off up until approximately a month to six weeks after the surgery, there is a possibility that some discomfort could last slightly longer and there are many factors that determine how long the patient will experience pain after the surgery. They may require some physiotherapy after which they gain strength back in the knee and this usually helps alleviate some of the postoperative pain. There is a small risk that pain can persist even up to a year after the unicompartmental knee replacement surgery, however, this is rare.

The unicompartmental knee replacement is a surgery that will replace one single compartment of the patient’s knee with artificial prostheses. A normal total knee replacement will replace the three compartments present within a normal knee joint – the medial compartment, the lateral compartment and the patellofemoral compartment. In unicondylar knee arthroplasty, only a single compartment is replaced and it is usually the medial compartment as it is the most frequently affected in unicompartmental knee osteoarthritis, although there are implants that exist for replacing only the lateral and patellofemoral compartments as well.

A unicompartmental knee replacement is a replacement for a single compartment within the knee joint that focuses on the area where the osteoarthritis has been confined to thus far. The patients who undergo unicompartmental knee arthroplasty only have arthritis restricted to a single compartment of the knee and unfortunately, there are a subset of patients who receive unicompartmental knee arthroplasty that go on to have their arthritis spread into other compartments of the knee and at that point, they would be a considered a candidate for a total knee replacement.

Unicompartmental knee replacements are indicated only for patients who have arthritis restricted to a single compartment within the knee.

After the surgery, the patient should expect to have some postsurgical pain for approximately two weeks or so. This will be temporary and will be controlled with pain medications that you will be prescribed to take home after your surgery. Most patients find that they can leave hospital the day after surgery or even in some cases the day of surgery depending on the time of day that you receive your surgery.

After your discharge, you will be sent home and you will be given exercises to perform at home in order to keep the knee moving while the knee joint heels. You may also require some physiotherapy with a qualified physiotherapist either at home or in the clinic. If this is deemed to be the case then you will be told this ahead of time. The important thing is to keep the knee bending well and as pain free as possible during the recovery. You will also be expected to bear weight on your knee immediately following the surgery (or following the wearing off the anesthetic that you received in order for the surgery to be able to be performed).

The patient should expect to make a relatively quick recovery and within the first 6 weeks after the surgery, you should notice that your pain level is significantly diminished and you will gain strength back in the knee slowly to the point where you will restore the strength in your knee to the point where you will be ambulating close to normally and by 3 months, you should be fully recovered from the procedure and the recovery period thereafter.

The unicompartmental knee replacement will look like a metal stripe on an x-ray on the edge of your femur as well as a metal tray with a gap in between. These are the replacement components that we have implanted into your knee and in between these two metal components fits a special type of plastic called polyethylene which enables the knee to articulate normally. You will notice your surgical scar being slightly to the side of midline from your surgery and this is all you will notice in terms of the appearance of your knee itself.

Although it may take some time to gain strength back in your knee to get back to running, many patients who do undergo unicompartmental knee arthroplasty are eventually able to get back into moderate intensity running. Although it is not recommended that you subject your knee to large amounts of strain and heavy shear stresses including activities like heavy long distance road running, running on a treadmill and light jogging on softer ground would be perfectly achievable for the vast majority of unicondylar knee arthroplasty patients.

Although there is no physical reason why you should be unable to kneel after a unicompartmental knee replacement, you may find that you are unable to do this comfortably. This is a normal finding after most knee replacement surgeries and although a greater portion of patients who received unicondylar knee arthroplasties do find that they cannot kneel down without discomfort as compared to the total knee arthroplasty population, there is a small risk that you may not be able to kneel comfortably after the surgery.

You will notice some swelling that will likely increase for the first few days after the surgery provided that you engage in exercise and ambulate on the knee normally as would be expected after the surgery. The swelling should begin to subside after the first few days and should be mostly gone by 2 weeks after the surgery.

The unicompartmental knee replacement is performed by first gaining access to the knee joint by making an incision through the skin on the knee and then into the capsule of the knee joint exposing the compartment of the knee that we intend to replace. Importantly, the unicompartmental knee replacement keeps both of your cruciate ligaments intact; indeed having an intact anterior cruciate ligament is one of the requirements for being a candidate for the surgery.

We will first make marks in the bone to measure out where the bony cuts to remove the arthritis should be made and we then cut out the arthritic part of both the femur and the tibia taking care to preserve as much bone as possible. Once we have done this, we then measure the appropriate size components that we are going to put into your knee with trial components and then we carefully balanced the knee joint to ensure that it functions as biomechanically closely to your native knee joint as possible. This is done by varying the thickness of the plastic insert which allows the knee to articulate fully.

Once we have decided on the final sizes for both components of the unicompartmental knee arthroplasty as well as the size of the plastic polyethylene liner, we then used bone cement to cement these components onto your bone and they function as a replacement for the cartilage that you have lost during the process of the development of arthritis within your knee. Once the components are cemented in place and the plastic liner is in place also, the knee is then fully washed out to remove any debris from the surgery and final checks are made to ensure the knee is bending well and is well balanced and then incisions through the capsule and the skin are closed in sequence.

You may be prescribed narcotic analgesics for pain relief after your unicompartmental knee arthroplasty. These come in many forms, one of which is oxycodone. Oxycodone is a very effective pain reliever, but also has numerous possible side effects including drowsiness, nausea and constipation. As such, it is preferable to only take the oxycodone when you feel that you need to. Usually, the pain after unicompartmental knee arthroplasty becomes manageable within 3 to 4 days following the surgery.

Beyond this point, it is usually adequate for you to wean off the oxycodone medication and use medication that is designed to take care of low levels of pain including acetaminophen and ibuprofen. However, if you continue to require oxycodone for slightly longer period then this does not mean there was anything wrong with the knee replacement or your recovery, it may simply mean that your experience of the pain is slightly worse in the majority of patients who undergo this surgery. This is normal and not something to worry about.

This is a very good question and is one that many orthopedic surgeons to this day will debate with great enthusiasm. One thing we can all agree on as surgeons who perform this procedure is that, provided that we are careful in selecting the patients that we offer the surgery to, it is certainly known to be a very successful surgery. Your surgeon will counsel you as to whether they feel that you are candidate for a unicompartmental knee arthroplasty and this is based on a number of factors including how extensive your arthritis is as well as the possibility of damage to your anterior cruciate ligaments and whether you have an associated malalignment to your knee, or a limitation in the bend of your knee that would render you unsuitable for unicompartmental arthroplasty.

You will also be counseled regarding the success rates of unicompartmental knee arthroplasty and the most common reasons for requiring these versions of a knee replacement to require revision surgery in the future and these include extension of the arthritis to other compartments in the knee joint as well as the more standard complications such as infection or aseptic loosening.

Essentially, you will continue to be in pain. Arthritis is a progressive disease that, if left untreated will simply only get worse over time. There is a potential that, if you leave it too long, arthritis may set into your knee more extensively and you may go from being a possible candidate for unicompartmental knee arthroplasty to someone who would unfortunately be left only with the option of a total knee arthroplasty.

You should be seeking the advice of an orthopedic surgeon if you have ongoing knee pain that has been refractory to control with pain medications and that has progressively worsened over the period of time that you have noticed it. Also if you notice that there is abnormal alignment to your leg or knee, you should seek the attention of an orthopedic surgeon.

If you are told that you have arthritis, your surgeon will counsel you with regards to how extensive this arthritis is and based on how your arthritis has responded to the nonsurgical management strategies for osteoarthritis, your surgeon will be able to advise you as to whether you require any knee replacement surgery and also if you would be a candidate to receive a unicompartmental knee arthroplasty.

As with most orthopedic implants, the components of a unicompartmental knee arthroplasty are made out of metal. The metal is usually an alloy of some kind usually involving titanium and one or two other metals depending on the specific design of the knee arthroplasty component. Between the two metal components of the knee, there will be a plastic polyethylene liner. Polyethylene is a special kind of plastic that has numerous uses, one of which is plastic liners in hip or knee replacements of many different types.

If you are to be considered a candidate for surgery, you must have demonstrable evidence of osteoarthritis in your knee on a plain film radiograph x-ray, but more importantly your levels of pain must be significantly bothersome such that you have to sought the attention of a medical professional. The severity and frequency should be such that they have worsened over time and are now intolerable to you and your personal context. Your physical examination findings should also be consistent with pain related to osteoarthritis and not some other cause of your pain. This is something that your surgeon will be able to advice you on once you have consulted with him/her about your pain.

Like all orthopedic implants, the unicompartmental knee arthroplasty components are designed to be exceptionally sturdy and withstand a good deal of stress and strain across the knee as we would expect from a normal knee joint. They are, however, not indestructible, and should you experience an accident or high energy trauma, there is a possibility that not only could the knee replacement components become damaged, but the bone surrounding the knee replacements could also become damaged in what is known as a periprosthetic fracture. I

n this case, you should seek the attention of your orthopedic surgeon who will be able to advise you further as to what surgical solution to your injuries would be most appropriate at that time.

For some patients, the answer is unfortunately never. Although we are performing a surgery to replace the arthritis in your knee that is causing you pain with artificial knee joint components, your knee may never feel like a normal knee afterwards. We do expect you will have a significant relief in your levels of pain and that you should be able to function normally in terms of ambulating and even light sporting activity after your surgery.

This does not mean that your knee will feel normal, however, as it has essentially been replaced with artificial components and some patients report that it does not feel like a normal knee despite being pain free after the surgery. Over time, this is something that you will get used to and most patients who undergo unicompartmental knee arthroplasty having gained their strength back and, in their recovery reach a point after the surgery where they do not notice that they have an artificial knee as they have accommodated their gait patterns to the new knee components.

There are no limits to the amount of walking that we would advise you to undergo after your knee replacement. You will find that you are limited in the immediate postoperative period and that it will take some time to gain some strength back in your knee to be able to walk longer distances, but once you fully recovered from the surgery and you have regained the strength in your knee, there is no limit to the amount of distance that we would allow you to walk.

Technically speaking, you could potentially have six separate unicompartmental knee replacements as each knee has three compartments within it. The most commonly replaced when performing the unicompartmental knee replacements are medial and lateral unicompartmental knee arthroplasties. There are also exists patellofemoral replacement components; however, these are not widely used currently.

However, this is rarely done and if a patient receives a unicompartmental knee arthroplasty and then has extension of the arthritis into another compartment, the unicompartmental knee arthroplasty is usually then revised to a total knee arthroplasty which replaces all three components at once.

The methods of breaking down scar tissue that forms during the healing process after unicompartmental knee surgery is essentially the same as the process of breaking up scar tissue after total knee arthroplasty. That is to say that movement of the knee and specifically working on range of motion exercises will cause the scar tissue to break down in such a way that allows for good range of motion in the knee which has been shown to be linked with success of the total knee arthroplasty and lower levels of pain.

Unfortunately, to date there has been no effective solution to preventing the onset of arthritis in the medical literature. There are many factors that determine whether a patient is going to have arthritis and whether this will be confined to one compartment or whether it would be throughout the knee joint. What has been shown to be effective in helping relieve the symptoms of arthritis is significant weight loss, use of a gait aid such as a cane or a walker and supplementing with over-the-counter analgesic medications such as Tylenol and Advil.

Although intraarticular injections of hyaluronic acid and cortisone are effective in some patients as are knee braces that can be purchased from sports orthotics stores, neither of these have shown to be effective in preventing the onset or slowing the onset of arthritis, but rather addressing the symptoms that arthritis cause.

Given that the unicompartmental knee arthroplasty is a less invasive surgery than a total knee arthroplasty, the levels of pain that you will experience after the surgery will be relatively lower. Thus not to say that you will not experience any pain, however, as it is very common for unicompartmental knee arthroplasty patients who experience pain and soreness in the knee after the surgery. Fortunately, this should only last a week or two and can be controlled usually very well by narcotic analgesics such as oxycodone followed by stepping down to lower levels of analgesics including Tylenol and Advil.

Although knee replacement surgery generally prefers to a total knee replacement, the most common format of a knee replacement, unicompartmental knee arthroplasty is still a widely performed surgery and has been widely researched and has been shown to be effective in the appropriate patient. Although it is not as common as the total knee arthroplasty, usually surgeons who perform total knee arthroplasties will also be able to perform unicompartmental knee arthroplasties if they deem the patient to be appropriate for one.

Although there is no specific weight that surgeons consider to be too obese to receive a unicompartmental knee arthroplasty, we use body mass index or BMI as a surrogate to predict the likelihood that a unicompartmental knee arthroplasty will fail. Generally speaking, a BMI of greater than 40 is considered a contraindication to performing a unicompartmental knee arthroplasty; however, some research has used the figure 82 kg to be a cut off for offering this type of surgery to patients.

The goal of unicompartmental knee replacement is to remove the arthritis that is present in a single compartment of the knee and replace the arthritic bone that has worn away the knee cartilage with artificial replacement components. In this sense, yes it does get rid of arthritis in the knee. However, one of the most common reasons to have to re-operate on knees that have undergone unicompartmental knee arthroplasty is extension of the arthritis into other compartments of the knee.

As such, your surgeon will advise you as to whether they feel that your arthritis is truly limited to a single compartment of the knee and it is likely to remain so or whether they feel that you have arthritis that has extended beyond one compartment of the knee or they feel you are likely to experience extension of the arthritis into other compartments of the knee in the near future. If this is the case then your surgeon will advise you would be better to undergo a total knee replacement as opposed to a unicompartmental knee arthroplasty.

This is a common concern to patients who I believe they have metal allergies. Although no definitive research has been done that shows that patients who have sensitivity to metal ever experienced adverse symptoms that can be proven to be directly related to the materials that their knee arthroplasty components are made of. If the patient does have a metal allergy, almost specifically a nickel allergy then special types of knee replacement do exist that do not contain any trace elements of this metal.

Unicompartmental knee replacements, however, do not have a wide range of metal alloys that they are made from. Consequently if you are concerned that your metal allergy will be a factor when deciding whether or not to undergo unicompartmental knee arthroplasty, this is something that you should discuss with your surgeon as you may better served with a total knee arthroplasty that does not contain trace elements of nickel in it.

In the immediate postoperative phase after surgery, heat and swelling in the knee are very normal as this is part of the normal inflammatory action to the surgery and should gradually settle down over the first two postoperative weeks. If you notice that your redness and swelling appears to be worsening, this is something that you should inform the surgeon immediately, as it could indicate the presence of an infection and you should seek the attention of your surgeon right away for further examination.

However, studies have shown that knee replacement surgery in general, temperature differences between the surgical knee and the nonsurgical knee can persist for up to 2 years after the operation. As such if your knee appears normal and not swollen, but feels warmer than your other knee, this would likely be a normal finding. However, if you are concerned then you should contact you surgeon and consult with them as they will be able to reassure you if everything appears normal, whether there may be a problem, and if you will need further treatment.