Overview of Arthroplasty Knee Unicompartmental
Unicompartmental knee arthroplasty, or UKA, is a kind of knee surgery. It’s used to treat osteoarthritis, a condition that causes joint pain and stiffness, in one part of the knee. This type of surgery is most often needed for the medial compartment of the knee, which is the inner part of the knee.
Another type of surgery used for treating osteoarthritis in the whole knee, not just one part, is total knee arthroplasty, or TKA. UKA was first introduced in the 1970s. Supporters believed that UKA more closely replicated normal knee movement, had fewer complications during and after the surgery, and let people start moving and begin physical therapy earlier than traditional knee arthroplasty, a surgical procedure that helps to restore motion to severely damaged knee joints.
However, the early results were disappointing with many cases resulting in surgeries failing, meaning 28% of patients ended up needing a TKA at an average of six years after the first surgery.
Over time, changes in the design of the implants used in the surgery, as well as the surgical techniques, and firmer guidelines on which patients should have the surgery have led to a renewed interest in UKA. The popularity of this surgery has also grown because it’s less invasive than TKA, as it requires a smaller cut in the knee. Additionally, the use of robotics-assisted techniques, which provide better precision in surgery and help in placing the component of the knee implant correctly, aims to improve the life span of the implant.
Anatomy and Physiology of Arthroplasty Knee Unicompartmental
The knee can be divided into three sections, or ‘compartments’: inner, outer, and the front part where the knee cap, or ‘patella’, is located. The inner compartment is the part where the inner side of the thigh bone, or ‘femur’, meets the shin bone, or ‘tibia’. The outer compartment is where the outer side of the femur meets the tibia. The front part is where the kneecap rubs against a groove on the femur.
A person can develop a kind of joint disease called arthritis in any of these compartments, or in all three. The way your leg aligns itself when you stand or walk can influence where arthritis pops up. For instance, if you’re bow-legged, you have a higher chance of having arthritis in the inner compartment of your knee. On the other hand, if you’re knock-kneed, this means you’re more likely to develop arthritis in the outer part of your knee.
Why do People Need Arthroplasty Knee Unicompartmental
Before considering surgery as a solution, a patient should have tried other less dramatic treatments, such as changing their activities, physical therapy, anti-inflammatory medicine, supporting the affected area with a brace, or getting injections. Only if these simpler methods have not eased the problem, can surgical intervention be considered.
In the case of a type of knee surgery (unicompartmental knee arthroplasty, or UKA), the guidelines for when patients should have this surgery have changed since it was first introduced. Established indicators suggested for candidates should be those over 60 years old, under 182 pounds, having either osteoarthritis or osteonecrosis (types of joint disease) in only one part of the knee, with mild pain at rest, still able to move the knee at least 90 degrees, with mild bend in the knee when it’s relaxed (flexion contracture) less than 5 degrees and less than 15 degrees of angular knee deformity that can be corrected to a straight position. However, it was challenging to stick to these criteria, and some analyses evidenced that only a small fraction of total knee surgeries met these conditions.
More recent data has revealed better outcomes and lasting effects in younger (less than 60 years old) and obese patients undergoing UKA. The improvements in the design of the implant, partly contributed to the broadening or traditional indicators to have a UKA done. It was conventionally thought that high body mass index (BMI), indicating overweight or obesity, can increase the risk of the implant loosening due to the excessive load on it. Similarly, younger patients typically have a more active lifestyle and higher expectations for the functionality. These factors could potentially also predispose them to early loosening of the implant due to excessive use. However, a recent inclusive study reported no increased chances of revisions (repeat surgeries) or poor outcomes in obese patients when compared to others. The same study found a higher risk of revision surgeries in younger patients and women.
When a Person Should Avoid Arthroplasty Knee Unicompartmental
There are certain factors that can make UKA, or Unicompartmental Knee Arthroplasty (a form of knee replacement surgery that only involves a part of the knee), not a good fit for some patients. When this surgery was first developed by Kozinn and Scott, they listed specific conditions that could make the surgery not suitable. However, medical practitioners have been questioning how strict these criteria are, because many patients who need knee surgery are not eligible to get UKA because of those conditions.
Some of the conditions that could make UKA unsuitable include inflammation of the knee joint, arthritis affecting the kneecap (known as the patellofemoral joint) or another part of the knee, issues with the anterior cruciate ligament (ACL, which is a major ligament in the knee that helps with stability), and certain patient characteristics or anatomic factors.
Recent research has shown that patients with arthritis of the kneecap can still have good outcomes after UKA with no differences in how well they function or in the rates of needing further surgery compared to people who don’t have this type of arthritis.
Historically, the success rate of UKA was low in people who had an unstable or deficient ACL. Research showed that without an ACL, the knee was biomechanically unstable, which could lead to faster wear and tear of the knee implant and worse arthritis in the kneecap and other parts of the knee. However, newer research has shown that even people with an unstable or deficient ACL can have good outcomes after UKA compared to people with a functioning ACL. There’s also been successful outcomes reported in patients who had both the knee replacement surgery and an ACL reconstruction at the same time, which further supports that having a deficient ACL does not automatically rule out the option of UKA.
Preparing for Arthroplasty Knee Unicompartmental
Before you have a knee operation, doctors will perform a detailed check-up. This includes asking about your medical history and carrying out a physical inspection of your knee. They will also assess the knee’s flexibility and strength, using a commonly accepted method set out by medical experts Kozinn and Scott. Doctors will study pictures of the knee – while the patient is standing – to see if the knee tilts too far to one side. They will also use pictures from different angles to examine the knee cap and check for any unnatural movement. Moreover, advanced scans, such as a CT scan, might be necessary before a robot-assisted knee operation. These scans help guide the placement of the artificial knee parts and adjust surrounding tissues appropriately. However, MRI scans, which create very detailed pictures of the knee, are often unnecessary and might present the knee damage more severely than it actually is.
How is Arthroplasty Knee Unicompartmental performed
In a procedure called UKA (unicompartmental knee arthroplasty), or what is often termed a partial knee replacement, the surgeon needs to expose the inside part of the knee with as little damage as possible to the surrounding soft tissues. When the bone of the shin (tibia) is prepared for this surgery, the cut should follow the natural slope of your bone. This preparation then needs to be as close as possible to the natural bony bumps (tibial spine) to ensure the artificial component fits well, without causing any damage to certain knee ligaments (such as ACL).
The positioning of the artificial parts should be done in such a way that avoids implant sinking into bone (implant subsidence) or causing harm to your knee ligaments. The surgeon will also take care to prevent putting too much pressure on the inner knee tissues and stop more degeneration of the outside part of your knee.
The surgeon then proceeds to place the thigh bone (femoral) component of the implant. Ideally, this should be in the center or slightly to the outside part on the rounded end of your thigh bone. This ensures the smooth movement and alignment with the shin bone (tibial) component. If the specific circumstances of your surgery might cause the patella (kneecap) to strike the femoral implant, your surgeon will avoid implant placement or sizing that might cause this issue.
When considering options for your UKA surgery, your doctor may choose between using a mobile-bearing implant designed to spread the load over a large surface, or a fixed-bearing implant, which offers greater movement and reduces the wear on the backside of the implant. However, research has not shown one option to be clearly better than the other.
Another point your doctor will consider is whether to use a type of paste (cement) to fix the implant. Using cement can be slightly tricky in this type of surgery because of limited space and having to apply it correctly which also extends the surgery time. While using cement can lead to the implant gradually shifting position over time as seen on x-rays (radiographic subsidence), this does not usually lead to issues with the implant coming loose. Furthermore, research suggests similar long-term results with both cemented and non-cemented implants used in UKA surgeries.
Possible Complications of Arthroplasty Knee Unicompartmental
Since the creation of the Partial Knee Replacement (PKR) surgery method, the main reason they fail has remained the same for many years. They often fail due to the implant coming loose in a way not involving infection, known as aseptic loosening, or because of the continuing degeneration of the joint, also known as progressive osteoarthritis.
A detailed review of PKR showed that aseptic loosening (25%) and osteoarthritis progression (20%) caused more than half of all the cases where the knee implant had to be replaced within the first five years. Infections (5%) and wearing down of the plastic part of the implant (4%) were less common reasons. About 40% of implant replacements happening at later stages were due to osteoarthritis progression.
Even with improvements in PKR implants, the rate at which they successfully work without needing a replacement has stayed the same. This is different from Total Knee Replacement (TKR), which have seen increased success rates over time. Some experts believe this is because surgeons find it easier to replace a PKR with a TKR. On the other hand, replacing a TKR is seen as more complex and has risks of more health problems. Recent studies have disputed these ideas, showing similar rates of complications and replacements after PKR and after TKR surgeries.
What Else Should I Know About Arthroplasty Knee Unicompartmental?
Since it was first introduced, the uses for a Partial Knee Replacement (UKA) have greatly increased. According to wide-ranging studies and health data, UKA has repeatedly shown long-term success and durability in the right patients. UKA is a less invasive surgery when conducted under the right circumstances and for the correct reasons. It can help a patient get back to their usual levels of physical activity.
However, it’s worth noting that if the patient has high expectations – especially those who are younger or more active – it could lead to the artificial knee wearing out sooner and needing to be replaced again. Still, if a UKA does fail, changing it to a Total Knee Replacement (TKA) is generally accompanied by fewer health problems as compared to redoing a TKA.