When your knee doesn’t respond to medications and treatments, knee replacement surgery is an option. There are two types of replacement surgeries: total knee replacement, the more commonly performed of the two, and partial knee replacement.
Total knee replacement
The traditional method for repairing a damaged knee is a total knee replacement surgery (TKR).
Since the first operation in 1968, doctors have dramatically improved the procedure. In fact, advancements in medical technology have led to precise and highly functional artificial knee implants that nearly duplicate the way the human knee moves — and are custom fit to your body. A TKR is now among the safest and most effective of all standard orthopedic surgeries.
During a TKR, a surgeon removes the surface of your bones that have been damaged by osteoarthritis or other causes and replaces the knee with an artificial implant that is selected to fit your anatomy. The surgeon uses special surgical instruments to cut away the arthritic bone accurately and then shape the healthy bone underneath to fit precisely into the implant components.
Essentially, the surgery is a four-step process. The first part involves preparing the bone by removing the damaged cartilage surfaces at the ends of the thighbone (femur) and shinbone (tibia), as well as a small portion of underlying bone.
During the next phase, the surgeon positions the metal tibial and femoral implants and either cements them to the bone or press-fits them. “Press-fitting” refers to implants that are built with rough surfaces to encourage the bone in your knee to grow into them, thus securing the implants organically.
The next step is to insert a plastic button underneath the kneecap (patella). This may require resurfacing the undersurface of the kneecap in order to better affix it to the button.
Finally, the surgeon implants a medical grade plastic spacer between the tibial and femoral metal components in order to create a smooth surface that glides easily and mimics the motion of the natural knee. In order to ensure a successful outcome, the surgeon must align the implants precisely and carefully fit them to the bone.
The American Academy of Orthopaedic Surgeons reports that 90 percent of those who’ve undergone TKR experience a dramatic reduction in knee pain and benefit from improved mobility and movement. Most are able to resume daily activities.
However, it’s critical to set proper expectations and avoid high-impact activities such as running and skiing. Moderate use of your artificial knee will increase the odds that the implant will last for many years. About 85 to 90 percent of TKR implants continue to work well 15 to 20 years after the operation.
Be aware that there are risks are associated with a TKR. These risks include infection that could result in additional surgery, blood clots that could lead to stroke or death, and continued knee instability and pain. A TKR also requires an extended rehabilitation program and home planning to accommodate the recovery period. You should plan on using a walker, crutches, or a cane immediately after surgery.
In addition, implant loosening or failures can occur — especially if misalignment occurred between the implant and the bone during surgery or afterward. Although these failures are uncommon, and usually occur in the weeks following the original surgery, they would require a return to the operating room for a revision surgery. During this procedure, the surgeon removes the failed implant, once again prepares the bone, and installs a new implant.
Cruciate retaining vs. posterior stabilized
There are two different variations of a TKR. Speak to your doctor about which approach is best for you.
Removal of the posterior cruciate ligament (posterior-stabilized). The posterior cruciate ligament is a large ligament in the back of the knee that provides support when the knee bends. If this ligament can’t support an artificial knee, a surgeon will remove it during the TKR procedure. In its place, special implant components (a cam and post) are used to stabilize the knee and provide flexion.
Preservation of the posterior cruciate ligament (cruciate-retaining). If the ligament can support an artificial knee, the surgeon may leave the posterior cruciate ligament in place when implanting the prosthesis. The artificial joint used is “cruciate-retaining” and generally has a groove in it that accommodates and protects the ligament, allowing it to continue providing knee stability. Preserving the cruciate ligament is thought to allow for more natural flexion.
Partial knee replacement
Partial knee replacement (PKR), sometimes referred to as a uni-compartmental knee replacement, is an option for a small percentage of people. Far fewer PKRs are performed than TKRs in the United States.
As the name implies, only a part of the knee is replaced in order to preserve as much original healthy bone and soft tissue as possible. Candidates for this type of surgery generally have osteoarthritis in only one compartment of their knee. So surgery takes place in any of three anatomical compartments of the knee where diseased bone presents the most pain: the medial compartment located on the inside of the knee, the lateral compartment on the outside of the knee, or the patella femoral compartment that’s positioned on the front of the knee between the thighbone and kneecap.
During a PKR, a surgeon removes the arthritic portion of the knee — including bone and cartilage — and replaces that compartment with metal and plastic components.
A PKR surgery offers a few key advantages, including a shorter hospital stay, faster recovery and rehabilitation period, less pain following surgery, and less trauma and blood loss. Compared with those who receive a TKR, people who receive a PKR often report that their knee bends better and feels more natural.
However, there’s less assurance that a PKR will reduce or eliminate the underlying pain. And because the preserved bone is still susceptible to arthritis, there’s also a greater chance that follow-up TKR surgery may be required at some point in the future.
Surgeons usually perform PKRs on younger patients (under age 65) who have plenty of healthy bone remaining. The procedure is performed on one of the three knee compartments. If two or more knee compartments are damaged, it’s probably not the best option.
PKRs are most suitable for those who lead an active lifestyle and might require a follow-up procedure — perhaps a TKR — in 20 years or so, after the first implant wears out. However, it’s also used for some older individuals who live relatively sedentary lifestyles.
Because a PKR is less invasive and involves less tissue, you are likely to be up and about sooner. In many cases, a PKR recipient is able to move around without the aid of crutches or a cane in about four to six weeks — approximately half the time for a TKR. They also experience less pain and better functionality — and report high levels of satisfaction.
Types of knee replacement approaches
Your doctor will also choose a surgical approach (as well as the approach to anesthesia, whether general or regional) that’s best suited to your needs. You and the medical team will engage in pre-operative planning that covers the type of procedure you receive and associated medical requirements.
In order to ensure a smooth procedure, a skilled orthopedic surgeon will map out your knee anatomy in advance so that they may plan their surgical approach and anticipate special instruments or devices. This is an essential part of the process. Possible procedures are discussed below.
In the traditional approach, the surgeon makes an 8- to 12-inch incision and operates on the knee using standard surgical technique. Generally, the incision is made along the front and toward the middle (midline or anteromedial) or along the front and to the side (anterolateral) of the knee.
The traditional surgical approach usually involves cutting into the quadriceps tendon in order to turn the kneecap over and expose the arthritic joint. This approach typically requires three to five recovery days in the hospital and about 12 weeks of recovery time.
Minimally invasive surgery
A surgeon may suggest a minimally invasive surgery (MIS) that reduces trauma to tissue, lessens pain, and decreases blood loss — consequently speeding recovery. A minimally invasive approach reduces the incision to 3 to 4 inches. A key difference between this approach and the standard surgery is that the kneecap is pushed to the side rather than being turned over. This results in a smaller cut into the quadriceps tendon and less trauma to the quadriceps muscle. Because the surgeon cuts less muscle, healing occurs faster, and you are likely to experience better range of motion after recovery.
The procedure modifies the techniques used in traditional surgery while using the same implants from traditional surgery. Manufacturers provide specialized instruments that help to place the implant accurately but also allow for incisions to be made as small as possible. Since the only change between MIS and traditional surgery is in the surgical technique, the long-term clinical outcomes are similar.
Types of minimally invasive approaches include:
After making a minimal incision, the surgeon shifts the kneecap to the side and cuts away the arthritic bone without cutting through the quadriceps tendon. The quadriceps-sparing method, as the name suggests, is less invasive than traditional surgery. It spares the quadriceps muscle from as much trauma as possible.
Another term for this approach is “subvastus” because access to the joint is taken from under (sub) the vastus muscle (the largest part of the quadriceps muscle group).
Another variation of a quadriceps-sparing approach is called midvastus. It also avoids cutting the quadriceps tendon, but instead of completely sparing the vastus muscle by going under it, in this surgical approach the muscle is split along a natural line through the middle. The decision to use one approach versus another depends on the condition of your knee and surrounding tissues.
The subvastus and midvastus approaches often take longer to perform but may result in a faster rehab process. This is because there is little to no trauma to the underlying thigh muscle, making it easier to walk sooner after the operation.
This approach is rarely used. It’s more common for those whose knees tend to bend outward. The surgeon enters the knee joint laterally, or from the side of the knee. The lateral approach is less invasive than traditional surgery because it spares much of the quadriceps, making it easier for patients to return to walking faster.
Minimally invasive surgery trims the hospital stay to three to four days and it can shorten the recovery period to four to six weeks. People who get a PKR experienced less pain and were able to resume daily activities faster and better than those who had standard surgery. At one year, however, there were no significant differences between the two groups.
Minimally invasive approaches aren’t appropriate for everybody. Surgeons carefully evaluate each patient and select the approach that’s best. Also, minimally invasive surgery is more difficult to perform and requires a more specific technique, instruments, and surgical training. One study found that it requires about one hour longer than a traditional surgery. Consult your surgeon to discuss your options.
Computer-assisted surgery (CAS)
Increasingly, surgeons are also turning to computer-assisted methods for both TKRs and PKRs involving both traditional and minimally invasive procedures. A surgeon enters a patient’s anatomical data into a computer — a process called “registration” — and the computer generates a 3-D model of the knee.
The software provides the surgeon with a more precise, computer-aided image of the knee. The computer helps the surgeon align the knee components more precisely in the bone and increases the odds that the device will work effectively.
A computer-based approach also allows a surgeon to operate with a smaller incision and benefits the patient by reducing recovery time. A more precise fit can also reduce wear and increase the longevity of the new joint.
The bottom line
Today’s procedures are increasingly sophisticated and safe. They’re paving the way for millions of people to enjoy a healthier and more active life. Talk with your surgeon to determine what procedure is best for your specific needs.