Knee Replacement Surgery (Partial & Full)

Total/Partial Knee Replacement Surgery

There are several different options when it comes to knee replacement surgery. Your surgeon will discuss with you the best option for your particular needs. This overview educates patients on knee anatomy and types of surgery options available.

Normal Anatomy of the Knee

The knee joint is made up of three bones: the femur (thigh bone), the tibia (shin bone), and the patella (knee cap). There is a fourth bone, the fibula which lies along the side of the tibia, but it has only a small role in the function of the knee joint. These three bones work together to allow for flexing and extending the leg at the knee joint. The lower part of the femur connects to the upper part of the tibia and to the patella with ligaments, tendons, and other connective tissues. Amongst these connective tissues is a 2-part structure called the meniscus. The two parts are the inner (medial) side and the outer (lateral) side. The meniscus helps to reduce friction, balance out the weight distribution in the knee, and acts as a shock absorber. The surfaces of the bones where they meet in the knee joint are covered in a special type of cartilage called articular cartilage. This cartilage is very strong and smooth, and it acts to reduce the friction in the knee joint even more. The patella (knee cap) is vital for knee function. Without the patella the knee joint would have a much more difficult time bending and straightening. You can think of the patella like a fulcrum and the leg bones like levers. You use a lot less energy to lift something using a lever with a fulcrum under it than just trying to move it with a lever alone. Since our knees have to support virtually all of our body weight, and have a lot of stress upon them during daily activities, things can sometimes go wrong.

Injuries and Problems of the Knee Joint

The knee joint is vulnerable to stresses, traumatic injury, overuse, and arthritis. The articular cartilage in the knee can be damaged by disease, injury, or normal wear and tear over time. When the cartilage is damaged, the joint surfaces may no longer be smooth. Moving bones along a rough, damaged joint surface is difficult and causes pain. Damaged cartilage can also lead to arthritis in the joint. Articular cartilage does not heal itself well, so sometimes surgical intervention is required. Also, damage to the shock absorbing meniscus, tendons, and ligaments can occur. This is common in traumatic injuries such as in sports, but also in falls. When the knee is not able to properly support the weight of the body, joint damage and arthritis can occur. Often, when there is pain and dysfunction, you will hear that the knee joint is “bone on bone.” This means that the articular cartilage and the meniscus have become damaged, and there is no more friction reduction or shock absorption in the knee. Additionally, certain conditions such as infections or diseases such as rheumatoid arthritis and avascular necrosis can lead to damage in the knee joint. Conditions like these may require surgical intervention to restore pain-free function of the knee joint.

Types of Surgical Interventions for the Knee

There are several different options when it comes to knee replacement surgery. Your surgeon will discuss with you the best option for your particular needs.

Partial Knee Replacement

This procedure, also called uni-compartimental partial knee replacement, involves only one side of the knee joint. As mentioned above, you have an inner (medial) side and an outer (lateral) side of the knee structures. Sometimes the damage or arthritis only affects either the inner or outer portion of the joint. In those cases you may be a candidate for partial knee replacement. This procedure can have a quicker recovery time and may even have better short-term functionality in the joint as there is preservation of more of your own bone and tissues. The incision for a partial knee replacement is also smaller, and certain minimally invasive surgical techniques can be employed to further reduce recovery time. It is important to note that in order to have a partial knee replacement you should have good quality bone structure in the knee, and the ligaments and tendons need to be in good shape too. You should still have essentially a normal range of motion in the knee as well. In a partial knee replacement procedure, a small part of the patella is removed, and the damaged portion of the top surface of the tibia (tibial plateau) is removed to make room for the lower implant. The lower portion of the thigh bone (femoral condyle) is removed to make room for the upper part of the implant. Finally, a portion of the meniscus is removed. The femoral implant component is a smooth, curved piece of metal that mimics the shape of the natural bone. The tibial implant component is a flat shaped piece of metal which will hold a special plastic spacer. The metal components are typically cemented into position on the bone. After the metal components are affixed to the bones, a final polymer plastic spacer is inserted into the tibial component. This plastic spacer will act as a friction reducer and shock absorber, much like the natural meniscus. After range of motion and stability in the joint are assessed, the surgeon will suture the tissues and a splint will be wrapped around the leg to prevent excessive movement. Note that over time, partial knee replacements can wear out faster than total knee replacements, and would require a revision knee replacement surgery.

Total Knee Replacement

This procedure, called a total knee arthroplasty (TKA), involves replacing all of the joint surfaces in the knee. In a total knee replacement, sometimes the under-surface of the patella (knee cap) is resurfaced and polymer plastic implant is attached to it. This is done when the arthritis has damaged the under-surface of the knee cap and there is bone rubbing on bone. Total knee replacement surgery accounts for about 90% of knee replacement surgeries. In a total knee replacement surgery, the lower portion of the thigh bone (femoral condyles) is removed to make a space for the upper implant. The damaged top surface of the tibia (tibial plateau) is removed to make a space for the lower implant. The under-surface of the patella is shaved down to make room for the polymer plastic implant. Any bone spurs would also be removed at this time. Finally, the meniscus is removed. Some surgical techniques involve the use of robotic arm technology. This technology helps the surgeon to get the proper alignments when removing portions of the bone. Note that the robotic arm does not perform the surgery; it just assists the surgeon during the surgical procedure. The femoral implant component is a smooth, curved piece of metal that mimics the shape of the natural bone. The tibial implant component is a flat shaped piece of metal which will hold a special polymer plastic spacer. The patellar component is a rounded polymer plastic piece that is affixed to the underside of the knee cap. The metal components are typically cemented into position on the bone. After the metal components are affixed to the bones, a final polymer plastic spacer is inserted into the tibial component. This plastic spacer will act as a friction reducer and shock absorber, much like the natural meniscus. After all components have been fit into proper position, the knee is assessed for range of motion and stability. When everything looks good, the tissues will be sutured and a splint will be wrapped around the leg to prevent unnecessary movement. Although total knee replacement surgery takes longer, and there is a higher rate of complications and cost, the lifetime of the implants is longer than for partial knee replacement implants. Physical therapy will be a bit more challenging with a total knee replacement as well, but the benefits of greater patient satisfaction, higher functioning, and longer lasting components may make this a better choice for your particular needs.

Patellofemoral Arthroplasty

This procedure is a patella (knee cap) replacement. It involves removing a portion of the front of the lower end of the femur. This is the surface that contacts the underside of the patella. The underside of the patella is then shaved off and is fitted with a polymer plastic implant. This helps to restore pain free movement of the patella on the knee joint. This technique can be used in patients who have arthritis limited to only the patellofemoral region. It can also be performed on patients who have a condition called trochlear dysplasia, which is an abnormally shaped under-surface of the patella. The success of patellofemoral arthroplasty seems to depend more upon patient suitability than other factors. This technique is not performed very often as it is less common to have arthritis limited to only the patellofemoral area, and some surgeons believe that the long term outcomes are better with a total knee replacement.

Complex or Revision Knee Replacement

This procedure is done when the original knee replacement surgery has either failed or has reached the end of its useful life. Sometimes, an artificial joint can become infected necessitating removal and replacement of the implanted components. Another reason for a revision knee replacement is a fracture of the bone in the area of an implant component. A revision knee replacement procedure is more complicated as the knee has previously been surgically altered. Specialized implants need to be used, and there is a lot more planning involved for this procedure. Often these implants have thicker stems that fit deeper into the bones of the femur and tibia.

References

https://medlineplus.gov/ency/article/007256.html

hipknee.aahks.org/full-vs-partial-knee-replacement-whats-the-difference/

Chawla H, van der List JP, Christ AB, Sobrero MR, Zuiderbaan HA, Pearle AD. Annual revision rates of partial versus total knee arthroplasty: A comparative meta-analysis. The Knee. 2017;24(2):179-190.

Christ, AB. et al. Patellofemoral arthroplasty conversion to total knee arthroplasty: Retrieval analysis and clinical correlation. The Knee, Volume 24, Issue 5, 1233 – 1239

Odgaard A, Eldridge J, Madsen F. Patellofemoral Arthroplasty. JBJS Essent Surg Tech. 2019;9(2):e15. Published 2019 Apr 24. doi:10.2106/JBJS.ST.18.00094

https://orthoinfo.aaos.org/en/treatment/revision-total-knee-replacement/

Crawford DA, et.al. Low complication rates in outpatient total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. 2019 May 18. doi: 10.1007/s00167-019-05538-8. [Epub ahead of print]

This page is for information purposes only, and describes general information.  You should always talk to your physician regarding specific details of your surgery.

Knee Replacement Frequently Asked Questions

There’s no precise formula for determining when you should have a knee replacement. But if you’re having trouble getting up to answer the phone or walk to your car, you may be a candidate. A thorough examination by an orthopedic surgeon should yield a recommendation.

The surgeon will make an incision on the top of your knee in order to expose the damaged area of your joint. During the operation, the surgeon moves your kneecap aside and cuts away damaged bone and cartilage, which are then replaced with new metal and plastic components. The components combine to form a synthetic (but biologically compatible) joint that mimics the movement of your natural knee. Most knee replacement procedures take 1.5 to 2 hours to complete.

Implants are comprised of metal and medical-grade plastic. To seal these components to your bone, two methods are used: application of bone cement, which typically takes about 15 minutes to set, and a cement-less approach that uses components with a porous coating that grows into tissue or attaches to bone. In some cases, a surgeon may use both techniques in the same surgery.

Although you’ll experience some pain after surgery, it should diminish quickly. You may receive a nerve block the day of surgery, or your surgeon may use a long-acting anesthetic during your surgery to help with pain relief postoperatively. After you’ve recovered from surgery, you should experience significantly less pain in your knee, but there’s no way to predict exact results.

You will wake up with a bandage over your knee and, possibly, a drain to remove fluid from the joint. You may wake up with your knee elevated and cradled in a continuous passive motion (CPM) machine that gently extends and flexes your leg while you’re lying down, but you may wake up with just your knee elevated. A doctor might also insert a catheter so you don’t have to get out of bed to get to a toilet. The catheter will usually be removed the day of surgery or the following day. In addition, you may wear a compression bandage or sock around your leg to improve blood circulation or foot pumps to reduce the odds of a clot. Your doctor will administer antibiotics intravenously, and you may receive anticoagulants (blood thinners) to reduce the odds of a clot.

Most people are up and walking the day of surgery or the next — with the aid of a walker or crutches. A physical therapist will help you bend and straighten your knee a few hours after your surgery. After you return home, therapy will continue regularly for weeks, and you’ll be asked to engage in specific exercises designed to improve the functionality of the knee.

If you live in a multiple-story house, prepare a bed and space on the ground floor so that you can avoid the stairs when you first return. Make sure the house is free of obstructions and hazards including power cords, area rugs, clutter, and furniture. Focus especially on pathways, hallways, and other places where you’re likely to walk through. It’s wise to make sure that handrails are secure and a grab bar is available in the tub or shower you plan to use. You may want to add a bath or shower seat.

Your doctor will prescribe any mobility equipment that you need, like a walker or crutch.

You should be able to resume normal daily activities — such as walking and bathing — within several days. Low-impact exercise should also be doable after your rehabilitation period, typically 6 to 12 weeks. Consult with your physical therapist about introducing new activities during this rehabilitation period. You should avoid running, jumping, bicycling up and down hills, and other high impact activities. Discuss with your orthopedic surgeon any questions concerning your activities.

Studies show that upward of 85 percent of people who undergo this surgery still have a functioning artificial joint 15 to 20 years after receiving it. However, wear and tear on the joint can adversely affect its performance and lifespan. Younger people are more likely to have the joint wear out and require a revision during their lifetime.

Preparing for Joint Replacement Surgery

Preparing for Surgery

The Day Before Your Surgery

The Morning of Surgery

Arrival at the Center

After Surgery

Going Home