> Skip repeated content

Knee Replacement

What is knee replacement surgery?

Knee replacement surgery, or knee arthroplasty, offers pain relief and improved movement to those suffering from advanced arthritis of the knee or a weakened knee joint. In most cases, the cartilage is worn away and the surface of the knee becomes pitted, eroded, and uneven. This causes pain, stiffness, instability, and a change in body alignment. Total knee replacement (TKR) is most common and involves removing the damaged bone and cartilage and replacing the knee joint with implants to restore the natural motion and function of the knee. In a partial knee replacement, damaged cartilage and bone are removed and replaced only in the diseased compartment of a person's knee.

To understand TKR, you should be familiar with the structure of the knee, a complex joint consisting of three bones: the femur (thighbone), the tibia (shinbone) and the patella (kneecap).

Knee joint diagram with labels clockwise from top indicating the femur, femoral condyle, medial collateral ligament (MCL), medial meniscus, tibia, anterior cruciate ligament (ACL) and the patella (kneecap)

Strong ligaments also connect the powerful muscles of the thigh and calf to the bones around the knee and power the knee motion and function. Conditioning and strengthening the muscles through physical therapy and dedicated exercise is most important in restoring and maintaining good knee function and comfort. Cartilage (such as the meniscus) and other soft tissues cover and cushion the bones to help them glide together smoothly. When you bend or straighten your knee, the end of the femur rolls against the end of the tibia, and the patella glides in front of the femur.

When the cartilage cushions wears thin or away completely, the knee becomes arthritic. This is known as osteoarthritis of the knee. The bones then rub together and become rough. The resulting inflammation and pain cause reduced motion and difficulty in walking.

In a partial knee replacement, damaged cartilage and bone are removed and replaced only in the diseased compartment of a person's knee. This differs from a total knee replacement, in which bone and cartilage from the entire joint are replaced.

What are the types of knee replacement surgery?

There are generally two types of knee replacement:

  • Partial knee replacement (also known as unicompartmental knee arthroplasty or unicondylar knee arthroplasty) is suitable for people who experience arthritis only in one compartment (section) of the knee joint, rather than throughout the joint. It can also provide relief from pain and stiffness in some people who have medical conditions that make them poor candidates for total knee replacement surgery.
  • Total knee replacement (also known as condylar arthroplasty) is what most patients will require. It involves replacing the entire joint. In this case, surgeons shave down the damaged bone areas and fix implants, or prosthesis, over the ends of the bone so that they glide smoothly against one another. These implants are generally made of metal and plastic and each implant is customized for the individual to provide maximum compatibility.

The weightbearing surfaces of a TKR are smooth, as in a normal knee. A femoral component covers the end of the thighbone, a tibial component covers the top of the shinbone and the patellar component covers the underside of the kneecap.

Graphic showing elements of the healthy knee, arthritic knee, and total knee replacement.

Most femoral components are metal alloys (cobalt chromium) or metal-ceramic alloys (oxidized zirconium). The patellar component is plastic (polyethylene). The tibial insert component is also plastic (polyethylene). The tibial tray component can be made of the following materials:

  • Cobalt chromium (metal alloy)
  • Titanium (metal alloy)
  • Polyethylene (plastic)

See the following animations for the difference between partial and total knee replacement:

Total Knee Replacement Animation Video
Total knee replacement animation video

Partial knee replacement animation video
Partial knee replacement animation video


What is same-day knee replacement?

Same-day, rapid recovery or outpatient knee replacement surgery means that a patient goes home to recover on the day of their procedure. This is possible due to advancements in technology, technique and pain management, and it offers many benefits to those who qualify for this procedure. Patients who are in good general health, do not smoke, are motivated and have a good support team at home are the best candidates. Those who qualify are given special education on their recovery, which must be followed closely. The benefits of this surgery include:

  • Lower risk of infection
  • Quicker return to normal activities
  • A more comfortable recovery at home

HSS joint replacement specialists perform a thorough evaluation of each patient’s individual circumstance in order to determine their eligibility for same-day knee replacement surgery.

Do I need knee replacement surgery?

Treatment for damage and arthritis of the knee joint depends on multiple factors, such as the condition of the knee and the patient’s age and activity level. At first, nonsurgical methods including physical therapy, anti-inflammatory medication, and weight loss are used to manage the condition.

You may need surgery if:

  • Your knees are stiff and swollen
  • There is pain throughout the day, even at rest
  • Walking, getting up, or climbing stairs is difficult and painful
  • Medication and therapy do not offer enough relief

How long does a knee replacement last?

Improvements in surgical techniques, technology, and materials have made knee replacement surgery one of the most successful orthopedic procedures, with over 700,000 performed successfully in the US annually. Most people experience less pain, increased movement, and improved quality of life afterwards. However, the implants do not last forever.

Implants are expected to function for at least 15 to 20 years in 85% to 90% of patients. Over time, general wear and tear will loosen the implants and may cause pain, loose particles, infection, and instability. Once this occurs, orthopedic surgeons recommend having knee revision surgery.

While infection after surgery is rare, a knee replacement implant cannot defend itself from infection if bacteria are introduced to the body. Learn more about infection prevention in joint replacement.

What can I expect at HSS?

Hospital for Special Surgery has been at the forefront of modern knee replacement since the operation's inception in 1968. Each year, HSS leads the field in these ways:

  • The Numbers: HSS is the No. 1 Hospital in Orthopedic Surgery according to US News & World Report. Along with high rankings in patient satisfaction, HSS performs the most knee replacements with the lowest reported infection rates in the United States.
  • Research and Advancement: Smaller incisions, new implant materials and design, and sophisticated instrumentation have been – and continue to be – the areas of expertise of the surgeons in the HSS Adult Reconstruction & Joint Replacement Division.
  • Regional Anesthesia: Isolating the anesthesia to a particular body area helps avoid the potential problems that may accompany a general anesthetic. These techniques have been developed and refined by the Department of Anesthesiology at HSS.
  • Learn more about Safe Knee Surgery: How Anesthesiology Plays a Role

How to prepare for knee replacement

If you have already decided on surgery, there are certain steps that can improve your recovery time and results. It is always important to follow your knee replacement surgeon’s instructions before and after surgery, as well as your rehabilitation therapist’s recommendations.

TKR surgery generally takes 1 to 1.5 hours, but you can expect to be in the operating room for over two hours. Once your surgery is complete, you will recover and begin your rehabilitation within 24 hours. Your nurse or therapist will help you sit up and stand. Patients begin with a walker and within a few days usually progress to using a straight cane and climbing stairs.

Here is additional material on preparing for knee replacement:

Back in the Game Patient Stories

Need Help Finding a Physician?

Specialized Centers, Departments and Services: