Total knee replacement is one of the most commonly performed orthopedic surgeries in the United States, helping hundreds of thousands of adults each year regain mobility and reduce knee pain. The surgery removes the damaged surfaces of the knee joint and replaces them with smooth artificial parts that allow the joint to glide again. For people whose knee pain has reached a point where walking, climbing stairs, or sleeping is difficult, knee replacement can mean a return to daily life.
This guide walks through what total knee replacement actually involves, the different types available, what the implants are made of, and the conditions that most often lead to surgery. The goal is to give a clear, plain-English foundation before going deeper into causes, the procedure, or specific patient questions.
Significance and Prevalence of Knee Replacement in the United States
Knee replacement is one of the two most common joint replacement surgeries in America, alongside hip replacement. The American Joint Replacement Registry (AJRR) 2024 Annual Report tracks more than 4.3 million hip and knee arthroplasties performed across nearly 5,000 surgeons in 1,447 sites across all 50 states and Washington D.C. Total knee replacement accounts for the majority of those procedures.
Knee replacement is most common in adults aged 65 and older, but the surgery is increasingly performed on younger active adults whose joints have been worn down by arthritis or injury. According to the CDC National Center for Health Statistics, the rate of total knee replacement nearly doubled between 2000 and 2010 in adults aged 45 and over, and demand has continued to grow since then. A growing share of patients are now discharged home the same day or the day after surgery, rather than to a rehabilitation facility.
What Is Total Knee Replacement?
A total knee replacement, also called total knee arthroplasty (TKA), is a surgery in which a surgeon removes the damaged cartilage and bone at the surfaces of the knee joint and replaces them with artificial parts. The American Academy of Orthopaedic Surgeons describes it as a “resurfacing” procedure, since only the worn surfaces of the bones are replaced rather than the whole joint.
The goal is straightforward: relieve pain, restore smooth knee movement, and help patients return to walking, climbing stairs, and other daily activities that arthritis or injury had made difficult.
How the Knee Joint Works (Simple Anatomy)
Three bones meet at the knee:
- The femur, the thighbone above the knee
- The tibia, the shinbone below the knee
- The patella, the kneecap that sits in front of the joint
Several other structures help the knee bend, straighten, and absorb impact:
- Articular cartilage is a smooth tissue that covers the bone surfaces inside the joint, letting them glide against each other.
- Menisci are two C-shaped pads of cartilage that cushion between the femur and tibia.
- Ligaments connect bone to bone and keep the joint stable.
- The synovial membrane is a thin lining that produces a fluid to lubricate the joint.
When cartilage wears thin, the menisci tear, or the joint surfaces are damaged by arthritis or trauma, the smooth gliding motion is lost. The bones begin to rub against one another, which creates pain, stiffness, and limited mobility. Total knee replacement replaces the damaged surfaces so the joint can glide smoothly again.
What Gets Replaced in a Total Knee Replacement?
A total knee implant is designed to recreate the natural surfaces of the knee. According to NIAMS, a typical implant has these parts:
- A metal cap placed on the lower end of the femur
- A metal plate secured to the top of the tibia
- A medical-grade plastic spacer (polyethylene) that sits between the metal parts and acts like cartilage
- A plastic button on the back of the patella, used in some patients but not all
These components work together so the bones can glide smoothly. The implants are designed to last many years with normal use.
Three Types of Knee Replacement Surgery
Although “knee replacement” is often used as a single term, there are actually three related procedures. The right choice depends on which part or parts of the knee are damaged.
Total Knee Replacement (TKA)
This is the most common type. All three knee compartments (the inside, outside, and front of the joint) are resurfaced. It is the most common option when arthritis or damage affects the whole joint.
Partial Knee Replacement (Unicompartmental)
In a partial knee replacement, only one of the three knee compartments is resurfaced. The other parts of the joint are left intact. This option is used for patients whose damage is limited to a single area, often the inner (medial) side. Partial replacements typically involve smaller incisions and faster early recovery, but candidacy is more selective.
Patellofemoral Knee Replacement
A patellofemoral replacement is a specific kind of partial knee replacement that resurfaces only the kneecap and the groove on the femur it slides in. It is used in a smaller group of patients whose arthritis is concentrated in that area.
A surgeon decides which type fits each patient based on imaging, the location of joint damage, age, activity level, and overall health.
Surgical Techniques at a High Level
Most knee replacements are still performed using traditional manual techniques. Some surgeons use minimally invasive approaches with smaller incisions of about 4 to 6 inches, while others use computer-navigated or robotic-assisted systems to guide implant placement. The AAOS notes that all techniques use the same kinds of implants, and current evidence suggests long-term outcomes are similar regardless of technique. The right approach depends on the surgeon’s training, the patient’s anatomy, and the type of damage to be repaired. A more detailed comparison of techniques is in our procedure and recovery guide.
Implant Materials and Fixation
Modern knee implants come in several materials and can be held in place in different ways.
Common Implant Materials
- Metal alloys, typically cobalt-chrome or titanium, for the femur and tibia surfaces
- Medical-grade polyethylene (a strong, smooth plastic) for the spacer between the metal parts
- Ceramic-on-polyethylene combinations are available in some cases
All implant materials used in the U.S. are cleared by the U.S. Food and Drug Administration before they are used in surgery.
How Implants Stay in Place
Implants are secured in one of three ways:
- Cemented: Held in place with a medical-grade bone cement at the time of surgery. This is the most common method in knee replacement.
- Uncemented (press-fit): Has a textured surface that natural bone grows into over time.
- Hybrid: A combination, for example a cemented tibia with a press-fit femur.
Each method has its place, and the choice often depends on bone quality, age, activity level, and the surgeon’s preference.
Who Might Need a Knee Replacement?
Knee replacement is generally considered after non-surgical treatments have been tried and ongoing pain or stiffness is interfering with daily life. The conditions that most often lead to surgery include:
- Osteoarthritis, the most common cause, which gradually wears down cartilage with age
- Rheumatoid arthritis, an autoimmune condition that damages the joint lining and cartilage
- Post-traumatic arthritis, which develops after fractures, ligament tears, or meniscus damage
- Avascular necrosis (osteonecrosis) of the knee, where bone tissue dies due to reduced blood supply
- Severe joint deformity caused by chronic knee disease
A deeper look at how each of these conditions damages the knee, plus how doctors diagnose the problem and decide when surgery is needed, is in our causes and diagnosis guide.
Early Warning Signs of Knee Joint Damage
Knee problems often build slowly. Some of the earliest signs that the joint may be wearing down include:
- Persistent knee pain that does not improve with rest
- Pain that disturbs sleep or makes morning movement difficult
- Stiffness when getting up from a chair, the car, or the floor
- Trouble with stairs, kneeling, or walking longer distances
- Knee buckling, locking, clicking, or grinding
- Limited improvement from medications, physical therapy, or injections
Not everyone with these symptoms will need surgery, and many people manage knee arthritis successfully with conservative care. The Arthritis Foundation and AAOS both recommend an evaluation by an orthopedic specialist when knee symptoms begin to limit daily activities.
Your Knee Replacement Journey at a Glance
Each patient’s journey is unique, but most knee replacement experiences follow a similar arc:
- Initial evaluation. A primary care doctor or orthopedic specialist reviews symptoms, performs a physical exam, and orders imaging.
- Diagnosis and decision. Imaging confirms the type and severity of joint damage. The patient and surgeon decide together whether surgery is the right next step.
- Pre-surgery preparation. Health checks, dental clearance, medication review, and home setup happen in the weeks before surgery.
- Surgery. The damaged joint surfaces are replaced with the implant.
- Recovery and rehabilitation. Physical therapy and a gradual return to daily activities follow over the weeks and months after surgery.
If you are starting to research knee replacement for yourself or a loved one, this overview is a strong first step. From here, our cluster goes deeper into the causes and diagnosis, the procedure and recovery, and the questions patients most often ask. For readers also considering hip replacement, our Total Hip Replacement Overview covers the sister procedure.
Frequently Asked Questions
What is the difference between a total knee replacement and a partial knee replacement?
A total knee replacement resurfaces all three compartments of the knee, while a partial knee replacement (also called unicompartmental) replaces just one. Total knee replacement is more common because most patients have damage in more than one area of the joint. Partial knee replacement may be appropriate when the damage is limited to a single compartment.
What is a knee implant made of?
A typical knee implant has a metal cap on the femur, a metal plate on the tibia, and a medical-grade plastic spacer between them. Some patients also receive a small plastic button on the back of the kneecap. All materials used in the U.S. are FDA-cleared.
How do I know if I might need a knee replacement someday?
Early signs include persistent knee pain that does not improve with rest, stiffness that limits daily movement, knee buckling or grinding, and reduced benefit from medication or physical therapy. Not everyone with these symptoms needs surgery, but ongoing pain that affects daily life is a reason to see a healthcare provider.
Disclaimer: This article is for general informational and educational purposes only. It is not intended as medical advice, diagnosis, or treatment. Always talk with a qualified healthcare professional for guidance about your individual situation. The information presented here does not replace a consultation with a licensed medical provider.
