Partial knee replacement
Partial Knee
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Dr. Stephen J. Incavo

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Arthritis and Less Invasive Knee Joint Replacement

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What is knee arthritis?

Arthritis, specifically “osteoarthritis,” is the end result of lifelong injuries, conditions and everyday wear and tear on the musculoskeletal system.

Defined as “joint inflammation,” arthritis is the degeneration of the cartilage and other soft tissue facilitating joint movement. As the joint tissue breaks down, the bones it connects at the joint begin to rub against one another causing friction, inflammation and pain. While there are many different kinds of arthritis, osteoarthritis is among the most common.

As a load bearing joint, the knee joint is one of the most commonly affected joints in the body. There are multiple causes of knee arthritis, including a genetic predisposition, heavy activity, excessive body weight, and previous injuries or surgery to the joint. Other causes of knee arthritis include generalized inflammatory conditions, such as rheumatoid arthritis and related syndromes.

Healthy Knees - visible articular cartilage / joint spaceLess Invasive Knee Joint Replacement

Healthy Knees – visible articular cartilage / joint space

 

Healthy Knees - visible articular cartilage / joint space

Arthritic Knees – diminished articular cartilage and joint space

 

As arthritis progresses, the inside aspect of the knee slowly wears out and this may produce a bow-legged deformity. If the arthritis is primarily on the outside aspect of the knee, with time this may produce a “knockkneed” deformity. Knee joint replacement can also help correct these deformities.

 

Healthy Knees - visible articular cartilage / joint space Healthy Knees - visible articular cartilage / joint space
Before and after example demonstrating a varus (bow-legged) correction possible with knee joint replacement surgery  

 

Before and after x-rays demonstrating a valgus (knock-kneed) correction possible with knee joint replacement surgery.

Healthy Knees - visible articular cartilage / joint space
Healthy Knees - visible articular cartilage / joint space  

 

What is a knee joint replacement?

A knee replacement is a procedure which removes degenerative (arthritic) joint tissue and replaces it with prosthetic (artificial) implants or components designed tomove as your natural knee.

Placed on the surface of the bones meeting at the joint, these new components re-establish a smooth junction to restore the fluid movement that healthy tissue once allowed. A total knee replacement involves femoral, tibialand patellar components.

Healthy Knees - visible articular cartilage / joint space Healthy Knees - visible articular cartilage / joint space
Total Knee Joint Replacement (TKR) Partial Knee Joint Replacement(PKR)

A partial knee replacement, a less invasive or minimally invasive procedure, removes only the damaged area of the knee joint and replaces it with just those components required to restore normal knee function. Healthy tissue is left intact.

What is a Partial Knee Replacement (PKR)?

A partial knee replacement is a smaller version of a total knee replacement. It involves replacing only the arthritic/damaged portion of the knee joint.

"In partial knee replacement surgery, accurate
placement is the key to the implant working
well and lasting a long time," -
Stephen Incavo, M.D.

For example, if the inner (medial) aspect of the knee is worn out, a medial unicompartmental arthroplasty (replacement) can be performed.

 

Healthy Knees - visible articular cartilage / joint space Healthy Knees - visible articular cartilage / joint space
Partial Knee Replacement (PKR) PKR Components

There are also partial knee replacements of the patellofemoral portion of the knee joint and the lateral portion of the knee joint. New procedures such as the NavioPFS system, manufactured by Blue Belt Technologies allow surgeons to upload imaging to the system and maps out exactly where the implant needs to go. If the surgeon needs to adjust the implant a few degrees, the robotic system allows them to do that with more precision.

PKR surgeries have the advantage of maintaining the non-damaged, native part of the knee joint. Because of this, partial replacements may be preferable to traditional total knee replacement in the right candidate.

Total Knee Replacement (TKR) / Arthroplasty (TKA) Systems

Healthy Knees - visible articular cartilage / joint space Healthy Knees - visible articular cartilage / joint space
Microport medial-pivot TKA implants with
ball-in-socket articulation
Microport medial-pivot TKA – lateral view
Healthy Knees - visible articular cartilage / joint space Healthy Knees - visible articular cartilage / joint space
Smith & Nephew TKA, all polyethylene tibial
component
Zimmer TKA

 

Prevention of blood clots and pulmonary embolisms after joint replacement surgery

Watch Partial Knee Replacement VideoWatch Knee Replacement Video

Limitations of Partial Knee Replacements

A disadvantage of PKR is, while the normal portions of the knee joint are maintained, these normal portions may wear out in time, requiring further surgery. Another important limitation of partial knee replacements is that there is statistical evidence that the components do not function as long as total knee replacements. For example, on average, the majority (over 95%) of total knee replacements last for 10-15 years without “wearing out” or loosening. While some available data demonstrates similar longevity for partial knee replacements, other data states that there is a higher wear and/ or loosening rate of these components, as well as a potential for complications rarely seen in knee replacement (e.g., fracture of the tibia). If you are interested in a partial knee replacement you should discuss these issues with your orthopedic surgeon.

Read more about Minimally Invasive Joint Replacement.

Read more about Partial Knee Joint Replacement Surgery.

Read more about Total Knee Replacement Surgery.

Read more about Revision Knee Joint Replacement.

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