Stephen J. Incavo MD Hip & Knee Surgeon Department Chair of Total Joint Replacement Houston, Texas

Arthritis literally means “joint inflammation.” The knee joint is one of the most commonly affected joints in the body.  There are multiple causes of knee arthritis, but most arthritis is termed osteoarthritis and is a relatively common degenerative condition seen occurring in human beings. Most likely, this has a genetic predisposition but can be worsened with heavy activity, excessive body weight, and injuries to the joint. Other causes of knee arthritis include generalized inflammatory conditions, such as rheumatoid arthritis and related syndromes. Another factor in the development of knee arthritis is previous knee injury or knee surgery.

Patients with knee arthritis experience pain and swelling of the knee joint, as well as slowly progressive deformity of the knee joint. The pain most often occurs on the inside (medial) aspect of the knee, but may occur in the region of the kneecap or the outside (lateral) part of the knee. 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 “knock-kneed” deformity.

A normal knee x-ray, shown below, reveals the thigh bone (femur), the shinbone (tibia), and the kneecap (patella). Notice that there is a space between the bones. In a healthy knee, this space is where the articular cartilage is located. On an x-ray, space between the bones is a good sign. When arthritis becomes severe, the articular cartilage is worn away, the space between the bone narrows, and eventually this leads to “bone-on-bone” contact, which can be very painful.

What is a knee replacement?

A knee replacement involves the placement of prosthetic (artificial) implants on the surface of the bones to reestablish a smooth junction between the bones and to improve the deformity. A total knee replacement involves femoral, tibial and patellar components.

What is a partial knee replacement?

A partial knee replacement is smaller, limited version of a total knee replacement. It involves replacing only the arthritic portion of the knee joint – for example, if the inner (medial) aspect of the knee is worn out, a medial unicompartmental arthroplasty can be performed. There are also partial replacements of the patellofemoral portion of the knee joint and the lateral portion of the knee joint. Partial knee replacements have the advantage of maintaining the non-damaged, normal part of the knee joint. Because of this, partial replacements may be preferable to traditional total knee replacement. The disadvantage of partial replacements is that while the normal portions of the knee joint are maintained, these normal portions may in fact wear out in time, requiring further surgery. Another important limitation of partial knee replacements is that there is statistical evidence that then 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 data is available that demonstrates similar longevity for partial knee replacements, other data is available that states 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 orthopaedic surgeon.

Here are 2 examples demonstrating the varus and valgus correction possible with knee replacement surgery