Tabor Orthopedics

As the U.S. population ages and as Americans become more physically active, the incidence of knee arthritis is increasing. Arthritis can be divided into two main categories – inflammatory arthritis (like rheumatoid arthritis and lupus) and osteoarthritis. Osteoarthritis, which is by far the most common kind, simply means that the smooth cartilage covering on the end of the bone is damaged or worn out. As the cartilage deteriorates, there is more friction between the moving bones, which causes pain, swelling, and stiffness.

Most patients are able to successfully manage their knee arthritis with anti-inflammatory medications such as Advil or Aleve or by receiving occasional injections such as a steroid. Some patients, however, will get only partial or temporary relief from these treatments. Many of these patients will eventually require knee replacement.

The most common type of knee replacement is a “total knee”, where the entire ends of the thighbone (femur) and shinbone (tibia) as well as the underside of the kneecap are resurfaced. In addition, two natural shock absorbers (menisci) and stabilizers (ligaments) are removed.

While a total knee replacement is generally successful and long lasting, the procedure is quite invasive and has some uncommon but significant risks including blood loss, risk of infection, blood clots and stiffness.

Another important consideration is that recovery can be difficult and painful. Knee-replacement patients may spend as much as a day or so longer in the hospital and experience a longer recovery time than a partial-knee replacement patient.

In patients who have damaged cartilage in all three of the “compartments” of the knee, a total knee is the best option. Many patients, however, have arthritis confined to just one of the three knee compartments and may be candidates for a less invasive procedure called a “unicompartmental” or partial knee replacement. Advantages of the unicompartmental compared to total knee replacement include:

• Shorter incisions
• Less blood loss and lower risk of transfusion
• Lower risks of infection
• Greater flexibility and less stiffness
• Faster recovery rates and hospital time
• Less bone is removed so the knee feels more “normal”
• Certain motions such as kneeling and squatting are easier
• Revision can be less complicated

Primary, or “first time”, unicompartmental and total knee replacements usually last a long time, with more than 90 percent of each type of knee lasting longer than 10 years, and over 80 percent lasting 20 years or more. If the implant eventually wears out or loosens, it has to be “revised”. Because the “uni” surgery removes less bone and retains more of the original knee than does the “total knee”, revision is simpler if the original implant fails. Revision of a total knee replacement, while usually successful, has many potential pitfalls and the results are usually not as good as those of a primary total knee replacement. Results of revision of unicompartmental knee replacements to total knees are similar to those of primary, or first time, total knee replacements.

Partial knee replacements do have some drawbacks, too. While the long term results of a partial knee are almost as good as those of total knees, they are not equal. Unicompartmental knees have a slightly higher failure rate than total knees. In the first year, about 3 percent of uni knees will fail because of implant loosening (compared to 1 percent of total knees). As time goes on, the native cartilage left behind can wear out, requiring revision to a total knee. As with a total knee, the implant is made of metal and plastic, and it can wear out also.

Unicompartmental knees can be more operator dependent. While total knees are done using a variety of cutting guides, uni knees are sometimes done “free-hand”, which requires the surgeon to make accurate cuts for optimal implant placement.

Also, not all knees cases are clear cut. While some knees clearly have arthritis involving only one compartment, many knees have advanced arthritis in one area, and mild arthritis in others. These knees require the surgeon to make a judgment call on whether a “uni” is the appropriate implant. Factors such as patient age, size, and activity level also play a role. For these reasons, many surgeons choose not to perform a uni replacement, but rather to replace the total knee.

When patients and physicians have a good picture of knee health, or lack of it, choosing the right treatment options throughout a patient’s life becomes a clear process and one that is likely to restore mobility and health.

By Owen Tabor Jr, M.D. - Owen Tabor Jr. is a board certified orthopedic surgeon. He received his medical degree from The University of Virginia in 1993 and completed his residency training at the Carolinas Medical Center in Charlotte, NC in 1999. He practices general orthopedics with a special interest in hip and knee replacement.