Robert Greene, M.D.
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MIS Partial Knee Replacement


Medial Compartment Osteoarthritis
Medial Compartment Osteoarthritis: This photo demonstrates the complete loss of cartilage on only the medial femoral condyle and medial tibia of the knee. Notice the small exposure needed for partial knee replacement.

Outpatient Partial Knee Replacement

Osteoarthritis is one of the most common causes of severe pain in the active patient and is the most common diagnosis leading to knee replacement surgery. Traditional knee replacement has an extensive, long-term track record and is considered to be one of the most successful surgeries done today. However, standard knee replacement includes a large operation, days in the hospital, arduous rehabilitation, and prolonged time off work. In roughly 12% - 15% of patients with osteoarthritis of the knee, the arthritic changes are involve only one small area of the knee. These patients may be eligible for partial knee replacement. Partial knee replacement can be an important alternative, especially in younger patients. This article reviews minimally invasive unicondylar knee replacement done in an outpatient surgery and compares to total knee replacement done in a hospital setting.


Partial Knee Replacement Implants
Partial knee replacement implants: This photo shows the tibial and femoral resurfacing after a completed partial knee replacement..

Partial Knee Replacement

Like total knee replacement, a partial knee replacement consists of metal and plastic parts designed to resurface the worn ends of arthritic joints. Where total joint replacements resurface all of the joint surfaces, partial knee replacements are used to resurface only one side of the knee (Figure 1). Partial knee arthroplasty is a minimally invasive alternative with less blood loss, less postoperative pain, and a lower post-operative infection rate. It has an excellent range of motion. Since the cruciate ligaments are retained, it feels more like a normal knee than most total knees do. Partial knee arthroplasty is characterized as a procedure with a reliable 8 to ten-year outcome improperly selected patients with osteoarthritis who receive a skillfully implanted, proper design. Partial knee replacement is a bone conserving, soft tissue friendly operation that sets the stage for an easier, and more successful revision arthroplasty, making it an important option for the younger patient who needs to anticipate revision surgery in the future. These characteristics make partial knee replacement particularly attractive to the high-demand patient who seeks rapid return of function and normal lifestyle.


Patient Selection

Partial knee replacement can only be done is patients with limited arthritis. More severe arthritis requires total knee replacement. As osteoarthritis progresses, the knee becomes more misaligned, stiff, and deformed. Proper alignment is critical for the long-term success of a partial knee replacement. Precise position of the implants is another critically important element of the durable partial knee replacement.


Computer navigation is a recent advancement in joint replacement surgery. It utilizes light-emitting diodes actually attached to the limb during knee replacement surgery. (Figure 2) These devices communicate directly with a camera attached to a computer and allow the surgeon the create digital reproduction of the entire surgery. Computer navigation used during partial knee replacement helps to minimize the amount of surgical dissection and to ensure proper positioning of the implants. Component position, range of motion, ligament tensioning, and overall limb alignment are accurately and clearly viewed at every step during the operation. Errors in techniques that would otherwise go unnoticed can be quickly seen and corrected.


Minimally Invasive Surgical Techniques For Unicondylar Knee Replacement

Minimally invasive surgical techniques have been shown to be safe and effective in knee replacement. Minimally invasive surgical techniques for unicondylar knee replacement are also well established. These techniques utilize a small incision and decrease the stress on the quadriceps muscle. This allows less postoperative pain, early return of function (stair climbing and strait-leg raising), more normal range of motion, and the potential for outpatient surgery. The combination of minimally invasive surgical technique and computer navigation has created the opportunity for this surgery to ideally be performed in an outpatient setting.


There are important advantages of performing minimally invasive unicondylar knee replacements in an outpatient setting:

  • Lower infection rates
  • Lower cost
  • Improved comfort
  • Increased convenience and ease
  • Greater Patient Satisfaction

Summary: MIS UKA

Unicondylar knee replacement can be much more than a minimally invasive resurfacing of worn out tibial and femoral joint surfaces. This procedure can and should adhere to the basic principles that have established total knee replacements as one of the most successful, reliable and durable operations available. Authors have shown that results of unicondylar knee replacement can be comparable to those of total knee replacement, even in younger patients. The use of modern component designs and computer navigation enables precise management of component position and alignment. Modern component design combined with precise and conservative bone resections provides stable, reliable, and durable results after partial knee replacement. Computer navigation techniques can help to insure accurate and precise placement of components and restoration of ideal alignment. Still, only a limited number of patients will be appropriate for unicondylar knee replacement. Other patients will need to consider total knee replacement.

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