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Orthopedics and Sports Medicine

Partial Knee Replacement

Image: Partial knee replacement device (front view of the right knee) Image: Partial knee replacement device (side view of the right knee)
Partial knee replacement (front view of right knee) Partial knee replacement (side view of right knee) 
Partial knee replacement — also known as unicompartmental knee arthroplasty — was first offered to patients in the early 1970s. However it wasn't until the 1990s that perfections in design and materials — cobalt chrome, titanium alloy and molded polyethylene — provided better comfort, fit and durability. The modern partial knee implant mimics the natural motion of the knee joint and gives patients functionality earlier than would be expected after a total knee replacement.

Patient Selection Crucial to Success
The appropriate candidates for partial knee replacements are adults, 40 to 60 years of age who are in good health and who have exhausted conservative measures for managing their knee pain, such as:

  • Medication use
  • Bracing 
  • Limitation on activities

These patients may have had a torn meniscus (cartilage) or avascular necrosis (dead tissue) in the past that led to arthritis later in one part of the knee.

For younger adults, a partial knee implant is considered "a bridge to the future," surgically amending what can be repaired now before further degeneration in the joint occurs. Older adults, age 70 and above also may be candidates for this implant, which is then expected to last the remainder of their lives.

Partial Knee Replacement Surgery
Image: Partial knee replacement deviceThe device implanted at Virginia Mason is manufactured in a variety of sizes and interchangeable parts, including various surface thicknesses for better patient fit. 

Surgery involves a three- to three-and-a-half-inch incision, commonly on the inside half or medial side of the knee, which exposes the damaged bone surface and cartilage. The damaged surfaces on the femur (the thigh bone) and tibia (the leg bone) as well as the diseased cartilage are all removed. A cobalt chrome polished surface is attached to the end of the femur and a titanium alloy base plate is attached to the end of the tibia, with a molded polyethylene insert then secured to the tibial plate. The surgery lasts approximately one hour, with a one or two-day stay in the hospital.

With the majority of the joint surfaces, cartilage and all of the knee ligaments retained during surgery, patients experience less pain and a quicker recovery than they would during a total knee replacement. Additionally, the surgical scar is much smaller.

What to Expect After Surgery
On the same day as your surgery, a physical therapist will help you sit up in bed and show you how to perform light exercises. You may even walk a short distance with the help of a cane or walker on this first day. Each day you are in the hospital, and several times a day, the physical therapist will work with you and help you walk a little bit farther. Your road to recover begins with these simple exercises that will eventually help you regain strength and functional use of your knee.

Your surgeon or a physical therapist also will talk to you about progressive exercises to do at home. Additionally, rehabilitation services are available through Virginia Mason's Department of Physical Medicine and Rehabilitation and Sports Medicine Clinic. Without any complications, you can expect your rehabilitation to take about eight weeks, compared to approximately 12 weeks for a total knee replacement.

Risks of a Partial Knee Replacement  
All precautions to ensure patient safety are taken prior to every operation at Virginia Mason. However, as with any surgery, some risks remain. There are, for example, risks of:

  • Infection
  • Excessive blood loss
  • Development of blood clots.

The incidence of these risks occurring in patients is very small.

Over time, some implants can loosen and require revision. This risk occurs infrequently because of better patient selection and improvements in implant materials. Over a 10-year period and longer, a partial knee replacement is still functioning in 95 percent to 97 percent of patients. Your surgeon will discuss in more detail the risks associated with your surgery.

How long will my knee implant last?
Many patients ask how long the knee implant will last. That answer must take into account several factors, including your age, weight and activity level. Because these devices are made with durable materials that provide a secure fit, a partial knee implant is expected to last beyond 10 years. If, at a later date, a total knee replacement of the same knee is required, revision surgery can be performed. Studies have shown few complications with this second surgery.

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