Knee osteoarthritis usually occurs first in the medial (inside) portion of the knee joint. Unlike total knee replacement that removes all the knee joint surfaces, a unicondylar or partial knee replacement replaces only one part of the knee joint. In knees that are otherwise healthy, a partial knee replacement can preserve the healthy bone, cartilage, and ligaments; potentially preventing or delaying the need for total knee replacement.
Some advantages of a partial knee replacement are that it removes less bone and cartilage, may require a shorter hospital stay, may be less painful, may enable a more rapid recovery, and may provide more natural motion when compared to a total knee replacement. Early results of unicondylar (partial) replacement from the 1970s and 1980s tended to support the idea that this procedure was appropriate only for the sedentary, elderly patient. Since that time, advancements in materials, design, instrumentation, and operative technique have expanded the indications to include younger, more active patients.