Archive June 2017 XVIII, No. 6

Partial to Uni Knees

What's fueling the growing demand for unicompartmental knee replacement?

Jared Foran

Jared Foran, MD


proper patient selection GOOD CHOICE With proper patient selection, unis can be performed safely and easily — usually within 1 to 2 hours — to maximize cost savings.

Ten years ago, you probably wouldn't have heard a surgeon say what I'm about to tell you, which is the same thing I tell my patients: A partial knee replacement is not a partial solution — it's a total solution to a partial problem.

Some patients (some orthopedic surgeons, too) remain skeptical about unicompartmental knee arthroplasty, but from the patient outcomes I've seen (and published on), unis rival total knees in terms of long-term survivorship ( Although the uni currently represents a relatively small piece of the knee-replacement pie, it's poised to become the next darling of orthopedic surgery. Here's why:

  • The implants themselves are better and more specific to each patient's anatomy;
  • surgeons better understand who is going to be a good candidate for the surgery; and
  • surgeons can better perform the surgery, thanks to shifts in technology and technique.

Let's examine 4 factors that have helped to fuel the demand for unis.

1 Patient selection
In 1989, Brigham and Women's Hospital orthopods Stuart C. Kozinn, MD, and Richard Scott, MD, wrote a landmark paper about the indications used to determine who was a good candidate for this surgery ( In it, the 2 surgeons offered a rather conservative definition of an ideal candidate: no one weighing more than 180 pounds; no one younger than 60; no one who had more than minimal erosive changes in patellofemoral articulation; and no one who was physically active or performing heavy labor. Based on those strict criteria, the field of acceptable candidates was limited to less than 15% of patients with osteoarthritic knees.

Thankfully, our understanding has grown considerably in the years since. Take obesity as just one example. Obesity is now a relative contraindication, as the patient's bone quality and weight distribution — not just BMI — must also be considered. In my practice, we encourage patients to lose weight before surgery for 2 reasons: First, obese patients are more likely to experience perioperative complications, such as infection and blood clots; and second, having a patient trim down to a healthier weight is critical for not only the longevity of the knee but also for the overall well-being of the patient. And as for the age factor, both younger and older patients have shown excellent medium- and long-range results with unis.

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