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Living Well

Custom Knee Replacements Are a Natural Fit

Last updated: Jun 21, 2016

Claire Stepleton, 58, has always been an active person. So when the former marathon runner and avid hiker developed arthritis in her hips and knees, she refused to let it slow her vibrant lifestyle down.

“The final straw was when I could no longer sit in the car without my knee locking. When I tried to get up it felt like someone was hammering on my joint,” she describes.

“Everyone said to wait as long as possible for a knee replacement, but I wanted to be active and enjoy the next 20 years of my life.”

Ms. Stepleton joins a growing number of forty- and fifty-something adults who are choosing to have knee replacements at younger ages. The surgery, however, can be tricky:

  • Studies show that nearly one in five people are not happy with their knee replacement.
  • Knee surgery is a more difficult healing process when compared to the hip.
  • Traditionally, knee implants are chosen from a selection of six to ten off-the-shelf models that surgeons fit into the joint.

What is a ConforMIS knee?

Ms. Stepleton opted for a custom-designed knee replacement. For the past ten years, a company known as ConforMIS has used computer models to create knee implants that specifically match each patient’s unique anatomy.

Every person’s knee is different. With an individually-tailored design, every knee implant exactly matches the size, shape, contour, and curves of the patient’s natural joint,” explains Richard Rosa, MD, an orthopedic surgeon at Summit Medical Group.

For years, Dr. Rosa says he has watched surgeons compromise the implant fit, rotation, or alignment with off-the-shelf designs. As a result, many patients complain of pain or discomfort after the procedure.

“Too often I would hear patients who are completely healed describe that there was still an unnatural feeling with their new knee,” describes Dr. Rosa.

“However, when I see patients just two weeks after an operation with a ConforMIS design, they are more likely to report that their implant feels natural. Many of them have also regained more range of motion.” 

Ms. Stepleton certainly did. Recently, she enjoyed several 10-mile hikes with her husband on vacation in Colorado.

“It is like day and night. Before my replacement I had to carefully plan everything I was going to do,” she says. “Today, I do not even think twice about my knee.”

Knee implants are made of a metal alloy and high performance plastic. Patients who choose the custom design have a detailed CT scan. Using those images, a computer generates a model based on the patient’s exact measurements. The company also tailors several instruments specifically for the surgery.

Benefits of ConforMIS Knees

Since a custom knee is an exact fit, Dr. Rosa says the surgery has numerous advantages including:   

  • Bone preservation

During a knee replacement, the surgeon removes bone and cartilage from the joint surface and re-surfaces the knee to make the metal implant rest naturally on the surface. With a custom knee, more bone can be saved. This is particularly important if future procedures become necessary.

  • Better ligament balance

“With an off-the-shelf knee, the contour is not matched exactly and even the best human hands can only do so much,” explains Dr. Rosa. “The custom knee exactly reproduces the normal arc of motion such that those ligaments are precisely balanced through the entire range of motion, which allows for a more natural feel, less pain, and faster recovery.”

  • Reduced overhang

“While prefabricated designs match very closely, there is often an area or two that is more prominent. This causes patients to report pain after they heal from surgery because areas of the implant are rubbing against the tissue,” says Dr. Rosa.

Dr. Rosa’s Qualifications

For more than 30 years, Dr. Rosa has been involved in the evolution of knee implant technology. He has:

  • Worked directly with the physician who performed the first knee replacement at the Hospital for Special Surgery in the 1970s.
  • Implanted more than 300 customs knees
  • Become the first surgeon in the New York metropolitan area, and among the first in the world, to implant ConforMIS knees.


1. Interview with Richard Rosa, MD, orthopedic surgeon

2. Clinical Orthopaedics and Related Research, Patient Satisfaction after Total Knee Arthroplasty: Who is Satisfied and Who is Not?

3. American Academy of Orthopaedic Surgeons Arthritis Foundation, Knee Replacement and Revision Surgeries on the Rise