April 2, 2020

Patient-Specific Knee Implants for the Treatment of Osteoarthritis and Joint Damage

By Robert J. Snyder, MD

ladykneeW14It’s a fact of life that as we age, our knees deteriorate and develop arthritis. Some patients are genetically blessed and don’t seem to develop significant arthritis. Others aren’t as lucky, and older age, previous injuries and damage to the knee produce severe, life-style altering changes.

Knee replacement surgery has evolved significantly over the past 40 years in terms of materials and designs available. The holy grail of replacement has been to develop a system that most naturally replicates the normal knee.

Historically, most knee replacement systems utilize pre-made metal alloy pieces to fit on the femur and tibia bones. Between the metal is a plastic spacer to act as a bearing. Each manufacturer has proprietary minor changes that separate its knee system from those competitors. These include geometric changes to the metal pieces or altering the manufacturing and processing of the plastic.

However, one fact remains. With the exception of one company, ALL knee replacement companies manufacture their implants in bulk. This means they produce an array of different sizes of implants and a variety of different thicknesses for the plastic to cover the spectrum of expected patients.

Recently, imaging, 3-D modeling and manufacturing processes have improved, making it possible for a company called ConforMis (www.ConforMis.com) to produce truly custom, patient-specific implants to treat arthritis of the knee. ConforMis also made it possible to selectively replace only the worn areas of a knee, allowing replacement of the medial or lateral side only, replacement of a medial or lateral side with the knee cap or a replacement of all three areas of the knee.

The steps involved require a pre-op CT scan of the knee from which a digital 3-D model is made. ConforMis then makes the actual metal and plastic pieces and sends them to the hospital to be available for a patient’s surgery. The new knee has the same curves and size of the patient’s old knee. It will feel like their old knee did before it had arthritis.

A word of caution. Some companies advertise their knee is custom-made and they may order a pre-op CT scan or MRI, BUT their implants are still mass-produced. They use the pre-op study to manufacture a plastic cutting block that guides the surgeon in making the first bone cut. After that, the surgeon utilizes the older style guides until the practice pieces fit and then the actual pieces are opened and assembled. Another company uses a robotic approach that lets the surgeon remove a precise amount of bone. If the surgeon deviates from the programmed cuts, the robotic arm freezes, preventing the surgeon from cutting outside the line.

ConforMis has made it possible to produce a knee replacement, that when compared with other companies’ products, most naturally replicates a normal knee.


Dr.-SnyderRobert J. Snyder, MD is an Orthopaedic Surgeon who practices at Orthopaedic & Spine Center in Newport News, Va. For more information on Dr. Snyder or OSC, call 757-596-1900 or go to www.osc-ortho.com.