Uncemented Partial Knee Replacement

A partial knee, or unicompartmental, replacement is a less invasive procedure compared to total knee replacement, suitable for patients who have the majority of their arthritis in one area of the knee. Scientific studies have shown that the recovery from a unicompartmental knee replacement (UKR) is quicker than TKR and that once healed, has a greater range of motion and higher activity level. Patients feel that a UKR is "more normal" than a TKR, likely because the natural knee ligaments have been preserved and the kinematics of the knee are maintained.

However, the revision rate (need for a future operation) is higher for a UKR than a TKR, for 2 major reasons. One is that the cartilage in the rest of the knee can undergo deterioration and develop arthritis, thus requiring treatment down the road. The second major reason is that the UKR implant may loosen over time and thus require another operation to change it to a TKR. A possible reason for this is that the implants for a UKR are quite small, with limited surface area to attach to a patient's own bone. At this point, all partial knee replacements in the US are attached to the bone with cement, an artificial substance that may breakdown over time. The increased activity load on the knee, combined with small surface area of the implant and deterioration of cement are all potential factors that result in implant loosening.

In other joints such as the hip, uncemented attachment of the implants through bone ingrowth, has been shown to improved the longevity of the implants by reducing the rate of implant loosening. Thus, in total hip replacements, the gold standard implants achieve osseointegration, whereby the bone attaches to the artificial implant. This has not been possible in partial knee replacements performed in the United States because the FDA requires rigorous testing of the implants to ensure safety, and as of November 2019, none of them had been approved.

Dr. Su has been developing an uncemented UKR implant with another knee surgeon, Dr. Andrew Pearle, and a team of engineers, using a unique patented technology designed to enhance bone integration with the implant. Together, they have formed a company called Engage Surgical, and are proud to have received FDA approval for their implant in November 2019. The technology used in the UKR has over 30 worldwide patents and can be seen in this brief video. Dr. Su is planning to begin implantation of this uncemented partial knee replacement in the summer of 2020. For more information, please visit the Engage Surgical website.