Comparing outcomes of modern cementless knee implant with standard knee replacement surgery

Cementless knee replacement, an alternative approach to traditional cemented knee replacement surgery, is garnering interest in the field of orthopedic surgery. Researchers at Hospital for Special Surgery (HSS) launched a study to compare outcomes of a modern cementless knee implant to the standard knee implant that requires bone cement for fixation.

HSS hip and knee surgeon Geoffrey H. Westrich, MD, and his colleagues found no difference in hospital length of stay, complications, hospital readmission within 90 days of surgery, or rates of revision surgery at two-year patient follow-up. The findings were presented today at the American Academy of Orthopaedic Surgeons 2022 Annual Meeting in Chicago.

With respect to time spent in the operating room (OR), researchers found that using the cementless implant reduced OR time by 25%, saving an average of 27 minutes.

In a cementless total knee replacement, you do not have to wait for the cement to harden and dry like you do in a cemented knee replacement."

Brian P. Chalmers, MD, hip and knee surgeon at HSS and study co-author

"Reduced time in the OR under anesthesia is advantageous to patients, but that is not the only potential benefit of the cementless prosthesis," added Dr. Westrich, who is also the research director emeritus of the Adult Reconstruction and Joint Replacement Service at HSS. "With the cementless knee replacement, the components are press fit into place for 'biologic fixation,' which basically means the bone will grow into the implant. If there is initial biologic fixation, implant loosening over time should be less likely and a total knee replacement could potentially last much longer."

In a traditional knee replacement, implant components are secured in the joint using bone cement. It's a tried-and-true technique that has worked well for decades. But eventually, over time, the cement starts to loosen from the bone and/or the implant. When it wears out or loosens, patients generally need a second knee replacement, known as a revision surgery.

Dr. Westrich believes that a well-designed cementless implant will make loosening over time less likely, enabling a total knee replacement to last much longer. Implant longevity is an important consideration, especially for younger patients with arthritis who opt for joint replacement to maintain their active lifestyle. They generally put more demands on their joint, causing more wear and tear and potential loosening. The cemented knee implant used in a traditional joint replacement usually lasts 15 to 20 years.

"Cementless implants have been used successfully in total hip replacement surgery for many years. It has been much more challenging to develop a cementless prosthesis that would work well in the knee because of the knee's particular anatomy," Dr. Westrich explained.

"In the past, a number of cementless knee implants were shown to have design flaws, with loosening from the tibia," he added. "The newer cementless prosthesis used in our study did not demonstrate this type of loosening as in previous published studies. We set out to see how the implant fared in HSS patients."

Researchers reviewed 598 primary unilateral total knee replacements at HSS (170 cementless and 428 cemented) of the same design from 2016 to 2018. Demographic information, operative details and any complications were obtained from patients' medical records. Patients undergoing the cementless procedure were younger overall, with a mean age of 63, versus 68 for those having a traditional cemented knee replacement. Good bone quality is important in the success of cementless knee fixation. Therefore, orthopedic surgeons preferentially select younger patients for the cementless procedure, Dr. Chalmers noted.

There was no statistically significant difference in hospital length of stay, complications, or hospital readmission for a problem in the first 90 days after surgery. Ninety-six percent of cementless knee replacement patients versus 95% of those with a cemented knee replacement maintained their implant without the need for revision surgery at two-year follow-up.

"The biggest question now is whether or not cementless total knee replacement will have better long-term durability and fixation than cemented knee replacement," Dr. Chalmers said. "Following these patients to assess long-term outcomes is the next step."