Joint damage caused by arthritis or injury can make even the simplest tasks seem impossible. Knee replacement surgery is generally a highly effective treatment of degenerative joint disease and one of the most successful procedures in all of medicine, with survival rates of more than 90 percent at 10-19 years of follow-up.
More than 600,000 knee replacements are performed each year in the United States, and that number is expected to exceed 3 million by 2030. Because of the sheer volume of surgeries performed, surgeons and hospital administrators are looking for products to increase operational efficiency. One of the ways that many hospitals and surgeons have attempted to streamline the surgical process is by changing the type of bone cement used during the procedure.
During knee replacement surgery, doctors attach components of the new knee joint to the femur (thigh bone) and tibia (shin bone), using an epoxy cement. This bone cement comes in two separate components – a powder and a liquid that have to be mixed together. High-viscosity cement (HVC) boasts shorter mixing and waiting times and longer working and hardening phases. These shorter times mean that surgeons can handle and apply the cement earlier than with low- or medium-viscosity cements.
Although high-viscosity cement may be more convenient to use, there is mounting evidence that the bond it produces is not as strong. Researchers have observed more early failures with the use of high-viscosity bone cement, even when used in combination with a previously well-performing implant. A 2016 case series evaluated 13 cases of tibial component debonding (where the implant fails to adhere to the cement interface on the shin bone) in implants performed with high-viscosity cement.
The study authors believe that these implant failures were likely related to the use of high-viscosity cement after finding no instances of aseptic loosening or tibial component debonding in cases using the same implant and non-high viscosity cement. Study authors advised that surgeons should be aware of the possibility of debonding of the tibial component when using HVC. Another case series report from 2013 observed only nine early failures out of 3,048 total knee replacements – all of the failures involved high viscosity cement.
There are key differences between HVC and non-HVC that may contribute to the observed differences in outcomes. First, high-viscosity cement has only about half the intrusion depth of non-HVC. Additionally, researchers have observed superior mean pore size and total porosity in non-HVC in comparison to the HVC. These differences may play a significant role in the strength of the bond between the cement and bone and the cement and the implant.
High viscosity bone cements are another example of manufacturers bypassing the usual approval path, which requires an independent demonstration of safety and effectiveness. Instead, manufacturers use the 510k approval process and claim that these high-viscosity bone cements are “substantially equivalent” to the low-viscosity cements that have been in use for decades.
American Academy of Orthopaedic Surgeons, Beyond Surgery Day: The Full Impact of Knee Replacement, http://www.anationinmotion.org/value/knee/; http://www.ors.org/Transactions/60/1849.pdf;
Hazelwood, KJ et al, Knee, Case series report: Early cement-implant interference fixation failure in total knee replacement, https://www.ncbi.nlm.nih.gov/pubmed/25795544;
Kopinski, JE et al, J. Arthroplasty, Failure at the Tibial Cement-Implant Interfact With the Use of High-Viscosity Cement in Total Knee Arthroplasty, https://www.ncbi.nlm.nih.gov/pubmed/27155996;
and The Stone Clinic, Total knee replacement surgical technique, http://www.stoneclinic.com/tkrillustration.