Editor’s note: The following content was originally scheduled for the AAOS Now Daily Edition, which publishes each year onsite at the AAOS Annual Meeting, but this year’s meeting in March was canceled due to COVID-19. Despite the cancellation, members can access virtual content from the Annual Meeting by visiting the Academy’s Annual Meeting Virtual Experience webpage.
The practice of switching to a fresh knife blade after the incision is made remains a subject of debate, as data are conflicting as to whether the practice reduces contamination. A study that was presented as part of the Annual Meeting Virtual Experience found that contamination rates did not differ regardless of whether the knife blade was switched following incision.
Study author Eric B. Smith, MD, chief of orthopaedic surgery at Riddle Memorial Hospital and associate professor of orthopaedic surgery at Sidney Kimmel Medical College, Thomas Jefferson University, and the Rothman Orthopaedic Institute, said the risk of periprosthetic joint infection (PJI) is a significant concern because of associated significant complications.
“As a participant of the International Consensus Meeting of the Musculoskeletal Infection Society, we did a deep dive into this topic. We questioned the dogma that the knife blade used for making the initial skin incision should be changed due to the risk of contamination as it passes through the skin layer. This is theoretical, as bacteria could be harbored in skin pores and hair follicles despite using antiseptics on the skin,” Dr. Smith told AAOS Now.
The present study was conducted in four ORs at a high-volume suburban orthopaedic hospital. At the start of each case, two knife blades were opened and placed on the scrub nurse’s table. The surgeon used one blade to make the skin incision, after which the knife blade was handed off the table and cultured. Both sides of the blade were pushed onto a replicate organism detecting and counting (RODAC) plate. The control blade was not used and sat on the OR table. Once the skin knife blade was plated, the control knife blade was cultured on a second RODAC plate.
“Both the skin and control blades were exposed to air for the same amount of time prior to being tested,” the study authors noted. “After sampling, each RODAC plate was immediately taped shut and labeled corresponding to specimen type, date, time, case type, room number, and case order.”
The specimens were stored at 36 degrees Celsius for two days. Bacterial counts were reported as colony-forming units (CFU) and divided per gram stain results. A positive result was defined as a specimen with any CFU growth on the center of the agar.
A total of 688 specimens were gathered from 344 cases (344 skin knife blades and 344 control blades). Overall, 35 specimens (5.1 percent) had a positive result. The rates of positive results did not largely differ between the skin blade and control blade groups (4.9 percent versus 5.2 percent). The rates of positive specimens by surgical procedure in the skin blade group were 7.4 percent for total hip arthroplasty (THA), 3.4 percent for total knee arthroplasty (TKA), 7.7 percent for cervical spine, and 3.9 percent for lumbar spine. Positive results in the control blade group were 2.5 percent for THA, 4.1 percent for TKA, 7.7 percent for cervical spine, and 9.2 percent for lumbar spine.
The fact that sterile knife blades that were sitting on sterile tables had the same contamination rates as the knives used to make incisions was a surprise, Dr. Smith noted. “Although efforts should never cease in our fight to reduce contamination and eliminate PJI, it appears that changing the knife blade after making the skin incision is not an effective way to reduce contamination,” he said.
Speaking to the study’s limitations, Dr. Smith said, “Taking surface specimens of instruments can indicate contamination levels, and one could use this as a proxy for wound contamination during surgery; however, it is not an actual measurement of wound contamination, nor is it an actual link to PJI.”
Dr. Smith’s coauthors of “After Incision, the Skin Knife Blade is No More Contaminated than a Fresh Knife Blade” are Kimberly A. Russo, BSN; Mitchell G. Maltenfort, PhD; Peter F. Sharkey, MD; and Jeffery Rihn, MD.
Kaitlyn D’Onofrio is the associate editor for AAOS Now. She can be reached at firstname.lastname@example.org.