Dentists tell us to brush, floss, and use mouthwash to upkeep our oral hygiene. A 65-year-old woman with a knee replacement in Wisconsin took her at-home dental routine one step further by vigorously flossing her teeth until her gums bled. The unidentified woman landed in the emergency room after complaining of pain and swelling around her knee, but ultimately doctors found her tooth flossing to be the cause, according to the report published in the journal BMJ Case Reports.

After arriving at the hospital with chills and in excruciating pain, doctors obtained a fluid sample from around the prosthetic. The knee replacement was found to be infected with Streptococcus gordonii, a bacterium usually found in the mouth.

"This bacteria lives in the mouth, [but doctors] happened to find it in a place where we don't typically find it, which is the knee joint," said Dr. Ala Dababneh, co-author of the report and an infectious diseases doctor at the Mayo Clinic in Minnesota, LiveScience reported.

The bacterium appeared in her knee joint most likely due to flossing, which introduced it into her bloodstream through the tiny cuts in the bleeding gums. It then proceeded to make its way through the bloodstream and settled on her knee replacement. Bacteria tend to easily settle on prosthetic joints compared to other places in the body because of no immune system, according to the Mayo Clinic. This makes it easy for bacteria to gather together and cause infection.

Bacteria can make biofilms on prostheses, meaning the organisms can build a wall or a fortress of bacteria on the implant’s surface, which makes it extremely difficult to remove the structure. In these cases, the prosthesis may need to be removed, whereas serious infections can lead to the loss of a limb, or even life.

Luckily, doctors were able to treat the woman’s infection by opening up her knee and washing out the bacteria that they could. They then prescribed her a long-term course of antibiotics, allowing her to keep her original knee replacement. She will have to take antibiotics for as long as she maintains her prosthesis.

A similar case report identified the same bacterium in the knee replacement of a 78-year-old woman in Belgium. She also experienced swelling around her prosthetic joint, in addition to swelling in her aorta. Unlike the most recent case, doctors had her knee prosthesis replaced as well as a valve replacement in her heart.

Currently, there is an ongoing discussion among orthopedic surgeons and dentists on whether people with joint replacements should receive antibiotics before undergoing dental procedures. The antibiotics could work in conjunction with the patient’s immune system to rid bacteria from the bloodstream and prevent it from settling down in the prosthesis. However, it is a rare occurrence for people to get oral bacterial infections on their joint replacements. Prescribing what can be unnecessary antibiotics can breed the grounds for resistant bacteria, says the Centers for Disease control and Prevention, making these infections less treatable when they exist.

The American Dental Association (ADA) advises dentists against using prophylactic antibiotics on their patients prior to dental procedures to prevent prosthetic joint infection.

As for flossing, this case is an isolated incident, meaning it is safe for people to still floss and have a prosthetic joint. We all have small amounts of oral bacteria in our bloodstream from dental routines like tooth brushing, flossing, and eating crunchy foods. Flossing at least once a day can help remove plaque from the areas between the teeth where the toothbrush can’t reach.

Source: Dababneh AS, Klein R, Varatharaj Palraj BR. Streptococcus gordonii prosthetic joint infection in the setting of vigorous dental flossing. BMJ Case Reports. 2015.