Saturday, February 4, 2017

Preventing total joint infections

Intra-Articular Vancomycin Powder Eliminates Methicillin-Resistant S. aureus in a Rat Model of a Contaminated Intra-Articular Implant

These authors point out that topical vancomycin powder has been shown to decrease infection in many procedures such as spine surgery. They evaluated the efficacy of intra-articular vancomycin powder in preventing infection in a rat model of a femoral intramedullary wire with 1 mm of intra-articular communication that was contaminated by inoculating the knee joint with 15 million colony forming units (CFU)/mL of methicillin-resistant Staphylococcus aureus (MRSA).

Four treatment groups were studied: (1) no antibiotics (control), (2) preoperative systemic vancomycin, (3) intra-articular vancomycin powder, and (4) both systemic vancomycin and intra-articular vancomycin powder. The animals were killed on postoperative day 6, and distal femoral bone, joint capsule, and the implanted wire were harvested for bacteriologic analysis. 

There were no postoperative deaths, wound complications, signs of vancomycin-related toxicity, or signs of systemic illness in any of the treatment groups. 

There were significantly fewer positive cultures in the group that received vancomycin powder in combination with systemic vancomycin compared with the group that received systemic vancomycin alone (bone: 0% versus 75% of 8, p = 0.007; Kirschner wire: 0% versus 63% of 8, p = 0.026; whole animal: 0% versus 88% of 8, p = 0.01). 

Only animals that received both vancomycin powder and systemic vancomycin showed evidence of complete elimination of bacterial contamination.

Comment: The logic of topical antibiotics is compelling: bactericidal concentrations can be achieved locally without the risk systemic toxicity. This is especially important for a potentially toxic antibiotic such as Vancomycin. Here's a photo of a man with Vancomycin related red man's syndrome.

In this study, the Vancomycin was applied to the joint in the treatment groups before it was inoculated with the bacteria. This means that the bacteria encountered the antibiotic before they had a chance to form a biofilm or to penetrate the tissues. In the systemically treated animals the intraperitoneal Vancomycin was administered before incision. Thus this is a study of prophylaxis and not treatment.

In the shoulder world, there is good reason to believe that many arthroplasty wounds are contaminated with Propioinibacterium when the incision transects the bacterial-charged dermal hair bulbs and sebaceous glands that cannot be sterilized by skin surface preparation at the time of surgery.

At surgery we have several opportunities to reduce the risk of these bacteria forming a biofilm on the implants.

First is to reduce the size of the inoculum using (1) systematic antibiotics, (2) copious irrigation of the surgical field with antibiotic-containing saline solution,  and (3) by lining the wound edge with an antibiotic-soaked sponge as shown below.

Second, by applying topical antibiotics not only into the joint but also in the medullary canal - a relatively anaerobic environment where Propionibacterium are invited to form a biofilm on the titanium alloy stem (see Infections with Propionibacterium - the necessity of a surgical implant).

Other measures may be of benefit as well, such as minimizing the surgical time during which the wound is open and minimizing the surgical hematoma that provides an iron-rich anaerobic environment for the bacteria. 

Ben Franklin may have been correct