Sunday, November 18, 2012

Increasing the Elution of Vancomycin from High-Dose Antibiotic-Loaded Bone Cement: A Novel Preparation Technique. JBJS

Increasing the Elution of Vancomycin from High-Dose Antibiotic-Loaded Bone Cement: A Novel Preparation Technique. JBJS

Vancomycin is commonly used in the cement used to fix total joint replacement arthroplasty components and in cement 'spacers' used to manage periprosthetic infections.

This in vitro study has some important findings: (1) the majority of the antibiotic elution was in the first 7 days (so the notion that prolonged topical treatment is achieved may be incorrect), (2) delaying the addition of Vancomycin until after 30 seconds of cement mixing resulted in greater antibiotic elution, (3) only 3 to 5% of the total added Vancomycin was eluted over 6 weeks, and (4)  irrespective of the time of addition, preparations of 5 gm of Vancomycin with 40 g of cement powder showed dramatic reduction of compressive strength of the cement at 6 weeks after elution. Here are the results for three different methods of mixing Vancomycin with cement:

The reasons for this loss of compressive strength are unclear. It would have been of great interest if the authors had included an antibiotic-free control to see if it also showed diminished strength with the same post-mixing protocol.

So, on one hand we have reports that Antibiotic-loaded bone cement reduces deep infection rates for primary reverse total shoulder arthroplasty: a retrospective, cohort study of 501 shoulders. While on the other hand we have this report on the limited duration of antibiotic elution combined with concerns about the effect of antibiotics on cement strength. We also recognize that while the authors of the recent JBJS paper tested compressive strength of cement cylinders, the failure mode of cement may be quite different -  including fatigue, distraction, sheer, and bending with crack propagation - and may be even more sensitive to changes in material and structural properties.

For these reasons, we continue to be attracted to cementless approaches to shoulder arthroplasty component fixation combined with careful surgical technique, strong antibiotic prophylaxis, and copious irrigation with antibiotic saline.

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