Brand and mixing order changed vancomycin release from cement spacers

Design

In vitro comparative laboratory study

Population

60 PMMA discs, 5 formulations, 4 g vancomycin each

Primary outcome

Cumulative vancomycin elution over 28 days

Effect

Best combination 2,897 ± 64 µg/mL, 120% above the other brand mixed the same way

This in vitro Journal of Bone and Joint Surgery study, published on 15 September, made 60 bone cement discs from five formulations, covering two brands, two viscosities and with or without premixed gentamicin. Each was loaded with 4 g of vancomycin, the high dose used in spacers for chronic periprosthetic joint infection, adding the drug either to the powder first or to the liquid monomer first.

Both brand and sequence mattered. The best-performing combination, a medium-viscosity cement mixed monomer-first, released 120% more vancomycin over 28 days than the other brand mixed the same way, and 57% more than the same maker's high-viscosity cement. For the other brand, mixing powder-first gave the highest release in the first hour and 52% more over 28 days than monomer-first. Porosity and antibacterial activity were unaffected.

This is bench work: elution in a dish is not eradication in a joint. But it costs nothing to act on. The theatre routine for mixing a spacer is usually whatever the scrub team does by habit, and this suggests it should be a deliberate choice matched to the cement on the shelf.

• Decide the mixing sequence for your cement deliberately; it changed elution by up to half.
• Check which cement brand and viscosity your theatre stocks for spacers.
• Premixed gentamicin raised vancomycin release only in high-viscosity cement.
• Write the chosen method into the local spacer protocol so it is repeatable.

Why it matters

A step surgeons rarely think about may decide how much antibiotic the spacer actually delivers.

Don't overread it

This was an in vitro study; it did not measure infection eradication in patients.

The statistics, in plain English

Results are means with standard errors from small numbers of discs per group. Large percentage differences in elution are credible in the lab, but how they translate into tissue levels in a joint is unknown.

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