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Saturday, February 26, 2005

Antibiotics reduce fatigue life of acrylic bone cement

Loading bone cement with antibiotics reduces its fatigue life and may result in structurally inferior cement, according to researchers for Scientific Exhibit 002. They found that prepackaged admixtures had a mechanical advantage over hand-blended cement.

The use of antibiotic-loaded bone cement is a well-accepted adjunct in treating infected joint arthroplasty and is also employed as a prophylaxis measure in primary joint reconstruction. However, antibiotic inclusion may influence the mechanical properties of cement, specifically fatigue, which determines its resistance to crack formation and the long-term in vivo structural integrity of the cement mantle.

Researchers compared the in vitro mechanical characteristics of three commercially available acrylic bone cements, with and without antibiotics, using the manufacturers' recommended vacuum mixing system and a hand-blended antibiotic bone cement. Fatigue life was determined by diametral (splitting) tension of fully polymerized, wet specimens at body temperature under sinusoidal loading (n=10 per cement). Percent area porosity was determined by digital optical microscopy (n=10 per cement).

The addition of antibiotics reduced the mean fatigue life of all cements, whether prepackaged or hand-blended. Researchers did not find a statistical correlation between porosity and fatigue life for any individual cement (p>0.05). However, in general the prepackaged inclusion of 0.5g to 1.0g Gentamycin or Tobramycin reduced the fatigue life of the bone cements studied by 15 percent to 20 percent, although this reduction is not statistically significant (p>0.05).

Hand blending the antibiotic produced structurally inferior cement by comparison to prepackaged (p<0.01) and nonantibiotic bone cements (p<0.01). Because prepackaged admixtures have a mechanical advantage and the Food and Drug Administration now has approved prepackaged, antibiotic-loaded bone cements for use in revision arthroplasty, researchers recommend their use.

Researchers include Paul D. Postak, BSc and A. Seth Greenwald, DPhil(Oxon), both of Cleveland, Ohio. Research support was provided by DePuy, Smith + Nephew, and Stryker.

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