Effects of acetylsalicylic acid on intramuscular bone matrix implants and composite grafts in rats.

Antigen-extracted, autolyzed, demineralized bone matrix and bone matrix combined with isogeneic bone marrow (i.e., a composite graft) were placed in the musculature of young male rats. The influence of acetylsalicylic acid (ASA) on the osteogenic potential of these bone-inducing materials was studied during an 18-day period. ASA (150 mg/kg/12 h) was used to obtain anti-inflammatory serum levels comparable with those in humans. Resorption of the implanted matrix and new formation of bone were quantified using collagen- and mineral-tracing radioisotopes and collagen and calcium analyses. The matrix implants showed a slow tissue turnover and produced only small amounts of new bone, with no significant differences between ASA-treated and control rats. However, during the last 24 h of the study the ASA-treated implants had a significantly hampered rate of new bone formation. The tissue turnover and new bone yield, as well as the rate of new bone formation, increased in the control composite grafts but not in the ASA-treated composite grafts. Thus, the results indicate an inhibitory effect of ASA on the bone-forming capacity of bone marrow.