Dilution Effect of Intra-articular Injection Administered After Knee Arthroscopy

The hypothesis was that agents delivered intra-articularly after knee arthroscopy will be diluted by residual arthroscopic fluid. Diagnostic arthroscopy was performed on six cadaver knees. Each procedure was followed by an intra-articular injection of a dye solution. Intra-articular aspirates were gathered from three locations. With significance set at p < .05, the aspirates were compared with the initial dye concentration and with each other. No significant difference was noted among the sites, indicating that no specific knee area was exposed to a higher dye concentration. There was a significant difference in dye concentration of the aspirates when compared with the dye's initial concentration. The concentration of fluid injected intra-articularly after arthroscopy was diluted by 27%. These data indicate that agents injected into the knee postarthroscopy are significantly diluted. In vitro and in vivo experiments evaluating chondrotoxicity of various anesthetic agents may not accurately reflect the actual concentration of the drug within the knee joint unless dilution effects are taken into account.