The fluorescent microsphere (FM) method is considered the best technique to determine regional bone blood flow (RBBF) in acute experiments. In this study we verified the accuracy and validitiy of this technique for measurement of RBBF in a long-term experiment and examined RBBF after meniscectomy. 24 anesthetized female New Zealand rabbits (3 groups, each n=8) received consecutive left ventricular injections of FM in defined time intervals after meniscectomy. Group 1 from preoperatively to 3 wks postoperatively, group 2 from 3 wks to 7 wks, and group 3 from 7 wks to 11 wks postoperatively. To test the precision of the FM-method in long-term experiments two FM-species were injected simultaneously at the first and last measurement. After the experiment both humeri, femora, and tibiae and reference organs (kidney, lung, brain) were removed and dissected according to standardized protocol. Fluorescence was determined in each reference blood and tissue sample and blood flow values were calculated. Blood flow in kidney, lung, and brain revealed no significant difference between right and left side and remained unchanged during the observation period excluding errors due to shunting and dislodging of spheres in our experiments. Comparison of relative bone blood flow values obtained by simultaneously injected FM showed an excellent correlation at the first and last injection indicating valid RBBF measurements in long-term experiment. We found a significant increase of RBBF 3 wks after meniscectomy in the right tibial condyles compared to the non-operated left side. Similar changes were found in the femoral condyles. RBBF in other regions of tibia, femur, and humerus revealed no significant difference between right and left bone samples of the same region. Our results demonstrate that the FM method is also valid for measuring regional bone blood flow in long-term experiments. In addition we could demonstrate that meniscectomy leads to an increase of RBBF in the tibial condyles very early. This increase might be caused by stress-induced alterations of the subchondral bone.
