The effect of intermittent pneumatic compression on the bone uptake of 99mTc-labelled methylene diphosphonate in the lower limb

Abstract

Venous compression of the lower limbs will obstruct outflow through the deep and superficial veins, yet inflow will continue, without continual swelling of the limb. It is hypothesised that venous channels in the long bones act as collateral channels to restore outflow, and therefore general blood flow through bone will increase. Such a hemodynamic change should affect the uptake of radiopharmaceuticals by the bone, though uptake changes in themselves would not definitely indicate flow changes. The purpose of this study, therefore, was to determine whether bone uptake in the lower limb is affected by intermittent venous compression, irrespective of the mechanism involved. The effect of intermittent pneumatic compression of the thigh and calf on the uptake of (99m)Tc-methylene diphosphonate (MDP) was studied in 24 patients. All were undergoing routine bone imaging for medical conditions that were not focused on their lower limbs, and received 1 h of the therapy at 60 mmHg on one limb only, after injection of the radiopharmaceutical. Three hours after injection the relative difference in uptake (net counts per pixel) between the two limbs was calculated. The standard imaging protocol was otherwise unchanged. The median differences in uptake in the intermittently compressed limb compared with the contralateral limb were +7.6% (interquartile range +3.9% to +16.0%, p<0.0005 [Wilcoxon]) for the anterior aspect of the femur; +11.7% (interquartile range +4.3% to +22.2%, p<0.0005) posterior, femur; +10.5% (interquartile range +6.5% to +13.8%, p<0.0005) anterior, tibia; +10.6% (interquartile range +5.5% to +17.6%, p<0.0005) posterior, tibia. Intermittent pneumatic compression clearly and significantly increased the uptake of (99m)Tc-MDP in long bones. These data are consistent with increases in blood flow through bone, though a direct mechanical influence on the bone cannot be excluded. This effect should be given consideration during routine therapeutic and thromboprophylactic use of intermittent compression, and if the mechanism of the uptake changes can be established, their possible clinical uses should be investigated.