Altering local soft-tissue circulation fails to halt venous drainage from the femur

It has been suggested that tourniquet application proximal to bone biopsy in an extremity can reduce the number of tumor cells spread through circulation. This study investigates the anatomical pathway through which rapid cell spread could occur. Radioactively labeled 15-mu microspheres were injected into the medullary canal of rat femurs. The ratio of injected particles found in the femur was compared among groups that received application of a tourniquet prior to injection, no tourniquet, or transection of all soft tissue proximal to the injection site. Obliteration of circulation in the soft tissue surrounding the femur with a tourniquet or tissue transection did not alter the spread of particles from the femur. The pulmonary circulation trapped approximately 95% of particles reaching the lungs, limiting their access to peripheral arterial circulation. If the number of particles injected into the femur was increased, the number of particles leaving the femur increased at an even greater rate. These data suggest that (1) a particle can exit the femur without traveling through the soft tissue surrounding the femur; (2) most particles that reach the lung are retained; and (3) the injected bone acts as a sponge, retaining some particles and permitting the rest to enter the venous drainage.