We have determined rates of leakage of radioactivity from a rabbit
synovial pouch in vivo for a number of particle systems of varying sizes
and differing resistance to degradation. The estimates were made using a
gamma scintillation camera and without killing the test animals. The lowest
leakage at twenty-four hours was seen with inert carbonized microspheres
and the highest rates were seen with surface-labeled particles of
biodegradable denatured human serum albumin and with erythrocytes. The
carbonized microspheres had no adverse long-term effects on the health of
the animals' articular cartilage. Clinical Relevance: Results obtained with
inert particles indicate that reducing the biodegradability of the particle
or increasing its diameter, or both, reduces radioactivity losses from the
knee joint. Large (twenty-five-micrometer-diameter) microspheres of human
serum albumin incorporating the radioactivity and carbonized microspheres
are suggested as potential carriers of isotopes for human radiation
synovectomy.