Healing Bone Fractures and Simultaneous Administration of Radioisotopes of Sulfur, Calcium and Yttrium

Abstract

A mixture of carrier-free radioisotopes, Ca⁴⁵, S³⁵ and Y⁹¹, was injected into rats bearing left tibial fractures, in states of repair varying from 3–18 days. Twenty-four hours after injection, both tibias were removed and analyzed for content of each radioisotope. At all intervals up to 18 days, postfracture, the injured bone contained more of all three isotopes than the intact, contralateral mate. A maximum in 24 hour retention of radiosulfate in tissue at the fracture site, was reached by the 7th to 10th day, after which retentions of a dose of S³⁵ declined rapidly. Retentions of a dose of Ca⁴⁵ in the fractured bone also rose rapidly during the first 3–10 days of healing. Thereafter, 24 hour retention values continued to rise but at a reduced pace. The avidity of healing bone for yttrium increased sharply during the same 3–10 day interval during which radiosulfate deposition became most effective. After this time 24-hour retention values for Y91 increased only slightly, if at all. The data suggest that formation of the sulfated mucopolysaccharides of osteoid matrix and fibrocartilaginous callus began by at least the 3rd day, if not earlier. The healing fracture made its greatest demands for plasma sulfate during the 7th to 10th day, postfracture. New calcium was laid down at the fracture site just as early as new sulfate, but the demands for plasma Ca continued throughout the 18 days of observation, as might be expected for a mineralizing callus. Yttrium fixation in the healing bone appeared to be more closely related to events leading to organic matrix formation than to mineralization of the new tissue.