A Method for Determination of Bone-Salt Content of Cortical Bone

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Abstract
A different approach for "bone density measurement" is suggested: the hydroxyapatite content is determined per volume of cortical bone. Measurements are carried out by means of a relatively simple radiographic-densitometric method employing the following improvements over previously described methods: The standard calibrated wedge consists of a 100% (w/v) solution of dipotassium hydrogen phosphate (K2HPO4) in a plastic container (instead of the customary aluminum stepwedge). The advantage of such a standard lies in the similarity of the X-ray absorption by hydroxyapatite and K2HPO4 (effective atomic numbers 15.86 and 15.59 respectively, as compared to the atomic number of 13 for aluminum). The error produced by the soft tissues is largely eliminated by submerging the part examined in water and placing the calibrated wedge as close to the bone as possible. Variations in the basic field density are minimized by accurately controlling the position of the X-ray tube and by using a special plastic filter. Preliminary results indicate that normal cortical bone at the proximal end of the radius contains 1,000-1,400 mg. of hydroxyapatite per cubic centimeter. In 3 cases of hyper-parathyroidism, values of 800-960 mg./c.c. were obtained. Since low values have also been found in some other conditions of disturbed calcium metabolism, the method could prove useful in clinical investigation.

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