Extraction of minerals after experimental fractures of the tibia in dogs.

Abstract

In a study of a standardized fracture of the tibia in dogs, we examined the relationship between extraction of strontium-85, as measured by a multiple indicator-dilution technique, and blood flow, as determined by an iodoantipyrine-washout technique. Although the blood flow at the fracture site increased from a control value of 1.5 milliliters per 100 grams of bone per minute to a value of 6.65 milliliters per 100 grams of bone per minute at two weeks, the maximum instantaneous extraction of 85 Sr by the fractured tibiae did not change from a value of about 0.77 of the amount injected. These results suggest that the increase in blood flow is accomplished by recruitment of capillaries, that the permeabilities of the capillary beds in the fractured tibia and in the normal tibia are similar, and that the pattern of flow in the fractured tibia remains non-uniform. The increased capillary surface area available for exchange is suggested as the reason that strontium extraction was unchanged despite the increased flow.Clinical Relevance-This study has shown that calcium is only moderately rapidly exchangeable across the capillary membrane and made available for uptake by osteoblasts and deposition in callus at the fracture site. Because calcium delivery via capillary is essential, and because capillary surface area is ordinarily increased in the region of a healing fracture, we can now see clearly that clinical treatment, in particular manipulative intervention, should be carried out in a fashion that minimizes damage to the capillary bed. The exchange processes described in this study are the same as those involved in the deposition of agents used for bone-scanning, and thus this information provides a basis for the timing of scanning studies and for their interpretation.The use of tracer kinetics provides an important technique for the study of the metabolic activity of tissues. Tracers that concentrate in bone, such as the isotopes 85 Sr and 47 Ca, have been helpful in examining exchange between circulating blood and bone. The quantity of tracer that enters bone must be related to the blood flow -that is, to the amount of tracer delivered to the bone -and to the diffusion of tracer through the capillary wall of the capillary tube. If bone is like other tissues, the flux of ions and solutes across the capillary wall is related to the flow of the fluid carrying the ions and solutes, to the extraction of ions in the tissue, to the permeability of the capillary wall, and to the surface area of the capillaries.The quantity of tracer that enters bone can be expressed most simply as deposition for a given period of time. For example, if the period is ten minutes, deposition can be expressed by the formula: Dividing deposition by the time of the experiment, ten minutes, gives clearance, which has the units milliliters per gram of bone per minute, the same units as those for blood flow in bone. However, clearance may also be viewed as the minimum volume of blood entering an organ per unit of time which is capable ...

Transcapillary exchange and retention of fluoride, strontium, EDTA, sucrose, and antipyrine in bone

“…Recent experiments indicate that the blood-cortical bone partition coefficient, λ c , is 0.27 and the blood-marrow partition coefficient, λ m , is 0.17. These values were derived from two previously reported studies [20,21]. They are consistent with the water content of cortical bone determined by steady-state experiments with tritiated water [22] and the water content of tibial marrow determined by desiccation [13].…”

The role of skeletal blood flow in determining the uptake of99mTc-methylene diphosphonate

“…The data are therefore consistent with the model of capillary action proposed by Crone and Renkin. There is no evidence that the surface area available for exchange increases in response to flow, as has been suggested previously [14]. It has been suggested that only about 70% of capillaries in bone are patent at normal flow [4] and also that after sympathectomy there is an increase in the blood flow to bone and to the number of patent capillaries [15].…”

“…It has been stated that the maximum instantaneous extraction gave the best approximation of the initial unidirectional flux of molecules from the blood into the extravascular space [14].…”

Blood Flow Measurements with [15O]H2O and [18F]Fluoride Ion PET in Porcine Vertebrae

“…T HE MEASUREMENT OF BONE blood flow is particularly relevant in understanding the physiology of bone diseases and bone healing. Quantitation of bone blood flow has been performed with numerous experimental methods including direct physical cannulation of vessels, 1 clearance methods, and indicator‐dilution methods 2 , 3 . To date, all experimental approaches are invasive.…”