M.Brookes: Haemodynamic Data on the Osseous Circulation 101 



If a constant moderate load be applied to bone, the final deformation is usually 

 obtained within 10 minutes, with no further deformation appearing to occur after 

 this time. We have only studied this phenomenon for periods up to 30', this time 

 limit being used since it appeared to be the biological ultimate for substained load. It 

 can thus be stated that primary creep does not appear to exist in bone. 



As bone is dried, a more nearly linear response is obtained on a stress-strain 

 curve. In terms of the model, the damping effect of the dash-pot is reduced, and two 

 springs are left in series, tending to approximate a single spring, or perfect elastic. 



The modulus of elasticity is significantly changed by altering the rate of deforma- 

 tion. The more rapid o, the higher E becomes. 



As stated, the model is not complete. Qualitatively, it explains, fairly well, the 

 behavior of bone under various types of load approximating 50'Vo of the breaking 

 strength or less. To account for the behavior of bone near the failure point, a rigid 

 plastic or a series of rigid plastics will probably have to be inserted. In addition, in 

 order to predict quantitatively the behavior under all conditions of loading, constants 

 for the springs, dashpot, and plastic that may be added must be derived. This task is 

 currently underway. 



The use of a model system such as the one described, while old in theoretical 

 mechanics, is new to bone. Its advantages are many, but one of the chief ones is that 

 it enables one to predict behavior under complex circumstances which cannot be 

 tested in the laboratory. 



Summary 



Findings relative to the physical properties of femoral cortical bone tested in the 

 fresh, wet state have been described. A rheological model that explains the behavior 

 of bone under certain conditions has been presented. 



References 



Jaeger, J. O.: Elasticity, Fracture and Flow. London: Methuen 1956. 



Reiner, M.: Rheology. In Encyclopedia of Physics. Vol. VI, Flugge, S. (ed.). Berlin: Sprin- 

 ger 1958, p. 434. 



Sedlin, E. D., and C. Hirsch: Factors affecting the determination of the physical proper- 

 ties of femoral cortical bone. Acta orthop. scand. (in press). 



Haemodynamic Data on the Osseous Circulation 



M. Brookes 

 Department of Anatomy, Guy's Hospital, Medical School, London, England 



The physical constants of the blood in the osseous circulation are likely to be 

 significant factors in the regulation of calcification and bone growth. This paper 

 describes a method for estimating some formerly unknown data, including flow rates, 

 pertaining to a variety of subcompartments of the femoral circulation in the rat. 



