N84:18889

Control of Bone Remodelling by Applied Dynamic Loads

NASA Grant NAG 9-25

Lance E. Lanvon & Clinton T. Rubin

Dent, of Anatomy & Cellular Biology

Tufts University

School of Veterinary Medicine

Final Report
Progress in the third, and final, six month period of this grant has continued

in the following areas.

1) The data showing the relationship between bone mass and peak strain magnitude

have been prepared and submitted to Science for publication. Manuscript attached.

2) The data from experiments relating remodelling activity with static or

dynamic loads have been prepared and submitted to Journal of Biomechanics for

publication. Manuscript attached.

3) Development of programmes to relate the location of remodelling activity

with the natural and artificial dynamic strain distributions are continuing

but, at present, the data are insufficient to reach any definitive conclusions.

4) Experiments on the effect of different strain rates on the remodelling

response have continued. These experiments are confirming our previous reports

that strain rate is critical in determining the character and extent of the

remodelling response to loading. Experimental numbers as yet are inadequate

to reach definitive conclusions. However, when using a train of 100 consecutive 1 Hz load cycles on the functionally isolated avian preparation, it

appears that if the peak strain magnitudes are similar, and the strain

rates altered from 1,000 to 10,000 to 50,000 microstrain per second, then

both 1,000 microstrain and 50,000 microstrain produce greater remodelling

changes than 10,000. This result was not anticipated from our previous data

over a more limited range of 2,500 to 40,000 microstrain per second. The

extent to which this effect is the result of differences in strain rate

and/or the consequent differences in frequency and total time during which

loading occurs remains to be assessed.

All data produced over the period of this grant are consistent with those

from our previous experiments, which indicate that the remodelling processes

on which the mechanical competence of the skeleton depends are sensitive

to a number of aspects of the bones' strain regime. Use of exercise regimes

chosen for their empirical "convenience" rather than being related to such

location-dependent specific, strain related behaviour is liable to be

unsuccessful in preserving bone mass under conditions of weightlessness.

Further experiments on the relationship between remodelling and customary strains

will depend upon the availability of funds to continue our investigations.

The following articles arising from research conducted over the grant j

period have been published or submitted for publication.

i

Rubin, C.T., J. McA. Harris, B.H. Jones, H.B. Ernst, & L.E. Lanyon (1984) Stress

fractures: the remodelling response to excessive repetitive loading. 30th Annual

ORS, Atlanta, Georgia, Feb. 7-9, Trans, p. 303. ,

Rubin, C.T., G.W. Pratt, A.L. Porter, D.M. Whiteneck, G.F. Middleton, B.H. Jones,

L.E. Lanyon & B. Poss (1984) Acute change in bone properties caused by long distance i

running: Ultrasound measurements of tibia and patella before and after the Boston !

Marathon. 30th Annual ORS, Atlanta, Georgia, Feb. 7-9, Trans, p. 350. j
Progress report, page two.

Rubin, C.T. and L.E. Lanyon (1984) Regulation of bone mass by mechanical strain.

(Submitted to Science.)

Lanyon, L.E. and C.T. Rubin (1984) Static versus dynamic loads as an influence

on bone remodelling. (Submitted to Journal of Biomechanics.)

Lanyon, L.E. (1984) Functional strain as a determinant for bone remodelling. Calcif.

Tissue Int. 36: (in press).