Increased bone formation in rat tibiae following a single short
period of dynamic loading in vivo.
Forwood, Mark R., Ichiro Owan, Yuichi Takano, and Charles H. Turner.
Department of Anatomical Sciences, The University of Queensland,
Brisbane Australia 4072, Departments of Orthopaedic Surgery,
Mechanical Engineering and Anatomy and the Biomechanics and
Biomaterials Research Center, Indiana University Medical Center,
IUPUI, Indianapolis, IN 46202
APStracts 2:0214E, 1995.
Based on our quantum concept for mechanically adaptive bone formation,
we hypothesized that a single bout of loading would increase bone
formation at the endosteal surface in rat tibiae, with a maximal
response 4-8 days after loading, and a stimulus-response relationship
for load magnitude. Bending loads were applied to right tibiae of
rats at 31, 43, 53 or 65 N for a single bout of 36 or 360 cycles; and
bone formation assessed 1-4, 5-8 or 9-12 days after loading. A single
loading episode increased lamellar bone formation rate (BFR) in all
groups (P < 0.05), and was maximal 5-8 days after loading. A
distinct dose-response relationship was not evident among all load
magnitudes or for duration, but 65 N was significantly more
osteogenic than loads of 31-53 N (P < 0.05), consistent with a
threshold response to loading. There was also evidence for
significant increase in BFR (P < 0.05) and double labeled
surface (dLS /BS, P < 0.01) within 4 days of loading, suggesting
that bone lining cells were activated directly by the stimulus. Thus,
subtle changes in bone formation rate may occur by modulating the
activity of surface cells, but large modeling drifts and anabolic
responses require recruitment and differentiation of osteoprogenitor
cells near the bone surface.
Received 29 June 1995; accepted in final form 12 October 1995.
APS Manuscript Number E300-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95