Low-Level Accelerations Applied in the Absence of Weight Bearing Can Enhance Trabecular

ABSTRACT: High-frequency whole body vibrations can be osteogenic, but their efficacy appears limited to skeletal segments that are weight bearing and thus subject to the induced load. To determine the anabolic component of this signal, we investigated whether low-level oscillatory displacements, in the absence ofweight bearing, are anabolic to skeletal tissue. A loading apparatus, developed to shake specific segments of the murine skeleton without the direct application of deformations to the tissue, was used to subject the left tibia of eight anesthesized adult female C57BL/6Jmice to small (0.3 g or 0.6 g) 45Hz sinusoidal accelerations for 10min/day, while the right tibia served as an internal control. Video and strain analysis revealed that motions of the apparatus and tibia were well coupled, inducing dynamic cortical deformations of less than three microstrain. After 3 weeks, trabecular metaphyseal bone formation rates and the percentage of mineralizing surfaces (MS/BS) were 88 % and 64 % greater (p<0.05) in tibiae accelerated at 0.3 g than in their contralateral controls. At 0.6g, bone formation rates andmineral apposition rateswere 66%and22% greater (p<0.05) in accelerated tibiae. Changes in bone morphology were evident only in the epiphysis, where stimulated tibiae displayed significantly greater cortical area (þ8%) and thickness (þ8%). These results suggest that tiny acceleratory motions — independent of direct loading o