Mechanical loading thresholds for lamellar and woven bone formation

Abstract

Bone formation was measured in rat tibiae after 12 days of applied loading. Bending forces were applied using a four-point loading apparatus. Sham loads were applied at the same magnitudes as bending forces but the loading pads were arranged so that bending was minimized. Bending and sham loading were applied to the right tibiae of rats and the left tibiae served as contralateral controls. Loading was applied as a sine wave with a frequency of 2 Hz for 18 s (36 cycles) per day. The peak magnitude of applied load was 27, 33, 40, 52, and 64 N. Woven bone was observed on the periosteal surface in all animals subjected to loads of 40 N or greater. Periosteal woven bone formation occurred in both bending and sham loading groups. Woven bone formation on the periosteal surface was either absent or responded at a maximal rate if the stimulus threshold was surpassed. The amount of new woven bone and the woven bone-forming surface were independent of the magnitude of applied strain. Bone formation on the endocortical surface was exclusively lamellar. Lamellar bone formation was stimulated by applied bending of the tibia but not by sham loading. Bending strains above a loading threshold of 40 N or about 1050 mu strain increased both bone-forming surface and the mineral apposition rate and subsequently increased the bone formation rate as much as sixfold. No evidence of increased bone formation was seen for applied strains below 1050 mu strain. Examination of bulk stained sections from animals exposed to the highest applied loads showed no evidence of microcracks.(ABSTRACT TRUNCATED AT 250 WORDS)

Trabecular bone adaptation to loading in a rabbit model is not magnitude‐dependent

“…24,25 Similar to our results, other studies examining load levels above those involved in normal loading also observed an anabolic response in trabecular bone and did not see an effect of different load magnitudes on bone mass, suggesting a threshold response to loading. A previous study examining the response of trabecular bone to noninvasive axial compressive loading found no effects of load level (8,10, or 12 N) on trabecular microCT parameters in 7-or 22-month-old male BALB/c mice. 26 Additionally, Saxon et al 27 reported no effect of load magnitude (9, 11, 12N) on trabecular thickness in female C57BL/6J mice, although they did observe increased trabecular thickness in response to increased load magnitude (12.5, 14.5, 16N) in male mice.…”

“…Several experimental studies examining the influence of load magnitude did not observe an anabolic response below a certain threshold. [6][7][8] The response to loading has been theorized to include a ''lazy zone'' in which bone mass is not responsive to a range of normal load levels, but is responsive below or above this normal range. 22 Normal or habitual loading may confound the results of previous reports and mask a load magnitude threshold below which loading does not elicit a response.…”

“…22 Normal or habitual loading may confound the results of previous reports and mask a load magnitude threshold below which loading does not elicit a response. 7,8 When natural loading was minimized through neurectomy, a linear relationship was present between microCT-derived measures of trabecular bone mass and architecture and peak dynamic loads applied noninvasively to the mouse tibia. 23 Both load levels used in our study were well above the normal loading experienced at that anatomical location in the rabbit; therefore, normal loading likely did not contribute to our finding that load but not load magnitude had an influence on trabecular bone mass, density, or architecture.…”

“…In cortical bone, loading must be dynamic rather than static to elicit an anabolic response 4 and adaptive remodeling is preferentially responsive to short periods of strain change. 5 For example, high-magnitude strains, varied by regulating the applied load [6][7][8] and strain rate, 9 enhanced cortical bone mass.…”

Implant-Supported, Fiber-Reinforced Bridge: From Guided Surgery to Immediate Loading

“…For immediate loading, the first decision criterion is absolute passivity of the implant prosthesis on the implants, to obtain a non-pathological level of bone deformation (variable depending on the type of bone [5]), enabling the strain suffered by the bone to remain constantly below the threshold of irreversible microdamage; permanent strain on the posts due to an unsuitable rigid framework would obviously cause irreversible damage.…”