Regulation of bone formation by applied dynamic loads.

Molecular pathways mediating mechanical signaling in bone

“…1). Alterations in bone remodeling are sensitive to changes in magnitude Lanyon, 1984a, 1985), the number of loading cycles (Rubin and Lanyon, 1984a), distribution of the loading , and the rate of strain (Harrigan and Hamilton, 1993).…”

“…A number of in vivo animal models have been developed to study the effect of specific components of an applied mechanical load on bone tissue including the following examples: compression of the functionally isolated turkey ulna (Rubin and Lanyon, 1984a), bending of the rat and mouse ulna (Mosley et al, 1997) and tibia , and 4-point bending to rat tibia (Lee et al, 2003). Distinct parameters of the applied loads can be correlated to changes in bone morphology (Rubin and Lanyon, 1985;Rubin et al, 1996Rubin et al, , 2001aSrinivasan et al, 2002) as well as changes in gene and protein expression (Sun et al, 1995;Rawlinson et al, 1998;Lee et al, 2003;Judex et al, 2004) At the level of small volumes of tissue, all loads and bending moments resolve into strain, or change in length of a material from its original length.…”

“…Bone's sensitivity to mechanical demands in the "positive" direction is well illustrated by studies that show that the humerae in the "playing" arms of elite tennis players have 35% thicker cortices than the arm that simply throws the ball into the air, emphasizing the extent, and site specificity of the response (Jones et al, 1977;Haapasalo et al, 2000;Kontulainen et al, 2003). Exercise studies have shown that certain degrees of loading must be exceeded to elucidate changes (MacKelvie et al, 2003) and that the degree of the response is determined not only by the magnitude of the load (Rubin and Lanyon, 1985), but the rate (O'Connor et al, 1982), cycle number (Rubin and Lanyon, 1984a), and even the frequency of the load (Rubin and McLeod, 1994;Qin et al, 1998), emphasizing that "load" can be anabolic to bone, but that the relationship between loading and adaptation is complex, and that beyond deformation, such as fluid flow and streaming potentials, may help mediate the mechanical challenge into an adaptive response.…”

Biomechanics of phalangeal curvature

“…Strain (e) describes the deformations that result from an imposed load, and is defined as the change in length divided by original length (AL/L) (Currey, 2002). Results are reported here in terms of strain because of its probable role in bone formation and maintenance (Rubin and Lanyon, 1985a;Gross et al, 1997), and in order to facilitate comparisons with results from cadaver strain gage validation experiments. By convention, stretching a bone in tension is represented as positive strain (a positive change in length), and compression is represented as negative strain.…”

Pause Insertions During Cyclic In Vivo Loading Affect Bone Healing

“…Cyclic compressive loads applied with a pause between each cycle are more osteogenic than repetitive, continuous cyclic loads [23,26,31]. An increased duration of repetitive cyclic loading does not lead to proportional increases in bone mass, presumably because cellular sensitivity to the mechanical stimulus diminishes quickly once an initial threshold for a response has been exceeded [10,26,29,33]. For example, in a rat jumping model, the femoral compressive force in rats that jumped five times a day led to considerable bone hypertrophy compared with controls, but when jumps were increased to 100 per day, no additional increase occurred [33].…”