Periosteal Response Research Articles

Nasal Adenocarcinoma in a Horse with Metastasis to Lung, Liver, and Bone and Review of Metastasis in Nine Horses with Sinonasal Tumors

Sinonasal neoplasia metastasizing to distant organs is rare in horses. This case report describes the clinical and imaging findings of a horse with sinonasal neoplasia, which had metastasized to the lung, liver, and humerus. Additionally, the prevalence of sinonasal neoplasia and their incidence of distant metastasis among horses that presented to the Oregon State University Veterinary Teaching Hospital (OSU-VTH) were estimated. Of 5,558 equine patients who presented to the OSU-VTH in the last nine years, 1.4% were diagnosed with sinonasal disease and 10.3% of these cases had sinonasal neoplasia with only one having confirmed distant metastasis. This case was an eleven-year-old quarter horse which was evaluated due to a history of a right forelimb lameness of three weeks duration. Two and a half months later he presented again, this time for unilateral epistaxis and persistent right forelimb lameness. Radiography of the right elbow noted an increasingly irregular, periosteal response and osteolytic lesion of the right distal humeral condyle. At the time of the second presentation, nasosinal endoscopy identified a lobulated mass in the region of the ethmoid turbinates. Histopathology of this mass revealed an adenocarcinoma of nasal origin with metastasis to the lung, liver, and right humerus.

Uso do exame radiográfico no diagnóstico de Osteopatia Hipertrófica Pulmonar (OHP): relato de três casos em cães

A Osteopatia Hipertrófica Pulmonar (OHP) é uma patologia caracterizada por uma neoformação óssea decorrente da resposta periosteal nos ossos longos e nas extremidades, secundária a doenças intratorácicas como tumores primários ou metastáticos; doenças pielogranulomatosas e neoplasias primárias em órgãos pélvicos. Pode afetar várias espécies e não possui predisposição racial e nem relação com o biótipo; porém, é comumente encontrada em animais idosos. Os sinais clínicos comuns são: aumento da temperatura e edema nos membros acometidos, relutância ao movimento e claudicação; contudo, alguns sinais podem estar ligados à doença primária. A fisiopatologia ainda não está totalmente esclarecida; porém, existem diferentes teorias para explicar a ocorrência. O presente trabalho relata três casos, observados em cães atendidos, e diagnosticados como Osteopatia Hipertrófica Pulmonar em centros de Diagnóstico por Imagem.

The potential for vertical bone regeneration via maxillary periosteal elevation.

While many studies have been performed on the characteristics and regenerative capacity of long bone periosteum, the craniofacial periosteum remains poorly understood. The aim of this study was to investigate the potential for a maxillary periosteum tunnelling procedure to induce vertical alveolar bone regeneration. We employed a murine injury model that activates skeletal stem cells in the periosteum without overtly damaging the underlying cortical bone, preserving the integrity of the long bone and maxilla, and avoiding the introduction of pathological motion at the injury site. Further, we introduced a collagen sponge to serve as a scaffold, providing the necessary space for vertical bone regeneration. Periosteal elevation alone resulted in bone formation in the tibia and delayed bone resorption in the maxilla. With the presence of the collagen sponge, new bone formation occurred in the maxilla. Periosteal response to injury varies with anatomical location, so conclusions from long bone studies should not be extrapolated for craniofacial applications. Murine maxillary periosteum has the osteogenic potential to induce vertical alveolar bone regeneration.

A Platelet-Rich Plasma-Based Membrane as a Periosteal Substitute with Enhanced Osteogenic and Angiogenic Properties: A New Concept for Bone Repair

The periosteum plays a pivotal role during bone development and repair contributing to bone vascularization and osteoprogenitor cells source. We propose a periosteal substitute engineered using a platelet-rich plasma (PRP) membrane incorporating autologous bone marrow-derived mesenchymal stem cells (PRP/BMSC gel membrane) to be wrapped around an osteoconductive scaffold for regeneration of compromised bone defects. The PRP/BMSC gel membrane was optimized using different compositions for optimal release of vascular endothelial growth factor (VEGF) and platelet derived growth factor-BB (PDGF-BB). Survival and proliferation of cells in the PRP gel membrane with time were confirmed in addition to their osteogenic capacity. Furthermore, to evaluate the possible effects of the PRP/BMSC gel membrane on surrounding progenitor cells in the injury area, we found that the PRP gel membrane products could significantly induce the migration of human endothelial cells in vitro, and increased the expression of bone morphogenetic protein 2 in cultured BMSC. These cells also secreted significant amounts of soluble proangiogenic factors, such as PDGF-BB, VEGF, and interleukin-8 (IL-8). Finally, the functionality of the PRP/BMSC gel membrane periosteal substitute for bone regeneration was tested in vivo both in an ectopic mouse model as well as in a rabbit segmental bone defect model providing evidence of its capacity to biomimic a periosteal response enhancing bone regeneration.

Mechanotransduction in bone tissue: The A214V and G171V mutations in Lrp5 enhance load-induced osteogenesis in a surface-selective manner

Mechanotransduction in bone requires components of the Wnt signaling pathway to produce structurally adapted bone elements. In particular, the Wnt co-receptor LDL-receptor-related protein 5 (LRP5) appears to be a crucial protein in the mechanotransduction cascades that translate physical tissue deformation into new bone formation. Recently discovered missense mutations in LRP5 are associated with high bone mass (HBM), and the altered function of these proteins provide insight into LRP5 function in many skeletal processes, including mechanotransduction. We further investigated the role of LRP5 in bone cell mechanotransduction by applying mechanical stimulation in vivo to two different mutant mouse lines, which harbor HBM-causing missense mutations in Lrp5. Axial tibia loading was applied to mature male Lrp5 G171V and Lrp5 A214V knock-in mice, and to their wild type controls. Fluorochrome labeling revealed that 3days of loading resulted in a significantly enhanced periosteal response in the A214V knock in mice, whereas the G171V mice exhibited a lowered osteogenic threshold on the endocortical surface. In summary, our data further highlight the importance of Lrp5 in bone cell mechanotransduction, and indicate that the HBM-causing mutations in Lrp5 can alter the anabolic response to mechanical stimulation in favor of increased bone gain.

The Lichfield bone study: the skeletal response to exercise in healthy young men

The skeletal response to short-term exercise training remains poorly described. We thus studied the lower limb skeletal response of 723 Caucasian male army recruits to a 12-wk training regime. Femoral bone volume was assessed using magnetic resonance imaging, bone ultrastructure by quantitative ultrasound (QUS), and bone mineral density (BMD) using dual-energy X-ray absorptiometry (DXA) of the hip. Left hip BMD increased with training (mean ± SD: 0.85 ± 3.24, 2.93 ± 4.85, and 1.89 ± 2.85% for femoral neck, Ward's area, and total hip, respectively; all P < 0.001). Left calcaneal broadband ultrasound attenuation rose 3.57 ± 0.5% (P < 0.001), and left and right femoral cortical volume by 1.09 ± 4.05 and 0.71 ± 4.05%, respectively (P = 0.0001 and 0.003), largely through the rise in periosteal volume (0.78 ± 3.14 and 0.59 ± 2.58% for right and left, respectively, P < 0.001) with endosteal volumes unchanged. Before training, DXA and QUS measures were independent of limb dominance. However, the dominant femur had higher periosteal (25,991.49 vs. 2,5572 mm(3), P < 0.001), endosteal (6,063.33 vs. 5,983.12 mm(3), P = 0.001), and cortical volumes (19,928 vs. 19,589.56 mm(3), P = 0.001). Changes in DXA, QUS, and magnetic resonance imaging measures were independent of limb dominance. We show, for the first time, that short-term exercise training in young men is associated not only with a rise in human femoral BMD, but also in femoral bone volume, the latter largely through a periosteal response.

Aged mice have enhanced endocortical response and normal periosteal response compared with young-adult mice following 1 week of axial tibial compression

With aging, the skeleton may lose its ability to respond to positive mechanical stimuli. We hypothesized that aged mice are less responsive to loading than young-adult mice. We subjected aged (22 months) and young-adult (7 months) BALB/c male mice to daily bouts of axial tibial compression for 1 week and evaluated cortical and trabecular responses using micro–computed tomography (µCT) and dynamic histomorphometry. The right legs of 95 mice were loaded for 60 rest-inserted cycles per day to 8, 10, or 12 N peak force (generating mid-diaphyseal strains of 900 to 1900 µɛ endocortically and 1400 to 3100 µɛ periosteally). At the mid-diaphysis, mice from both age groups showed a strong anabolic response on the endocortex (Ec) and periosteum (Ps) [Ec.MS/BS and Ps.MS/BS: loaded (right) versus control (left), p < .05]. Generally, bone formation increased with increasing peak force. At the endocortical surface, contrary to our hypothesis, aged mice had a significantly greater response to loading than young-adult mice (Ec.MS/BS and Ec.BFR/BS: 22 months versus 7 months, p < .001). Responses at the periosteal surface did not differ between age groups (p > .05). The loading-induced increase in bone formation resulted in increased cortical area in both age groups (loaded versus control, p < .05). In contrast to the strong cortical response, loading only weakly stimulated trabecular bone formation. Serial (in vivo) µCT examinations at the proximal metaphysis revealed that loading caused a loss of trabecular bone in 7-month-old mice, whereas it appeared to prevent bone loss in 22-month-old mice. In summary, 1 week of daily tibial compression stimulated a robust endocortical and periosteal bone-formation response at the mid-diaphysis in both young-adult and aged male BALB/c mice. We conclude that aging does not limit the short-term anabolic response of cortical bone to mechanical stimulation in our animal model. © 2010 American Society for Bone and Mineral Research.

Healing of non-displaced fractures produced by fatigue loading of the mouse ulna

We developed a fatigue loading protocol in mice to produce a non-displaced ulnar fracture in vivo, and characterized the early healing response. Using adult (5 month) C57Bl/6 mice, we first determined that cyclic compression of the forelimb under load-control leads to increasing applied displacement and, eventually, complete fracture. We then subjected the right forelimbs of 80 mice to cyclic loading (2 Hz; peak force ∼ 4 N) and limited the displacement increase to 0.75 mm (60% of the average displacement increase at complete fracture). This fatigue protocol created a partial, non-displaced fracture through the medial cortex near the ulnar mid-shaft, and reduced ulnar strength and stiffness by > 50%. Within 1 day, there was significant upregulation of genes related to hypoxia ( Hif1a) and osteogenesis ( Bmp2, Bsp) in loaded ulnae compared to non-loaded, contralateral controls. The gene expression response peaked in magnitude near day 7 (e.g., Osx upregulated 8-fold), and included upregulation of FGF-family genes (e.g., Fgfr3 up 6-fold). Histologically, a localized periosteal response was seen at the site of the fracture; by day 7 there was abundant periosteal woven bone surrounding a region of cartilage. From days 7 to 14, the woven bone became denser but did not increase in area. By day 14, the woven-bone response resulted in complete recovery of ulnar strength and stiffness, restoring mechanical properties to normal levels. In the future, the fatigue loading approach can be used create non-displaced bone fractures in transgenic and knockout mice to study the mechanisms by which the skeleton rapidly repairs damage.

Functional Adaptation to Loading of a Single Bone Is Neuronally Regulated and Involves Multiple Bones

Regulation of load-induced bone formation is considered a local phenomenon controlled by osteocytes, although it has also been hypothesized that functional adaptation may be neuronally regulated. The aim of this study was to examine bone formation in multiple bones, in response to loading of a single bone, and to determine whether adaptation may be neuronally regulated. Load-induced responses in the left and right ulnae and humeri were determined after loading of the right ulna in male Sprague-Dawley rats (69 ± 16 days). After a single period of loading at −760μe, −2,000μe, or −3,750μe initial peak strain, rats were given calcein to label new bone formation. Bone formation and bone neuropeptide concentrations were determined at 10 days. In one group, temporary neuronal blocking was achieved by perineural anesthesia of the brachial plexus with bupivicaine during loading. We found right ulna loading induces adaptive responses in other bones in both thoracic limbs when compared to sham controls, and that neuronal blocking during loading abrogated bone formation in the loaded ulna and other thoracic limb bones. Skeletal adaptation was more evident in distal long bones, when compared with proximal long bones. We also found that the single period of loading modulated bone neuropeptide concentrations persistently for 10 days. We conclude that functional adaptation to loading of a single bone in young rapidly growing rats is neuronally regulated and involves multiple bones. Persistent changes in bone neuropeptide concentrations after a single loading period suggest that plasticity exists in the innervation of bone.

Ultrasound mimics the effect of mechanical loading on bone formation in vivo on rat ulnae

While the effect of ultrasound as an extreme example of low-magnitude high-frequency stimulation has been explored in the response of bone to injury, little is known about its effect on normal bone. This experiment was designed to test the hypothesis that ultrasound exerts a similar influence on bone as mechanical stimulation at a physiological level. Three groups of female Wistar rats were anaesthetised (6 per group). In one group, the left ulna was loaded cyclically in vivo 40 times, repeated on a further 5 occasions on alternate days. In a second group, transcutaneous low-intensity pulsed ultrasound stimulation was applied to the left ulnae for the same duration as the period of loading. In a third group, loading and ultrasound stimulation were applied concurrently. The right ulna served as non-loaded control in each animal. At the end of the experiment after 14 days, both ulnae were removed. Induced bone formation was assessed by measuring the proportion of medial periosteal bone surface with double label (dLS/BS, %) and by calculation of mineral apposition rate (MAR) from the inter-label distance. All three treatments induced a significant periosteal response, increasing dLS/BS values from <10% in control limbs to >80% in treated limbs. Increases in MAR of experimental ulnae versus contralateral control ulnae were 2.9 (±0.9), 8.6 (±2.4) and 8.7 μm (±3.2) for the ultrasound only, ultrasound and load, and load only groups, respectively. The effects of loading plus ultrasound were not significantly different from ultrasound alone. These data suggest that ultrasound is able to induce changes in bone that share at least some features with mechanical loading.

In vivo skeletal imaging of 18F-fluoride with positron emission tomography reveals damage- and time-dependent responses to fatigue loading in the rat ulna

The skeletal response to damaging fatigue loading is not fully understood. We used 18F-fluoride PET to describe the time course of the skeletal response following the creation of increasing levels of in vivo, fatigue-induced damage. The right forelimbs of 40 adult rats were loaded in vivo in cyclic compression to four levels of subfracture, fatigue displacement: 30, 45, 65, or 85% of fracture displacement. Rats were injected with a bone-seeking radionuclide ( 18F-fluoride) on days 0 (4 h), 2, 4, 7, 9, 11, 18, 24, and 30, and imaged using a small animal positron emission tomography (PET) scanner. We quantified fluoride uptake in the central 50% of the right (loaded) and left (control) forelimbs. There were significant increases in fluoride uptake in loaded forelimbs compared to control on day 0 for all displacement groups. Normalized uptake (loaded/control) reached peak levels 4 to 9 days after loading. Normalized uptake depended significantly on the level of fatigue displacement. Normalized uptake increased progressively from the 30 to the 45% displacement level ( P < 0.001), and from the 45 to the 65% level ( P < 0.001) but did not differ between 65 and 85% ( P = 0.41). Histologically, we observed a rapid periosteal response with increased vascularity as early as day 1 and abundant woven bone formation between days 3 and 7. Periosteal and woven bone thicknesses were greater in bones subjected to more fatigue displacement. We conclude that a single bout of fatigue loading leads to a transient increase in the uptake of 18F-fluoride, that the uptake is in proportion to the level of initial damage and is associated with increased vascularity and woven bone formation in the first week after loading.

Assessing Tumor Growth and Distribution in a Model of Prostate Cancer Metastasis using Bioluminescence Imaging

Bioluminescence imaging (BLI) has greatly facilitated the development of animal models of cancer, allowing sensitive detection of luciferase-expressing cancer cells in living mice. Previous efforts characterizing such models have involved small numbers of animals, limiting understanding of their performance features. We employed BLI to serially image the growth and distribution of a prostate cancer cell line, 22Rv1, after intracardiac injection into scid mice (n = 85). This approach models hematogenous dissemination of cancer cells and allows inquiry of the process of metastatic colonization at various organ sites, although accurately injecting cancer cells into the left ventricle remains challenging. Therefore, to predict injection success we measured the ratio of the thoracic bioluminescence signal to the whole body bioluminescence signal (T/WB ratio) immediately following intracardiac injection. A T/WB ratio less than 0.50 predicted the development of tumors outside of the thoracic cavity while a T/WB greater than 0.50 predicted the development of tumors entirely within the thoracic cavity, suggestive of a failed injection. Progressive tumor growth was quantified using BLI. Tumors colonized multiple organ sites including bone, liver, and adrenal glands resembling the spectrum of metastases in autopsy studies of patients with prostate cancer. Tumors growing in bone exhibited mixed osteolytic and osteoblastic features, eliciting a spiculated periosteal response. With the ability to more accurately predict injection success, we can now monitor efficacy of intracardiac injections facilitating the performance of this model.

Microvascular Response in the Periosteum Following Mucoperiosteal Flap Surgery in Dogs: Angiogenesis and Bone Resorption and Formation

When surgical stress reaches the periosteum, bone resorption and formation that occur as a periosteal response are closely related to angiogenesis and hemodynamics. Thus, we investigated bone remodeling in the healing process after mucoperiosteal flap surgery, focusing our attention on the microcirculation. Mucoperiosteal flap surgery was performed on 12 adult beagle dogs. The periosteal vascular plexus was observed on days 7, 14, 21, and 28 after surgery, using three different techniques: in histological specimens into which India ink was injected into blood vessels, under a light microscope; in ultrathin sections, using a transmission electron microscope; and in acryl plastic-injected vascular corrosion cast specimens, under a scanning electron microscope. On day 7 after surgery, the interstitum of the elevated mucoperiosteal vascular plexus was filled with sinusoidal new blood vessels. Bone resorption by osteoclasts was observed around these new blood vessels and many highly permeable fenestrations were present in the vascular endothelium. On day 14 after surgery, sinusoidal new blood vessels were more markedly developed and some regions exhibited glomeruluslike morphology consistent with bone resorption cavities. Activated osteoblasts were present around these new blood vessels and highly permeable vesicles, which were considered to be possible vesiclo-vacuolar organelles (VVOs) and caveolae, were noted in the vascular endothelium. On days 21 and 28 after surgery, the mucoperiosteal vascular plexus was dissected through regression of endothelial cells and fibroblasts and reconstructed into a rough mesh structure, and simultaneously the bone surface became smooth. The morphology of the mucoperiosteal vascular plexus changed with bone metabolism and these changes contributed to transport of substances involved in periodontal repair.

Spiculated periosteal response induced by intraosseous injection of 22Rv1 prostate cancer cells resembles subset of bone metastases in prostate cancer patients

Prostate cancer bone metastasis is distinguished by the predominance of osteoblastic lesions. This phenotype has been difficult to reproduce in animal models. Here, we describe a model utilizing the 22Rv1 human prostate cancer cell line that generates osteolytic lesions and a prominent spiculated periosteal osteoblastic response following intraosseous injection in scid mice. We injected 22Rv1-luciferase prostate cancer cells directly into the tibiae of C.B-17 scid mice. We analyzed tumor growth and pathology every 2 weeks using radiographic and histologic techniques. X-ray analysis revealed that 22Rv1 tumors elicit a mixed-type lesion including some osteolysis and a robust induction of periosteal bone formation, in contrast to PC3M-luciferase intraosseous tumors which induce only extensive osteolysis. Micro-computerized tomographic imaging shows that 22Rv1 tumors exhibit both osteolytic and osteoblastic features which become apparent between 4 and 6 weeks post injection. There is initial disruption of the cortex and corresponding invasion of the periosteum which is associated with a vigorous osteoblastic response. Histological analysis of late stage tumors shows that the tumor has grown outside of the medullary cavity and surrounds the tibia underneath the periosteum and intermixed with spicules of woven bone which is detected in the radiographic analysis. The overall pattern of this model is suggestive of clinical cases of prostate cancer metastasis in which periosteal responses are noted, often in association with rapidly progressive disease. We expect that intraosseous injection of 22Rv1 cells will provide a new experimental model for the study of osteoblastic prostate cancer metastasis.

Chronic Osteomyelitis in Children

Summary: In developing countries, chronic osteomyelitis often results from untreated acute hematogenous osteomyelitis but may also be seen as sequelae of trauma (war injuries). This condition is characterized by areas of devitalized bone/soft tissue (sequestra), which serve as a nidus for recurrent episodes of infection. The periosteal response (involucrum) serves to restore structural integrity, and partial or complete reabsorption of sequestra usually accompany this host response. In addition to providing adequate nutritional support, and treating any coexisting medical or infectious diseases, the treatment of chronic osteomyelitis involves surgical removal of all infected/devitalized tissue with or without antibiotic therapy. Sequestrectomy is usually delayed until a suitable involucrum has formed to preserve stability and minimize the chances of fracture and/or segmental bone loss. The disease and/or its treatment may result in focal or segmental loss of bone, requiring further intervention to restore osseous continuity, alignment, and length. Treatment options for focal bone loss include conventional bone grafting and open cancellous bone grafting (subcutaneous bones), and the limb should be protected (cast or external fixator) until healing is complete. For segmental loss of bone, options include conventional bone grafting (external fixator to maintain length and stability) or bone transport. The latter technique, if technically feasible, allows the simultaneous management of limb malalignment and limb length discrepancy. The choice depends on the local resources, and either technique may result in a suitable outcome for the majority of patients. For segmental defects in the tibia, the ipsilateral fibula may be used as a bypass graft. Creation of a single-bone forearm may represent the best option in cases with significant loss of the radius or ulna, provided that the wrist and elbow are normal.

On bone adaptation due to venous stasis

This paper addresses the question of whether or not interstitial fluid flow due to the blood circulation accounts for the observed periosteal bone formation associated with comprised venous return (venous stasis). Increased interstitial fluid flow induced by increased intramedullary pressure has been proposed to account for the periosteal response in venous stasis. To investigate the shear stresses acting on bone cell processes due to the blood circulation-driven interstitial fluid flow, a poroelastic model is extended to the situation in which the interstitial fluid flow in an osteon is driven by the pulsatile extravascular pressure in the osteonal canal as well as by the applied cyclic mechanical loading. Our results show that under normal conditions, the pulsatile extravascular pressure in the osteonal canal due to cardiac contraction (10 mm Hg at 2 Hz) and skeletal muscle contraction (30 mm Hg at 1 Hz) induce peak shear stresses on the osteocyte cell processes that are two orders of magnitude lower than those induced by physiological mechanical loading (100 microstrain at 1 Hz). In venous stasis the induced peak shear stress is reduced further compared to the normal conditions because, although the mean intramedullary pressure is increased, the amplitude of its pulsatile component is decreased. These results suggest that the interstitial fluid flow is unlikely to cause the periosteal bone formation in venous stasis. However, the mean interstitial fluid pressure is found to increase in venous stasis, which may pressurize the periosteum and thus play a role in periosteal bone formation.

Toward an expanded understanding of the role of the periosteum in skeletal health.

Toward an expanded understanding of the role of the periosteum in skeletal health.

Validation of a technique for studying functional adaptation of the mouse ulna in response to mechanical loading

Functional adaptation of the mouse ulna in response to artificial loading in vivo was assessed using a technique previously developed in the rat. Strain gauge recordings from the mouse ulnar midshaft during locomotion showed peak strains of 1680 με and maximum strain rates of 0.03 sec −1. During falls from 20 cm these reached 2620 με and 0.10 sec −1. Axial loads of 3.0 N and 4.3 N, applied through the olecranon and flexed carpus, engendered peak strains at the lateral ulnar midshaft of 2000 με and 3000 με, respectively. The left ulnae of 17, 17-week-old female CD1 mice were loaded for 10 min with a 4 Hz trapezoidal wave engendering a strain rate of 0.1 sec −1 for 5 days/week for 2 weeks. The mice were killed 3 days later. The response of the cortical bone of the diaphysis was assessed histomorphometrically using double calcein labels administered on days 3 and 12 of the loading period. Loading to peak strains of 2000 με stimulated lamellar periosteal bone formation, but no response endosteally. The greatest increase in cortical bone area was 4 mm distal to the midshaft (5 ± 0.4% compared with 0.1 ± 0.1% in controls [ p < 0.01]). Periosteal bone formation rate (BFR) at this site was 0.73 ± 0.06 μm 2/μm per day, compared with 0.03 ± 0.02 μm 2/μm per day in controls ( p < 0.01). Loading to peak strains of 3000 με induced a mixed woven/lamellar periosteal response and lamellar endosteal bone formation. Both of these were greatest 3–4 mm distal to the ulnar midshaft. At this level, the loading-induced periosteal response increased cortical bone area by 21 ± 4% compared with 0.03 ± 0.02% in controls, and resulted in a BFR of 2.84 ± 0.42 μm 2/μm per day, compared with 0.01 ± 0.01 μm 2/μm per day in controls ( p < 0.05). Endosteal new bone formation resulted in a 2 ± 0.4% increase in cortical bone area, compared with 0.4 ± 0.3% in controls, and a BFR of 1.05 ± 0.23 μm 2/μm per day, compared with 0.22 ± 0.15 μm 2/μm per day in controls ( p < 0.05). These data show that the axial ulna loading technique developed in the rat can be used successfully in the mouse. As in the rat, a short daily period of loading results in an osteogenic response related to peak strain magnitude. One important advantage in using mice over rats involves the potential for assessing the effects of loading in transgenics.

Low-magnitude mechanical loading becomes osteogenic when rest is inserted between each load cycle.

Strategies to counteract bone loss with exercise have had fairly limited success, particularly those regimens subjecting the skeleton to mild activity such as walking. In contrast, here we show that it is possible to induce substantial bone formation with low-magnitude loading. In two distinct in vivo models of bone adaptation, we found that insertion of a 10-s rest interval between each load cycle transformed a locomotion-like loading regime that minimally influenced osteoblast activity into a potent anabolic stimulus. In the avian ulna model, the minimal mean (+SE) periosteal labeled surface (Ps.LS) observed in the intact contralateral bones (1.6 +/- 1.5%) was doubled after 3 consecutive days of low-magnitude loading (3.8 +/- 1.5%; p = 0.03). However, modifying the regimen by inserting 10 s of rest between each load cycle significantly enhanced the periosteal response (21.9 +/- 4.5%; p = 0.03). In the murine tibia model, 5 consecutive days of 100 low-magnitude loading cycles did not significantly alter mean periosteal bone formation rate (BFR) compared with contralateral bones (0.011 +/- 0.005 microm3/microm2 per day vs. 0.021 +/- 0.013 microm3/microm2 per day). In contrast, separating each of 10 of the same loading cycles with 10 s of rest significantly elevated periosteal BFR (0.167 +/- 0.049 microm3/microm2 per day; p = 0.01). Endocortical bone formation parameters were not altered by any loading regimen in either model. We conclude that 10 s of rest between each load cycle of a low-magnitude loading protocol greatly enhances the osteogenic potential of the regimen.

Mechanical loading of diaphyseal bone in vivo: the strain threshold for an osteogenic response varies with location.

Bone tissue responds to elevated mechanical loading with increased bone formation, which is triggered either directly or indirectly by the mechanical strain engendered in the bone tissue. Previous studies have shown that mechanical strain magnitude must surpass a threshold before bone formation is initiated. The objective of this study was to estimate the strain thresholds at three different locations along the ulna of adult rats. We hypothesized that the strain threshold would be greater in regions of the ulna habitually subjected to larger mechanical strains. New bone formation was measured on the periosteal and endocortical surfaces of the ulnar diaphysis in adult female rats exposed to controlled dynamic loading. Axial, compressive loading was applied daily at five different magnitudes for a period of 2 weeks. Bone formation rate (BFR) was measured, using double-label histomorphometry at the ulnar middiaphysis and at locations 3 mm proximal and 3 mm distal to the middiaphysis. Loading induced lamellar bone formation on the periosteal surface that was greater at the distal ulnar location and lower at the proximal location when compared with the middiaphysis. Likewise, peak strains on the periosteal surface were greatest distally and less proximally. There was a significant dose-response relationship between peak strain magnitude and periosteal new bone formation when the mechanically induced strain surpassed a threshold. The strain threshold varied from 1343 microstrain (mu strain) proximally to 2284 mu strain at the midshaft to 3074 mu strain distally. Unlike the periosteal response to mechanical loading, there was not a clear dose-response relationship between applied load and bone formation on the endocortical surface. Endocortical strains were estimated to be < 20% of periosteal strains and may not have been sufficient to initiate a bone formation response. Our results show that the osteogenic response on the periosteal surface of the ulna depends on peak strain level once a strain threshold is surpassed. The threshold strain is largest distally, where locomotor bone strains are typically higher and smallest proximally where locomotor bone strains are lower.