An approach to quantifying bone overloading and hypertrophy with applications to multiple experimental studies

Mechanoregulated trabecular bone adaptation: Progress report on in silico approaches

Adaptation is the process by which bone responds to changes in loading environment and modulates its properties and spatial organization to meet the mechanical demands. Adaptation in trabecular bone is achieved through increase in bone mass and alignment of trabecular-bone morphology along the loading direction. This transformation of internal microstructure is governed by mechanical stimuli sensed by mechanosensory cells in the bone matrix. Realisation of adaptation in the form of local bone-resorption and -formation activities as a function of mechanical stimuli is still debated. In silico modelling is a useful tool for simulation of various scenarios that cannot be investigated in vivo and particularly well suited for prediction of trabecular bone adaptation. This progress report presents the recent advances in in silico modelling of mechanoregulated adaptation at the scale of trabecular bone tissue. Four well-established bone-adaptation models are reviewed in terms of their recent improvements and validation. They consider various mechanical factors: (i) strain energy density, (ii) strain and damage, (iii) stress nonuniformity and (iv) daily stress. Contradictions of these models are discussed and their ability to describe adequately a real-life mechanoregulation process in bone is compared.

The effect of running on foot muscles and bones: A systematic review

Despite the widespread evidence of running as a health-preserving exercise, little is known concerning its effect on the foot musculature and bones. While running may influence anatomical foot adaptation, it remains unclear to what extent these adaptations occur. The aim of this paper is to provide a systematic review of the studies that investigated the effects of running and the adaptations that occur in foot muscles and bones. The search was performed following the PRISMA guidelines. Relevant keywords were used for the search through PubMed/MEDLINE, Scopus and SPORTDiscus. The methodological quality of intervention studies was assessed using the Downs and Black checklist. For cross-sectional studies, the Newcastle-Ottawa scale was used. Sixteen studies were found meeting the inclusion criteria. In general, the included studies were deemed to be of moderate methodological quality. Although results of relevant literature are limited and somewhat contradictory, the outcome suggests that running may increase foot muscle volume, muscle cross-sectional area and bone density, but this seems to depend on training volume and experience. Future studies conducted in this area should aim for a standard way of reporting foot muscle/bone characteristics. Also, herein, suggestions for future research are provided.

Effect of the same mechanical loading on osteogenesis and osteoclastogenesis in vitro

PURPOSE

To investigate the influence of the same mechanical loading on osteogenesis and osteoclastogenesis in vitro.

METHODS

Primary osteoblasts, bone marrow-derived mesenchymal stem cells (BMSCs, cultured in osteoinductive medium) and RAW264.7 cells cultured in osteoclast inductive medium were all subjected to a 1000 μstrain (μs) at 1 Hz cyclic mechanical stretch for 30 min (twice a day).

RESULTS

After mechanical stimulation, the alkaline phosphatase (ALP) activity, osteocalcin protein level of the osteoblasts and BMSCs were all enhanced, and the mRNA levels of ALP and collagen type I increased. Additionally, extracellular-deposited calcium of both osteoblasts and BMSCs increased. At the same time, the activity of secreted tartrate-resistant acid phosphatase, the number of tartrate-resistant acid phosphatase-positive multinucleated cells, matrix metalloproteinase-9 protein levels of RAW264.7 cells and the extracellular calcium solvency all decreased.

CONCLUSION

The results demonstrated that 1000 μs cyclic mechanical loading enhanced osteoblasts activity, promoted osteoblastic differentiation of BMSCs and restrained osteoclastogenesis of RAW264.7 cells in vitro.

Development of an in vivo rabbit ulnar loading model

Ulnar and tibial cyclic compression in rats and mice have become the preferred animal models for investigating the effects of mechanical loading on bone modeling/remodeling. Unlike rodents, rabbits provide a larger bone volume and normally exhibit intracortical Haversian remodeling, which may be advantageous for investigating mechanobiology and pharmaceutical interventions in cortical bone. Therefore, the objective of this study was to develop and validate an in vivo rabbit ulnar loading model. Ulnar tissue strains during loading of intact forelimbs were characterized and calibrated to applied loads using strain gauge measurements and specimen-specific finite element models. Periosteal bone formation in response to varying strain levels was measured by dynamic histomorphometry at the location of maximum strain in the ulnar diaphysis. Ulnae loaded at 3000 microstrain did not exhibit periosteal bone formation greater than the contralateral controls. Ulnae loaded at 3500, 4000, and 4500 microstrain exhibited a dose-dependent increase in periosteal mineralizing surface (MS/BS) compared with contralateral controls during the second week of loading. Ulnae loaded at 4500 microstrain exhibited the most robust response with significantly increased MS/BS at multiple time points extending at least 2weeks after loading was ceased. Ulnae loaded at 5250 microstrain exhibited significant woven bone formation. Rabbits required greater strain levels to produce lamellar and woven bone on periosteal surfaces compared with rats and mice, perhaps due to lower basal levels of MS/BS. In summary, bone adaptation during rabbit ulnar loading was tightly controlled and may provide a translatable model for human bone biology in preclinical investigations of metabolic bone disease and pharmacological treatments.

Relationship between proximal femoral and acetabular alignment in normal hip joints using 3-dimensional computed tomography

BACKGROUND

The bony architecture of the hip depends upon functional adaptation to mechanical usage via the dynamic interaction between the acetabulum and femoral head. Acetabular retroversion is thought to be a contributing factor of pincer-type femoroacetabular impingement. Studies of pathological hip joints suggest proximal femoral anatomy compensates for acetabular retroversion. HYPOTHESIS/ PURPOSE: The purpose of this study was to determine if a predictable relationship exists between proximal femoral and acetabular angles, age, and gender in normal hip joints. We hypothesized that, through functional adaptation to mechanical loading, a complementary developmental relationship exists between the acetabulum and proximal femur.

STUDY DESIGN

Descriptive laboratory study.

METHODS

The femoral neck version, femoral neck shaft angle, acetabular version, acetabular inclination, and center edge angle were measured in 230 normal hip joints in 115 adults using 3-dimensional reconstruction software. Correlations between the angles, age, and gender were examined using the methods of stepwise regression and backward elimination.

RESULTS

Regarding side-to-side comparison and variability, there was no statistically significant difference between the left and right sides in the average value of each angle measurement. The correlations specifically between angles, age, and gender were similar on the left and right sides for all pairs except femoral version and acetabular inclination. Regarding significant findings of the study, a positive correlation (P < .05) was found between femoral version and acetabular version (0.38° to 1°). A positive correlation was found between femoral neck shaft angle and acetabular version (0.21° to 1°). A negative correlation was found between femoral neck shaft angle and age (-0.17° to 1°). A positive correlation was found between acetabular version and female gender (2.6° to 1°). A positive correlation was found between center edge angle and female gender (2.8° to 1°). A negative correlation was found between femoral version and acetabular inclination (-0.49° to 1°), although this latter relationship was only observed unilaterally (ie, left hip).

CONCLUSION

This study demonstrates that a correlation exists between multiple proximal femoral and acetabular angles in normal hip joints. These findings support the hypothesis that a complementary developmental relationship occurs between the femoral head and acetabulum.

CLINICAL RELEVANCE

The results of this study suggest that, in some patients, what is thought to be pathological acetabular retroversion may actually be normal anatomy with a compensated femoral version. Investigating the relationship between these angles in patients with the signs and symptoms of pincer-type femoroacetabular impingement may alter a surgeon's approach to this patient population.

Rap system of stress stimulation can promote bone union after lower tibial bone fracture: a clinical research

BACKGROUND

Lower tibial bone fracture may easily cause bone delayed union or nonunion because of lacking of dynamic mechanical load.

OBJECTIVE

Research Group would design a new instrument as Rap System of Stress Stimulation (RSSS) to provide dynamic mechanical load which would promote lower tibial bone union postoperatively.

METHODS

This clinical research was conducted from January 2008 to December 2010, 92 patients(male 61/female 31, age 16-70 years, mean 36.3 years) who suffered lower tibial bone closed fracture were given intramedullary nail fixation and randomly averagely separated into experimental group and control group(according to the successively order when patients went for the admission procedure). Then researchers analysed the clinical healing time, full weight bearing time, VAS (Visual Analogue Scales) score and callus growth score of Lane-Sandhu in 3,6,12 months postoperatively. The delayed union and nonunion rates were compared at 6 and 12 months separately.

RESULTS

All the 92 patients had been followed up (mean 14 months). Clinical bone healing time in experimental group was 88.78±8.80 days but control group was 107.91±9.03 days. Full weight bearing time in experimental group was 94.07±9.81 days but control group was 113.24±13.37 days respectively (P<0.05). The delayed union rate in 6 months was 4.3% in experimental group but 10.9% in control group(P<0.05). The nonunion rate in 12 months was 6.5% in experimental group but 19.6% in control group(P<0.05). In 3, 6, 12 months postoperatively, VAS score and Lane-Sandhu score in experimental group had more significantly difference than them in control group.

CONCLUSIONS

RSSS can intermittently provide dynamic mechanical load and stimulate callus formation, promote lower tibial bone union, reduce bone delayed union or nonunion rate. It is an adjuvant therapy for promoting bone union after lower tibial bone fracture.

Mouse tail vertebrae adapt to cyclic mechanical loading by increasing bone formation rate and decreasing bone resorption rate as shown by time-lapsed in vivo imaging of dynamic bone morphometry

It is known that mechanical loading leads to an increase in bone mass through a positive shift in the balance between bone formation and bone resorption. How the remodeling sites change over time as an effect of loading remains, however, to be clarified. The purpose of this paper was to investigate how bone formation and resorption sites are modulated by mechanical loading over time by using a new imaging technique that extracts three dimensional formation and resorption parameters from time-lapsed in vivo micro-computed tomography images. To induce load adaptation, the sixth caudal vertebra of C57BL/6 mice was cyclically loaded through pins in the adjacent vertebrae at either 8 N or 0 N (control) three times a week for 5 min (3000 cycles) over a total of 4 weeks. The results showed that mechanical loading significantly increased trabecular bone volume fraction by 20% (p<0.001) and cortical area fraction by 6% (p<0.001). The bone formation rate was on average 23% greater (p<0.001) and the bone resorption rate was on average 25% smaller (p<0.001) for the 8 N group than for the 0 N group. The increase in bone formation rate for the 8 N group was mostly an effect of a significantly increased surface of bone formation sites (on average 16%, p<0.001), while the thickness of bone formation packages was less affected (on average 5% greater, p<0.05). At the same time the surface of bone resorption sites was significantly reduced (on average 15%, p<0.001), while the depth of resorption pits remained the same. For the 8 N group, the strength of the whole bone increased significantly by 24% (p<0.001) over the loading period, while the strain energy density in the trabecular bone decreased significantly by 24% (p<0.001). In conclusion, mouse tail vertebrae adapt to mechanical loading by increasing the surface of formation sites and decreasing the surface of resorption sites, leading to an overall increase in bone strength. This new imaging technique will provide opportunities to investigate in vivo bone remodeling in the context of disease and treatment options, with the added value that both bone formation and bone resorption parameters can be nondestructively calculated over time.

Variations in habitual bone strains in vivo: long bone versus mandible

Little is known about the similarities and dissimilarities between daily in vivo strain histories of different bones, other than the generally accepted view that most bones need daily loading to maintain their mass. Similarities in daily strain histories might uncover a common basic mechanical stimulus for homeostatic bone maintenance, whereas dissimilarities might explain why bones respond differently to changes in their environment. We compared the daily strain histories of two different bones from the rabbit: the tibiofibula and the mandible. Bone strain was recorded wirelessly in freely moving animals up to 57 h. Habitual strain amplitudes, rates, and frequencies were compared. The exponential decrease in occurrence of greater strain amplitudes was similar in long and mandibular bone. Also similar was the exponentially decreasing incidence of higher strain rates. Mandibular-bone strains distinguished themselves from long-bone strains, however, through the presence of a plateau in the occurrence of compressive strains with amplitudes between 200 and 450 microstrain (με) and in the occurrence of compressive-strain rates between 5000 and 10,000 με/s. The frequency spectrum of the mandibular-bone strain history contained peaks at 4.4 Hz and 8.9 Hz, which were absent in the long-bone strain spectrum. We hypothesise that the exponentially decreasing incidence of larger strain amplitudes and rates might outline the minimum amount of mechanical stimuli needed for bone maintenance. Furthermore, the strong presence of rhythmicity in mandibular strains might provide an important clue in confirming or improving the anabolic character of cyclic-loading regimes employed in clinical settings.