Influence of physical activity on the regulation of bone density

Increased response of postmenopausal bone to interval walking training depends on baseline bone mineral density

PURPOSE

To examine the hypothesis that an increase in response of postmenopausal bone to interval walking training (IWT) depends on baseline bone mineral densities (BMDs).

METHODS

Two hundred and thirty-four postmenopausal women (64±5 (SD) yr) with no medication for osteoporosis performed 5-month IWT, repeating fast and slow walking at ≥70% and ~40% peak aerobic capacity, respectively, for 3 minutes each per set, ≥5 sets/day, ≥4 days/week. They were recruited from those who had performed IWT ≥6 months before participating in the study so that their physical fitness and lifestyle-related disease symptoms had almost reached a steady state at the time of their participation. We measured BMDs for the lumbar spine (LS), bilateral femoral neck (FN), and bilateral total hip (TH) by dual-energy X-ray absorptiometry (DXA) before and after the intervention. We used a multiple regression analysis to identify significant independent factors for increasing BMDs after the intervention as baseline physical characteristics, exercise intensity, and exercise time during IWT were the candidates. For any bone site where the independent factor identified was singular, we analyzed the relationship between the identified factor vs increases in BMD after the intervention (ΔBMD) by the locally weighted scatterplot smoothing (LOWESS) method.

RESULTS

Almost all subjects completed the designated protocol with minimal adverse events. We found that significant determinants for increasing BMDs were the baseline BMDs for all bone sites, as well as age and body mass index for TH (all, P<0.02). Furthermore, the LOWESS trendline between ΔBMDs vs the baseline BMDs, divided equally into 10 bins for LS and FN, respectively, showed that ΔBMD responses (Y) were attenuated as the baseline BMDs (X) increased in the lower 4 bins and then showed a flat line (Y = ~0) in the remaining higher 6 bins for LS and FN. When the lower 4 bins and the higher 6 bins of the baseline BMD were pooled, respectively, BMDs significantly increased by 1.8% and 1.0% in the lower groups for LS and FN, respectively (both, P<0.001) while not in the higher groups after the intervention (both, P>0.3).

CONCLUSIONS

IWT may be of benefit with minimal adverse events to postmenopausal women, although the effects were greater in those with lower baseline BMDs.

TRIAL REGISTRATION

UMIN000047428. https://rctportal.niph.go.jp/s/detail/um?trial_id=UMIN000047428#.

ESMAC Best Paper Award 2023: Increased knee flexion in participants with cerebral palsy results in altered stresses at the distal femoral growth plate compared to a typically developing cohort

INTRODUCTION

Femoral deformities are highly prevalent in children with cerebral palsy (CP) and can have a severe impact on patients' gait abilities. While the mechanical stress regime within the distal femoral growth plate remains underexplored, understanding it is crucial given bone's adaptive response to mechanical stimuli. We quantified stresses at the distal femoral growth plate to deepen our understanding of the relationship between healthy and pathological gait patterns, internal loading, and femoral growth patterns.

METHODS

This study included three-dimensional motion capture data and magnetic resonance images of 13 typically developing children and twelve participants with cerebral palsy. Employing a multi-scale mechanobiological approach, integrating musculoskeletal simulations and subject-specific finite element analysis, we investigated the orientation of the distal femoral growth plate and the stresses within it. Limbs of participants with CP were grouped depending on their knee flexion kinematics during stance phase as this potentially changes the stresses induced by knee and patellofemoral joint contact forces.

RESULTS

Despite similar growth plate orientation across groups, significant differences were observed in the shape and distribution of growth values. Higher growth rates were noted in the anterior compartment in CP limbs with high knee flexion while CP limbs with normal knee flexion showed high similarity to the group of healthy participants.

DISCUSSION

Results indicate that the knee flexion angle during the stance phase is of high relevance for typical bone growth at the distal femur. The evaluated growth rates reveal plausible results, as long-term promoted growth in the anterior compartment leads to anterior bending of the femur which was confirmed for the group with high knee flexion through analyses of the femoral geometry. The framework for these multi-scale simulations has been made accessible on GitHub, empowering peers to conduct similar mechanobiological studies. Advancing our understanding of femoral bone development could ultimately support clinical decision-making.

The effect of early weight-bearing on bone fusion after triple arthrodesis

Triple arthrodesis is an effective method for treating stiff horseshoe feet and severe osteoarthritis. However, it is still a challenge to improve postoperative bone fusion by changing early weight-bearing. This study improved the classical bone remodeling algorithm, established a mathematical relationship between density change rate and mechanical stimulation, and combined it with finite element theory. The proposed algorithm can not only predict the effect of early weight-bearing on triple arthrodesis but also visually demonstrate the change of bone mineral density with time. The analysis results indicated that 2.5% of the initial load was a potential factor leading to bone nonunion, and 50% of the initial load would result in bone resorption. Meanwhile, it was found that 25% of the external load was more conducive to postoperative rehabilitation. The study results have theoretical significance for enhancing the effect of postoperative bone fusion and formulating a more scientific rehabilitation program, thereby supporting patients' postoperative rehabilitation exercise.

Seasonal variations in vitamin D do not change the musculoskeletal health of physically active ambulatory men with cerebral palsy: a longitudinal cross-sectional comparison study

Increased levels of vitamin D in the summer months from natural seasonal variations in sun exposure have been linked to improvements in musculoskeletal health and function in UK populations; however, studies have shown that differences in lifestyles because of disability can inhibit the natural vitamin D increase in these populations. We hypothesized that men with cerebral palsy (CP) will experience smaller increases in 25-hydroxyvitamin D (25(OH)D) from winter to summer and men with CP will not experience any improvements in musculoskeletal health and function during the summer. A longitudinal observational study in 16 ambulant men with CP aged 21.0 ± 1.3 years and 16 healthy, physical activity matched, typically developed controls aged 25.4 ± 2.6 years, completed assessments of serum 25(OH)D and parathyroid hormone during winter and summer. Neuromuscular outcomes included vastus lateralis size, knee extensor strength, 10-m sprint, vertical jumps, and grip strength. Bone ultrasounds were performed to obtain radius and tibia T and Z scores. Men with CP and typically developed controls showed a 70.5% and 85.7% increase in serum 25(OH)D from winter to summer months, respectively. Neither group showed seasonal effect on neuromuscular outcomes muscle strength, size, vertical jump, or tibia and radius T and Z scores. A seasonal interaction effect was seen in the tibia T and Z scores (P < .05). In conclusion, there were similar seasonal increases in 25(OH)D observed in men with CP and typically developed controls, but serum 25(OH)D levels were still considered insufficient to improve bone or neuromuscular outcomes.

Independently ambulatory children with spina bifida experience near-typical knee and ankle joint moments and forces during walking

BACKGROUND

Spina bifida, a neurological defect, can result in lower-limb muscle weakness. Altered ambulation and reduced musculoskeletal loading can yield decreased bone strength in individuals with spina bifida, yet individuals who remain ambulatory can exhibit normal bone outcomes.

RESEARCH QUESTION

During walking, how do lower-limb joint kinematics and moments and tibial forces in independently ambulatory children with spina bifida differ from those of children with typical development?

METHODS

We retrospectively analyzed data from 16 independently ambulatory children with spina bifida and 16 children with typical development and confirmed that tibial bone strength was similar between the two groups. Plantar flexor muscle strength was measured by manual muscle testing, and 14 of the children with spina bifida wore activity monitors for an average of 5 days. We estimated tibial forces at the knee and ankle using motion capture data and musculoskeletal simulations. We used Statistical Parametric Mapping t-tests to compare lower-limb joint kinematic and kinetic waveforms between the groups with spina bifida and typical development. Within the group with spina bifida, we examined relationships between plantar flexor muscle strength and peak tibial forces by calculating Spearman correlations.

RESULTS

Activity monitors from the children with spina bifida reported typical daily steps (9656 [SD 3095]). Despite slower walking speeds (p = 0.004) and altered lower-body kinematics (p < 0.001), children with spina bifida had knee and ankle joint moments and forces similar to those of children with typical development, with no detectable differences during stance. Plantar flexor muscle weakness was associated with increased compressive knee force (p = 0.002) and shear ankle force (p = 0.009).

SIGNIFICANCE

High-functioning, independently ambulatory children with spina bifida exhibited near-typical tibial bone strength and near-typical step counts and tibial load magnitudes. Our results suggest that the tibial forces in this group are of sufficient magnitudes to support the development of normal tibial bone strength.

Symmetry breaking and effects of nutrient walkway in time-dependent bone remodeling incorporating poroelasticity

Bone is an extraordinary biological material that continuously adapts its hierarchical microstructure to respond to static and dynamic loads for offering optimal mechanical features, in terms of stiffness and toughness, across different scales, from the sub-microscopic constituents within osteons—where the cyclic activity of osteoblasts, osteoclasts, and osteocytes redesigns shape and percentage of mineral crystals and collagen fibers—up to the macroscopic level, with growth and remodeling processes that modify the architecture of both compact and porous bone districts. Despite the intrinsic complexity of the bone mechanobiology, involving coupling phenomena of micro-damage, nutrients supply driven by fluid flowing throughout hierarchical networks, and cells turnover, successful models and numerical algorithms have been presented in the literature to predict, at the macroscale, how bone remodels under mechanical stimuli, a fundamental issue in many medical applications such as optimization of femur prostheses and diagnosis of the risk fracture. Within this framework, one of the most classical strategies employed in the studies is the so-called Stanford’s law, which allows uploading the effect of the time-dependent load-induced stress stimulus into a biomechanical model to guess the bone structure evolution. In the present work, we generalize this approach by introducing the bone poroelasticity, thus incorporating in the model the role of the fluid content that, by driving nutrients and contributing to the removal of wastes of bone tissue cells, synergistically interacts with the classical stress fields to change homeostasis states, local saturation conditions, and reorients the bone density rate, in this way affecting growth and remodeling. Through two paradigmatic example applications, i.e. a cylindrical slice with internal prescribed displacements idealizing a tract of femoral diaphysis pushed out by the pressure exerted by a femur prosthesis and a bone element in a form of a bent beam, it is highlighted that the present model is capable to catch more realistically both the transition between spongy and cortical regions and the expected non-symmetrical evolution of bone tissue density in the medium–long term, unpredictable with the standard approach. A real study case of a femur is also considered at the end in order to show the effectiveness of the proposed remodeling algorithm.

Mechanical Differences between Men and Women during Overground Load Carriage at Self-Selected Walking Speeds

Few studies have directly compared physical responses to relative loading strategies between men and women during overground walking. This study aimed to compare gait mechanics of men and women during overground load carriage. A total of 30 participants (15 male, 15 female) completed three 10-min walking trials while carrying external loads of 0%, 20% and 40% of body mass at a self-selected walking speed. Lower-body motion and ground reaction forces were collected using a three-dimensional motion capture system and force plates, respectively. Female participants walked with a higher cadence (p = 0.002) and spent less absolute time in stance (p = 0.010) but had similar self-selected walking speed (p = 0.750), which was likely due to the female participants being shorter than the male participants. Except for ankle plantarflexion moments, there were no sex differences in spatiotemporal, kinematic, or kinetic variables (p > 0.05). Increasing loads resulted in significantly lower self-selected walking speed, greater stance time, and changes in all joint kinematics and kinetics across the gait cycle (p < 0.05). In conclusion, there were few differences between sexes in walking mechanics during overground load carriage. The changes identified in this study may inform training programs to increase load carriage performance.

A Parametric Study on a Dental Implant Geometry Influence on Bone Remodelling through a Numerical Algorithm

To ensure the long-term success of a dental implant, it is imperative to understand how chewing loads are transferred through the implant prosthetic components to the surrounding bone tissue. The stress distribution depends on several factors, such as load type, bone–implant interface, shape and materials of the fixture and quality and quantity of the bone. These aspects are of fundamental importance to ensure implant stability and to evaluate the remodelling capacity of the bone tissue to adapt to its biomechanical environment. A bone remodelling algorithm was formulated by the authors and implemented by means of finite element simulations on four different implants with several design characteristics. Internal bone microstructure and density, apposition/resorption of tissue and implant stability were evaluated over a period of 12 months, showing the influence of the geometry on bone tissue evolution over time. Bone remodelling algorithms may be a useful aid for clinicians to prevent possible implant failures and define an adequate implant prosthetic rehabilitation for each patient. In this work, for the first time, external bone remodelling was numerically predicted over time.

Finite element analysis of human skull bone adaptation to mechanical loading

Bones self-optimize their mechanical behavior in response to mechanical stimulus. The objective of this research was to develop an integrated bone remodeling and stress binning algorithms into a finite element environment to elucidate the evolution of the bone properties as a function of loading. The bone remodeling algorithm was used to calculate the change in the density and elastic modulus based on the strain energy stimulus. The stress-binning procedure seeks to assign the properties to each element based on the levels of stress from the previous cycle, eliminating pseudo-lazy-zoning and stress dilation effects. The developed algorithms were used to analyze the response skull to loading associated with orthodontic devices. Specifically, a load was applied between the roots of the canine teeth and the first premolars while constraining the foramen magnum. Full-field contours of the displacement, strain, and strain energy were extracted after each remodeling cycle at nine commonly cephalometric landmarks. The results indicate that the overall mechanical response and the associated properties reached a steady-state behavior after nearly 50 cycles of applying the algorithm, where different zones within the skull exhibited unique evolution based on the locations from the loading and boundary sites. When approaching this steady-state condition, it was found that the upper incisor displacement is reduced by 72%, and the density is reduced by almost 7.5%. The finite element approach can be used in defining the treatment process by dynamically changing the loads. Future research will focus on integrating the time-dependent behavior of the bone.

Impact of Size and Shape of Equine Femoral Subchondral Bone Cysts With a Transcondylar Screw on Predicted Bone Formation Area in a Finite Element Model

Equine subchondral bone cysts (SBCs) develop most often in the medial femoral condyle (MFC) of yearlings intended for performance. SBCs often cause lameness and can cause secondary injuries to the meniscus and tibial cartilage. A novel surgical technique using a transcondylar lag screw (TLS) across an MFC SBC has shown success in lameness resolution and radiographic healing of MFC SBC. In a previous study using finite element analysis, our lab showed that a TLS stimulated bone formation on the inner surface of the SBC and altered third principal stress vectors to change the direction of surface compression to align with the screw axis. This work extended the previous study, which was limited by the use of only one idealized SBC. Our objective was to test SBCs of several sizes and shapes in a newly developed equine stifle FEM with a TLS to determine how cyst size affects bone formation stimulation. This study found that a transcondylar screw is most effective in stimulating bone formation in cysts of greater height (proximal-distal). The TLS increases stress stimulus in the bone around the cyst to promote bone apposition and directs compression across the cyst. If full penetration of the screw through the cyst is possible, it is recommended that the transcondylar screw be used to treat subchondral bone cysts. For the treatment of smaller cysts that are not accessible by the current screw surgical approach, future work could study the efficacy of a dual-pitch headless screw that may reach smaller cysts.

The interplay between bone healing and remodeling around dental implants

Long-term bone healing/adaptation after a dental implant treatment starts with diffusion of mesenchymal stem cells to the wounded region and their subsequent differentiation. The healing phase is followed by the bone-remodeling phase. In this work, a mechano-regulatory cellular differentiation model was used to simulate tissue healing around an immediately loaded dental implant. All tissue types were modeled as poroelastic in the healing phase. Material properties of the healing region were updated after each loading cycle for 30 cycles (days). The tissue distribution in the healed state was then used as the initial condition for the remodeling phase during which regions healed into bone adapt their apparent density with respect to a homeostatic remodeling stimulus. The short- (bone healing) and long-term (bone remodeling) effects of initial implant micromotion during the healing phase were studied. Development of soft tissue was observed both in the coronal region due to high fluid velocity, and on the vertical sides of the healing-gap due to high shear stress. In cases with small implant micromotion, tissue between the implant threads differentiated into bone during the healing phase but resorbed during remodeling. In cases with large implant micromotion, higher percentage of the healing region differentiated into soft tissue resulting in smaller volume of bone tissue available for remodeling. However, the remaining bone region developed higher density bone tissue. It was concluded that an optimal range of initial implant micromotion could be designed for a specific patient in order to achieve the desired long-term functional properties.

Quality over quantity: skeletal loading intensity plays a key role in understanding the relationship between physical activity and bone density in postmenopausal women

OBJECTIVE

Increasing physical activity (PA) is regularly cited as a modifiable target to improve health outcomes and quality of life in the aging population, especially postmenopausal women who exhibit low bone mineral density (BMD) and high fracture risk. In this cross-sectional study, we aimed to quantify real-world PA and its association with BMD in postmenopausal women.

METHODS

Seventy postmenopausal women, aged 46 to 79 years, received a dual-energy X-ray absorptiometry scan measuring total hip BMD and wore bilateral triaxial accelerometers on the ankles for 7 days to measure PA in their free-living environment. Custom step detection and peak vertical ground reaction force estimation algorithms, sensitive to both quantity and intensity of PA, were used to calculate a daily bone density index (BDI) for each participant. Multiple regression was used to quantify the relationship between total hip BMD, age, step counts, and mean BDI over the span of 7 days of data collection.

RESULTS

All participants completed the full 7 days of PA monitoring, totaling more than 7 million detected steps. Participants averaged 14,485 ± 4,334 steps daily with mean peak vertical ground reaction force stepping loads of 675 ± 121 N during daily living. Across the population, total hip BMD was found to be significantly correlated with objective estimates of mean BDI (r = 0.44), as well as participant age (r = 0.285).

CONCLUSION

Despite having higher-than-expected PA, the low stepping loads observed in this cohort, along with half of the participants having low BMD measures, underscores the need for PA intensity to be considered in the management of postmenopausal bone health.

Stimulation of subchondral bone cyst healing by placement of a transcondylar screw in the equine medial femoral condyle

OBJECTIVE

To predict the bone formation stimulus of a transcondylar screw across an equine subchondral bone cyst (SBC) in an equine medial femoral condyle (MFC).

STUDY DESIGN

Finite element modeling (FEM) of an equine MFC with a 2 cm³ SBC under several transcondylar screw conditions.

SAMPLE POPULATION

The right stifle of a yearling thoroughbred without stifle disease that had been euthanized for reasons unrelated to this study and donated to the University.

METHODS

The FEM was derived from computed tomography of a yearling thoroughbred and analyzed in ABAQUS v6.14. The transcondylar screw was modeled as a 4.5-mm stainless steel cylinder. The region of interest was the centrodistal MFC, and bone stimulus was calculated. The stimulus threshold for bone formation (BFT) was >60 MPa and is presented as the percentage of total bone surface area (BFA) and frontal plane maps. Principal compressive stress vectors were also determined. Tested variables were daily cycles, load, and screw compression and position.

RESULTS

At 750 cycles and 900-N load, <3% of the BFA exceeded the BFT. Increases in BFA > BFT occurred proportionally with load, screw compression, and daily cycles (steps). Compressive stress was oriented vertically on the SBC surface without a screw but aligned with the long axis of well-placed lag screws. Screw placement through the void also increased the number and magnitude of compressive vectors.

CONCLUSION

This model predicted that a transcondylar lag screw across an MFC SBC increased surface BFA stimulation and reoriented the compression vector. Increasing screw compression, load, and steps per day increased the bone formation stimulus.

CLINICAL SIGNIFICANCE

This study provides evidence that supports the use of a lag screw thorough an MFC SBC to promote bone formation.

Trabecular architecture of the great ape and human femoral head

Studies of femoral trabecular structure have shown that the orientation and volume of bone are associated with variation in loading and could be informative about individual joint positioning during locomotion. In this study, we analyse for the first time trabecular bone patterns throughout the femoral head using a whole-epiphysis approach to investigate how potential trabecular variation in humans and great apes relates to differences in locomotor modes. Trabecular architecture was analysed using microCT scans of Pan troglodytes (n = 20), Gorilla gorilla (n = 14), Pongo sp. (n = 5) and Homo sapiens (n = 12) in medtool 4.1. Our results revealed differences in bone volume fraction (BV/TV) distribution patterns, as well as overall trabecular parameters of the femoral head between great apes and humans. Pan and Gorilla showed two regions of high BV/TV in the femoral head, consistent with hip posture and loading during two discrete locomotor modes: knuckle-walking and climbing. Most Pongo specimens also displayed two regions of high BV/TV, but these regions were less discrete and there was more variability across the sample. In contrast, Homo showed only one main region of high BV/TV in the femoral head and had the lowest BV/TV, as well as the most anisotropic trabeculae. The Homo trabecular structure is consistent with stereotypical loading with a more extended hip compared with great apes, which is characteristic of modern human bipedalism. Our results suggest that holistic evaluations of femoral head trabecular architecture can reveal previously undetected patterns linked to locomotor behaviour in extant apes and can provide further insight into hip joint loading in fossil hominins and other primates.

Bone changes in the lower limbs from participation in an FES rowing exercise program implemented within two years after traumatic spinal cord injury

Objective: To determine the effect of a functional electrical stimulation (FES) rowing program on bone mineral density (BMD) when implemented within two years after SCI.Design: Prospective.Setting: Health Care Facility.Participants: Convenience sample; four adults with recent (<2 years) traumatic, motor complete SCI (C7-T12 AIS A-B).Intervention: A 90-session FES rowing exercise program; participants attended 30-minute FES training sessions approximately three times each week for the duration of their participation.Outcome Measures: BMD in the distal femur and tibia were measured using peripheral Quantitative Computed Tomography (pQCT) at enrollment (T₀) and after 30 (T₁), 60 (T₂), and 90 (T₃) sessions. Bone stimulus was calculated for each rower at each time point using the average number of weekly loading cycles, peak foot reaction force, and bone mineral content from the previous time point. A regression analysis was used to determine the relationship between calculated bone stimulus and change in femoral trabecular BMD between time points.Results: Trabecular BMD in the femur and tibia decreased for all participants in T_0-1, but the rate of loss slowed or reversed between T_1-2, with little-to-no bone loss for most participants during T_2-3. The calculated bone stimulus was significantly correlated with change in femoral trabecular BMD (P = 0.016; R²= 0.458).Conclusion: Consistent participation in an FES rowing program provides sufficient forces and loading cycles to reduce or reverse expected bone loss at the distal femur and tibia, at least temporarily, in some individuals within two years after SCI.Trial Registration: NCT02008149.

Trabecular bone patterning in the hominoid distal femur

BACKGROUND

In addition to external bone shape and cortical bone thickness and distribution, the distribution and orientation of internal trabecular bone across individuals and species has yielded important functional information on how bone adapts in response to load. In particular, trabecular bone analysis has played a key role in studies of human and nonhuman primate locomotion and has shown that species with different locomotor repertoires display distinct trabecular architecture in various regions of the skeleton. In this study, we analyse trabecular structure throughout the distal femur of extant hominoids and test for differences due to locomotor loading regime.

METHODS

Micro-computed tomography scans of Homo sapiens (n = 11), Pan troglodytes (n = 18), Gorilla gorilla (n = 14) and Pongo sp. (n = 7) were used to investigate trabecular structure throughout the distal epiphysis of the femur. We predicted that bone volume fraction (BV/TV) in the medial and lateral condyles in Homo would be distally concentrated and more anisotropic due to a habitual extended knee posture at the point of peak ground reaction force during bipedal locomotion, whereas great apes would show more posteriorly concentrated BV/TV and greater isotropy due to a flexed knee posture and more variable hindlimb use during locomotion.

RESULTS

Results indicate some significant differences between taxa, with the most prominent being higher BV/TV in the posterosuperior region of the condyles in Pan and higher BV/TV and anisotropy in the posteroinferior region in Homo. Furthermore, trabecular number, spacing and thickness differ significantly, mainly separating Gorilla from the other apes.

DISCUSSION

The trabecular architecture of the distal femur holds a functional signal linked to habitual behaviour; however, there was more similarity across taxa and greater intraspecific variability than expected. Specifically, there was a large degree of overlap in trabecular structure across the sample, and Homo was not as distinct as predicted. Nonetheless, this study offers a comparative sample of trabecular structure in the hominoid distal femur and can contribute to future studies of locomotion in extinct taxa.

Cementless unicompartmental knee replacement allows early return to normal activity

Background

Physical activity and regular participation in recreational sports gain importance in patients’ lifestyle after knee arthroplasty. Cementless unicompartimental Knee replacement with the Oxford System has been introduced into clinical routine. Currently there is no data reporting on the physical activity, return to sports rate and quality of live after medial cementless Oxford Unicompartimental Knee Replacement (OUKR).

Methods

This retrospective cohort study reports on the functional outcome of the first 27 consecutive patients (30 knees) that were consecutively treated with a cementless medial OUKR between 2007 and 2009 in our hospital. Physical activity and quality of life were measured using the Tegner-Score, the UCLA-Activity Score, the Schulthess Clinical Activity Questionnaire and the SF-36 Score. The patients’ satisfaction with the outcome was measured using a visual analogue scale.

Results

Mean age at surgery was 62.5 years. Patients showed a rapid recovery with 17 out of 27 patients returning to sports within 3 months, 24 within 6 months after surgery. The Return-to-activity-rate was 100%. 10 out of 27 patients showed a high activity level (UCLA ≥7 points) with a mean postoperative UCLA-Score of 6.1 points.

Conclusions

Patients recover rapidly after cementless OUKR with a return to sports rate of 100% and patients are able to participate in high impact sports disciplines.

Biomechanical Factors in the Adaptations of Insect Tibia Cuticle

Insects are among the most diverse groups of animals on Earth. Their cuticle exoskeletons vary greatly in terms of size and shape, and are subjected to different applied forces during daily activities. We investigated the biomechanics of the tibiae of three different insect species: the desert locust (Schistocerca gregaria), American cockroach (Periplaneta americana) and Death's Head cockroach (Blaberus discoidalis). In a previous work, we showed that these tibiae vary not only in geometry (length, radius and thickness) but also in material quality (Young's modulus) and in the applied stress required to cause failure when loaded in bending. In the present work we used kinematic data from the literature to estimate the forces and stresses arising in vivo for various different activities, and thus calculated factors of safety defined as the ratio between the failure stress and the in vivo stress, adjusting the failure stress to a lower value to allow for fatigue failure in the case of frequently repeated activities. Factors of safety were found to vary considerably, being as little as 1.7 for the most strenuous activities, such as jumping or escaping from tight spaces. Our results show that these limbs have evolved to the point where they are close to optimal, and that instantaneous failure during high-stress activities is more critical than long-term fatigue failure. This work contributes to the discussion on how form and material properties have evolved in response to the mechanical functions of the same body part in different insects.

THE MANDIBLE REMODELING INDUCED BY DENTAL IMPLANTS: A MESHLESS APPROACH

This work aims to evaluate the prediction efficiency of a recently developed numerical approach in the mandible bone tissue remodeling process. The remodeling algorithm, seeking the minimization of the strain energy density, includes a phenomenological anisotropic material law capable of predicting the bone tissue mechanical properties based on the bone apparent density. The key factor of the proposed numerical approach is the inclusion of a flexible and efficient meshless method, which is used to obtain the strain energy density field. The inclusion of this advance discretization technique in the process is an asset since meshless methods produce smoother and more accurate strain energy density fields when compared with other numerical approaches. The bone tissue remodeling process of the molar region of the mandible, due to the inclusion of an implant system, is studied. The obtained results are in accordance with other numerical approach results available in the literature.

The effect of rowing ergometry and resistive exercise on skeletal muscle structure and function during bed rest

Exposure to microgravity causes functional and structural impairment of skeletal muscle. Current exercise regimens are time-consuming and insufficiently effective; an integrated countermeasure is needed that addresses musculoskeletal along with cardiovascular health. High-intensity, short-duration rowing ergometry and supplemental resistive strength exercise may achieve these goals. Twenty-seven healthy volunteers completed 5 wk of head-down-tilt bed rest (HDBR): 18 were randomized to exercise, 9 remained sedentary. Exercise consisted of rowing ergometry 6 days/wk, including interval training, and supplemental strength training 2 days/wk. Measurements before and after HDBR and following reambulation included assessment of strength, skeletal muscle volume (MRI), and muscle metabolism (magnetic resonance spectroscopy); quadriceps muscle biopsies were obtained to assess muscle fiber types, capillarization, and oxidative capacity. Sedentary bed rest (BR) led to decreased muscle volume (quadriceps: -9 ± 4%, P < 0.001; plantar flexors: -19 ± 6%, P < 0.001). Exercise (ExBR) reduced atrophy in the quadriceps (-5 ± 4%, interaction P = 0.018) and calf muscle, although to a lesser degree (-14 ± 6%, interaction P = 0.076). Knee extensor and plantar flexor strength was impaired by BR (-14 ± 15%, P = 0.014 and -22 ± 7%, P = 0.001) but preserved by ExBR (-4 ± 13%, P = 0.238 and +13 ± 28%, P = 0.011). Metabolic capacity, as assessed by maximal O2 consumption, (31)P-MRS, and oxidative chain enzyme activity, was impaired in BR but stable or improved in ExBR. Reambulation reversed the negative impact of BR. High-intensity, short-duration rowing and supplemental strength training effectively preserved skeletal muscle function and structure while partially preventing atrophy in key antigravity muscles. Due to its integrated cardiovascular benefits, rowing ergometry could be a primary component of exercise prescriptions for astronauts or patients suffering from severe deconditioning.

Beneficial association of serum ghrelin and peptide YY with bone mineral density in the Newfoundland population

BACKGROUND

Ghrelin and peptide YY (PYY) are appetite regulating hormones secreted from the gastrointestinal tract (gut). Aside from their known effect on energy homeostasis, accumulating data indicates that these gut hormones also affect bone metabolism. However, data regarding the influence of ghrelin and PYY on bone density in humans is very limited, and the results are inconclusive. Therefore, this study was designed to investigate the potential association between circulating ghrelin and PYY with bone density indices in the general population.

METHODS

A total of 2257 adult subjects from the CODING (Complex Diseases in the Newfoundland Population: Environment and Genetics) study participated in this investigation. Acylated ghrelin and total PYY were measured in serum after a 12-hour fasting, with the Enzyme- Linked Immunosorbent Assay (ELISA) method. Bone mineral density was measured by dual-energy X-ray absorptiometry at the spine, femoral neck, and total hip. Multiple regression analyses adjusting for age, BMI, physical activity, smoking, and alcohol consumption were employed to analyze the association between serum ghrelin and PYY with bone mineral density parameters.

RESULTS

Significant positive associations of ghrelin concentration with L2-L4 BMD, L2-L4 Z-score, femoral neck BMD, femoral neck Z-score, total hip BMD, and total hip Z-score were found in women. No significant correlations between ghrelin and bone density indices were present in men. After dividing the female group into pre-menopausal and post-menopausal, ghrelin was positively correlated with femoral neck Z-score, and total hip Z-score in pre-menopausal women and L2-L4 BMD, and Z-score in post-menopausal group. Moreover, no significant association was discovered between serum PYY and bone density at any site.

CONCLUSION

Our results suggest a beneficial association of circulating ghrelin concentration with bone density in women at the population level. This association is independent of major confounding factors including BMI, physical activity, age, alcohol consumption, and smoking. Effect of menopause on this association seemed to be site specific. However, PYY does not seem to be associated with bone density parameters.

A comparison of proximal humeral cancellous bone of great apes and humans

The shoulder is the most mobile joint in the primate body, and is involved in both locomotor and manipulative activities. The presumed functional sensibility of trabecular bone can offer a way of decoding the activities to which the forelimbs of fossil primates were subjected. We examine the proximal humeral trabecular architecture in a relatively closely related group of similarly sized hominids (Pongo pygmaeus, Pan troglodytes, and Homo sapiens), in order to evaluate the effect of diverging habitual motion behaviors of the shoulder complex in a coherent phylogenetic group. In order to characterize and compare the humeral trabecular architectures of the three species, we imaged a large sample by high-resolution computed tomography (HrCT) and quantified their trabecular architectures by standard bone 3D morphometric parameters. Univariate statistical analysis was performed, showing significant differences among the species. However, univariate statistics could not highlight the structural particularity in the cancellous bone of each species. A principal component analysis also showed clear separation of the three taxa and enabled a structural characterization of the humeral trabecular bone of each species. We conclude that the differences in the architectural setup of the three hominids likely reflect multiple differences in their habitual activity patterns of their shoulder joint, although individual structural features are difficult to relate to specific loading conditions.

Maintaining femoral bone density in adults: how many steps per day are enough?

The amount and intensity of walking to maintain a healthy skeleton is unknown. This study examined the relationship between habitual walking activity and femoral bone mineral density (BMD) in healthy individuals using a quantitative theory for bone maintenance. Our results suggest a gender, weight, and speed sensitivity of walking interventions.

INTRODUCTION

Walking has been extensively promoted for the prevention of osteoporosis. The amount and intensity of walking to maintain a healthy skeleton is unknown and evidence to support a specific target of steps per day is lacking. The goal of our study was to examine the relationship between habitual walking activity and femoral bone mineral density (BMD) in healthy individuals using a quantitative theory for bone maintenance.

METHODS

Habitual walking activity and total femur BMD were measured in 105 individuals (49-64 years). An index of cumulative loading (bone density index, BDI) was examined as a predictor of BMD. The BDI-BMD relationship was used to predict the steps per day to maintain healthy BMD values for a range of body weights (BW) and walking speeds.

RESULTS

For females but not for males, BDI was correlated with BMD (r (2) = 0.19, p < 0.001). The total required steps per day to maintain a T-score of -1.0 for a female with the average BW of the study cohort, walking at 1.00 m/s is 4,892 steps/day. Substantially more steps (18,568 steps/day) are required for a female with a BW 20% lighter than the average for our female cohort. For these lighter females, only at a walking speed greater than 1.32 m/s was 10,000 steps/day sufficient to maintain a T-score of -1.0.

CONCLUSIONS

Our results suggest a gender, weight, and speed sensitivity of walking interventions for osteoporosis. In persons of low BW, the necessary steps per day to maintain BMD can be substantially greater than the often-quoted 10,000 steps.

Numerical model of bone remodeling sensitive to loading frequency through a poroelastic behavior and internal fluid movements

In this article, a phenomenological numerical model of bone remodeling is proposed. This model is based on the poroelasticity theory in order to take into account the effects of fluid movements in bone adaptation. Moreover, the proposed remodeling law is based on the classical 'Stanford' law, enriched in order to take into account the loading frequency, through fluid movements. This coupling is materialized by a quadratic function of Darcy velocity. The numerical model is carried out, using a finite element method, and calibrated using experimental results at macroscopic level, from the literature. First results concern cyclic loadings on a mouse ulna, at different frequencies between 1 Hz and 30 Hz, for a force amplitude of 1.5 N and 2 N. Experimental results exhibit a sensitivity to the loading frequency, with privileged frequency for bone remodeling between 5 Hz and 10 Hz, for the force amplitude of 2 N. For the force amplitude of 1.5 N, no privileged frequencies for bone remodeling are highlighted. This tendency is reproduced by the proposed numerical computations. The model is identified on a single case (one frequency and one force amplitude) and validated on the other ones. The second experimental validation deals with a different loading regime, an internal fluid pressure at 20 Hz on a turkey ulna. The same framework is applied, and the numerical and experimental data are still matching in terms of gain in bone mass density.

Mechanical, biochemical and morphometric alterations in the femur of mdx mice

The bone tissue abnormalities observed in patients with Duchenne muscular dystrophy are frequently attributed to muscle weakness. In this condition, bones receive fewer mechanical stimuli, compromising the process of bone modeling. In the present study we hypothesize that other factors inherent to the disease might be associated with bone tissue impairment, irrespective of the presence of muscle impairment. Mdx mice lack dystrophin and present cycles of muscle degeneration/regeneration that become more intense in the third week of life. As observed in humans with muscular dystrophy, bone tissue abnormalities were found in mdx mice during more intense muscle degeneration due to age. Under these circumstances, muscle deficit is probably one of the factors promoting these changes. To test our hypothesis, we investigated the changes that occur in the femur of mdx mice at 21 days of age when muscle damage is still not significant. The mechanical (structural and material) and biochemical properties and morphometric characteristics of the femur of mdx and control animals were evaluated. The results demonstrated a lower strength, stiffness and energy absorption capacity in mdx femurs. Higher values for structural (load and stiffness) and material (stress, elastic modulus and toughness) properties were observed in the control group. Mdx femurs were shorter and were characterized by a smaller cortical area and thickness and a smaller area of epiphyseal trabecular bone. The hydroxyproline content was similar in the two groups, but there was a significant difference in the Ca/P ratios. Thermogravimetry showed a higher mineral matrix content in cortical bone of control animals. In conclusion, femurs of mdx mice presented impaired mechanical and biochemical properties as well as changes in collagen organization in the extracellular matrix. Thus, mdx mice developed femoral osteopenia even in the absence of significant muscle fiber degeneration. This weakness of the mdx femur is probably due to genetic factors that are directly or indirectly related to dystrophin deficiency.

Foot forces during exercise on the International Space Station

Long-duration exposure to microgravity has been shown to have detrimental effects on the human musculoskeletal system. To date, exercise countermeasures have been the primary approach to maintain bone and muscle mass and they have not been successful. Up until 2008, the three exercise countermeasure devices available on the International Space Station (ISS) were the treadmill with vibration isolation and stabilization (TVIS), the cycle ergometer with vibration isolation and stabilization (CEVIS), and the interim resistance exercise device (iRED). This article examines the available envelope of mechanical loads to the lower extremity that these exercise devices can generate based on direct in-shoe force measurements performed on the ISS. Four male crewmembers who flew on long-duration ISS missions participated in this study. In-shoe forces were recorded during activities designed to elicit maximum loads from the various exercise devices. Data from typical exercise sessions on Earth and on-orbit were also available for comparison. Maximum on-orbit single-leg loads from TVIS were 1.77 body weight (BW) while running at 8mph. The largest single-leg forces during resistance exercise were 0.72 BW during single-leg heel raises and 0.68 BW during double-leg squats. Forces during CEVIS exercise were small, approaching only 0.19 BW at 210W and 95RPM. We conclude that the three exercise devices studied were not able to elicit loads comparable to exercise on Earth, with the exception of CEVIS at its maximal setting. The decrements were, on average, 77% for walking, 75% for running, and 65% for squats when each device was at its maximum setting. Future developments must include an improved harness to apply higher gravity replacement loads during locomotor exercise and the provision of greater resistance exercise capability. The present data set provides a benchmark that will enable future researchers to judge whether or not the new generation of exercise countermeasures recently added to the ISS will address the need for greater loading.

Bone mineral density and bone turnover in male masters athletes aged 40-64

We evaluated areal bone mineral density (aBMD), bone mineral content (BMC), and markers of bone turnover in male competitive masters athletes representing different training profile in the past and at present, aged 40-64 (14 endurance runners, and 12 speed-power athletes), and non-sport controls (n = 13). Dual-energy X-ray absorptiometry measurements of total body and regional aBMD, BMC and soft tissue composition were acquired. Serum concentrations of osteocalcin (OC), C-terminal crosslinking telopeptide of type I collagen (CTX), tumour necrosis factor-alpha (TNF-alpha), total testosterone (TT), free testosterone (FT) and insulin like growth factor-1 (IGF-1) were measured. Adjusted total and regional aBMD and BMC (covariates: body mass, body height and age) were significantly greater in all measured regions in speed-power athletes than in endurance athletes and control subjects, but adjusted aBMD and BMC values were not significantly different between endurance athletes and controls. No differences in bone formation (OC), bone resorption (CTX), and serum concentrations of TNF-alpha, TT, FT and IGF-1 were noted. This suggests that weight-bearing exercise in young age and the training continuation in later life may be an important contributor to the aBMD and BMC in the middle age and in the elderly. It seems also that training-related bone differences in men are not caused by present alterations in bone turn-over or somatotropic effects. However, conclusions must be drawn with caution due to a large variability of biochemical markers.

Direction-specific diaphyseal geometry and mineral mass distribution of tibia and fibula: a pQCT study of female athletes representing different exercise loading types

Bones adapt to prevalent loading, which comprises mainly forces caused by muscle contractions. Therefore, we hypothesized that similar associations would be observed between neuromuscular performance and rigidity of bones located in the same body segment. These associations were assessed among 221 premenopausal women representing athletes in high-impact, odd-impact, high-magnitude, repetitive low-impact, and repetitive nonimpact sports and physically active referents aged 17-40 years. The whole group mean age and body mass were 23 (5) and 63 (9) kg, respectively. Bone cross sections at the tibial and fibular mid-diaphysis were assessed with peripheral quantitative computed tomography (pQCT). Density-weighted polar section modulus (SSI) and minimal and maximal cross-sectional moments of inertia (Imin, Imax) were analyzed. Bone morphology was described as the Imax/Imin ratio. Neuromuscular performance was assessed by maximal power during countermovement jump (CMJ). Tibial SSI was 31% higher in the high-impact, 19% in the odd-impact, and 30% in the repetitive low-impact groups compared with the reference group (P < 0.005). Only the high-impact group differed from the referents in fibular SSI (17%, P < 0.005). Tibial morphology differed between groups (P = 0.001), but fibular morphology did not (P = 0.247). The bone-by-group interaction was highly significant (P < 0.001). After controlling for height, weight, and age, the CMJ peak power correlated moderately with tibial SSI (r = 0.31, P < 0.001) but not with fibular SSI (r = 0.069, P = 0.313). In conclusion, observed differences in the association between neuromuscular performance and tibial and fibular traits suggest that the tibia and fibula experience different loading environments despite their anatomical vicinity.

Neuromuscular performance and body mass as indices of bone loading in premenopausal and postmenopausal women

The strong association between body mass and skeletal robusticity has been attributed to increasing skeletal loading with increasing mass. However, it is unclear whether body mass is merely a coarse substitute for bone loading rather than a true independent predictor of bone strength. As indices of neuromuscular performance, impulse and peak power were determined from vertical ground reaction force during a maximal counter movement jump test in 221 premenopausal and 82 postmenopausal women. Bone compressive (BSI(d) g(2)/cm(4)) and bending (SSImax(mid) mm(3)) strength indices were measured with peripheral quantitative computed tomography (pQCT) at the distal ((d)) and midshaft ((mid)) sites of the tibia. A two-step forced regression model for predicting bone strength indices was constructed. Age, height and body mass were entered first, followed by impulse as an indicator of skeletal loading. The basic model explained 14% (P<0.001) of the variance in BSI(d) in the premenopausal group and 16% (P=0.004) in the postmenopausal group, and 32% (P<0.001) and 25% (P<0.001) of the variance in SSImax(nud) respectively. Entering impulse into the model increased the explanatory power by 9% (P<0.001) and 7% (P<0.001) for BSI(d) and by 8% (P<0.001) and 12% (P<0.001) for SSImax(mid). Furthermore, impulse replaced body mass as an independent significant factor explaining the variance in bone strength. These results indicate that neuromuscular performance should be measured and preferred over body mass in models predicting skeletal robusticity.

Elastomeric high-mineral content hydrogel-hydroxyapatite composites for orthopedic applications

The design of synthetic bone grafts that mimic the structure and composition of bone and possess good surgical handling characteristics remains a major challenge. We report the development of poly(2-hydroxyethyl methacrylate) (pHEMA)-hydroxyapatite (HA) composites termed "FlexBone" that possess osteoconductive mineral content approximating that of human bone yet exhibit elastomeric properties enabling the press-fitting into a defect site. The approach involves crosslinking pHEMA hydrogel in the presence of HA using viscous ethylene glycol as a solvent. The composites exhibit excellent structural integration between the apatite mineral component and the hydroxylated hydrogel matrix. The stiffness of the composite and the ability to withstand compressive stress correlate with the microstructure and content of the mineral component. The incorporation of porous aggregates of HA nanocrystals rather than compact micrometer-sized calcined HA effectively improved the resistance of the composite to crack propagation under compression. Freeze-dried FlexBone containing 50 wt % porous HA nanocrystals could withstand hundreds-of-megapascals compressive stress and >80% compressive strain without exhibiting brittle fractures. Upon equilibration with water, FlexBone retained good structural integration and withstood repetitive moderate (megapascals) compressive stress at body temperature. When subcutaneously implanted in rats, FlexBone supported osteoblastic differentiation of the bone marrow stromal cells pre-seeded on FlexBone. Taken together, the combination of high osteoconductive mineral content, excellent organic-inorganic structural integration, elasticity, and the ability to support osteoblastic differentiation in vivo makes FlexBone a promising candidate for orthopedic applications.

Predicting the structural integrity of bone defects repaired using bone graft materials

Bone defects create stress concentrations which can cause fracture under impact or cyclic loading. Defects are often repaired by filling them with a bone graft material; this will reduce the stress concentration, but not completely, because these materials have lower stiffness than bone. The fracture risk decreases over time as the graft material is replaced by living bone. Many new bone graft materials are being developed, using tissue engineering and other techniques, but currently there is no rational way to compare these materials and predict their effectiveness in repairing a given defect. This paper describes, for the first time, a theoretical model which can be used to predict failure by brittle fracture or fatigue, initiating at the defect. Preliminary results are presented, concentrating on the prediction of stress fracture during the crucial post-operative period. It is shown that the likelihood of fracture is strongly influenced by the shape of the defect as well as its size, and also by the level of post-operative exercise. The most important finding is that bone graft materials can be successful in preventing fracture even when their mechanical properties are greatly inferior to those of bone. Future uses of this technique include pre-clinical assessment of bone replacement materials and pre-operative planning in orthopaedic surgery.

A mathematical approach to bone tissue engineering

Tissue engineering is becoming consolidated in the biomedical field as one of the most promising strategies in tissue repair and regenerative medicine. Within this discipline, bone tissue engineering involves the use of cell-loaded porous biomaterials, i.e. bioscaffolds, to promote bone tissue regeneration in bone defects or diseases such as osteoporosis, although it has not yet been incorporated into daily clinical practice. The overall success of a particular bone tissue engineering application depends strongly on scaffold design parameters, which do away with long and expensive clinical protocols. Computer simulation is a useful tool that may reduce animal experiments and help to identify optimal patient-specific designs after concise model validation. In this paper, we present a novel mathematical approach to bone regeneration within scaffolds, based on a multiscale framework. Results are presented over an actual scaffold microstructure, showing the potential of computer simulation, and how it can aid in the task of making bone tissue engineering a reality in clinical practice.

The Use of External Transducers for Estimating Bone Strain at the Distal Tibia During Impact Activity

Noninvasive methods for monitoring the in vivo loading environment of human bone are needed to determine osteogenic loading patterns that reduce the potential for bone injury. The purpose of this study was to determine whether the vertical ground reaction impact force (impact force) and leg acceleration could be used to estimate internal bone strain at the distal tibia during impact activity. Impact loading was delivered to the heels of human-cadaveric lower extremities. The effects of impact mass and contact velocity on peak bone strain, impact force, leg acceleration, and computed impact force (leg acceleration∗impact mass) were investigated. Regression analysis was used to predict bone strain from six different models. Apart from leg acceleration, all variables responded to impact loading similarly. Increasing impact mass resulted in increased bone strain, impact force, and computed impact force, but decreased leg acceleration. The best models for bone strain prediction included impact force and tibial cross-sectional area (R2=0.94), computed impact force and tibial cross-sectional area (R2=0.84), and leg acceleration and tibial cross-sectional area (R2=0.73). Results demonstrate that when attempting to estimate bone strain from external transducers some measure of bone strength must be considered. Although it is not recommended that the prediction equations developed in this study be used to predict bone strain in vivo, the strong relationship between bone strain, impact force, and computed impact force suggested that force platforms and leg accelerometers can be used for a surrogate measure of bone strain.