Bone and aging: Effects on the maxillofacial skeleton

Buccal Mesenchymal Stromal Cells as a Source of Osseointegration of Titanium Implants

We studied the interaction of human buccal mesenchymal stem cells (MSCs) and osteoblasts differentiated from them with the surface of titanium samples. MSCs were isolated by enzymatic method from buccal fat pads. The obtained cell culture was presented by MSCs, which was confirmed by flow cytometry and differentiation into adipocytes and osteoblasts. Culturing of buccal MSCs on titanium samples was accompanied by an increase in the number of cells for 15 days and the formation of a developed network of F-actin fibers in the cells. The viability of buccal MSCs decreased by 8 days, but was restored by 15 days. Culturing of osteoblasts obtained as a result of buccal MSC differentiation on the surface of titanium samples was accompanied by a decrease in their viability and proliferation. Thus, MSCs from buccal fat pads can be used to coat implants to improve osseointegration during bone reconstruction in craniofacial surgery and dentistry. To improve the integration of osteoblasts, modification of the surface of titanium samples is required.

Insight into age-related changes of the human facial skeleton based on medieval European osteological collection

Aging changes in the facial skeleton are concentrated mostly in orbits, maxilla and mandible. The aim of this study was to analyze metric traits of the adult viscerocranium in a medieval sample from Cedynia (Poland, Central Europe) and confront the results with literature data for modern populations. It was assumed that diet-related greater biomechanical forces generated during mastication in medieval versus modern times led to slower rate of bone resorption with age. 3D models of the facial skeleton are created for 230 individuals, categorized into young, middle and old adults, and a subgroup of edentulous middle adults is distinguished. Orbits, piriform aperture, maxilla and mandible are measured using Geomagic Studio 12 and analyzed among age categories as well as dentate and edentulous subgroups. The values of the orbital and piriform aperture measurements tend to increase with age and reached statistical significance in males (right orbit height, left orbit width, piriform aperture surface area). In females, maxillary height significantly decrease at right first premolar and first molar, together with height of the right mandibular ramus. In edentulous individuals of both sexes the orbits are wider, and maxillary and mandibular heights are lower than in dentate individuals. This study reveals similar character and direction of the aging process of the facial skeleton in medieval and modern adults, however slower rate of resorptive changes is found in the former sample, which suggests, that diet-related biomechanical forces can influence intensification of the aging processes in the facial skeleton.

Is alveolar ridge preservation an overtreatment?

The morphology and dimensions of the postextraction alveolar ridge are important for the surgical and restorative phases of implant treatment. Adequate new bone formation and preservation of alveolar ridge dimensions following extraction will facilitate installation of the implant in a restorative position, while preservation of soft tissue contour and volume is essential for an aesthetic and implant-supported restoration with healthy peri-implant tissues. Alveolar ridge preservation (ARP) refers to any procedure that aims to: (i) limit dimensional changes in the alveolar ridge after extraction facilitating implant placement without additional extensive bone and soft tissue augmentation procedures (ii) promote new bone formation in the healing alveolus, and (iii) promote soft tissue healing at the entrance of the alveolus and preserve the alveolar ridge contour. Although ARP is a clinically validated and safe approach, in certain clinical scenarios, the additional clinical benefit of ARP over unassisted socket healing has been debated and it appears that for some clinicians may represent an overtreatment. The aim of this critical review was to discuss the evidence pertaining to the four key objectives of ARP and to determine where ARP can lead to favorable outcomes when compared to unassisted socket healing.

Pathophysiology of Medication-Related Osteonecrosis of the Jaw-A Minireview

Medication-related osteonecrosis of the jaw (MRONJ) is a rare but serious adverse effect of antiresorptive medications administered for control of osseous malignancy, osteoporosis, or other bone metabolic diseases. Despite being reported in the literature two decades ago, MRONJ etiology, pathophysiology, and progression remain largely unknown, and current nonoperative or operative treatment strategies are mostly empirical. Several hypotheses that attempt to explain the mechanisms of MRONJ pathogenesis have been proposed. However, none of these hypotheses alone is able to capture the complex mechanistic underpinnings of the disease. In this minireview, we aim to highlight key findings from clinical and translational studies and propose a unifying model for the pathogenesis and progression of MRONJ. We also identify aspects of the disease process that require further investigation and suggest areas for future research efforts toward calibrating methodologic approaches and validating experimental findings. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Early Pixel Value Ratios to Assess Bone Healing During Distraction Osteogenesis

Background: Distraction osteogenesis (DO) is an approach for bone lengthening and reconstruction. The pixel value ratio (PVR), an indicator calculated from X-ray images, is reported to assess the final timing for the external fixator removal. However, the early PVR and its potential influencing factors and the relationship between the early PVR and clinical outcomes are rarely discussed. Therefore, this study was employed to address these issues.

Methods: A total of 125 patients with bone lengthening were investigated retrospectively. The early PVR of regenerated bone was monitored in the first 3 months after osteotomy. The potential effect of sex, chronological age, BMI, lengthening site, and involvement of internal fixation during the consolidation period was analyzed. Moreover, the associations of the healing index (HI) and lengthening index (LI) with early PVR were also investigated.

Results: The early PVRs were 0.78 ± 0.10, 0.87 ± 0.06, and 0.93 ± 0.06 in the first 3 months after osteotomy, respectively. Moreover, the PVR in juvenile was significantly higher than that in adults in the first 3 months after osteotomy (0.80 ± 0.09 vs. 0.74 ± 0.10; p = 0.008), (0.89 ± 0.06 vs. 0.83 ± 0.06; p = 0.018), and (0.94 ± 0.05 vs. 0.87 ± 0.05; p = 0.003). In addition, the PVR in males was significantly higher than that in females in the first month after osteotomy (0.80 ± 0.09 vs. 0.76 ± 0.10; p = 0.015), and the PVR in femur site was significantly higher than that in the tibia site in the second and third months after osteotomy (0.88 ± 0.07 vs. 0.87 ± 0.06; p = 0.015) and (0.93 ± 0.06 vs. 0.92 ± 0.06, p = 0.037). However, the BMI and involvement of the internal fixator during the consolidation period seem to not influence the early PVR of regenerated callus during DO. Interestingly, the early PVR seems to be moderately inversely associated with HI (mean = 44.98 ± 49.44, r = -0.211, and p = 0.029) and LI (mean = 0.78 ± 0.77, r = -0.210, and p = 0.029), respectively.

Conclusion: The early PVR is gradually increasing in the first 3 months after osteotomy, which may be significantly influenced by chronological age, sex, and the lengthening site. Moreover, the early PVR of callus may reflect the potential clinical outcome for DO. Our results may be beneficial to the clinical management of the subjects with bone lengthening.

GHRH expression plasmid improves osteoporosis and skin damage in aged mice

The hormone secretion of GHRH-GH-IGF-1 axis in animals was decreased as aging. These hormones play an important role in maintaining bone mass and bone structure, and also affect the normal structure and function of the skin. We used plasmid-based technology to deliver growth hormone releasing hormone (GHRH) to elderly mice. In the current study, 80 and 120 μg/kg pVAX-GHRH plasmid expression plasmid were injected into old mice, the serum GHRH and insulin-like growth factor-1(IGF-1) content were increased within three weeks (P < 0.05). In the groups of 80 and 120 μg/kg plasmid, the content of procollagen type I N-terminal pro-peptide (PINP) in the serum was increased(P < 0.05), and the content of C-terminal telopeptides of type I collagen (CTX-1) in the serum was reduced significantly (P < 0.05). Furthermore, the expression of osteoprotegerin (OPG) and osteocalcin (OCN) in the femur also was increased(P < 0.05). The bone mineral density(BMD)、trabecular bone volume (BV/TV) and trabecular number(Tb.N) of mouse femur were increased significantly (P < 0.05) and trabecular separation(Tb.Sp) was decreased(P < 0.05). There were more trabecular bones in the bone marrow cavity and the trabecular bones are thicker in the groups of 80 and 120 μg/kg plasmid relative to control. The superoxide dismutase (SOD) content in the skin was increased(P < 0.05), and the malondialdehyde (MDA) content was reduced significantly (P < 0.05). Meanwhile, the skin moisture content also increased significantly(P < 0.05). Moreover, the expression of matrix metalloproteinase 3(MMP3) and matrix metalloproteinase 9(MMP9) was decreased in the skin(P < 0.05). The thickness of the dermis and epidermis of the skin had increased significantly(P < 0.05). Skin structure is more dense and complete in the two groups. These results indicate that 80 and 120 μg/kg plasmid-mediated GHRH supplementation can improve osteoporosis and skin aging in aged mice.

Individualized tDCS modeling predicts functional connectivity changes within the working memory network in older adults

BACKGROUND

Working memory decline has been associated with normal aging. The frontal brain structure responsible for this decline is primarily located in the prefrontal cortex (PFC). Our previous neuroimaging study demonstrated a significant change in functional connectivity between the left dorsolateral PFC (DLPFC) and left ventrolateral PFC (VLPFC) when applying 2 mA tDCS in MRI scanner during an N-Back task. These regions were part of the working memory network. The present study is the first study that utilizes individualized finite element models derived from older adults' MRI to predict significant changes of functional connectivity observed from an acute tDCS application.

METHODS

Individualized head models from 15 healthy older adults (mean age = 71.3 years) were constructed to create current density maps. Each head model was segmented into 11 tissue types: white matter, gray matter, CSF, muscle, blood vessels, fat, eyes, air, skin, cancellous, and cortical bone. Electrodes were segmented from T1-weighted images and added to the models. Computed median and maximum current density values in the left DLPFC and left VLPFC regions of interest (ROIs) were correlated with beta values as functional connectivity metrics measured in different timepoint (baseline, during stimulation) and stimulation condition (active and sham).

MAIN RESULTS

Positive significant correlations (R2 = 0.523 for max J, R2 = 0.367 for median J, p < 0.05) were found between the beta values and computed current densities in the left DLPFC ROIs for active stimulation, but no significant correlation was found during sham stimulation. We found no significant correlation between connectivity and current densities computed in the left VLPFC for both active and sham stimulation.

CONCLUSIONS

The amount of current within the left DLPFC ROIs was found positively correlated with changes in functional connectivity between left DLPFC and left VLPFC during active 2 mA stimulation. Future work may include expansion of number of participants to further test the accuracy of tDCS models used to predict tDCS-induced functional connectivity changes within the working memory network.

Stepping into Trouble: Craniomaxillofacial Trauma in the Geriatric Population From Stairway Falls

PURPOSE

The purpose of this study is to determine what potential factors are associated with increased risk of hospital admission among the geriatric population who suffer stairway falls.

MATERIALS AND METHODS

This is a 10-year cross-sectional study that was conducted using the National Electronic Injury Surveillance System (NEISS). Entries whose primary product was categorized under the code 1239 (stairs or steps) were included in this study. Reports were excluded if the injury did not occur within the craniomaxillofacial region. The principal outcome variable was admission rate. Patient and injury characteristics were compared using χ2 and independent sample t tests.

RESULTS

Admission rates were significantly associated with sex (P < .01), age group (P < .01), race (P < .05), craniomaxillofacial region (P < .01), and primary diagnosis (P < .01). Relative to the females, males (OR, 1.458; P < .01) were independently associated with an increased odds of admission. Relative to patients aged 65 to 69 years old, patients aged 70 to 79 (OR, 1.247; P < .01), 80 to 89 (OR, 1.438; P < .01), and 90 & over (OR, 1.569; P < .01) were each independently associated with an increased odds of admission. Relative to white patients, black patients (OR, 1.238; P < .01) were each independently associated with an increased odds of admission. Relative to mouth injuries, eyeball injuries (OR, 4.574; P < .01) and head injuries (OR, 4.105; P < .01) were independent risk factors for admission. Relative to abrasions, fractures (OR, 6.013; P < .01) and internal organ injuries (OR, 4.814; P < .01) were each independently associated with an increased odds of admission.

CONCLUSIONS

Age, gender, craniomaxillofacial region, type of injury, and primary diagnosis are all independent risk factors for hospital admissions. Preventative measures need to be taken to safeguard the older geriatric population from craniomaxillofacial trauma associated with stairway falls.

Geriatric Rheumatology: The Need for a Separate Subspecialty in the Near Future

Rheumatology is a broad specialty in itself, and it involves caring for patients of all age groups. Patients of different age groups have different characteristics and a one-size-fits-all approach is not feasible in catering to their diverse medical needs. The presentation and the manifestations of diseases vary in different age groups. We have pediatric rheumatology as a separate subspecialty where pediatric patients with rheumatological diseases are provided specific care best suited to their needs. However, for older patients, such a separate subspecialty is not widely available in medical practice. Geriatric rheumatology or gerontorheumatology is a branch of rheumatology dealing with older patients with rheumatological diseases. It is high time to consider establishing geriatric rheumatology as a separate subspecialty to provide better care for older patients.

Osteocyte numbers decrease only in postcranial but not in cranial bones in humans of advanced age

BACKGROUND

Bone ageing is governed by the linked activities of short-lived osteoblasts and osteoclasts in conjunction with long-lived osteocytes present in osseous structure. Besides their maintenance function, osteogenic cells also gain specific positional information, which may potentially trigger ageing-associated cellular deviations in terminally differentiated osteocytes differently in cranial versus postcranial tissues.

METHODS

We therefore investigated bone taken from deceased aged humans explanted at five distinct anatomical positions throughout the body and assessed physical and biological determinants applying radiologic and histologic measures.

RESULTS

We were able to show that significantly more osteocytes reside in aged cortical bone at cranial positions than within axial or limb skeleton. These cellular states and conditions were not found in the corresponding trabecular bone, where osteocyte numbers remain also high at postcranial positions. Parallel comparative analyses of bone microstructure as analyzed by means of computer tomography showed no significant differences.

CONCLUSIONS

Considering differences and commonalities regarding the bone samples, such as loading, mechanisms of ossification or the surrounding stromal cell compartment, our findings indicate that positional information laid down during ontogenetic processes is instructive during the entire life thus potentially also moulding spatial-specific mechanistic distinctions of bone ageing.

Frontal sinus ontogeny and covariation with bone structures in a modern human population

In humans, the frontal sinus (FS) is located in the medial part of the supraorbital region, sometimes expanded throughout the frontal squama. It exhibits high morphological variability, but its general form appears to be constrained by surrounding structures. The goal of this study is to analyze FS growth and test for covariation between FS volume and the glabellar region, upper nasal region, bone thickness and endocranial size in a human sample from Argentina. The sample comprises 149 reconstructions derived from computed tomography images of individuals aged 0-31 years. Volume of the FS and measurements of the surrounding structures were recorded. The FS growth trajectory was assessed by parametric and nonparametric methods, and covariation was determined using correlations and partial correlations. The FS volume could be measured at an age of about 6 years and older; adults had no aplasia but hyperplasia was found in some cases. Since the most conspicuous characteristic found was variation among individuals, the nonparametric smoothing spline produced very poor fitting. The modified logistic function was the only parametric method providing significant parameters. Sexes differed in the age at which FS growth began and ended, with FS developing earlier but at a slower rate in females than in males. The FS volume did not correlate with either upper nasal width or endocranial volume, but it correlated with bone thickness measurements (mainly from the glabellar region), even when age was held constant. Expansion of the FS at the frontal poles also correlated with frontal bone thickness. Despite the difficulty in modeling and predicting the trajectory and morphology of FS, our results suggest that it is affected by its surrounding bony environment.

Elderly patients with facial trauma: a 10 year review

Abstract Objective: to analyze the epidemiological profile of geriatric patients with facial trauma treated at a Maxillofacial Surgery Department in southern Brazil over a period of 10 years. Methods: a retrospective analysis of the medical records of patients aged over 60 years treated for facial trauma in the period from January 2001 to December 2010 was performed. Result: of a total of 1,385 analyzed medical records of patients with facial trauma, 86 (6.2%) belonged to the group aged 60-89 years. The male gender was the most affected and the age group 60-69 years was the most frequently involved. The middle third was the most affected, and the zygomatic bone was the most commonly fractured. Conclusion: special attention should be given to the 60-69 age group, as while such patients present physiological changes inherent to aging, they remain active in society and exposed to risk factors for facial trauma.

Analysis of the relationships between edentulism, periodontal health, body composition, and bone mineral density in elderly women

Objective

The relationship between bone mineral density (BMD) and tooth loss in conjunction with periodontal disease is not clear. The suggested effects include alteration in bone remodeling rates as well as the multifaceted etiology of edentulism. There is also a question if other body-related variables besides BMD, such as body composition, may be associated with tooth number and general periodontal health. The aim of this study was to evaluate if tooth number and marginal periodontal status are associated with body composition and BMD in a sample of elderly women.

Materials and methods

The study involved 91 postmenopausal women. Data included basic anthropometric characteristics, body composition via bioelectrical impedance analysis, and BMD analysis at the distal end of the radial bone of the nondominant arm via peripheral dual-energy X-ray absorptiometry. A dental examination was performed to assess tooth number, periodontal pocket depth (PD), and gingival bleeding.

Results

In nonosteoporotic women, a significant positive correlation was found between BMD and lean body mass, total body water, and muscle mass. The indicators of bone metabolism correlated negatively with PD. Such relationships did not appear in osteoporotic women. In both groups, basic anthropometric characteristics and body composition were significantly and positively correlated with PD and bleeding on probing.

Conclusion

The results suggest that body composition and BMD are not significantly correlated with tooth number and gingival bleeding.

Maxillofacial Fractures in Women and Men: A 10-Year Retrospective Study

PURPOSE

The purpose of this study was to evaluate and compare the demographic characteristics of maxillofacial fractures between women and men in China.

PATIENTS AND METHODS

The sample was composed of all patients who sustained maxillofacial fractures during a 10-year period (2000 through 2009). Incidences, age distributions, etiologies, fracture patterns, associated injuries, and occupation distributions were recorded and analyzed. Data analysis included the χ(2) test, the Fisher exact test, and the t test. A P value less than .05 was considered significant.

RESULTS

There were 1,131 patients (881 male and 250 female) who sustained maxillofacial fractures, with a male-to-female ratio of 3.5:1. Male patients sustained injuries most frequently during the autumn (P = .048), whereas female patients sustained more maxillofacial injuries during the summer (P = .006). Men sustained motorcycle (P = .023) and assault-related accidents (P = .036) more frequently than women, whereas women were more frequently injured in bicycle-related accidents (P < .001) or falling while at ground level (P = .001) than men. Women presented more frequently with condylar fracture than men (P = .028), whereas men were more prone to symphysis fractures than women (P = .037). For drivers, only men were involved (P = .001). Male workers sustained maxillofacial fractures more frequently than female workers (P < .001). Female children, students, and company staff were more prone to maxillofacial fractures than their male counterparts (P = .010, P = .004, and P = .044 respectively).

CONCLUSIONS

The demographic characteristics of maxillofacial fractures in female patients considerably differ from those in male patients.

Anatomical considerations for implant placements in first maxillary molar extracted sites in East Asian patients

PURPOSE

With the advent of cone-beam computed tomography (CBCT) for maxillofacial imaging, there has been a paradigm shift from two dimensional panoramic radiography to three dimensional imaging. This study investigated the microanatomy of the maxillary permanent first molar socket and its relationship to the floor of the maxillary sinus, especially for immediate or early implant placement.

MATERIALS AND RESULTS

Sixty CBCT scans of 30 Malay and 30 Chinese subjects were selected from over 300 archived images. Ninety-five percent of the subjects had sinus floor extending anterior to the first molar, while 72% had the floor dipping between the roots. Seventy-five percent of the patients had inter-radicular bone and almost 50% had intrusion of root apices into the floor of the maxillary sinus. The dimensions of the socket were as follows: the mean width was 11.42 ± 0.86 mm; the mean length was 7.70 ± 0.56 mm; the mean height on the coronal plane was 6.48 ± 3.77 mm while on the sagittal plane it was 6.85 ± 3.67 mm.

CONCLUSIONS

Any implant length greater than the mean height of the socket (approximately 7 mm) has a fair chance of perforation into the maxillary sinus if placed without any additional adjunct procedures. In addition, 50% of the apices opened into the maxillary sinus, thereby risking the creation of perforations or root displacements into the maxillary sinus during exodontia-mandating CBCT scanning prior to any surgical implant procedures.

Composition and Modifications of Dental Implant Surfaces

Since Brånemark discovered the favorable effects of titanium in bone healing in 1965, titanium has emerged as the gold standard bulk material for present-time dental implantology. In the course of years researchers aimed for improvement of the implants performance in bone even at compromised implant sites and multiple factors were investigated influencing osseointegration. This review summarizes and clarifies the four factors that are currently recognized being relevant to influence the tissue-implant contact ratio: bulk materials and coatings, topography, surface energy, and biofunctionalization. The macrodesigns of bulk materials (e.g., titanium, zirconium, stainless steel, tantalum, and magnesium) provide the mechanical stability and their influence on bone cells can be additionally improved by surface treatment with various materials (calcium phosphates, strontium, bioglasses, diamond-like carbon, and diamond). Surface topography can be modified via different techniques to increase the bone-implant contact, for example, plasma-spraying, grit-blasting, acid-etching, and microarc oxidation. Surface energy (e.g., wettability and polarity) showed a strong effect on cell behavior and cell adhesion. Functionalization with bioactive molecules (via physisorption, covalent binding, or carrier systems) targets enhanced osseointegration. Despite the satisfying clinical results of presently used dental implant materials, further research on innovative implant surfaces is inevitable to pursuit perfection in soft and hard tissue performance.

Traumatology of the facial skeleton in octogenarian patients: a retrospective analysis of 96 cases

AIM

The aim of this retrospective study was to evaluate the frequency and distribution of maxillofacial trauma patients over 80 years, with regard to type and environment of accidents as well as treatment and complications.

PATIENTS AND METHODS

Data for 94 patients (96 cases; aged 80-94 years) with maxillofacial fractures were retrospectively analysed.

RESULTS

Data of 30 male and 64 female patients with an average age of 85 years were analysed. In 90% of the study population, the cause of fractures was a fall, followed by traffic accidents (9%) and assault (1%). Seventy-two patients had fractures of the midface, 10 had factures of the mandible, 9 had fractures of both the midface and mandible and 5 had fractures of the neurocranium and midface. Surgical intervention was required in 57% of the patients. Post-operative complications were: four cases of diplopia, two cases of infected plates, four cases of lower eyelid ectropion and in one case a retrobulbar haematoma.

CONCLUSION

Facial trauma in the elderly can often be treated conservatively unless the patient complains of functional problems. Due to co-morbidities, special attention should be paid to hypertension, anticoagulant agents and the surgical approach.

Vitamin C deficiency accelerates bone loss inducing an increase in PPAR-γ expression in SMP30 knockout mice

Senescence marker protein (SMP) 30 knockout (KO) mice display symptoms of scurvy, including spontaneous bone fractures, and this was considered to be induced by a failure of collagen synthesis owing to vitamin C deficiency. However, low bone mineral density is also known to be associated with spontaneous bone fracture. Therefore, we investigated the effects of vitamin C deficiency on the balance between osteoblasts and osteoclasts in SMP30 KO mice as evidenced by histopathology. All mice were fed a vitamin C-free diet, and only one group (KV) mice were given water containing 1.5 g/l of vitamin C, whereas wild-type (WT) and KO mice were given normal drinking tap water without vitamin C for 16 weeks. After 16 weeks, all femur samples were removed for histopathological examination. The femurs of KO mice showed significantly reduced bone area and decreased number of osteoblasts compared with those of WT mice and KV mice. KO mice also exhibited the lowest level of alkaline phosphatase (ALP) expression in their femurs. However, KO mice showed the most elevated expression of the receptor activator of nuclear factor kappa-B ligand (RANKL). Moreover, KO mice had the strongest peroxisome proliferator-activated receptor (PPAR)-γ expression level in their osteoblasts and the highest number of TUNEL-positive bone marrow cells. Therefore, we concluded that vitamin C deficiency plays an important role in spontaneous bone fracture by inhibiting osteoblast differentiation and promoting transition of osteoblasts to adipocytes, and this could in turn be related to the increased PPAR-γ expression.

The design and use of animal models for translational research in bone tissue engineering and regenerative medicine

This review provides an overview of animal models for the evaluation, comparison, and systematic optimization of tissue engineering and regenerative medicine strategies related to bone tissue. This review includes an overview of major factors that influence the rational design and selection of an animal model. A comparison is provided of the 10 mammalian species that are most commonly used in bone research, and existing guidelines and standards are discussed. This review also identifies gaps in the availability of animal models: (1) the need for assessment of the predictive value of preclinical models for relative clinical efficacy, (2) the need for models that more effectively mimic the wound healing environment and mass transport conditions in the most challenging clinical settings (e.g., bone repair involving large bone and soft tissue defects and sites of prior surgery), and (3) the need for models that allow more effective measurement and detection of cell trafficking events and ultimate cell fate during the processes of bone modeling, remodeling, and regeneration. The ongoing need for both continued innovation and refinement in animal model systems, and the need and value of more effective standardization are reinforced.

Role of genetic background in determining phenotypic severity throughout postnatal development and at peak bone mass in Col1a2 deficient mice (oim)

Osteogenesis imperfecta (OI) is a genetically and clinically heterogeneous disease characterized by extreme bone fragility. Although fracture numbers tend to decrease post-puberty, OI patients can exhibit significant variation in clinical outcome, even among related individuals harboring the same mutation. OI most frequently results from mutations in type I collagen genes, yet how genetic background impacts phenotypic outcome remains unclear. Therefore, we analyzed the phenotypic severity of a known proalpha2(I) collagen gene defect (oim) on two genetic backgrounds (congenic C57BL/6J and outbred B6C3Fe) throughout postnatal development to discern the phenotypic contributions of the Col1a2 locus relative to the contribution of the genetic background. To this end, femora and tibiae were isolated from wildtype (Wt) and homozygous (oim/oim) mice of each strain at 1, 2 and 4 months of age. Femoral geometry was determined via muCT prior to torsional loading to failure to assess bone structural and material biomechanical properties. Changes in mineral composition, collagen content and bone turnover were determined using neutron activation analyses, hydroxyproline content and serum pyridinoline crosslinks. muCT analysis demonstrated genotype-, strain- and age-associated changes in femoral geometry as well as a marked decrease in the amount of bone in oim/oim mice of both strains. Oim/oim mice of both strains, as well as C57BL/6J (B6) mice of all genotypes, had reduced femoral biomechanical strength properties compared to Wt at all ages, although they improved with age. Mineral levels of fluoride, magnesium and sodium were associated with biomechanical strength properties in both strains and all genotypes at all ages. Oim/oim animals also had reduced collagen content as compared to Wt at all ages. Serum pyridinoline crosslinks were highest at two months of age, regardless of strain or genotype. Strain differences in bone parameters exist throughout development, implicating a role for genetic background in determining biomechanical strength. Age-associated improvements indicate that oim/oim animals partially compensate for their weaker bone material, but never attain Wt levels. These studies indicate the importance of genetic background in determining phenotypic severity, but the presence of the proalpha2(I) collagen gene defect and age of the animal are the primary determinants of phenotypic severity.

Fracture healing in the elderly patient

Clinical experience gives rise to the impression that there are differences in fracture healing in different age groups. It is evident that fractures heal more efficiently in children than in adults. However, minimal objective knowledge exists to evaluate this assumption. Temporal, spatial, and cellular quantitative and qualitative interrelationships, as well as signaling molecules and extracellular matrix have not been comprehensively and adequately elucidated for fracture healing in the geriatric skeleton. The biological basis of fracture healing will provide a context for revealing the pathophysiology of delayed or even impaired bone regeneration in the elderly. We will summarize experimental studies on age-related changes at the cellular and molecular level that will add to the pathophysiological understanding of the compromised bone regeneration capacity believed to exist in the elderly patient. We will suggest why this understanding would be useful for therapeutics focused on bone regeneration, in particular fracture healing at an advanced age.