Clinical Contrast-Enhanced Computed Tomography With Semi-Automatic Segmentation Provides Feasible Input for Computational Models of the Knee Joint.

Computational models can provide information on joint function and risk of tissue failure related to progression of osteoarthritis (OA). Currently, the joint geometries utilized in modeling are primarily obtained via manual segmentation, which is time-consuming and hence impractical for direct clinical application. The aim of this study was to evaluate the applicability of a previously developed semi-automatic method for segmenting tibial and femoral cartilage to serve as input geometry for finite element (FE) models. Knee joints from seven volunteers were first imaged using a clinical computed tomography (CT) with contrast enhancement and then segmented with semi-automatic and manual methods. In both segmentations, knee joint models with fibril-reinforced poroviscoelastic (FRPVE) properties were generated and the mechanical responses of articular cartilage were computed during physiologically relevant loading. The mean differences in the absolute values of maximum principal stress, maximum principal strain, and fibril strain between the models generated from semi-automatic and manual segmentations were <1 MPa, <0.72% and <0.40%, respectively. Furthermore, contact areas, contact forces, average pore pressures, and average maximum principal strains were not statistically different between the models (p >0.05). This semi-automatic method speeded up the segmentation process by over 90% and there were only negligible differences in the results provided by the models utilizing either manual or semi-automatic segmentations. Thus, the presented CT imaging-based segmentation method represents a novel tool for application in FE modeling in the clinic when a physician needs to evaluate knee joint function.

Histomorphometric and osteocytic characteristics of cortical bone in male subtrochanteric femoral shaft.

The histomorphometric properties of the subtrochanteric femoral region have rarely been investigated. The aim of this study was to investigate the age-associated variations and regional differences of histomorphometric and osteocytic properties in the cortical bone of the subtrochanteric femoral shaft, and the association between osteocytic and histological cortical bone parameters. Undecalcified histological sections of the subtrochanteric femoral shaft were obtained from cadavers (n = 20, aged 18-82 years, males). They were cut and stained using modified Masson-Goldner stain. Histomorphometric parameters of cortical bone were analysed with ×50 and ×100 magnification after identifying cortical bone boundaries using our previously validated method. Within cortical bone areas, only complete osteons with typical concentric lamellae and cement line were selected and measured. Osteocytic parameters of cortical bone were analyzed under phase contrast microscopy and epifluorescence within microscopic fields (0.55 mm2 for each). The cortical widths of the medial and lateral quadrants were significantly higher than other quadrants (P < 0.01). Osteonal area per cortical bone area was lower and cortical porosities were higher in the posterior quadrant than in the other quadrants (P < 0.05). Osteocyte lacunar number per cortical bone area was found higher in the young subjects (≤ 50 years) than in the older ones (> 50 years) both before and after adjustments for body height and weight (P < 0.05). Moreover, significant but low correlations were found between the cortical bone and osteocytic parameters (0.20 ≤ R2  ≤ 0.35, P < 0.05). It can be concluded that in healthy males, the cortical histomorphometric parameters differ between the anatomical regions of the subtrochanteric femoral shaft, and are correlated with the osteocytic parameters from the same site. These findings may be of use when discussing mechanisms that predispose patients to decreasing bone strength.

Porosity predicted from ultrasound backscatter using multivariate analysis can improve accuracy of cortical bone thickness assessment.

A rapidly growing area of interest in quantitative ultrasound assessment of bone is to determine cortical bone porosity from ultrasound backscatter. Current backscatter analyses are based on numerical simulations, while there are no published reports of successful experimental measurements. In this study, multivariate analysis is applied to ultrasound reflections and backscatter to predict cortical bone porosity. The porosity is then applied to estimate cortical bone radial speed of sound (SOS) and thickness using ultrasound backscatter signals obtained at 2.25 and 5 MHz center frequencies from cortical bone samples (n = 43) extracted from femoral diaphyses. The study shows that the partial least squares regression technique could be employed to successfully predict (R2 = 0.71-0.73) cortical porosity. It is found that this multivariate approach can reduce uncertainty in pulse-echo assessment of cortical bone thickness from 0.220 to 0.045 mm when porosity based radial SOS was applied, instead of a constant value from literature. Upon further validation, accurate estimation of cortical bone porosity and thickness may be applied as a financially viable option for fracture risk assessment of individuals.

Bone mineral crystal size and organization vary across mature rat bone cortex.

The macro- and micro-features of bone can be assessed by using imaging methods. However, nano- and molecular features require more detailed characterization, such as use of e.g., vibrational spectroscopy and X-ray scattering. Nano- and molecular features also affect the mechanical competence of bone tissue. The aim of the present study was to reveal the effects of mineralization and its alterations on the mineral crystal scale, by investigating the spatial variation of molecular composition and mineral crystal structure across the cross-section of femur diaphyses in young rats, and healthy and osteoporotic mature rats (N=5). Fourier transform infrared spectroscopy and scanning small- and wide-angle X-ray scattering (SAXS/WAXS) techniques with high spatial resolution were used at identical locations over the whole cross-section. This allowed quantification of point-by-point information about the spatial distribution of mineral crystal volume. All measured parameters (crystal dimensions, degree of orientation and predominant orientation) varied across the cortex. Specifically, the crystal dimensions were lower in the central cortex than in the endosteal and periosteal regions. Mineral crystal orientation followed the cortical circumference in the periosteal and endosteal regions, but was less well-oriented in the central regions. Central cortex is formed rapidly during development through endochondral ossification. Since rats possess no osteonal remodeling, this bone remains (until old age). Significant linear correlations were observed between the dimensional and organizational parameters, e.g., between crystal length and degree of orientation (R(2)=0.83, p<0.001). Application of SAXS/WAXS provides valuable information on bone nanostructure and its constituents, effects of diseases and, prospectively, mechanical competence.

A first-in-human, double-blind, randomised, placebo-controlled, dose ascending study of intra-articular rhFGF18 (sprifermin) in patients with advanced knee osteoarthritis.

OBJECTIVES: To evaluate the safety of intra-articular sprifermin (primary), and to evaluate systemic exposure, biomarkers, histology, and other cartilage parameters in patients with advanced osteoarthritis (OA). METHODS: This was a first-in-human, double-blind, randomised, placebo-controlled trial of single and multiple ascending doses of sprifermin from 3-300 µg in knee OA patients scheduled for total knee replacement. Patients were randomised 3:1 to sprifermin or placebo, injected into the target knee once or once weekly for 3 weeks, and followed-up for 24 weeks. RESULTS: Fifty-five patients were treated with sprifermin, 25 with single and 30 with multiple doses, 18 received placebo. There was no clear difference between the active and placebo groups in incidence, severity, and nature of reported treatment emergent adverse events. Acute inflammatory reactions were slightly more common with sprifermin 300 µg, but none led to discontinuation. No clear difference was seen between placebo and sprifermin in physician-assessed local tolerability, pain, or swelling in the knee. No meaningful changes over time, or differences between treatment groups, were observed for safety laboratory parameters or ECG. Although individual abnormalities were observed, no patterns were evident suggesting a relation to treatment or potential safety concern. No systemic sprifermin exposure, anti-FGF18 antibodies, or clear-cut effects on systemic biomarkers were detected. CONCLUSIONS: This first clinical trial of sprifermin revealed no serious safety concerns, although larger studies are needed. The possibility of positive effects of intra-articular sprifermin on histological and other cartilage parameters in knee OA also warrant further investigation.

Finite difference time domain model of ultrasound propagation in agarose scaffold containing collagen or chondrocytes.

Measurement of ultrasound backscattering is a promising diagnostic technique for arthroscopic evaluation of articular cartilage. However, contribution of collagen and chondrocytes on ultrasound backscattering and speed of sound in cartilage is not fully understood and is experimentally difficult to study. Agarose hydrogels have been used in tissue engineering applications of cartilage. Therefore, the aim of this study was to simulate the propagation of high frequency ultrasound (40 MHz) in agarose scaffolds with varying concentrations of chondrocytes (1 to 32 × 10(6) cells/ml) and collagen (1.56-200 mg/ml) using transversely isotropic two-dimensional finite difference time domain method (FDTD). Backscatter and speed of sound were evaluated from the simulated pulse-echo and through transmission measurements, respectively. Ultrasound backscatter increased with increasing collagen and chondrocyte concentrations. Furthermore, speed of sound increased with increasing collagen concentration. However, this was not observed with increasing chondrocyte concentrations. The present study suggests that the FDTD method may have some applicability in simulations of ultrasound scattering and propagation in constructs containing collagen and chondrocytes. Findings of this study indicate the significant role of collagen and chondrocytes as ultrasound scatterers and can aid in development of modeling approaches for understanding how cartilage architecture affects to the propagation of high frequency ultrasound.

Differences in acoustic impedance of fresh and embedded human trabecular bone samples-Scanning acoustic microscopy and numerical evaluation.

Trabecular bone samples are traditionally embedded and polished for scanning acoustic microscopy (SAM). The effect of sample processing, including dehydration, on the acoustic impedance of bone is unknown. In this study, acoustic impedance of human trabecular bone samples (n = 8) was experimentally assessed before (fresh) and after embedding using SAM and two-dimensional (2-D) finite-difference time domain simulations. Fresh samples were polished with sandpapers of different grit (P1000, P2500, and P4000). Experimental results indicated that acoustic impedance of samples increased significantly after embedding [mean values 3.7 MRayl (fresh), 6.1 MRayl (embedded), p < 0.001]. After polishing with different papers, no significant changes in acoustic impedance were found, even though higher mean values were detected after polishing with finer (P2500 and P4000) papers. A linear correlation (r = 0.854, p < 0.05) was found between the acoustic impedance values of embedded and fresh bone samples polished using P2500 SiC paper. In numerical simulations dehydration increased the acoustic impedance of trabecular bone (38%), whereas changes in surface roughness of bone had a minor effect on the acoustic impedance (-1.56%/0.1 µm). Thereby, the numerical simulations corroborated the experimental findings. In conclusion, acoustic impedance measurement of fresh trabecular bone is possible and may provide realistic material values similar to those of living bone.

Optical coherence tomography enables accurate measurement of equine cartilage thickness for determination of speed of sound.

Background and purpose - Arthroscopic estimation of articular cartilage thickness is important for scoring of lesion severity, and measurement of cartilage speed of sound (SOS)-a sensitive index of changes in cartilage composition. We investigated the accuracy of optical coherence tomography (OCT) in measurements of cartilage thickness and determined SOS by combining OCT thickness and ultrasound (US) time-of-flight (TOF) measurements. Material and methods - Cartilage thickness measurements from OCT and microscopy images of 94 equine osteochondral samples were compared. Then, SOS in cartilage was determined using simultaneous OCT thickness and US TOF measurements. SOS was then compared with the compositional, structural, and mechanical properties of cartilage. Results - Measurements of non-calcified cartilage thickness using OCT and microscopy were significantly correlated (ρ = 0.92; p < 0.001). With calcified cartilage included, the correlation was ρ = 0.85 (p < 0.001). The mean cartilage SOS (1,636 m/s) was in agreement with the literature. However, SOS and the other properties of cartilage lacked any statistically significant correlation. Interpretation - OCT can give an accurate measurement of articular cartilage thickness. Although SOS measurements lacked accuracy in thin equine cartilage, the concept of SOS measurement using OCT appears promising.

Cortical bone histomorphometry in male femoral neck: the investigation of age-association and regional differences.

Low bone volume and changes in bone quality or microarchitecture may predispose individuals to fragility fractures. As the dominant component of the human skeleton, cortical bone plays a key role in protecting bones from fracture. However, histological investigations of the underlying structural changes, which might predispose to fracture, have been largely limited to the cancellous bone. The aim of this study was to investigate the age-association and regional differences of histomorphometric properties in the femoral neck cortical bone. Undecalcified histological sections of the femoral neck (n = 20, aged 18-82 years, males) were cut (15 µm) and stained using modified Masson-Goldner stain. Complete femoral neck images were scanned, and cortical bone boundaries were defined using our previously established method. Cortical bone histomorphometry was performed with low (×50) and high magnification (×100). Most parameters related to cortical width (Mean Ct.Wi, Inferior Ct.Wi, Superior Ct.Wi) were negatively associated with age both before and after adjustment for height. The inferior cortex was the thickest (P < 0.001) and the superior cortex was the thinnest (P < 0.008) of all cortical regions. Both osteonal size and pores area were negatively associated with age. Osteonal area and number were higher in the antero-inferior area (P < 0.002) and infero-posterior area (P = 0.002) compared to the postero-superior area. The Haversian canal area was higher in the infero-posterior area compared to the postero-superior area (P = 0.002). Moreover, porosity was higher in the antero-superior area (P < 0.002), supero-anterior area (P < 0.002) and supero-posterior area (P < 0.002) compared to the infero-anterior area. Eroded endocortical perimeter (E.Pm/Ec.Pm) correlated positively with superior cortical width. This study describes the changes in cortical bone during ageing in healthy males. Further studies are needed to investigate whether these changes explain the increased susceptibility to femoral neck fractures.

Development of new criteria for cortical bone histomorphometry in femoral neck: intra- and inter-observer reproducibility.

Histomorphometry is commonly applied to study bone remodeling. Histological definitions of cortical bone boundaries have not been consistent. In this study, new criteria for specific definition of the transitional zone between the cortical and cancellous bone in the femoral neck were developed. The intra- and inter-observer reproducibility of this method was determined by quantitative histomorphometry and areal overlapping analysis. The undecalcified histological sections of femoral neck specimens (n = 6; from men aged 17-59 years) were processed and scanned to acquire histological images of complete bone sections. Specific criteria were applied to define histological boundaries. "Absolute cortex area" consisted of pure cortical bone tissue only, and was defined mainly based on the size of composite canals and their distance to an additional "guide" boundary (so-called "preliminary cortex boundary," the clear demarcation line of density between compact cortex and sparse trabeculae). Endocortical bone area was defined by recognizing characteristic endocortical structures adjacent to the preliminary cortical boundary. The present results suggested moderate to high reproducibility for low-magnification parameters (e.g., cortical bone area). The coefficient of variation (CV %) ranged from 0.02 to 5.61 in the intra-observer study and from 0.09 to 16.41 in the inter-observer study. However, the intra-observer reproducibility of some high-magnification parameters (e.g., osteoid perimeter/endocortical perimeter) was lower (CV %, 0.33-87.9). The overlapping of three histological areas in repeated analyses revealed highest intra- and inter-observer reproducibility for the absolute cortex area. This study provides specific criteria for the definition of histological boundaries for femoral neck bone specimens, which may aid more precise cortical bone histomorphometry.

Inter-individual changes in cortical bone three-dimensional microstructure and elastic coefficient have opposite effects on radial sound speed.

Knowledge about simultaneous contributions of tissue microstructure and elastic properties on ultrasound speed in cortical bone is limited. In a previous study, porosities and elastic coefficients of cortical bone in human femurs were shown to change with age. In the present study, influences of inter-individual and site-dependent variation in cortical bone microstructure and elastic properties on radial speed of sound (SOS; at 4, 6, and 8 MHz) were investigated using three-dimensional (3D) finite difference time domain modeling. Models with fixed (nominal model) and sample-specific (sample-specific model) values of radial elastic coefficients were compared. Elastic coefficients and microstructure for samples (n = 24) of human femoral shafts (n = 6) were derived using scanning acoustic microscopy and micro-computed tomography images, respectively. Porosity-related SOS varied more extensively in nominal models than in sample-specific models. Linear correlation between pore separation and SOS was similar (R = 0.8, p < 0.01, for 4 MHz) for both models. The determination coefficient (R(2)= 0.75, p < 0.05) between porosity and radial SOS, especially at 4 MHz, was highest in the posterior quadrant. The determination coefficient was lower for models with sample-specific values of radial elastic coefficient implemented (R(2) < 0.33, p < 0.05), than for nominal models (0.48 < R(2)< 0.63, p < 0.05). This information could be useful in in vivo pulse-echo cortical thickness measurements applying constant SOS.

Importance of material properties and porosity of bone on mechanical response of articular cartilage in human knee joint--a two-dimensional finite element study.

Mechanical behavior of bone is determined by the structure and intrinsic, local material properties of the tissue. However, previously presented knee joint models for evaluation of stresses and strains in joints generally consider bones as rigid bodies or linearly elastic solid materials. The aim of this study was to estimate how different structural and mechanical properties of bone affect the mechanical response of articular cartilage within a knee joint. Based on a cadaver knee joint, a two-dimensional (2D) finite element (FE) model of a knee joint including bone, cartilage, and meniscus geometries was constructed. Six different computational models with varying properties for cortical, trabecular, and subchondral bone were created, while the biphasic fibril-reinforced properties of cartilage and menisci were kept unaltered. The simplest model included rigid bones, while the most complex model included specific mechanical properties for different bone structures and anatomically accurate trabecular structure. Models with different porosities of trabecular bone were also constructed. All models were exposed to axial loading of 1.9 times body weight within 0.2 s (mimicking typical maximum knee joint forces during gait) while free varus-valgus rotation was allowed and all other rotations and translations were fixed. As compared to results obtained with the rigid bone model, stresses, strains, and pore pressures observed in cartilage decreased depending on the implemented properties of trabecular bone. Greatest changes in these parameters (up to -51% in maximum principal stresses) were observed when the lowest modulus for trabecular bone (measured at the structural level) was used. By increasing the trabecular bone porosity, stresses and strains were reduced substantially in the lateral tibial cartilage, while they remained relatively constant in the medial tibial plateau. The present results highlight the importance of long bones, in particular, their mechanical properties and porosity, in altering and redistributing forces transmitted through the knee joint.

Full-field strain measurement during mechanical testing of the human femur at physiologically relevant strain rates.

Understanding the mechanical properties of human femora is of great importance for the development of a reliable fracture criterion aimed at assessing fracture risk. Earlier ex vivo studies have been conducted by measuring strains on a limited set of locations using strain gauges (SGs). Digital image correlation (DIC) could instead be used to reconstruct the full-field strain pattern over the surface of the femur. The objective of this study was to measure the full-field strain response of cadaver femora tested at a physiological strain rate up to fracture in a configuration resembling single stance. The three cadaver femora were cleaned from soft tissues, and a white background paint was applied with a random black speckle pattern over the anterior surface. The mechanical tests were conducted up to fracture at a constant displacement rate of 15 mm/s, and two cameras recorded the event at 3000 frames per second. DIC was performed to retrieve the full-field displacement map, from which strains were derived. A low-pass filter was applied over the measured displacements before the crack opened in order to reduce the noise level. The noise levels were assessed using a dedicated control plate. Conversely, no filtering was applied at the frames close to fracture to get the maximum resolution. The specimens showed a linear behavior of the principal strains with respect to the applied force up to fracture. The strain rate was comparable to the values available in literature from in vivo measurements during daily activities. The cracks opened and fully propagated in less than 1 ms, and small regions with high values of the major principal strains could be spotted just a few frames before the crack opened. This corroborates the hypothesis of a strain-driven fracture mechanism in human bone. The data represent a comprehensive collection of full-field strains, both at physiological load levels and up to fracture. About 10,000 points were tracked on each bone, providing superior spatial resolution compared to ∼15 measurements typically collected using SGs. These experimental data collection can be further used for validation of numerical models, and for experimental verification of bone constitutive laws and fracture criteria.

Incidence and bone biopsy findings of atypical femoral fractures.

Bisphosphonates are widely used in the treatment of osteoporosis. It has been suggested that bisphosphonate treatment may be associated with atypical femoral fractures (AFFs), severely suppressed bone turnover rate, and decreased mineralization. We studied bone properties using bone quantitative histomorphometry and Fourier transform infrared spectroscopic imaging (FTIRI) on patients with AFFs. Further, the incidence of AFFs was estimated. Patient records of Kuopio University Hospital, Finland from January 2007 to June 2009 were reviewed to identify all patients who had sustained and had been operated for AFF (n = 8). The incidence of AFFs among patients on bisphosphonates was 0.61 fractures/1,000 patients per year, compared to 0.0067/1,000 per year among untreated patients. The patients that underwent bone biopsy (n = 4) were postmenopausal women (aged 55.5-81.1 years) who had been treated with bisphosphonates for over 4 years. Histomorphometry revealed low trabecular bone volume. Bone formation and resorption parameters tended to be low. Trabecular bone single labels were detected in one patient in the region of interest. In the extended label search, trabecular bone double labels were found in two patients. Based on FTIRI results, higher phosphate-to-amide I ratio and collagen maturity were found compared to normal samples. The heterogeneity of phosphate-to-amide I ratio was low. Overall incidence of atypical femoral fractures is low. The poor fracture resistance in some patients on long-term bisphosphonate-therapy could be explained by low bone formation, and changes in bone composition, i.e., higher degree of mineralization, increased collagen maturity, and decreased heterogeneity of the degree of mineralization.

Alcohol consumption and bone mineral density in elderly women.

OBJECTIVE: Findings regarding alcohol consumption and bone mineral density (BMD) in elderly women have been inconsistent. The objective of the present study was to explore the association of alcohol intake with BMD in elderly women. DESIGN: This cohort study included women from the population-based Kuopio Osteoporosis Risk Factor and Prevention - Fracture Prevention Study (OSTPRE-FPS). Alcohol intake and potential confounders were assessed at baseline and after 3 years of follow-up using a lifestyle questionnaire. In addition, an FFQ was distributed in the third year to measure dietary intake, including alcohol. Women underwent BMD measurements at the femoral neck and lumbar spine at baseline and after 3 years of follow-up. SETTING: Kuopio Province, Finland. SUBJECTS: Three hundred elderly women (mean age 67·8 years) who provided both BMD measurements and FFQ data. RESULTS: Alcohol consumption estimated from the FFQ and lifestyle questionnaire was significantly associated with BMD at both measurement sites after adjustment for potential confounders, including lifestyle and dietary factors (P < 0·05). Using the FFQ, women drinking >3 alcoholic drinks/week had significantly higher BMD than abstainers, 12·0 % at the femoral neck and 9·2 % at the lumbar spine. Results based on the lifestyle questionnaire showed higher BMD values for all alcohol-consuming women at the femoral neck and for women drinking 1-3 alcoholic beverages/week at the lumbar spine, compared with non-users. CONCLUSIONS: The results from OSTPRE-FPS suggest that low to moderate alcohol intake may exert protective effects on bone health in elderly women.

Experimental and computational analysis of soft tissue mechanical response under negative pressure in forearm.

BACKGROUND: Instrumentation, relying on the use of negative pressure (suction), has been introduced to reduce pathological tissue swelling. Then, relative contribution of skin, adipose tissue and muscle, to the overall mechanical response is not known. METHODS: Under suction, stretch of soft tissues in the forearm of human subjects (N = 11) was experimentally measured at rest and under venous occlusion. Three dimensional, fibril-reinforced hyperelastic finite element (FE) model was constructed, the model response was matched with the experimental measurement and the mechanical characteristics of each tissue were derived. Parametric analyses were conducted to evaluate the impact of different tissues on the total stretch. RESULTS: The model suggested that, at large strains, the stretch response was more sensitive to changes in the elastic modulus of skin than those in adipose tissue. During venous occlusion, reduction of the stretch of forearm tissues was related to stiffening of the skin and adipose tissue, as evidenced by increased modulus of 27 ± 21% and 35 ± 26%, respectively. CONCLUSION: The method based on suction may be used to diagnose and monitor changes in properties of soft tissues, especially those of skin, as well as tissue swelling typical to pathological conditions such as oedema.

Clustering of infrared spectra reveals histological zones in intact articular cartilage.

OBJECTIVE: Articular cartilage (AC) exhibits specific zonal structure that follows the organization of collagen network and concentration of tissue constituents. The aim of this study was to investigate the potential of unsupervised clustering analysis applied to Fourier transform infrared (FTIR) microspectroscopy to detect depth-dependent structural and compositional differences in intact AC. METHOD: Seven rabbit and eight bovine intact patellae AC samples were imaged using FTIR microspectroscopy and normalized raw spectra were clustered using the fuzzy C-means algorithm. Differences in mean spectra of clusters were investigated by quantitative estimation of collagen and proteoglycan (PG) contents, as well as by careful visual investigation of locations of spectral changes. RESULTS: Clustering revealed the typical layered structure of AC in both species. However, more distinct clusters were found for rabbit samples, whereas bovine AC showed more complex layered structure. In both species, clustering structure corresponded with that in polarized light microscopic (PLM) images; however, some differences were also observed. Spectral differences between clusters were identified at the same spectral locations for both species. Estimated PG/collagen ratio decreased significantly from superficial to middle or deep zones, which might explain the difference in clustering results compared to PLM. CONCLUSION: FTIR microspectroscopy in combination with cluster analysis allows detailed examination of spatial changes in AC. As far as we know, no previous single technique could reveal a layered structure of AC without any a priori information.

Muscle strength and body composition are clinical indicators of osteoporosis.

We examined the role of muscle strength, lean tissue distribution, and overall body composition as indicators of osteoporosis (OP) in a pooled sample of 979 Finnish postmenopausal women (mean age 68.1 years) from the Kuopio Osteoporosis Risk Factor and Prevention study. Bone mineral density (BMD) at the femoral neck (FN) and total body composition were assessed by dual-energy X-ray absorptiometry scans. The women (n = 979) were divided into three groups according to WHO criteria, based on FN BMD T score: normal (n = 474), osteopenia (n = 468), and OP (n = 37). Soft tissue proportions, fat mass index (FMI, fat/height²), lean mass index (LMI, lean/height²), and appendicular skeletal muscle mass (ASM, (arms + legs)/height²) were calculated. Handgrip and knee extension strength measurements were made. OP subjects had significantly smaller LMI (p = 0.001), ASM (p = 0.001), grip strength (p < 0.0001), and knee extension strength (p < 0.05) but not FMI (p > 0.05) compared to other subjects. Grip and knee extension strength were 19 and 16 % weaker in OP women compared to others, respectively. The area under the receiver operating characteristic curve was 69 % for grip and 71 % for knee extension strength. In tissue proportions only LMI showed predictive power (63 %, p = 0.016). An overall linear association of LMI (R² = 0.007, p = 0.01) and FMI (R² = 0.028, p < 0.001) with FN BMD remained significant. In the multivariate model, after adjusting for age, grip strength, leg extension strength, FMI, LMI, number of medications, alcohol consumption, current smoking, dietary calcium intake, and hormone therapy, grip strength (adjusted OR = 0.899, 95 % CI 0.84-0.97, p < 0.01), leg extension strength (OR = 0.998, 95 % CI 0.99-1, p < 0.05), and years of hormone therapy (OR = 0.905, 95 % CI 0.82-1, p < 0.05) remained as significant determinants of OP. Muscle strength tests, especially grip strength, serve as an independent and useful tool for postmenopausal OP risk assessment. In addition, lean mass contributes to OP in this age group. Muscle strength and lean mass should be considered separately since both are independently associated with postmenopausal BMD.

Influence of different DXA acquisition modes on monitoring the changes in bone mineral density after hip resurfacing arthroplasty.

Dual-energy X-ray absorptiometry (DXA) is a technique enabling the measurement of bone mineral density (BMD) around prostheses after hip resurfacing arthroplasty (HRA). In this study, we evaluated the consistency of different DXA acquisition modes with 33 patients who had undergone HRA. Patients were scanned with DXA immediately after surgery and at 3-, 6-, and 12-mo time points. All the patients were scanned with dual femur and orthopedic hip acquisition modes and analyzed using 10-region ROI model. With both acquisition modes, a statistically significant decrease (p<0.05, Wilcoxon's test) in BMD at 3mo was revealed in 3 ROIs, located to upper and lateral upper femur. Both acquisition modes detected similarly (p<0.01) preservation of the femoral bone stock within 12mo in all but 1 ROI. The applied acquisition protocols involved the use of different footplates for hip fixation. Because the differences between acquisition modes ranged between +1.6% and -7.1% and the reproducibility of BMD values can vary by as much as 28% due to hip rotation, it is proposed that both dual femur and orthopedic hip acquisition modes can be used to monitor the changes in BMD after HRA. However, the same hip rotation is recommended for all DXA measurements.

Minor influence of lifelong voluntary exercise on composition, structure, and incidence of osteoarthritis in tibial articular cartilage of mice compared with major effects caused by growth, maturation, and aging.

We investigated the effects of lifelong voluntary exercise on articular cartilage of mice. At the age of 4 weeks C57BL mice (n = 152) were divided into two groups, with one group serving as a sedentary control whereas the other was allowed free access to a running wheel from the age of 1 month onward. Mice were euthanized at four different time points (1, 2, 6, and 18 months of age). Articular cartilage samples were gathered from the load-bearing area of the tibial medial plateaus, and osteoarthritis was graded. Additionally, the proteoglycan content distribution was assessed using digital densitometry, collagen fibril orientation, and parallelism with polarized light microscopy, and collagen content using Fourier transform infrared imaging spectroscopy. The incidence of osteoarthritis increased with aging, but exercise had no effect on this trend. Furthermore, the structure and composition revealed significant growth, maturation, and age-dependent properties. Exercise exerted a minor effect on collagen fibril orientation in the superficial zone. Fibril orientation at 2 months of age was more perpendicular to surface (p < 0.05) in controls compared with runners, whereas the situation was reversed at the age of 18 months (p < 0.05). The collagen content of the superficial zone was higher (p < 0.01) at the age of 18 months in controls compared with runners but the proteoglycan content did not display any exercise-dependent changes. In conclusion, growth, maturation, and aging exerted a clear effect on integrity, structure, and composition of medial tibial plateau articular cartilage in mice, whereas lifelong voluntary exercise had only a minor effect on collagen architecture and content.