Proximal femoral fractures are a serious life-threatening injury with high morbidity and mortality. Magnetic resonance (MR) imaging has potential to non-invasively assess proximal femoral bone ...strength in vivo through usage of finite element (FE) modelling (a technique referred to as MR-FE). To precisely assess bone strength, knowledge of measurement error associated with different MR-FE outcomes is needed. The objective of this study was to characterize the short-term in vivo precision errors of MR-FE outcomes (e.g., stress, strain, failure loads) of the proximal femur for fall and stance loading configurations using 13 participants (5 males and 8 females; median age: 27 years, range: 21-68), each scanned 3 times. MR-FE models were generated, and mean von Mises stress and strain as well as principal stress and strain were calculated for 3 regions of interest. Similarly, we calculated the failure loads to cause 5% of contiguous elements to fail according to the von Mises yield, Brittle Coulomb-Mohr, normal principal, and Hoffman stress and strain criteria. Precision (root-mean squared coefficient of variation) of the MR-FE outcomes ranged from 3.3% to 11.8% for stress and strain-based mechanical outcomes, and 5.8% to 9.0% for failure loads. These results provide evidence that MR-FE outcomes are a promising non-invasive technique for monitoring femoral strength in vivo.
Off‐axis loading associated with a fall onto the outstretched hand has been hypothesized to induce distal radius failure at lower magnitudes than axially directed loading commonly used in ...biomechanical models for estimating fracture risk. However, this hypothesis has not been tested with side‐to‐side experimental testing. The objective of this study was to compare distal radius failure loads between forearm pairs experimentally tested in an axial or off‐axis loading configuration. We acquired 18 pairs of cadaveric forearms from 18 female donors (mean age (standard deviation): 84.4 (7.9) years). Each forearm pair was tested to failure using either an axial compression test (vertical orientation with 0° dorsal inclination, 3°‐6° radial inclination) or an off‐axis test corresponding to the hand position during a fall (15° dorsal inclination, 3°‐6° radial inclination). Failure testing was performed at 3 mm/s onto the palm of the hand until fracture occurred. Of the 18 pairs, 11 sustained a distal radius fracture. We compared failure loads between the two groups using a paired t test. Results indicated that failure load under off‐axis loading was 29% lower than failure load under axial compressive loading (mean difference: −0.31 kN; 95% confidence interval: −0.47 to −0.16 kN, P = .001). In conclusion, off‐axis loading associated with a fall onto the outstretched hand resulted in a 29% lower failure load. Integrating an off‐axis loading configuration into current biomechanical models of distal radius bone strength may prevent overestimating of failure load and may offer a clinically relevant option to estimate distal radius fracture risk and monitor therapy efficacy.
Our objective was to identify precise mechanical metrics of the proximal tibia which differentiated OA and normal knees. We developed subject-specific FE models for 14 participants (7 OA, 7 normal) ...who were imaged three times each for assessing precision (repeatability). We assessed various mechanical metrics (minimum principal and von Mises stress and strain as well as structural stiffness) across the proximal tibia for each subject. In vivo precision of these mechanical metrics was assessed using CV%
. We performed parametric and non-parametric statistical analyses and determined Cohen's d effect sizes to explore differences between OA and normal knees. For all FE-based mechanical metrics, average CV%
was less than 6%. Minimum principal stress was, on average, 75% higher in OA versus normal knees while minimum principal strain values did not differ. No difference was observed in structural stiffness. FE modeling could precisely quantify and differentiate mechanical metrics variations in normal and OA knees, in vivo. This study suggests that bone stress patterns may be important for understanding OA pathogenesis at the knee.
Subchondral bone cysts are a widely observed, but poorly understood, feature in patients with knee osteoarthritis (OA). Clinical quantitative computed tomography (QCT) has the potential to ...characterize cysts in vivo but it is unclear which specific cyst parameters (e.g., number, size) are associated with clinical signs of OA, such as disease severity or pain. The objective of this study was to use QCT-based image-processing techniques to characterize subchondral tibial cysts in patients with knee OA and to explore relationships between proximal tibial subchondral cyst parameters and subchondral bone density as well as clinical characteristics of OA (alignment, joint space narrowing (JSN), OA severity, pain) in patients with knee OA.
The preoperative knee of 42 knee arthroplasty patients was scanned using QCT. Patient characteristics were obtained, including OA severity, knee pain, JSN, and alignment. We used 3D image processing techniques to obtain cyst parameters including: cyst number, cyst number per proximal tibial volume, cyst volume per proximal tibial volume, as well as maximum and average cyst volume across the proximal tibia, as well as regional bone mineral density (BMD) excluding cysts. We used Spearman's correlation coefficients to explore associations between patient characteristics and cyst parameters.
At both the medial and lateral compartments of the proximal tibia, greater cyst number and volume were associated with higher BMD. At the lateral region, cyst number and volume were also associated with lateral OA severity, lateral JSN, alignment and sex. Pain was not associated with any cyst parameters at any region.
Cyst number and volume were associated with BMD at both the medial and lateral compartments. Lateral cyst number and volume were also associated with joint alignment, OA severity, JSN and sex. This is the first study to use clinical QCT to explore subchondral tibial cysts in patients with knee OA and provides further evidence of the relationships between subchondral cysts and clinical OA characteristics.
The objective of this study was to validate a single-spring model in predicting measured impact forces during an outstretched arm falling scenario. Using an integrated force plate, impact forces were ...assessed from 10 young adults (5 males; 5 females), falling from planted knees onto outstretched arms, from a random order of drop heights: 3, 5, 7, 10, 15, 20, and 25 cm. A single-spring model incorporating body mass, drop height plus the estimated linear stiffness of the upper extremity (hand, wrist and arm) was used to predict impact force on the hand. We used an analysis of variance linearity test to test the validity of using a linear stiffness coefficient in the model. We used linear regression to assess variance (R2) in experimental impact force predicted by the single-spring model. We derived optimum linear stiffness coefficients for male, female and sex-combined. Our results indicated that the association between experimental and predicted impact forces was linear (P < 0.05). Explain variance in experimental impact force was R2 = 0.82 for sex-combined, R2 = 0.88 for males and R2 = 0.84 for females. Optimum stiffness coefficients were 7436 N/m for sex-combined, 8989 N/m for males and 4527 N/m for females. In conclusion, a linear spring coefficient used in the single-spring model proved valid for predicting impact forces from fall heights up to 25 cm. Results also suggest the use of sex-specific spring coefficients when estimating impact force using the single-spring model. This model may improve impact force to bone strength ratios (factor-of-risk) and prediction of forearm and wrist fracture.
This 16‐month randomized, controlled school‐based study compared change in tibial bone strength between 281 boys and girls participating in a daily program of physical activity (Action Schools! BC) ...and 129 same‐sex controls. The simple, pragmatic intervention increased distal tibia bone strength in prepubertal boys; it had no effect in early pubertal boys or pre or early pubertal girls.
Introduction: Numerous school‐based exercise interventions have proven effective for enhancing BMC, but none have used pQCT to evaluate the effects of increased loading on bone strength during growth. Thus, our aim was to determine whether a daily program of physical activity, Action Schools! BC (AS! BC) would improve tibial bone strength in boys and girls who were pre‐ (Tanner stage 1) or early pubertal (Tanner stage 2 or 3) at baseline.
Materials and Methods: Ten schools were randomized to intervention (INT, 7 schools) or control (CON, 3 schools). The bone‐loading component of AS! BC included a daily jumping program (Bounce at the Bell) plus 15 minutes/day of classroom physical activity in addition to regular physical education. We used pQCT to compare 16‐month change in bone strength index (BSI, mg2/mm4) at the distal tibia (8% site) and polar strength strain index (SSIp, mm3) at the tibial midshaft (50% site) in 281 boys and girls participating in AS! BC and 129 same‐sex controls. We used a linear mixed effects model to analyze our data.
Results: Children were 10.2 ± 0.6 years at baseline. Intervention boys tended to have a greater increase in BSI (+774.6 mg2/mm4; 95% CI: 672.7, 876.4) than CON boys (+650.9 mg2/mm4; 95% CI: 496.4, 805.4), but the difference was only significant in prepubertal boys (p = 0.03 for group × maturity interaction). Intervention boys also tended to have a greater increase in SSIp (+198.6 mm3; 95% CI: 182.9, 214.3) than CON boys (+177.1 mm3; 95% CI: 153.5, 200.7). Change in BSI and SSIp was similar between CON and INT girls.
Conclusions: Our findings suggest that a simple, pragmatic program of daily activity enhances bone strength at the distal tibia in prepubertal boys. The precise exercise prescription needed to elicit a similar response in more mature boys or in girls might be best addressed in a dose–response trial.
To determine the agreement between cortical porosity derived from high resolution peripheral quantitative computed tomography (HR-pQCT) (via standard threshold, mean density and density inhomogeneity ...methods) and synchrotron radiation micro-CT (SR-μCT) derived porosity at the distal radius.
We scanned 10 cadaveric radii (mean donor age: 79, SD 11 years) at the standard distal region using HR-pQCT and SR-μCT at voxel sizes of 82 μm and 17.7 μm, respectively. Common cortical regions were delineated for each specimen in both imaging modalities. HR-pQCT images were analyzed for cortical porosity using the following methods: Standard threshold, mean density, and density inhomogeneity (via recommended and optimized equations). We assessed agreement in porosity measures between HR-pQCT methods and SR-μCT by reporting predicted variance from linear regression and mean bias with limits of agreement (LOA).
The standard threshold and mean density methods predicted 85% and 89% of variance and indicated underestimation (mean bias −9.1%, LOA −15.9% to −2.2%) and overestimation (10.4%, 4.6% to 16.2%) of porosity, respectively. The density inhomogeneity method with recommended equation predicted 89% of variance and mean bias of 14.9% (−4.3 to 34.2) with systematic over-estimation of porosity in more porous specimens. The density inhomogeneity method with optimized equation predicted 91% of variance without bias (0.0%, −5.3 to 5.2).
HR-pQCT imaged porosity assessed with the density inhomogeneity method with optimized equation indicated the best agreement with SR-μCT derived porosity.
•Compared distal radius cortical porosity from HR-pQCT (standard threshold, density-based and inhomogeneity methods) to SR-μCT•The standard threshold method underestimated porosity•The mean density method overestimated porosity•The density inhomogeneity method with recommended equation over-estimated porosity in more porous specimens•The density inhomogeneity method with optimized equation best explained variance in SR-μCT derived porosity without bias
Abstract Peripheral quantitative computed tomography (pQCT) imaging has been used to quantify muscle area and density as well as intermuscular adipose tissue (IMAT) and subcutaneous adipose tissue ...(SAT) area in the lower and upper limb. Numerous protocols have been reported to derive these soft-tissue outcomes, but their precision has not been assessed in community-dwelling postmenopausal women. The objective of this study was to compare the precision of previously reported analysis protocols for quantifying muscle area and density, as well as IMAT and SAT area in postmenopausal women. Six image analysis protocols using two available software suites (Stratec XCT, BoneJ) were identified from the pQCT literature. Analysis protocols were applied to a sample of 35 older female adults (mean age 73.7; SD 7.2 years), randomly selected from a population based-cohort and scanned twice within an average of 9.7 (SD 3.6) days. Relative precision was calculated as absolute values and as a percentage of the sample mean (root mean square coefficient of variation; CV%RMS ). Soft-tissue outcomes across protocols were compared on their log-transformed coefficients of variation using multilevel linear models and Tukey contrasts. For most protocols, CV%RMS for muscle area, density, and SAT area ranged between 2.1 and 3.7%, 0.7 and 1.9%, and 2.4 and 6.4%, respectively. Precision for IMAT area varied considerably, from 3 to 42%. Consideration of these study results will aid in the selection of appropriate image analysis protocols for pQCT-derived soft-tissue outcomes in postmenopausal women.
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