A comprehensive set of ultrashort echo time magnetic resonance imaging biomarkers to assess cortical bone health: A feasibility study at clinical field strength

INTRODUCTION

Conventional bone imaging methods primarily use X-ray techniques to assess bone mineral density (BMD), focusing exclusively on the mineral phase. This approach lacks information about the organic phase and bone water content, resulting in an incomplete evaluation of bone health. Recent research highlights the potential of ultrashort echo time magnetic resonance imaging (UTE MRI) to measure cortical porosity and estimate BMD based on signal intensity. UTE MRI also provides insights into bone water distribution and matrix organization, enabling a comprehensive bone assessment with a single imaging technique. Our study aimed to establish quantifiable UTE MRI-based biomarkers at clinical field strength to estimate BMD and microarchitecture while quantifying bound water content and matrix organization.

METHODS

Femoral bones from 11 cadaveric specimens (n = 4 males 67-92 yrs of age, n = 7 females 70-95 yrs of age) underwent dual-echo UTE MRI (3.0 T, 0.45 mm resolution) with different echo times and high resolution peripheral quantitative computed tomography (HR-pQCT) imaging (60.7 μm voxel size). Following registration, a 4.5 mm HR-pQCT region of interest was divided into four quadrants and used across the multi-modal images. Statistical analysis involved Pearson correlation between UTE MRI porosity index and a signal-intensity technique used to estimate BMD with corresponding HR-pQCT measures. UTE MRI was used to calculate T1 relaxation time and a novel bound water index (BWI), compared across subregions using repeated measures ANOVA.

RESULTS

The UTE MRI-derived porosity index and signal-intensity-based estimated BMD correlated with the HR-pQCT variables (porosity: r = 0.73, p = 0.006; BMD: r = 0.79, p = 0.002). However, these correlations varied in strength when we examined each of the four quadrants (subregions, r = 0.11-0.71). T1 relaxometry and the BWI exhibited variations across the four subregions, though these differences were not statistically significant. Notably, we observed a strong negative correlation between T1 relaxation time and the BWI (r = -0.87, p = 0.0006).

CONCLUSION

UTE MRI shows promise for being an innocuous method for estimating cortical porosity and BMD parameters while also giving insight into bone hydration and matrix organization. This method offers the potential to equip clinicians with a more comprehensive array of imaging biomarkers to assess bone health without the need for invasive or ionizing procedures.

Early bone loss in patients with obstructive sleep apnea: a cross-sectional study

BACKGROUND

Obstructive sleep apnea (OSA) and osteoporosis are both prevalent diseases with shared pathophysiological mechanisms and risk factors. However, the association between the two diseases is seldom studied. This study aimed to identify the link between OSA and bone metabolism.

METHODS

Male participants aged 30-59-years who visited the sleep clinic were continuously recruited. Polysomnography was used to evaluate sleep and respiratory conditions. Blood samples were collected to detect metabolic, inflammatory and bone turnover indicators. High-resolution peripheral quantitative computer tomography was used to measure the non-dominant lateral radius and tibia.

RESULTS

Ninety subjects were recruited. The cortical area (Ct.Ar) of tibia of the severe OSA group was significantly higher than that of the mild and moderate OSA groups (P = 0.06 and P = 0.048). There were significant differences between the four groups in terms of total volumetric bone mineral density (vBMD) (F = 2.990, P = 0.035), meta trabecular vBMD (F = 3.696, P = 0.015), trabecular thickness (Tb.Th) (F = 7.060, P = 0.000) and cortical thickness (Ct.Th) (F = 4.959, P = 0.003). The mean values of the OSA groups were lower than control group. Hypopnea index and percentage of total sleep time with SpO2 < 90% were both positively correlated with alkaline phosphatase (R = 0.213, P = 0.044; R = 0.212, P = 0.045). Sleep efficiency was correlated with multiple indicators of the radius.

CONCLUSIONS

In non-elderly male populations, OSA patients tended to have lower vBMD, Tb.Th and Ct.Th than non-OSA patients. The negative effect of OSA may mainly affect the osteogenesis process, and is presumed to be related to sleep-related hypoxemia and sleep efficiency.

A multi-stack registration technique to improve measurement accuracy and precision across longitudinal HR-pQCT scans

BACKGROUND

Recent applications of high-resolution peripheral quantitative computed tomography (HR-pQCT) have demonstrated that changes in local bone remodelling can be quantified in vivo using longitudinal three-dimensional image registration. However, certain emerging applications, such as fracture healing and joint analysis, require larger multi-stack scan regions that can result in stack shift image artifacts. These artifacts can be detrimental to the accurate alignment of the bone structure across multiple timepoints. The purpose of this study was to establish a multi-stack registration protocol for evaluating longitudinal HR-pQCT images and to assess the accuracy and precision error in comparison with measures obtained using previously established three-dimensional longitudinal registration.

METHODS

Three same day multi-stack HR-pQCT scans of the radius (2 stacks in length) and tibia (3 stacks in length) were obtained from 39 healthy individuals who participated in a previous reproducibility study. A fully automated multi-stack registration algorithm was developed to re-align stacks within a scan by leveraging slight offsets between longitudinal scans. Stack shift severity before and after registration was quantified using a newly proposed stack-shift severity score. The false discovery rate for bone remodelling events and precision error of bone morphology and micro-finite element analysis parameters were compared between longitudinally registered scans with and without the addition of multi-stack registration.

RESULTS

Most scans (82 %) improved in stack alignment or maintained the lowest stack shift severity score when multi-stack registration was implemented. The false discovery rate of bone remodelling events significantly decreased after multi-stack registration, resulting in median false detection of bone formation and resorption fractions between 3.2 to 7.5 % at the radius and 3.4 to 5.3 % at the tibia. Further, precision error was significantly reduced or remained unchanged in all standard bone morphology and micro-finite element analysis parameters, except for total and trabecular cross-sectional areas.

CONCLUSION

Multi-stack registration is an effective strategy for accurately aligning multi-stack HR-pQCT scans without modification of the image acquisition protocol. The algorithm presented here is a viable approach for performing accurate morphological analysis on multi-stack HR-pQCT scans, particularly for advanced application investigating local bone remodelling in vivo.

Comparison of Bone Quality Among Winter Endurance Athletes with and Without Risk Factors for Relative Energy Deficiency in Sport (REDs): A Cross-Sectional Study

Relative Energy Deficiency in Sport (REDs) is a syndrome describing the relationship between prolonged and/or severe low energy availability and negative health and performance outcomes. The high energy expenditures incurred during training and competition put endurance athletes at risk of REDs. The objective of this study was to investigate differences in bone quality in winter endurance athletes classified as either low-risk versus at-risk for REDs. Forty-four participants were recruited (M = 18; F = 26). Bone quality was assessed at the distal radius and tibia using high resolution peripheral quantitative computed tomography (HR-pQCT), and at the hip and spine using dual X-ray absorptiometry (DXA). Finite element analysis was used to estimate bone strength. Participants were grouped using modified criteria from the REDs Clinical Assessment Tool Version 1. Fourteen participants (M = 3; F = 11), were classified as at-risk of REDs (≥ 3 risk factors). Measured with HR-pQCT, cortical bone area (radius) and bone strength (radius and tibia) were 6.8%, 13.1% and 10.3% lower (p = 0.025, p = 0.033, p = 0.027) respectively, in at-risk compared with low-risk participants. Using DXA, femoral neck areal bone density was 9.4% lower in at-risk compared with low-risk participants (p = 0.005). At-risk male participants had 21.9% lower femoral neck areal bone density (via DXA) than low-risk males (p = 0.020) with no significant differences in females. Overall, 33.3% of athletes were at-risk for REDs and had lower bone quality than those at low-risk.

Bone deficits in children and youth with type 1 diabetes: A systematic review and meta-analysis

Deficits in bone mineral and weaker bone structure in children with type 1 diabetes (T1D) may contribute to a lifelong risk of fracture. However, there is no meta-analysis comparing bone properties beyond density between children with T1D and typically developing children (TDC). This meta-analysis aimed to assess differences and related factors in bone mineral content (BMC), density, area, micro-architecture and estimated strength between children with T1D and TDC. We systematically searched MEDLINE, Embase, CINAHL, Web of Science, Scopus, Cochrane Library databases, and included 36 in the meta-analysis (2222 children and youth with T1D, 2316 TDC; mean age ≤18 yrs., range 1-24). We estimated standardized mean differences (SMD) using random-effects models and explored the role of age, body size, sex ratio, disease duration, hemoglobin A1c in relation to BMC and areal density (aBMD) SMD using meta-regressions. Children and youth with T1D had lower total body BMC (SMD: -0.21, 95% CI: -0.37 to -0.05), aBMD (-0.30, -0.50 to -0.11); lumbar spine BMC (-0.17, -0.28 to -0.06), aBMD (-0.20, -0.32 to -0.08), bone mineral apparent density (-0.30, -0.48 to -0.13); femoral neck aBMD (-0.21, -0.33 to -0.09); distal radius and tibia trabecular density (-0.38, -0.64 to -0.12 and -0.35, -0.51 to -0.18, respectively) and bone volume fraction (-0.33, -0.56 to -0.09 and -0.37, -0.60 to -0.14, respectively); distal tibia trabecular thickness (-0.41, -0.67 to -0.16); and tibia shaft cortical content (-0.33, -0.56 to -0.10). Advanced age was associated with larger SMD in total body BMC (-0.13, -0.21 to -0.04) and aBMD (-0.09; -0.17 to -0.01) and longer disease duration with larger SMD in total body aBMD (-0.14; -0.24 to -0.04). Children and youth with T1D have lower BMC, aBMD and deficits in trabecular density and micro-architecture. Deficits in BMC and aBMD appeared to increase with age and disease duration. Bone deficits may contribute to fracture risk and require attention in diabetes research and care. STUDY REGISTRATION: PROSPERO (CRD42020200819).

Bone density, microarchitecture and strength in elite figure skaters is discipline dependent

OBJECTIVES

In elite figure skaters, to determine if there was a difference in volumetric bone mineral density and bone strength between 1) figure skaters and population-based normative data, 2) single or pair skaters and ice dancers, and 3) the landing and takeoff legs.

DESIGN

Cross-sectional.

METHODS

Figure skaters had their non-dominant distal radius and bilateral tibia scanned using high-resolution peripheral quantitative computed tomography. Volumetric bone mineral density was determined at the total, cortical and trabecular compartments, and finite element analysis estimated bone strength. Normative data was used to compare the total bone mineral density of figure skaters to a population-based cohort. Independent t-tests compared differences between skating discipline, and paired t-tests compared skeletal parameters for the landing and takeoff leg.

RESULTS

Twenty elite skaters (mean age 22 ± 6.2; female = 11, male = 9) completed scans. Compared with the general population, the mean percentile rank for skaters' total volumetric bone mineral density was below normal at the radius (27th percentile) and normal at the tibia (54th percentile). Single or pair skaters had more robust bone in the landing compared with their takeoff leg. Specifically, the landing leg had higher total bone mineral density (2.8%) and trabecular bone mineral density (6.5%), and superior bone strength (8.5%) than the takeoff leg (p < 0.05).

CONCLUSIONS

Volumetric bone mineral density and strength differences in figure skaters were discipline dependent. Side-to-side differences were observed in single and pair skaters where the landing leg is denser, larger and stronger than the takeoff leg.

A new approach for quantifying localized bone loss by measuring void spaces

The application of high resolution peripheral quantitative computed tomography (HR-pQCT) for the study of bone health has provided valuable insight into the role bone microarchitecture has in determining bone strength and fracture risk. However, conventional density and morphological parameters struggle to distinguish whether localized bone loss is present, visible as heterogeneous deterioration in the trabecular network. This is because current HR-pQCT parameters quantify a global average of properties in the cortical or trabecular compartment. This study proposes a new metric we term "void space" that segments volumes of localized deterioration in the trabecular bone network from HR-pQCT scans and quantifies void space as the void space to total volume ratio (VS/TV, %). A simple and fully automated protocol for segmenting and quantifying void space in HR-pQCT scans is presented, along with the assessment of accuracy, precision, and cross-calibration between generations of HR-pQCT systems. Finally, prevalence of void space and the association with standard HR-pQCT parameters is demonstrated using a large population-based cohort (n = 1236). Void space detection was found to be highly reproducible (accuracy >95%, least significant change <1.76% VS/TV) and correlation between scanner generations was strong (R² = 0.87), although the first generation system struggled to identify small voids. Assessment of void space prevalence in the population-based cohort revealed that void spaces were more common in females than males, prevalence increased with age, and void spaces were typically systemic (occurring at both scan sites rather than only one). A comparison of group-wise differences between participants with and without void space demonstrated that individuals with void spaces had significantly worse trabecular properties for both sexes and at both scan sites. Specifically, the median trabecular bone mineral density, bone volume fraction, and trabecular number were below the 25th percentile of the population, while trabecular separation and inhomogeneity were above the 75th percentile of the population in participants with void spaces. Cortical bone characteristics did not differ between participants with and without void spaces. When the void space region was excluded from morphological analysis so that only the remaining "functional bone" was considered, trabecular properties of participants with void spaces were greatly improved, especially for those who were the greatest outliers. Void space is an intuitive morphological parameter that captures localized deterioration in the trabecular bone network, and has the potential to provide valuable insight into the assessment of bone fragility.

Bone geometry and microarchitecture deficits in children with Alagille syndrome

Alagille syndrome (ALGS) is an autosomal dominant disorder attributed to mutations in the Notch signaling pathway. Children with ALGS are at increased risk for fragility fracture of unknown etiology. Our objective was to characterize bone mass, geometry, and microarchitecture in children with ALGS. This was a cross-sectional study of 10 children (9 females), ages 8-18 years, with a clinical diagnosis of ALGS. Bone density was assessed via DXA (Hologic Discovery A) at several skeletal regions. Tibia trabecular and cortical bone was assessed via pQCT (Stratec XCT 2000) at the distal 3% and 38% sites, respectively. Tibia bone microarchitecture was assessed via HR-pQCT (Scanco XtremeCT II) at an ultradistal site located at 4% of tibia length and a cortical site at 30% of tibia length. Z-scores were calculated for DXA and pQCT measures. In the absence of XtremeCT II HR-pQCT reference data, these outcome measures were descriptively compared to a sample of healthy children ages 5-20 years (n = 247). Anthropometrics and labs were also collected. Based on one-sample t-tests, mean Z-scores for height and weight (both p < .05), were significantly less than zero. DXA bone Z-scores were not significantly different from zero, but were highly variable. For pQCT bone measures, Z-scores for total bone mineral content at the distal 3% site and cortical bone mineral content, cortical area, and cortical thickness at the distal 38% site were significantly less than zero (all p < .05). There was good correspondence between pQCT measures of cortical thickness Z-scores and DXA Z-scores for aBMD at the whole body less head, 1/3 radius, and femoral neck (all p < .05). Compared to healthy children, those with ALGS generally had lower trabecular number and greater trabecular separation despite having greater trabecular thickness (measured via HR-pQCT). Bilirubin and bile acids, markers of hepatic cholestasis, were associated with poorer bone measures. For example, greater bilirubin was associated with lower trabecular number (Spearman's rho [ρ] = -0.82, p = .023) and greater trabecular separation (ρ = 0.82, p = .023) measured via HR-pQCT, and greater bile acids were associated with lower cortical area measured via pQCT (ρ = -0.78, p = .041) and lower serum insulin-like growth factor-1 (ρ = -0.86, p = .002). In summary, deficits in cortical bone size and trabecular bone microarchitecture were evident in children with ALGS. Further investigation is needed to understand the factors contributing to these skeletal inadequacies, and the manner in which these deficits contribute to increased fracture risk.

Bone remodeling following MR-guided focused ultrasound: Evaluation with HR-pQCT and FTIR

Magnetic resonance-guided focused ultrasound (MRgFUS) is a novel non-invasive ablation technique that uses focused sound energy to destroy focal tumors, primarily via heat deposition. It is widely used for palliation of pain from bone metastases and has also recently gained popularity as a technique for ablation of benign bone tumors and facet degenerative joint disease (rhizotomy). Clinically, in a subset of patients who have undergone MRgFUS of bone, a variety of treatment responses have been noted on follow-up imaging, including focal sclerosis within the target lesion or more exuberant proliferative changes associated with the periosteum. In this study, high resolution peripheral quantitative CT (HR-pQCT) was used to evaluate remodeling of bone following ablation in a swine model of MRgFUS and compared to samples from a control, non-treated femur. Within each treated femur, two lesions were created: a higher energy focused ultrasound dose was used for one lesion compared to a lower energy dose for the second lesion. Exuberant, extra-cortical bone formation was detected at the higher energy ablation zones, with volumes ranging from 340 mm³ to 1040 mm³. More subtle endosteal and cortical changes were detected in the lower energy ablation zones, however cortical thickness was significantly increased at these sites compared to control bone. For both high and low energy lesions, lower bone mineral density and tissue mineral density was noted in treated regions compared to control regions, consistent with the formation of newly mineralized tissue. Following HR-pQCT analysis, Fourier transform infrared (FTIR) spectroscopy was subsequently used to detect biochemical changes associated with remodeling of bone following MRgFUS, and compared to samples from the control, non-treated femur. Findings were compared with histopathologic examination following hematoxylin-eosin staining. FTIR analysis demonstrated lower mineral/phosphate ratio and increased crystallinity compared to the control samples (p = 0.013). Histopathologic review demonstrated associated areas of endosteal inflammation, scarring, fat necrosis, and new extra-cortical bone formation associated with the ablations. Overall, these findings provide novel characterization of new bone formation following MRgFUS ablation.

Reliability of HR-pQCT Derived Cortical Bone Structural Parameters When Using Uncorrected Instead of Corrected Automatically Generated Endocortical Contours in a Cross-Sectional Study: The Maastricht Study

Most HR-pQCT studies examining cortical bone use an automatically generated endocortical contour (AUTO), which is manually corrected if it visually deviates from the apparent endocortical margin (semi-automatic method, S-AUTO). This technique may be prone to operator-related variability and is time consuming. We examined whether the AUTO instead of the S-AUTO method can be used for cortical bone analysis. Fifty scans of the distal radius and tibia from participants of The Maastricht Study were evaluated with AUTO, and subsequently with S-AUTO by three independent operators. AUTO cortical bone parameters were compared to the average parameters obtained by the three operators (S-AUTOmean). All differences in mean cortical bone parameters between AUTO and S-AUTOmean were < 5%, except for lower AUTO cortical porosity of the radius (- 16%) and tibia (- 6%), and cortical pore volume (Ct.Po.V) of the radius (- 7%). The ICC of S-AUTOmean and AUTO was > 0.90 for all parameters, except for cortical pore diameter of the radius (0.79) and tibia (0.74) and Ct.Po.V of the tibia (0.89), without systematic errors on the Bland-Altman plots. The precision errors (RMS-CV%) of the radius parameters between S-AUTOmean and AUTO were comparable to those between the individual operators, whereas the tibia RMS-CV% between S-AUTOmean and AUTO were higher than those of the individual operators. Comparison of the three operators revealed clear inter-operator variability. This study suggests that the AUTO method can be used for cortical bone analysis in a cross-sectional study, but that the absolute values-particularly of the porosity-related parameters-will be lower.

An automated algorithm for the detection of cortical interruptions and its underlying loss of trabecular bone; a reproducibility study

Background

We developed a semi-automated algorithm that detects cortical interruptions in finger joints using high-resolution peripheral quantitative computed tomography (HR-pQCT), and extended it with trabecular void volume measurement. In this study we tested the reproducibility of the algorithm using scan/re-scan data.

Methods

Second and third metacarpophalangeal joints of 21 subjects (mean age 49 (SD 11) years, 17 early rheumatoid arthritis and 4 undifferentiated arthritis, all diagnosed < 1 year ago) were imaged twice by HR-pQCT on the same day with repositioning between scans. The images were analyzed twice by one operator (OP1) and once by an additional operator (OP2), who independently corrected the bone contours when necessary. The number, surface and volume of interruptions per joint were obtained. Intra- and inter-operator reliability and intra-operator reproducibility were determined by intra-class correlation coefficients (ICC). Intra-operator reproducibility errors were determined as the least significant change (LSC_SD).

Results

Per joint, the mean number of interruptions was 3.1 (SD 3.6), mean interruption surface 4.2 (SD 7.2) mm², and mean interruption volume 3.5 (SD 10.6) mm³ for OP1. Intra- and inter-operator reliability was excellent for the cortical interruption parameters (ICC ≥0.91), except good for the inter-operator reliability of the interruption surface (ICC = 0.70). The LSC_SD per joint was 4.2 for the number of interruptions, 5.8 mm² for interruption surface, and 3.2 mm³ for interruption volume.

Conclusions

The algorithm was highly reproducible in the detection of cortical interruptions and their volume. Based on the LSC findings, the potential value of this algorithm for monitoring structural damage in the joints in early arthritis patients needs to be tested in clinical studies.

Electronic supplementary material

The online version of this article (10.1186/s12880-018-0255-7) contains supplementary material, which is available to authorized users.

Methods and procedures for: A randomized double-blind study investigating dose-dependent longitudinal effects of vitamin D supplementation on bone health

The optimum dose of vitamin D and corresponding serum 25-hydroxyvitamin D (25OHD) concentration for bone health is still debated and some health practitioners are recommending doses well above the Canada/USA recommended Dietary Reference Intake (DRI). We designed a three-year randomized double-blind clinical trial investigating whether there are dose-dependent effects of vitamin D supplementation above the Dietary Reference Intake (DRI) on bone health. The primary aims of this study are to assess, whether supplementation of vitamin D₃ increases 1) volumetric bone mineral density measured by high-resolution peripheral quantitative computed tomography (HR-pQCT); 2) bone strength assessed by finite element analysis, and 3) areal bone mineral density by dual X-ray absorptiometry (DXA). Secondary aims are to understand whether vitamin D₃ supplementation improves parameters of bone microarchitecture, balance, physical function and quality of life. Participants are men and women aged 55-70 years, with women at least 5-years post-menopause. The intervention is daily vitamin D₃ supplementation doses of 400, 4000 or 10,000 IU. Participants not achieving adequate dietary calcium intake are provided with calcium supplementation, up to a maximum supplemental dose of 600 mg elemental calcium per day. Results from this three-year study will provide evidence whether daily vitamin D₃ supplementation with adequate calcium intake can affect bone density, bone microarchitecture and bone strength in men and women. Furthermore, the safety of high dose daily vitamin D₃ supplementation will be explored.

The Reliability of a Semi-automated Algorithm for Detection of Cortical Interruptions in Finger Joints on High Resolution CT Compared to MicroCT

We developed a semi-automated algorithm for the detection of cortical interruptions in finger joints using high-resolution peripheral quantitative computed tomography (HR-pQCT). Here, we tested its reliability compared to microCT (µCT) as gold standard. Nineteen joints of 10 female anatomic index fingers were imaged by HR-pQCT and µCT (82 and 18 µm isotropic voxel sizes, respectively). The algorithm was applied for detection of cortical interruptions of different minimum diameters (range >0.16 to >0.50 mm). Reliability was tested at the joint level with intra-class correlation coefficient (ICC) for the number of interruptions and interruption surface, and at the level of a single interruption for matching between HR-pQCT and µCT with a fixed interruption diameter (>0.10 mm) on µCT. The positive predictive value (PPV_0.10mm) and sensitivity_0.10mm were evaluated. The mean number of interruptions per joint depended on the diameter cut-off and ranged from 3.4 to 53.5 on HR-pQCT and from 1.8 to 45.1 on µCT for interruptions >0.50 to >0.16 mm, respectively. Reliability at the joint level was almost perfect (ICC ≥0.81) for both the number and surface of interruptions >0.16 and >0.33 mm. As expected, the PPV_0.10mm increased with increasing interruption diameter from 84.9 to 100%, for interruptions >0.16 and >0.50 mm, respectively. However, the sensitivity_0.10mm decreased with increasing interruption diameter from 62.4 to 4.7%. This semi-automated algorithm for HR-pQCT in finger joints performed best for the detection of cortical interruptions with a minimum diameter of >0.16 or >0.33 mm, showing almost perfect reliability at the joint level and interruptions matched with those on µCT.

Age-related changes in bone strength from HR-pQCT derived microarchitectural parameters with an emphasis on the role of cortical porosity

The high resolution peripheral computed tomography (HR-pQCT) technique has seen recent developments with regard to the assessment of cortical porosity. In this study, we investigated the role of cortical porosity on bone strength in a large cohort of women. The distal radius and distal tibia were scanned by HR-pQCT. We assessed bone strength by estimating the failure load by microfinite element analysis (μFEA), with isotropic and homogeneous material properties. We built a multivariate model to predict it, using a few microarchitecture variables including cortical porosity. Among 857 Caucasian women analyzed with μFEA, we found that cortical and trabecular properties, along with the failure load, impaired slightly with advancing age in premenopausal women, the correlations with age being modest, with |rage| ranging from 0.14 to 0.38. After the onset of the menopause, those relationships with age were stronger for most parameters at both sites, with |rage| ranging from 0.10 to 0.64, notably for cortical porosity and failure load, which were markedly deteriorated with increasing age. Our multivariate model using microarchitecture parameters revealed that cortical porosity played a significant role in bone strength prediction, with semipartial r(2)=0.22 only at the tibia in postmenopausal women. In conclusion, in our large cohort of women, we observed a small decline of bone strength at the tibia before the onset of menopause. We also found an age-related increase of cortical porosity at both scanned sites in premenopausal women. In postmenopausal women, the relatively high increase of cortical porosity accounted for the decline in bone strength only at the tibia.

Dynamics of interpedicular widening in spinal burst fractures: an in vitro investigation

BACKGROUND CONTEXT

Spinal burst fractures are a significant cause of spinal instability and neurologic impairment. Although evidence suggests that the neurologic trauma arises during the dynamic phase of fracture, the biomechanics underpinning the phenomenon has yet to be fully explained. Interpedicular widening (IPW) is a distinctive feature of the fracture but, despite the association with the occurrence of neurologic deficit, little is known about its biomechanics.

PURPOSE

To provide a comprehensive in vitro study on spinal burst fracture, with special attention on the dynamics of IPW.

STUDY DESIGN

Experimental measurements in combination with computed tomography scanning were used to quantitatively investigate the biomechanics of burst fracture in a cadaveric model.

METHODS

Twelve human three-adjacent-vertebra segments were tested to induce burst fracture. Impact was delivered through a drop-weight tower, whereas IPW was continuously recorded by two displacement transducers. Computed tomography scanning aided quantifying canal occlusion (CO) and evaluating sample anatomy and fracture appearance. Two levels of energy were delivered to two groups: high energy (HE) and low energy (LE).

RESULTS

No difference was found between HE and LE in terms of the residual IPW (ie, post-fracture), maximum IPW, or CO (median 20.2%). Whereas IPW was not found to be correlated with CO, a moderate correlation was found between the maximum and the residual IPW. At the fracture onset, IPW reached a maximum median value of 15.8% in approximately 20 to 25 milliseconds. After the transient phase, the pedicles were recoiled to a median residual IPW of 4.9%.

CONCLUSIONS

Our study provides for the first time insight on how IPW actually evolves during the fracture onset. In addition, our results may help shedding more light on the mechanical initiation of the fracture.

Cortical measurements of the tibia from high resolution peripheral quantitative computed tomography images: a comparison with synchrotron radiation micro-computed tomography

High resolution-peripheral quantitative computed tomography (HR-pQCT) measurements are carried out in clinical research protocols to analyze cortical bone. Micro-computed tomography (micro-CT) is a standard tool for ex vivo examination of bone in 3D. The aim of this work was to evaluate cortical measurements derived from HR-pQCT images compared to those from synchrotron radiation (SR) micro-CT in a distal position (4.2 cm from the distal pilon). Twenty-nine tibia specimens were scanned with HR-pQCT using protocols provided by the manufacturer. The standard measured outcomes included volumetric bone density (gHA/cm(3)) of the cortical region (Dcomp), and the cortical thickness (Ct.Th, mm). New features, such as cortical porosity (Ct.Po) and mean pore diameter (Ct.Po.Dm), were measured by an auto-contouring process. All tibias were harvested from the posterior region and imaged with SR micro-CT (voxel size=7.5 μm). The cortical thickness, (Ct.Thmicro-CT), porosity (PoV/TV), pore diameter, pore spacing, pore number, and degree of mineralization of bone (DMB) were obtained for SR micro-CT images. For standard measurements on HR-pQCT images, site matched analyses with micro-CT were completed to obtain Dcomplocal and Ct.Thlocal. Dcomp was highly correlated to PoV/TV (r=-0.84, p<10(-4)) but not to DMB. Dcomplocal was correlated to PoV/TV (r=-0.72, p<10(-4)) and to DMB (r=0.40, p>0.05). Ct.Thlocal and Ct.Thmicro-CT were moderately correlated (r=0.53, p<0.01). Ct.Th and Ct.Po results from the autocontouring process are influenced by the level of trabecularization of the cortical bone and need manual correction of the endosteal contour. Distal tibia is a reliable region to study cortical bone with Dcomp as the best parameter because it reflects both the micro-porosity (Havers canals) and macro-porosity (resorption lacunae) of the cortical bone.