Effect of trabecular bone contour on ultimate strength of lumbar vertebra after bilateral ovariectomy in rats

To test the hypothesis that the effect of trabecular microarchitecture on bone strength varies with the duration of estrogen loss, we evaluated the relationship between three-dimensional (3D) parameters for trabecular microarchitecture and bone minerals with the compressive load of the lumbar vertebra in rats. Female Sprague-Dawley rats (n = 190) were divided into 19 groups. Ten rats were killed at day 0. Half of the remaining rats underwent bilateral ovariectomy (ovx), and the others were subjected to sham surgery. Ten rats from each group were killed at 3, 7, 11, 14, 28, 42, 56, 70, and 84 days postsurgery. Urinary deoxypyridinoline and serum osteocalcin increased significantly in the ovx group from days 28 and 11, respectively, compared with the sham group. Bone mineral content (BMC) and bone mineral density (BMD) of the fifth lumbar body diminished from days 42 and 84, respectively, compared with the sham group. In ovx rats, trabecular bone volume (BV/TV), measured using 3D images of microcomputed tomography, diminished from day 28 compared with both baseline control and sham. The trabecular bone pattern factor (TBPf) and structure model index (SMI) increased from day 28 in the ovx group compared with both baseline control and sham. Ultimate compression loads diminished at day 28 compared with baseline control and decreased progressively thereafter. Neither of these parameters changed in the sham group during the same period. Within 4 weeks post-ovx, TBPf, SMI, and BV/TV correlated with load (p < 0.01). BMC and BMD correlated with load from 6 weeks post-ovx (p < 0.01). Stepwise regression analysis showed that TBPf was the most significant determinant of load within 4 weeks post-ovx (coefficient of determination [R²] = 0.669; p < 0.01). SMI correlated with TBPf (R² = 0.968; p < 0.01). Moreover, R² for ultimate load indicated higher values of 0.975 with TBPf and SMI. However, BMC was the most significant determinant of load from 6 weeks post-ovx (R² = 0.511; p < 0.01), as it was in the sham group. These data suggest that changes in trabecular bone contour with increased bone turnover are critical for reducing lumbar bone strength during the early post-ovx period in rats.     

Lumbar vertebral body compressive strength evaluated by dual-energy X-ray absorptiometry, quantitative computed tomography, and ashing

Bone densitometry with DXA (dual energy X-ray absorptiometry) and QCT (quantitative computed tomography) techniques are used for in vivo assessment of bone strength and thereby prediction of fracture risk. However, only few in vitro studies have investigated and compared these techniques’ ability to determine vertebral compressive strength. The aim of the present study was to (1) assess the predictive value of DXA, QCT, and pQCT (peripheral QCT) for vertebral bone compressive strength assessed by mechanical testing; (2) describe both linear and power relationship between density and strength; and (3) evaluate whether gender-related differences in the above relations were present. The material comprised human lumbar vertebrae L3 from 51 women and 50 men (age range: 18 to 96 years). The study showed that both DXA and CT techniques (QCT and pQCT) have a high predictive value for vertebral strength. The DXA BMD had a high correlation with maximum compressive load (r² = 0.86). The QCT and pQCT had high correlations with maximum compressive stress (r² = 0.75 and r² = 0.86, respectively). The correlation between ash density of the biomechanically tested specimen and maximum compressive stress was r² = 0.88. There were no differences between linear and power fit in the degree of determination between density and strength. There was no gender-related difference in the relationship between volumetric density and maximum compressive stress. In conclusion, it was demonstrated that DXA, QCT, and pQCT are ex situ equally capable of predicting vertebral compressive strength with a degree of determination (r²) between 75% and 86%. No differences were found between linear and power analysis of the relationship between density and strength, and no difference was found in the density strength relationship between women and men.     

Ultrasound velocity and broadband attenuation as predictors of load-bearing capacities of human calcanei

The main purpose of this study was to determine whether calcaneal ultrasound parameters, measured in the mediolateral direction, reflect load-bearing capacities of human calcanei. Broadband ultrasound attenuation (BUA) and ultrasound velocity (UV) were measured in 20 cadaveric calcanei with a mean age of 74.1 (SD 8.8). Normalized BUA (nBUA) was determined by dividing BUA by the calcaneal thickness obtained using a pulse-echo technique. The bone mineral density (BMD) of each calcaneus was measured by quantitative computed tomography. The calcanei were embedded in PMMA to simulate the midstance physiologic orientation during compressive testing in the load-bearing direction. The failure load, stiffness, and energy absorption were determined for each calcaneus. It was shown that BMD was well correlated with all ultrasound parameters (P < 0.0001). BMD, BUA, nBUA, and UV were all significantly associated with calcaneal failure load, stiffness, and energy absorption capacity (P < 0.05). nBUA was found to be the strongest predictor of all compressive properties. BUA and BMD demonstrated similar predictability of stiffness and energy absorption capacity, however, BUA showed a more significant relationship to the failure load of the calcaneus than did BMD. UV was found to be inferior to BMD, as well as BUA or nBUA, in assessing failure load, stiffness, and energy absorption capacity. It was also shown that nBUA was superior to BUA in the assessment of load-bearing capacity, but not in the prediction of BMD. Multivariate regression analysis showed that the combination of BUA or nBUA with UV did not improve the predictability of failure load, stiffness, and energy absorption capacity over that of BUA or nBUA alone (P > 0.5). Received: 29 December 1995 / Accepted: 3 May 1996     

Estimation of distal radius failure load with micro-finite element analysis models based on three-dimensional peripheral quantitative computed tomography images

There is increasing evidence that, in addition to bone mass, bone microarchitecture and its mechanical load distribution are important factors for the determination of bone strength. Recently, it has been shown that new high-resolution imaging techniques in combination with new modeling algorithms based on the finite element (FE) method can account for these additional factors. Such models thus could provide more relevant information for the estimation of bone failure load. The purpose of the present study was to determine whether results of whole-bone micro-FE (μFE) analyses with models based on three-dimensional peripheral quantitative computer tomography (3D-pQCT) images (isotropic voxel resolution of 165 μm) could predict the failure load of the human radius more accurately than results with dual-energy X-ray absorptiometry (DXA) or bone morphology measurements. For this purpose, μFE models were created using 54 embalmed cadaver arms. It was assumed that bone failure would be initiated if a certain percentage of the bone tissue (varied from 1% to 7%) would be strained beyond the tissue yield strain. The external force that produced this tissue strain was calculated from the FE analyses. These predictions were correlated with results of real compression testing on the same cadaver arms. The results of these compression tests were also correlated with results of DXA and structural measurements of these arms. The compression tests produced Colles-type fractures in the distal 4 cm of the radius. The predicted failure loads calculated from the FE analysis agreed well with those measured in the experiments (R² = 0.75 p < 0.001). Lower correlations were found with bone mass (R² = 0.48, p < 0.001) and bone structural parameters (R² = 0.57 p < 0.001). We conclude that application of the techniques investigated here can lead to a better prediction of the bone failure load for bone in vivo than is possible from DXA measurements, structural parameters, or a combination thereof.     

Regional variation in vertebral bone morphology and its contribution to vertebral fracture strength

Vertebral fractures may result in pain, loss of height, spinal instability, kyphotic deformity and ultimately increased morbidity. Fracture risk can be estimated by vertebral bone mineral density (BMD). However, vertebral fractures may be better defined by more selective methods that account for micro-architecture.

Our aim was to quantify regional variations in bone architecture parameters (BAPs) and to assess the degree with which regional variations in BAPs affect vertebral fracture strength. The influence of disc health and endplate thickness on fracture strength was also determined.

The soft tissue and posterior elements of 20 human functional spine units (FSU) were removed (T9 to L5, mean 74.45 ± 4.25 years). After micro-CT scanning of the entire FSU, the strength of the specimens was determined using a materials testing system. Specimens were loaded in compression to failure. BAPs were assessed for 10 regions of the vertebral cancellous bone. Disc health (glycosaminoglycan content of the nucleus pulposus) was determined using the degree of binding with Alcian Blue.

Vertebrae were not morphologically homogeneous. Posterior regions of the vertebrae had greater bone volume, more connections, reduced trabecular separation and more plate-like isotropic structures than their corresponding anterior regions. Significant heterogeneity also exists between posterior superior and inferior regions (BV/TV: posterior superior 12.6 ± 2.8%, inferior 14.6 ± 3%; anterior superior 10.5 ± 2.2%, inferior 10.7 ± 2.4%). Of the two endplates that abutted a common disc, the cranial inferior endplate was thicker (0.44 ± 0.15 mm) than the caudal superior endplate (0.37 ± 0.13 mm). Our study found good correlations between BV/TV, connective density and yield strength. Fracture risk prediction, using BV/TV multiplied by the cross sectional area of the endplate, can be improved through regional analysis of the underlying cancellous bone of the endplate of interest (R² 0.78) rather than analysis of the entire vertebra (R² 0.65) or BMD (R² 0.47). Degenerated discs lack a defined nucleus. A negative linear relationship between disc health and vertebral strength (R² 0.70) was observed, likely due to a shift in loading from the weaker anterior vertebral region to the stronger posterior region and cortical shell.

Our results show the importance of considering regional variations in cancellous BAPs and disc health when assessing fracture risk.     

Influence of bone volume fraction and architecture on computed large-deformation failure mechanisms in human trabecular bone

Large-deformation bending and buckling have long been proposed as failure mechanisms by which the strength of trabecular bone can be affected disproportionately to changes in bone density, and thus may represent an important aspect of bone quality. We sought here to quantify the contribution of large-deformation failure mechanisms on strength, to determine the dependence of these effects on bone volume fraction and architecture, and to confirm that the inclusion of large-deformation effects in high-resolution finite element models improves predictions of strength versus experiment. Micro-CT-based finite element models having uniform hard tissue material properties were created from 54 cores of human trabecular bone taken from four anatomic sites (age = 70 ± 11; 24 male, 27 female donors), which were subsequently biomechanically tested to failure. Strength predictions were made from the models first including, then excluding, large-deformation failure mechanisms, both for compressive and tensile load cases. As expected, strength predictions versus experimental data for the large-deformation finite element models were significantly improved (p < 0.001) relative to the small deformation models in both tension and compression. Below a volume fraction of about 0.20, large-deformation failure mechanisms decreased trabecular strength from 5–80% for compressive loading, while effects were negligible above this volume fraction. Step-wise nonlinear multiple regression revealed that structure model index (SMI) and volume fraction (BV/TV) were significant predictors of these reductions in strength (R² = 0.83, p < 0.03). Even so, some low-density specimens having nearly identical volume fraction and SMI exhibited up to fivefold differences in strength reduction. We conclude that within very low-density bone, the potentially important biomechanical effect of large-deformation failure mechanisms on trabecular bone strength is highly heterogeneous and is not well explained by standard architectural metrics.     

Nondestructive determination of iliac crest cancellous bone strength by pQCT

The close relationship between apparent bone density and compressive strength is well established. In clinical situations, histomorphometry, and determination of the compressive strength on bone biopsies are destructive methods and require two separate biopsies from each patient. The aim of this study was to evaluate whether volumetric bone density measured by peripheral quantitative computed tomography (pQCT) could be used as a nondestructive method for estimating trabecular bone strength of iliac crest bone biopsies, thereby allowing the same biopsy to be used for subsequent histomorphometry. Materials consisted of trabecular bone samples prepared from unilateral transiliac crest bone samples obtained at autopsy [total 95 specimens; 41 females (21–90 years) and 54 males (23–87 years)]. From these, the apparent density of the cancellous bone was evaluated by pQCT in a 1-mm-thick slice in the middle of the biopsy and also by ash density measurement. Bone strength was measured by compression test. A strong power relationship was found between density measured by pQCT and compressive strength (r = 0.93, p < 0.00001). Likewise, there was a strong power relationship between ash density and compressive strength (r = 0.97, p < 0.00001). A linear correlation was found between pQCT measurement and ash density (r = 0.98, p < 0.00001), indicating a very high accuracy for the pQCT measurement. In conclusion, pQCT provides a very good estimate of cancellous bone strength. This nondestructive assessment of strength of iliac crest bone biopsies thereby enables biomechanical information as well as histomorphometric measurements to be obtained from the same biopsy.     

Differences of Vertebral Area in Serial Bone Density Measurements: A Common Source of Potential Error in Interpretation of BMD Change

Vertebral projected areas in serial BMD scans should not differ significantly to avoid measurement error due to apparent change in projected bone size. This criterion is rarely achieved in clinical practice. We analyzed 103 consecutive pairs of DXA reports to determine the frequency and magnitude of serial differences in vertebral area. Scans were performed at qualified community radiology sites and included if free from any technical errors, artifacts or rotation. We calculated the proportion of paired scans having at least 2 vertebrae differing in area by < 2%, < 3%, < 4% or < 5%. Using these differing sets of validity criteria, vertebrae not meeting the areal standard were removed form the analysis and the overall change in BMD recalculated. The new, recalculated BMD was compared to the original report to determine the frequency and magnitude by which the re-analysis would change the final report. Of the paired scans, 5%, 16%, 27% and 35% had all 4 vertebrae differ in area by less than 2%, 3%, 4% and 5% respectively. When only two vertebrae were required to meet acceptability criteria, 51%, 73%, 85% and 89% of scans met the 2%, 3%, 4% and 5% difference criteria. 11% of scans were non-comparable by even the least stringent criteria of two vertebra differing by < 5% between scans. Re-analysis of BMD change in each group differed from the reported change by 0.012–0.015 g/cm². However, this amount was sufficient to change a clinical report from “significant change” to “non-significant change” in 26%, 27%, 21%, and 20% of scans in each of the four validity groups using a least significant change of 0.025 g/cm². Between 11%–17% of scans differed in the recalculated BMD change by an amount greater than the least significant change of 0.025 g/cm². Fewer serial BMD results were classified as non-acceptable when using the broader validity criteria of < 5% area difference, but when corrected for areal differences, a similar and large proportion of scans would have a major change in the clinical interpretation of BMD change. These results do not change the interpretation of population BMD change in randomized trials but highlight the need for more caution in data analysis of serial densitometry results when used to make individual patient management decisions.     

Meta-analysis of COL1A1 Sp1 polymorphism in relation to bone mineral density and osteoporotic fracture

Genetic factors play an important role in the pathogenesis of osteoporosis and several candidate gene polymorphisms have been implicated in the regulation of this process. One of the most widely studied is the Sp1 binding site polymorphism in the COL1A1 gene. This polymorphism has been associated with BMD and osteoporotic fracture in several studies, but the data from different studies have been conflicting. Here we have attempted to clarify the association between COL1A1 Sp1 alleles, BMD, and osteoporotic fracture by conducting a meta-analysis of 26 published studies including 7849 participants. Under a fixed effects model, BMD values at the lumbar spine (6800 subjects) were significantly lower in the “Ss” genotype group when compared with “SS” homozygotes (standardized mean DIFFERENCE = 0.131 [95% CI, 0.06,0.16], P = 0.00005) but the difference was not significant for the “ss” comparison (0.09 [−0.03,0.21], P = 0.13). At the femoral neck (6750 subjects) BMD values were lower in the “Ss” genotype (0.14 [0.08,0.19], P < 0.00001) and lower still in the “ss” genotype group (0.19 [0.07,0.31], P = 0.001). Similar results were found when the data were analyzed under a random effects model. Analysis of fracture data (6961 subjects) showed an increased odds ratio for any fracture in “Ss” subjects (1.26 [95% CI 1.09,1.46], P = 0.002) and an even greater increase in “ss” subjects (1.78 [1.30,2.43], P = 0.0003). Subgroup analysis showed that increased risk was largely attributable to vertebral fracture where the odds ratio was 1.37 [1.15,1.64] for “Ss” (P = 0.0004) and 2.48 [1.69,3.65] for “ss” (P < 0.00001). The risk of nonvertebral fracture was not increased in relation to the COL1A1 genotype, although power to detect an effect was limited by the fact that fewer studies had analyzed nonvertebral fracture. We conclude that the COL1A1 Sp1 alleles are associated with a modest reduction in BMD and a significant increase in risk of osteoporotic fracture, particularly vertebral fracture.     

Patient-specific microarchitecture of vertebral cancellous bone: a peripheral quantitative computed tomographic and histological study

This study directly compares peripheral quantitative computed tomography (pQCT) and histology for the assessment of 11 morphological parameters. Sixty-eight cylindrical cancellous bone samples were cored from the thoracic (T-9) thoracolumbar (T-12 or L-1), and lumbar (L-4) vertebral bodies of nine autopsy subjects (aged 44–88 years). Four transverse slices were acquired by pQCT from the bottom to the top of each cylinder. Slice thickness was 300 μm and pixel size was 70 × 70 μm. Thin sections (5 μm) were obtained at the same location in the samples, stained with Von Kossa, and photographed. Classical morphological parameters and strut analysis parameters were measured on all images (272 pQCT and 272 matched histological sections). Because of the partial volume effect and specific thresholding procedure, pQCT overestimated the absolute value of the bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) by a factor 2. The trabecular number (Tb.N), trabecular spacing (Tb.Sp), and total strut length (TSL) were correctly estimated. However, the direct correlation between pQCT and histology was excellent (r² > 0.85, p < 0.001) for BV/TV, Tb.N, Tb.Sp, TSL, and star surface. For Tb.Th, number of nodes, and number of free ends, the correlation was also good (r² > 0.6, p < 0.001). Using a random regression model, we also explored the ability of these parameters to add structural information to the readily available BV/TV or apparent density. The model identified significant (p < 0.001) differences between subjects. For a given BV/TV, some patients had more trabeculae (Tb.N) that were thinner (Tb.Th) and more disconnected (higher free ends and star). This was observed for both histology and pQCT morphometrical data. Our analysis demonstrates the capacity of both histology and pQCT to detect subjects with specific structural patterns in vertebral cancellous bone.     

Right internal thoracic artery through the transverse sinus in myocardial revascularization

Background. A major concern in evaluating dynamic cardiomyoplasty has been whether the synchronous stimulation of latissimus dorsi muscle is essential for benefit or not. We studied 10 patients to determine the efficacy of the systolic augmentation generated by the synchronous electrical stimulation of the latissimus dorsi muscle.

Methods. Left ventricular ejection fraction, end-systolic and end-diastolic volume indexes, and stroke volume index obtained during resting, peak exercise, and recovery periods (“on” values) were compared with those obtained 1 week after cessation of electrical stimulus (“off” values). Double product and estimated total body oxygen consumption at peak exercise were also calculated and compared.

Results. Higher ejection fractions (0.36 ± 0.07 versus 0.33 ± 0.06 at rest, 0.40 ± 0.07 versus 0.33 ± 0.07 peak exercise, and 0.37 ± 0.06 versus 0.31 ± 0.06 at recovery) and lower end-systolic volume indexes with relatively constant end-diastolic volume indexes were observed with the cardiomyostimulator on. Further, exercise response was better with the cardiomyostimulator on. Double product indirectly reflected better myocardial oxygen supply/demand ratio when on at peak exercise (17 ± 2.2 mm Hg × beats/min × 10⁻³ for on versus 19 ± 2.6 mm Hg × beats/min × 10⁻³ for off). Estimated total body oxygen consumption was improved at peak exercise when the cardiomyostimulator was functional (12 ± 2.7 mL · kg⁻¹ · min⁻¹ versus 11 ± 2.6 mL · kg⁻¹ · min⁻¹).

Conclusions. Current data suggest a true systolic assist during synchronous contractions of the latissimus dorsi muscle. It is thought, therefore, that synchronous electrical stimulation is essential for maximum benefit and all the beneficial effect of cardiomyoplasty certainly cannot be attributed to simple wrapping itself.     

Occlusive clothing and ultraviolet radiation in hip surgery

In a randomized study of 20 total hip arthroplasties, the staff wore shirts and trousers of a fabric impervious to bacteria underneath operating gowns of a non-woven material. Volumetric air sampling demonstrated a low number of colony-forming units with this clothing, further reduced by ultraviolet radiation to below 10 colony-forming units/m³, the upper limit of “ultraclean air,” in all the cases (median 2.6, range 1.1-7.1).     

Strategies to improve compliance with evidence-based clinical management guidelines

Background: Clinical management guidelines (CMGs) have been developed to standardize physician practices and ensure safe and cost-effective patient care. In June 1996, evidence-based CMGs were initiated at our urban Level I trauma center. This study compares physician compliance with two such CMGs before (PRE) and after (POST) the institution of continuous surveillance by a clinical resource manager.

Study Design: For 2 months PRE resource manager surveillance hospital records were reviewed retrospectively for compliance with two CMGs. POST data were collected prospectively for 2 months by the resource manager, who alerted practitioners to deviance from CMGs to justify or document therapy alternatives. The CMGs studied addressed deep venous thrombosis and stress ulcer prophylaxis. “Under” or “over” therapy described that which fell short of or exceeded guidelines. Data were analyzed by chi-square; p < 0.05 defined statistical significance.

Results: Compliance with the CMGs was 48% PRE and 74% POST (p = 0.001). All noncompliant instances POST (and none PRE) were altered or justified. Deep venous thrombosis and ulcer “over” therapy was significantly higher PRE (19% versus 2%, p = 0.003; 49% versus 19%, p = 0.001), resulting in $22,760.35 in costs. There was no difference in pulmonary embolism or gastrointestinal bleed rate (1%) PRE to POST.

Conclusions: The use of a clinical resource manager empowered to monitor and coordinate physician behavior improves compliance with CMGs. Further study is warranted to validate resultant outcomes benefit, specifically cost-effectiveness and duration of the need for such a program.     

Fatigue Behavior of Adult Cortical Bone: The Influence of Mean Strain and Strain Range

Uniaxial fatigue tests were conducted of devitalized cortical bone specimens machined from human femora. Specimens were tested at strain ranges from 0.005 to 0.010 under physiologic loading rates. The influence of compressive, zero, and tensile mean strains on fatigue life and on the stress/strain histories during fatigue were examined. Results showed that bone fatigue is a gradual damage process accompanied by a progressive increase in hysteresis and a loss of bone stiffness. The total number of cycles to fatigue failure was influenced only by the total strain range and was not affected by mean strain. Bone was shown to have extremely poor fatigue resistance. Fully reversed cyclic loading to one half of the yield strain caused fatigue fracture in 1000 cycles.

Biological implications. The bone regions which experience the highest strain ranges in vivo generally have a compressive mean strain. The results of this study indicate that mechanical fatigue damage accumulates more rapidly in these “compressive” areas than in “tensile” areas of bone.     

Aging and matrix microdamage accumulation in human compact bone

Bone matrix microdamage in bone matrix, evidenced as microcracks, occurs consequent to cyclic loading. Microdamage caused by in vivo loading has been described in human rib cortex; however, the existence and extent of microcracks in human long bone cortices are largely unknown. Using histomorphometric methods to examine the incidence and localization of microcracks in human femoral compact bone specimens, we found that the amount of microdamage present in femoral compact bone increases dramatically with increasing age. Least squares regression analysis showed that in males, microcrack density (Cr.De., #/mm²) increases exponentially with age (r² = 0.70). In females, Cr.De. also increases as an exponential function of increasing age (r² = 0.79), at a significantly higher rate than in male specimens (p < 0.001). The current studies indicate that with increasing age, bone microdamage accumulates more rapidly than intrinsic processes can effect its repair. A combination of cumulative loading history, focal changes in material properties and alteration in the ability of the tissue to perceive and/or react to microcracks may all play role in this accumulation of bone microdamage with aging. This accumulation of microdamage in bone will contribute to decreased strength and stiffness. In addition, and perhaps most significantly for understanding aging and increased bone fragility, matrix microdamage in composite materials like bone will result in a profoundly reduced resistance to fracture. The importance of this accumulation of matrix microdamage in human bone with increasing age in contributing to the increased fragility of the aging skeleton is discussed.     

Surgical experience with left ventricular free wall rupture

Background. Autopsy studies reveal that left ventricular free wall rupture (LVFWR) accounts for 7% to 24% of deaths after myocardial infarction. The condition occurs up to 10 times more often than papillary muscle or interventricular septal rupture. A high index of suspicion must be maintained to differentiate LVFWR from infarct extension, cardiogenic shock, pulmonary embolus, and even Dressler’s syndrome.

Methods. Since 1980, we have operated on 18 patients with LVFWR. Fourteen patients had experienced “blow-out” rupture associated with cardiogenic shock. Four patients had “stuttering” ruptures, a less spectacular occurrence. Echocardiography was the most important diagnostic tool. Repair was performed, usually using infarctectomy and direct suture closure.

Results. Eleven patients (61%) died after operation, 4 patients as a result of rerupture 1 to 12 hours after operation. Recently, we have used a “patch/glue” technique to repair ruptures in 2 patients. We believe this technique is superior to direct suture closure in preventing rerupture. There have been 7 long-term survivors (39%) from 6 months to 15 years.

Conclusions. Left ventricular free wall rupture is not always sudden and dramatic. Yet, the operating staff must be willing to race to the operating room even with the patient in full resuscitation. Echocardiography is the most sensitive and efficient diagnostic tool. All rupture sites should be aggressively repaired, possibly combining direct suture and patch/glue techniques.     

Patterns of osteocytic endothelial nitric oxide synthase expression in the femoral neck cortex: differences between cases of intracapsular hip fracture and controls

Evidence indicates that extensive amalgamation of adjacent resorbing osteons is responsible for destroying the microstructural integrity of the femoral neck’s inferior cortex in osteoporotic hip fracture. Such osteonal amalgamation is likely to involve a failure to limit excessive resorption, but its mechanistic basis remains enigmatic. Nitric oxide (NO) inhibits osteoclastic bone destruction, and in normal bone cells its generation by endothelial nitric oxide synthase (eNOS, the predominant bone isoform) is enhanced by mechanical stimuli and estrogen, which both protect against fracture. To determine whether eNOS expression in osteocytes reflects their proposed role in regulating remodeling, we have examined patterns of osteocyte eNOS immunolabeling in the femoral neck cortex of seven cases of hip fracture and seven controls (females aged 68–96 years). The density of eNOS⁺ cells (mm⁻²) was 53% lower in the inferior cortex of the fracture cases (p < 0.0004), but was similar in the superior cortex. eNOS⁺ osteocytes were, on average, 22% further from their nearest blood supply, than osteocytes in general (p < 0.0001) and the nearest eNOS⁺ osteocyte was 57% further from its nearest canal surface (p < 0.0001). This differential distribution of eNOS⁺ osteocytes was significantly more pronounced in the cortices of fracture cases (p < 0.0001). We conclude that the normal regional and osteonal pattern of eNOS expression by osteocytes is disrupted in hip fracture, particularly at sites that are loaded most by physical activity. These results suggest that eNOS⁺ osteocytes may normally act as sentinels confining resorption within single osteons. A reduction in their number, coupled to an increase in their remoteness from canal surfaces, may thus permit the irreversible merging of resorbing osteons, and thus contribute to the marked increase in the fragility of osteoporotic bone.     

Specimen-specific beam models for fast and accurate prediction of human trabecular bone mechanical properties

Direct assessment of bone competence in vivo is not possible, hence, it is inevitable to predict it using appropriate simulation techniques. Although accurate estimates of bone competence can be obtained from micro-finite element models (μFE), it is at the expense of large computer efforts. In this study, we investigated the application of structural idealizations to represent individual trabeculae by single elements. The objective was to implement and validate this technique.

We scanned 42 human vertebral bone samples (10 mm height, 8 mm diameter) with micro-computed tomography using a 20 μm resolution. After scanning, direct mechanical testing was performed. Topological classification and dilation-based algorithms were used to identify individual rods and plates. Two FE models were created for each specimen. In the first one, each rod-like trabecula was modeled with one thickness-matched beam; each plate-like trabecula was modeled with several beams. From a simulated compression test, assuming one isotropic tissue modulus for all elements, the apparent stiffness was calculated. After reducing the voxel size to 40 μm, a second FE model was created using a standard voxel conversion technique. Again, one tissue modulus was assumed for all elements in all models, and a compression test was simulated.

Bone volume fraction ranged from 3.7% to 19.5%; Young's moduli from 43 MPa to 649 MPa. Both models predicted measured apparent moduli equally well (R² = 0.85), and were in excellent agreement with each other (R² = 0.97). Tissue modulus was estimated at 9.0 GPa and 10.7 GPa for the beam FE and voxel FE models, respectively. On average, the beam models were solved in 219 s, reducing CPU usage up to 1150-fold as compared to 40 μm voxel FE models. Relative to 20 μm voxel models 10,000-fold reductions can be expected. The presented beam FE model is an abstraction of the intricate real trabecular structure using simple cylindrical beam elements. Nevertheless, it enabled an accurate prediction of global mechanical properties of microstructural bone. The strong reduction in CPU time provides the means to increase throughput, to analyze multiple loading configuration and to increase sample size, without increasing computational costs. With upcoming in vivo high-resolution imaging systems, this model has the potential to become a standard for mechanical characterization of bone.     

Impaired distensibility of neoaorta after arterial switch procedure

Background. Although the arterial switch operation has become the standard surgical procedure for treatment of complete transposition, postoperative problems have not been fully appreciated. One such problem may be the postoperative function of great arteries that are manipulated radically.

Methods. The diameters at four levels of the aorta were measured in 36 patients who had undergone arterial switch operation and the distensibilities were calculated. The data were compared with that of age-matched controls.

Results. At the level of the Valsalva sinus, aortic diameters after one-staged and two-staged operations were 137.0% ± 21.3%N and 152.4% ± 17.7%N of the normal aorta, respectively. The distensibilities at the Valsalva sinus in patients after one-staged and two-staged operations were 1.2 ± 0.7 and 1.5 ± 0.8 cm² · dyn⁻¹ · 10⁻⁶, and at the supraaortic ridge were 2.5 ± 1.5 and 1.9 ± 1.5 cm² · dyn⁻¹ · 10⁻⁶, respectively.

Conclusions. In patients after arterial switch procedure, the distensibility of the base of aorta is decreased. Long-term follow-up is necessary to clarify the influence of the “stiffness” of the base of aorta.