Characterization of a novel Streptococcus thermophilus rolling-circle plasmid used for vector construction

STUDY DESIGN: Bone mineral density and bone cross-sectional area of human cadaveric vertebral bodies were investigated radiologically and histologically, respectively. After ventral instrumentation with ventral derotation spondylodesis screws, axial pullout force was measured and compared with radiologic and histologic data. OBJECTIVES: To elucidate how well ventral derotation spondylodesis screw fixation strength can be estimated before surgery by specified applications of dual-energy x-ray absorptiometry, quantitative computed tomography, T2*-relaxation time in magnetic resonance imaging, and histomorphometry. SUMMARY OF BACKGROUND DATA: It is postulated that bone quality plays a crucial role in initial strength of the instrumented spine. Bone quality is even more important in anterior fixation because of the prevalence of spongy bone in the vertebral body. METHODS: Bone mineral density of human cadaveric lumbar-vertebral bodies was assessed by dual-energy x-ray absorptiometry and quantitative computed tomography (cancellous and cortical bone separately). Cancellous bone was also characterized by T2*-relaxation time, measured by magnetic resonance imaging and histomorphometric study. Vertebral bodies were instrumented ventrally with VDS screws, and screw axial pullout force was measured and correlated with each of the nonmechanical measures. Patients with manifest osteoporosis, osteomalacia and tumors were excluded. For statistical analysis, the Mann-Whitney rank sum test was used with a significance value of P < 0.05. RESULTS: The highest correlation with pullout force was for density of cancellous bone determined by quantitative computed tomography (r = 0.72; P < 0.001), immediately followed that determined by dual-energy x-ray absorptiometry (r = 0.70; P < 0.001). Results of measurement of T2*-relaxation time and those of histomorphometric study correlated moderately (r = 0.55; r = 0.50), whereas cortical bone density determined by quantitative computed tomography showed negligible correlation (r = 0.2). CONCLUSIONS: The absorptiometric techniques, quantitative computed tomographic scan of cancellous bone and dual-energy x-ray absorptiometric study, provide more accurate readings for preoperative estimation of initial VDS screw fixation strength than do the other methods studied.     

Anterior vertebral body screw pullout testing. A comparison of Zeilke, Kaneda, Universal Spine System, and Universal Spine System with pullout-resistant nut

STUDY DESIGN: A biomechanical study of pullout of anteriorly implanted screws in cadaveric vertebral bodies. OBJECTIVES: To investigate and compare the pullout strength of the Zielke, Kaneda, Universal Spine System (USS) pedicle screw, and USS pedicle screw with a new pullout-resistant nut. SUMMARY OF BACKGROUND DATA: A common problem with anterior purchase regardless of the implant system is screw pullout at the proximal and distal ends of multilevel constructs. There is limited information on a solution to this problem. METHODS: The L1 to L4 vertebral bodies from four cadavers had one each of Zielke and Kaneda pedicle screws (Acromed Corp., Cleveland, OH), USS pedicle screw (Synthes Spine, Paoli, PA), and USS pedicle screw with pullout-resistant nut implanted transversely across the center of the vertebral body with bicortical purchase in a similar fashion as would be used clinically. The screws were extracted using a servohydraulic material testing system. The maximum axial forces were recorded. RESULTS: The Zielke and Kaneda screws had no significant difference in mean pullout strength (P = 0.542). The USS screw alone was less strong (P = 0.009). The USS screw and pullout-resistant nut increased the pullout strength by twofold (P = 0.00006). In the screw pullout tests, the mode of failure was at the screw thread's interface. The USS screw and pullout-resistant nut failed by imploding the body around the nut. With the USS screw and pullout-resistant nut, the pullout strength was determined by the compressive strength of the bone. CONCLUSIONS: The addition of a pullout-resistant nut to an anterior vertebral body screw improves the pullout strength by twofold and changes the mode of failure to rely ultimately on the inherent vertebral body strength rather than the screw's characteristics. The addition of a pullout-resistant nut may be applicable to multilevel implant constructs to prevent screw pullout at the top and bottom.     

Structural characteristics of the pedicle and its role in screw stability

STUDY DESIGN: Cross-sectional regional bone mineral density of the pedicle was measured by peripheral quantitative computed tomography. Biomechanical tests were performed to clarify the role of the pedicle in screw stability. OBJECTIVES: To identify the structural characteristics of the pedicle that supports pedicle screw stability and the differences in these characteristics between normal and osteoporotic vertebrae. SUMMARY OF BACKGROUND DATA: The pedicle screw is an essential component of many systems used to align the spine. The contribution of the pedicle to screw stability, however, has not been fully investigated. METHODS: Trabecular, subcortical, and cortical bone mineral density and the area of the pedicle were measured by peripheral quantitative computed tomography. Bone mineral density also was recalculated in four circumferential layers. These parameters were compared between normal and osteoporotic individuals. The relative contribution of the pedicle to screw stability was evaluated by caudocephalad and pull-out loading in a vertebra with or without its body. RESULTS: Inner trabecular, middle subcortical, and outer cortical bone mineral density and cortical bone area in the pedicle were significantly lower in osteoporotic vertebrae than those in normal vertebrae. In the pedicle, bone mineral density increased close to the outer layer. Bone mineral density not as thick even in the outer layer in osteoporotic subjects. Approximately 80% of the caudocephalad stiffness and 60% of the pullout strength of the pedicle screw depended on the pedicle rather than on the vertebral body. CONCLUSION: Screw stability depends on the structural characteristics of the pedicle. The pedicle was denser in the subcortical bone, in which the threads of the screw engage, than in trabecular bone. In osteoporosis, bone mineral density was not as dense even in the outer layer, and the cortex was thinner than normal. A larger screw would not enhance screw stability and may break the thin cortex in osteoporotic vertebrae.     

Determination of bone mineral density in the third lumbar vertebral body using photon absorptiometry techniques

Dual-photon absorptiometry and triple-energy X-ray absorptiometry were used to investigate the total bone mineral content and density as well as the trabecular bone mineral density in the third lumbar vertebral body. Both anteroposterior (AP) and lateral (LAT) measurements were performed. By combining the two projections it was found that the mean trabecular bone mineral density for all 202 subjects included in the study was 52% (SD +/- 20%) of the total bone mineral density in the third lumbar vertebral body. The mean trabecular bone mineral density as a fraction of the total vertebral body bone mineral density decreased as a function of age. The relative annual change in this fraction differed between males and females. It was also found that neither trabecular nor total bone mineral density differed significantly between male and female subjects aged 25-35 years, and bone mineral density (BMD), expressed in g/cm3, showed no correlation to subject height, body weight or body mass index (BMI). Male and female individuals showed different rates of change of trabecular bone mineral density with age.     

Palliation of large-bowel obstruction due to recurrent rectosigmoid tumor using self-expandable endoprostheses

STUDY DESIGN: This study assessed the variability of segmental bone mineral density in the lower cervical spine (C4 through C7). A mean segmental bone mineral density value at each level was determined for all specimens, and a mean coefficient of variation among the 17 specimens was calculated. OBJECTIVES: To quantify the degree of intersegmental bone mineral density variations within cadaveric lower cervical spine segments. SUMMARY OF BACKGROUND DATA: Bone mineral density studies in the thoracic and lumbar spine have shown a high degree of variability between spinal segments; however, the extent of segmental bone mineral density variability in the cervical spine is unknown. METHODS: Seventeen human cadaveric cervical spine specimens (C4 through C7) were scanned in a water bath using dual energy x-ray absorptiometry in a lateral direction. Segmental bone mineral density of the vertebral bodies of all specimens were analyzed with respect to differences between segments within each specimen. RESULTS: The mean coefficient of segmental bone mineral density variations within each specimen for all spines was 14.8% (range, 5.8%-22.9%). Bone mineral density mean values and ranges at each level were as follows: C4, 0.720 g/cm2 (range, 0.367-1.161 g/cm2); C5, 0.784 g/cm2 (range, 0.348-1.268 g/cm2); C6, 0.735 g/cm2 (range 0.367-1.450 g/cm2); C7, 0.590 g/cm2 (range, 0.340-1.040 g/cm2). Paired analysis of difference between all levels for 16 specimens demonstrated the bone mineral density at the C7 level to be significantly lower than at all other levels (P < 0.05). CONCLUSION: Our data show that significant interlevel bone mineral density variability exists in the lower cervical spine, and suggests that random single segment bone mineral density sampling or mean specimen bone mineral density values may not be relevant.     

Development of mass, density, and estimated mechanical characteristics of bones in Caucasian females

Three hundred and thirty healthy Finnish girls and premenopausal women, aged 7-47 years, were examined to evaluate the natural development of bone mineral mass and density from early childhood to menopause. Bone mineral content (BMC,g) and areal density (BMD, g/cm2) were measured from the spine (L2-L4), femoral neck, trochanter region of the femur, and distal radius using dual-energy X-ray absorptiometry (DXA). In addition, the bone mineral apparent density (BMAD, g/cm3) was assessed from the above described skeletal sites, and the mechanical competence of the femoral neck was estimated. Special attention was paid to the timing of the peak values of these bone parameters as well as to the evidence of premenopausal bone loss. The BMC, BMD, and BMAD of the spine, femoral neck, and trochanter region of the femur achieved peak values around the age of 20, and the bone loss seemed to start soon thereafter. In contrast, the bone mass of the distal radius slightly increased between the ages of 20 and 47. In the femoral neck, the estimated bending strength achieved its peak value around the age of 20 and showed a slight decrease during the following decades. The highest body weight and neck-length adjusted strength values of the femoral neck were, however, found in early childhood, with the values decreasing linearly thereafter. In conclusion, this study supports previous findings of rapid bone mineral accumulation in late adolescence, and occurrence of the peak bone mass and density around the age of 20. Premenopausal bone loss seems to occur in the proximal femur and lumbar spine. Our observations of femur strength development imply that from childhood to menopause the mechanical strength of the femoral neck is well adjusted to the biomechanical loading requirements of the body.     

Body weight and bone mineral density in postmenopausal women with primary hyperparathyroidism

OBJECTIVE: To assess bone mineral density and body composition in postmenopausal women with primary hyperparathyroidism. DESIGN: Cross-sectional study with an age-matched control group. SETTING: University teaching hospital. PATIENTS: 41 postmenopausal women with mild primary hyperparathyroidism and 43 eucalcemic, age-matched controls. MEASUREMENTS: Total body, lumbar spine, and proximal femoral (femoral neck, Ward's triangle, and trochanter) bone mineral density; body composition; and fat distribution were measured using dual-energy x-ray absorptiometry. RESULTS: Women with primary hyperparathyroidism were heavier (75.5 kg compared with 66.3 kg; difference, 9.2 kg [95% CI, 3.7 to 14.7 kg]; P = 0.002), had a higher fat mass (33.3 kg compared with 26.1 kg; difference, 7.2 kg [CI, 3.0 to 11.4 kg]; P = 0.001), and had a more android pattern of fat distribution (android-to-gynoid fat ratio, 1.05 compared with 0.84; difference, 0.21 [CI, 0.1 to 0.32]; P = 0.0004) than the controls. Unadjusted bone mineral density was similar in patients and controls at all sites: total body, 0.990 compared with 1.023 g/cm2 (difference, 0.033; CI, -0.004 to 0.070); posteroanterior lumbar spine, 1.032 compared with 1.018 g/cm2 (difference, 0.014; CI, -0.031 to 0.059); lateral lumbar spine, 0.569 compared with 0.528 g/cm2 (difference, 0.041; CI, -0.022 to 0.104); femoral neck, 0.799 compared with 0.825 g/cm2 (difference, 0.026; CI, -0.072 to 0.124); Ward's triangle, 0.653 compared with 0.677 g/cm2 (difference, 0.024; CI, -0.035 to 0.089); trochanter, 0.734 compared with 0.733 g/cm2 (difference, 0.001; CI, -0.024 to 0.026); and arms, 0.720 compared with 0.739 g/cm2 (difference, 0.019; CI, -0.015 to 0.053). After adjustment for body weight, bone mineral density in women with primary hyperparathyroidism was lower than that in controls for total body (P = 0.0004), femoral neck (P = 0.001), Ward's triangle (P = 0.01), trochanter (P = 0.02), and arms (P = 0.0006). Spinal bone mineral density did not differ between groups. CONCLUSIONS: Body weight, total body fat mass, and proportion of android fat are increased in postmenopausal women with primary hyperparathyroidism; these unexplained factors may be relevant to the increased incidence of cardiovascular disease in this condition. Unadjusted bone mineral density values are similar in patients with primary hyperparathyroidism and in controls, suggesting that this condition is not associated with an increased risk for fracture.     

Influence of spontaneous calcium intake and physical exercise on the vertebral and femoral bone mineral density of children and adolescents

Peak bone mass is determined mainly by genetic-ethnic factors, but environmental factors such as calcium intake and physical activity during childhood and adolescence could play a role. We have measured the bone mineral density (BMD) of 151 healthy children and adolescents, ages 7-15.3 years. Density was measured by dual X-ray absorptiometry (DXA) at two sites (lumbar verterbrae L1-L4 and the upper femur), and the data were analyzed in terms of the height, weight, sexual maturation, spontaneous calcium intake, and physical activity. Of the children, 57-71% had calcium intakes below 1000 mg/day. BMD increased with pubertal maturation from 0.68 +/- 0.08 to 0.92 +/- 0.09 g/cm2 (vertebral bone density, VBD) and from 0.87 +/- 0.10 to 1.03 +/- 0.09 g/cm2 (femoral bone density, FBD) between Tanner stage 1 and 5. Multiple regression analysis showed that body weight and Tanner stage were main determinants of bone density when expressed as g/cm2. The weekly duration of sports activity also influenced both the vertebral (p < 0.001) and femoral (p = 0.01) sites, especially in girls and during puberty. Dietary calcium appeared to be another independent determinant of BMD, especially before puberty, at the vertebral (p = 0.02) site. Most important, dietary calcium was found to be the main determinant of vertebral mineral density, when expressed as z score, in both sexes. Moreover, 93% of the 28 children with low vertebral z score values (below -1) and 84% of the 31 children with low femoral z score values (below -1) had dietary calcium intakes below 1000 mg/day.     

Trying to control MRSA causes more problems than it solves

OBJECTIVE: To determine the effect of recombinant canine somatotropin (STH) on radiographic, densitometric, and biomechanical aspects of bone healing using an unstable ostectomy gap model. STUDY DESIGN: After an ostectomy of the midshaft radius, bone healing was evaluated over an 8-week period in control dogs (n = 4) and dogs receiving recombinant canine STH (n = 4). ANIMALS OR SAMPLE POPULATION: Eight sexually intact female Beagle dogs, 4 to 5 years old. METHODS: Bone healing was evaluated by qualitative and quantitative evaluation of serial radiographs every 2 weeks. Terminal dual-energy x-ray absorptiometry and three-point bending biomechanical testing were also performed. RESULTS: Dogs receiving STH had more advanced radiographic healing of ostectomy sites. Bone area, bone mineral content, and bone density were two to five times greater at the ostectomy sites of treated dogs. Ultimate load at failure and stiffness were three and five times greater in dogs receiving STH. CONCLUSIONS: Using the ostectomy gap model, recombinant canine STH enhanced the radiographic, densitometric, and biomechanical aspects of bone healing in dogs. CLINICAL RELEVANCE: Dogs at risk for delayed healing of fractures may benefit from treatment with recombinant canine STH.     

Diabetes during pregnancy does not alter whole body bone mineral content in infants

A previous study using single photon absorptiometry has reported low bone mineral density of the radius in infants of diabetic mothers. The aim of this study was to assess by dual x-ray absorptiometry the whole body bone mineral content (WbBMC) and the body composition of 40 infants of diabetic mothers at birth (mean gestational age +/- SD, 37.5 +/- 1.3 weeks; mean birth weight +/- SD, 3815 +/- 641 g). WbBMC was not correlated with gestational age, but was well correlated with birth weight (r = 0.73; P = 0.0001) and also with fat mass (r = 0.87; P = 0.0001) and lean mass (r = 0.42; P = 0.008). The z-scores +/- SD adjusted for weight for WbBMC and fat mass were significantly increased (1.3 +/- 0.9 and 2.6 +/- 1.3, respectively (P < 0.0001), but were not significantly influenced either by in utero growth or by the type of the diabetes mellitus of the mother. Bone mineralization and fat mass studied by whole body dual x-ray absorptiometry are increased at birth in these infants compared with reference curves.     

Laser''s effect on bone and cartilage change induced by joint immobilization: an experiment with animal model

OBJECTIVE: Influence of low-level (810 nm, Ga-Al-As semiconductor) laser on bone and cartilage during joint immobilization was examined with rats' knee model. MATERIALS AND METHODS: The hind limbs of 42 young Wistar rats were operated on in order to immobilize the knee joint. One week after operation they were assigned to three groups; irradiance 3.9 W/cm2, 5.8 W/cm2, and sham treatment. After 6 times of treatment for another 2 weeks both hind legs were prepared for 1) indentation of the articular surface of the knee (stiffness and loss tangent), and for 2) dual energy X-ray absorptiometry (bone mineral density) of the focused regions. RESULTS AND CONCLUSIONS: The indentation test revealed preservation of articular cartilage stiffness with 3.9 and 5.8 W/cm2 therapy. Soft laser treatment has a possibility for prevention of biomechanical changes by immobilization.     

Static and fatigue failure properties of thoracic and lumbar vertebral bodies and their relation to regional density

This study investigated (1) whether a characterization of the macroscopic architecture within the vertebral centrum would improve predictions of vertebral strength, (2) if regions in the centrum where least bone loss with age occurs are more predictive of vertebral strength, and (3) whether different patterns of the macroscopic architecture are predictive of static as compared to fatigue strength. To characterize the vertebral macroscopic architecture, a regional bone mineral density (rBMD) technique was used that estimated the cancellous density distribution (in 18 specific regions of the vertebral centrum) for vertebrae T7-L4, from spines of 20 female cadavers. Static and fatigue failure properties of whole vertebrae were obtained, and predictive models of static and fatigue failure properties of whole vertebrae were examined. We found that (1) vertebral failure properties were better predicted by combinations of vertebral regional cancellous density (multiple linear regressions) rather than by any individual region of cancellous density alone (simple linear regressions); (2) models using regions of density that demonstrated minimum decline with age [from the data of Flynn and Cody (Calcif. Tissue Int. 53, S170-S175 (1993))] resulted in better correlations with ex vivo vertebral static failure properties than models using density regions that showed maximum decline with age, and (3) static and fatigue characteristics required different density regions to reach significance. (A comparison of models predictive of static and fatigue failure properties revealed that anterior density regions were most often included in predictive models of the static properties while posterior regions were more predictive of the fatigue properties).(ABSTRACT TRUNCATED AT 250 WORDS)     

Sources of interracial variation in bone mineral density

Many studies have demonstrated significant differences in bone mineral density between various racial groups. Although it has been suggested that differences in body weight contribute to such interracial variation, the artifactual effect of the skeletal size inherent in projectional absorptiometry methods has been largely ignored. We have measured bone mineral density by dual-energy X-ray absorptiometry in the lumbar spine and at three femoral sites in 200 premenopausal women of Chinese, Indian, European, or Polynesian origin (50 of similar mean age in each group). In the Chinese and Indian women the measured bone mineral density measurements (g/cm2) were similar, but significantly less, at all sites, than those of European women (p < or = 0.005). The European women were, however, significantly taller than both the Chinese and Indian women (p < 0.0001), and when the scale artifact of absorptiometry was removed by dividing the measured bone mineral density either by the height of the subject, or by the square root of the area over which the X-ray beam was projected, then the differences in mean bone mineral density between the Chinese, Indian, and European women were almost completely eliminated. The Polynesian women were significantly more obese (as judged from mean body mass index) than all the other groups (p < 0.0001) and had significantly greater bone mineral density at all sites than all the other groups both before (p < 0.0001) and after (p < 0.0001) correcting for the scale artifact.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dual-energy bone densitometry using a single 100 ns x-ray pulse

A pulsed, portable hard x-ray source has been developed for medical imaging and flash x-ray absorptiometry. The source is powered by a Marx generator that drives a field emission x-ray tube which produces a 30-300 keV x-ray pulse of 100 ns duration. The x-ray fluence has dual-energy properties. The x-ray energy is relatively high early in the pulse and lower later in the pulse. The feasibility of using a single x-ray pulse for precision bone densitometry was analyzed. A computer simulation model was developed for the x-ray source, the filtration that enhances the dual-energy distribution, the absorption of the energy distribution by bone mineral and soft tissue, and the dual-energy detection system. It is feasible to determine the bone mineral density (BMD) of axial sites such as the lumbar spine and proximal femur with 2% precision over an area that is 15-20 mm in size, depending on the bone mineral and soft tissue thicknesses. An algorithm for determining the absolute BMD, to an accuracy of 2%, using a Plexiglas/TiO2 calibration phantom is discussed. At a distance of 50 cm from the source, the patient exposure is 3.7 mR. The average absorbed bone and tissue doses are 0.6 and 4.3 mrem, respectively. Factors that facilitate diagnostic measurements in clinical settings are the short patient observation time and the portability of the x-ray source.     

Anatomic considerations of anterior transarticular screw fixation for atlantoaxial instability

STUDY DESIGN: Anatomic parameters of C1 and C2 were measured in 30 dried human cervical spines. Anterior transarticular C1-C2 screws were placed in 15 cadaveric spines. OBJECTIVE: To provide anatomic data for anterior transarticular atlantoaxial screw or C1-C2 screw and plate fixation. SUMMARY OF BACKGROUND DATA: A posterior approach to fixation in the atlantoaxial joint has been well described. Damage to the vertebral artery is documented as a rare complication of posterior atlantoaxial transarticular screw fixation. An anterior surgical approach to exposing the upper cervical spine for internal fixation and bone graft recently has been developed. No anatomic information regarding the anterior transarticular atlantoaxial screw or screw and plate fixation between C1 and C2 is available in the literature. METHODS: Direct measurements using digital calipers and a goniometer were taken from 30 pairs of dried human C1 and C2 vertebrae. The anterior transarticular C1-C2 screw insertion point is at the junction of the lateral edge of the C2 vertebral body to 4 mm above the inferior edge of the C2 anterior arch. The parameters related to anterior transarticular atlantoaxial screw fixation or screw and plate fixation between the C1 lateral mass and the C2 vertebral body were measured. Fifteen embalmed cadavers were used for anterior C1-C2 transarticular screw placement. Longer screws (30-40 mm) were used to detect whether the screw tips violated the upper cervical canal or vertebral arteries. RESULTS: In the anterior transarticular atlantoaxial screw placement, lateral angulation of the screw placement relative to sagittal plane ranged from 4.8 +/- 1.8 degrees to 25.3 +/- 2.6 degrees. The posterior angulation of the screw placement relative to the coronal plane ranged from 12.8 +/- 3.1 degrees to 22.6 +/- 3.2 degrees. The length of the medial screw path ranged from 14.7 +/- 1.5 mm to 25.4 +/- 2.8 mm. In the anterior screw and plate fixation, the anteroposterior diameter of the inferior facet articular surface ranged from 16.2 +/- 1.6 mm to 17.1 +/- 1.8 mm. The anteroposterior diameter of the C2 vertebral body ranged from 9.3 +/- 1 mm to 16.2 +/- 1.8 mm. The anterior prevascular retropharyngeal approach appropriately exposed the atlantoaxial joint for anterior transarticular C1-C2 screw placement. No screws violated the vertebral artery and cervical canal. CONCLUSIONS: An anterior transarticular atlantoaxial screw 15-25 mm long can be inserted with a lateral angulation of 5-25 degrees relative to the sagittal plane and a posterior angulation of 10-25 degrees relative to the coronal plane. Additionally, in C1-C2 anterior plate fixation screws 15 mm long could be anchored in the inferior facet of the C1, and screws 9-15 mm long could be anchored in the C2 vertebral body.     

Monte Carlo modelling of an extended DXA technique

The precision achieved in measuring bone mineral density (BMD) by commercial dual-energy x-ray absorptiometry (DXA) machines is typically better than 1%, but accuracy is considerably worse. Errors, due to inhomogeneous distributions of fat, of up to 10% have been reported. These errors arise because the DXA technique assumes a two-component model for the human body, i.e. bone mineral and soft tissue. This paper describes an extended DXA technique that uses a three-component model of human tissue and significantly reduces errors due to inhomogeneous fat distribution. In addition to two x-ray transmission measurements, a measurement of the path length of the x-ray beam within the patient is required. This provides a third equation, i.e. T = ts + tb + tf where T, ts, tb and tf are the total, lean soft tissue, bone mineral and fatty tissue thicknesses respectively. Monte Carlo modelling was undertaken to make a comparison of the standard and extended DXA techniques in the presence of inhomogeneous fat distribution. Two geometries of varying complexity were simulated. In each case the extended DXA technique produced BMD measurements that were independent of soft tissue composition whereas the standard technique produced BMD measurements that were strongly dependent on soft tissue composition. For example, in one case, the gradients of the plots of BMD versus fractional fat content were for standard DXA (-0.183+/-0.037) g cm(-2) and for extended DXA (0.027+/-0.044) g cm(-2). In all cases the extended DXA method produced more accurate but less precise results than the standard DXA technique.     

Effects of the bisphosphonate tiludronate on bone resorption, calcium balance, and bone mineral density

Bone resorption inhibitors, such as bisphosphonates, are potentially useful in treatments aimed at increasing bone mass. Among bisphosphonates, tiludronate has proven efficacious in preventing bone loss in postmenopausal women. However, it is not clearly established whether bisphosphonates are more potent when given intermittently or continuously. We investigated the effects of tiludronate on (1) retinoid-stimulated bone resorption in thyroparathyroidectomized rats, (2) calcium balance in intact rats, and (3) bone mineral density (BMD) as measured by dual-energy x-ray absorptiometry at the levels of the lumbar spine, tail, and tibia in 6-month-old rats made osteoporotic by ovariectomy (OVX), in which an intermittent cyclic schedule of treatment was compared to continuous administration. Tiludronate induced a dose-dependent decrease in retinoid-stimulated bone resorption. It increased the intestinal absorption and body retention of calcium. In OVX rats it caused a time- and dose-dependent increase in BMD at the level of the three investigated sites, the effects being maintained for at least 8 weeks after the end of therapy. Continuous and intermittent cyclic regimens appeared to induce similar increases in BMD. These results indicate that tiludronate is efficacious in decreasing bone resorption and increasing calcium balance and bone mineral density in rats.     

Relationship between spine bone mineral density and vertebral body heights

The aim of this study was to investigate the correlation between lumbar spine bone mineral density (LS-BMD) and the vertebral body heights with advancing age and years since menopause. One hundred and sixty-three women ages 39-74 years (77 normal premenopausal, ages 39-54, and 86 normal postmenopausal, ages 46-74 years) were studied. LS-BMD was measured by dual energy X-ray absorptiometry. Vertebral heights were evaluated, using morphometry, as the sum of anterior (AHs), middle (MHs), and posterior (PHs) vertebral body heights from T4 to L5. The AHs/PHs ratio at the same level was also calculated. AHs, MHs, PHs, and AHs/PHs ratio directly correlated with LS-BMD; the correlations are AHs r = 0.80, P < 0.0001, MHs r = 0.75, P < 0.0001, PHs r = 0.76, P < 0.0001, and AHs/PHs r = 0.66, P < 0.001. Both LS-BMD and AHs are inversely correlated with age, and the regressions fit with both linear and cubic curves. The statistical significance of the correlations persists while maintaining age constant. The linear regression curve of AHs with age indicates that the spine height decrement rate is 2.12 mm/year, corresponding to 7.4 cm in 35 years. AHs decreases immediately after menopause fitting with a cubic curve model, with a decrement rate of about 3 cm in the first 5 years after menopause. We conclude that the measurement of the sum of vertebral body heights could usefully integrate LS-BMD evaluation in the clinical and epidemiological investigation of osteoporosis.     

Peripheral body fat has a protective role on bone mineral density in elderly women

OBJECTIVES: To determine whether bone mineral density is lower in women living in homes for the elderly as compared to free dwelling control subjects, and to investigate factors affecting possible differences. This is the first study with this objective as the primary aim. DESIGN: Case-control study. SUBJECTS AND METHODS: Institutionalised independent elderly women (n = 22, mean age = 75.1 y+/-6.43 s.d.) randomly selected in a home for the elderly and 22 age-matched control women randomly selected from a sample representative of the independent non institutionalised local population who underwent dual energy X-ray absorptiometry (DXA) at the lumbar spine and right femoral neck; anthropometric measurements (height, weight, subscapular and triceps skinfold thickness); general questionnaire. RESULTS: Mean bone mineral density at the femoral neck was 0.618 g/cm2 (+/-0.130s.d.) in institutionalised women and 0.709 g/cm2 (+/-0.106 s.d.) in controls (P = 0.02, t-test). Controlling for confounding factors in the analysis of covariance, triceps skinfold thickness and living in a home for the elderly turned out to be significant determinants of bone mineral density. CONCLUSION: When compared to free dwelling control subjects, institutionalised women show lower bone density, that is the main risk factor for fracture. Reduced peripheral body fat was significantly associated with the low bone mineral density observed. Health programs aimed at decreasing the incidence of fractures among institutionalised subjects will also have to consider the effect of nutritional or life style factors that reduce peripheral body fat.     

Differing effects of endogenous and synthetic inhibitors of metalloproteinases on intestinal tumorigenesis

The strength of the radius depends on the mechanical properties of cancellous and cortical bone. By assessing both compartments quantitatively with bone densitometry, we tried to identify the specificity of each in predicting the load at which the distal radius will fracture. Twenty human cadaver forearms were scanned for bone mineral and geometric properties with quantitative computed tomography and dual x-ray absorptiometry. In both a neutral loading situation and one in which the wrist was extended 45 degrees, the load distribution was determined with pressure-sensitive films, and a fracture simulating a fall on the hand was produced with a material testing machine. Fractures that occur with the wrist in extension were produced by a central impact of the scaphoid onto the radiocarpal joint, and those that occur under neutral loading conditions were produced by a more commonly distributed loading pattern. The load at fracture was most specifically predicted (r2=0.74) by bone mineral and geometric measures of the cortex at the shaft of the radius. Bone mineral density measures of trabecular (r2=0.64) and total (r2=0.66) bone were less successful in predicting the fracture load. After adjustment for bone size, the geometric and density measures revealed similar specificity. Cortical bone, therefore, contributes significantly to the strength of the distal radius and may play an important role in the prediction of osteoporotic wrist fractures.