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M L Bouxsein

Publications and source records attributed to M L Bouxsein.

32 records · Page 2Linked to original sources
PubMed1999

Effect of local density changes on the failure load of the proximal femur.

Hip fracture among the elderly is a large and growing public health issue. Presently, all therapies approved for treatment and prevention of osteoporosis involve pharmacological agents that act systemically. In this study, we evaluated the feasibility of preventing osteoporotic hip fractures with local, rather than systemic, therapy. Our hypothesis is that local therapy to increase bone density may be as effective as systemic therapy in reducing fracture risk. Thus, the goal of this investigation was to use finite element analyses to study the effect of a localized increase in bone density on the strength of an osteopenic, human femur. Finite element predictions of the failure load were made after increasing the bone density within small regions in the proximal femur. The outcome variable from these analyses was the predicted load required to break a femur in a simulated fall to the side with impact on the greater trochanter. Increasing the density by 25% relative to baseline values in a small region (0.86 cm3) of the femoral neck increased the predicted failure load by 6.2%. The same density increase in a much larger region (4.92 cm3) increased the failure load by 15%. Inclusion of more than one region of increased density provided little additional benefit. In comparison, when the density of the entire femur was increased by 5% relative to baseline values, the predicted failure load increased by 5.4%. These findings suggest that agents capable of inducing increased bone density in small regions of the proximal femur have the potential to reduce the risk of hip fracture.

Aged↗
PubMed1999

Forearm bone mineral densitometry cannot be used to monitor response to alendronate therapy in postmenopausal women.

Alendronate significantly increases bone mass and reduces hip and spine fractures in postmenopausal women. To determine whether forearm densitometry could be used to monitor the efficacy of alendronate, we examined changes in bone mineral density (BMD) at the forearm (one-third distal, mid-distal, ultradistal radius) versus changes at the hip (femoral neck, total hip) and spine (posteroanterior and lateral) in a double-masked, randomized, placebo-controlled clinical trial of 120 elderly women (mean age 70 +/- 4 years) treated with alendronate for 2.5 years. We found that among women in the treatment group, BMD increased by 4.0-12.2% at the hip and spine sites (all p<0.001), whereas BMD increased only nominally at the one-third distal radius (1.3%, p<0.001) and mid-radius (0.8%, p<0.05), and remained stable at the ultradistal radius. At baseline, forearm BMD correlated with that of the hip (r = 0.55-0.64, p<0.001), femoral neck (r = 0.54-0.61, p<0.001) and posteroanterior spine (r = 0.56-0.63, p<0.001). Changes in radial BMD after 1 year of therapy were not correlated with changes in hip and spine BMD after 2.5 years of therapy. In contrast, short-term changes in total hip and spine BMD were generally positively associated with long-term changes in total hip, femoral neck and spine BMD (r = 0.30-0.71, p<0.05). Furthermore, long-term BMD changes at the forearm did not correlate with long-term hip and spine BMD changes, in contrast to the moderate correlations seen between spine and hip BMD at 2.5 years (r = 0.38-0.45, p<0.01). We conclude that neither short- nor long-term changes in forearm BMD predict long-term changes in overall BMD for elderly women on alendronate therapy, suggesting that measurements of clinically relevant central sites (hip and spine) are necessary to assess therapeutic efficacy.

Absorptiometry, Photon↗
PubMed1999

Prediction of the strength of the elderly proximal femur by bone mineral density and quantitative ultrasound measurements of the heel and tibia.

Quantitative ultrasound (QUS) of the heel and tibia have recently been approved in the United States for diagnostic evaluation of low bone mass. The goal of this study was to use human cadaveric specimens to compare correlations among: a) strength of the proximal femur; b) bone mineral density of the femur, tibia, and heel; and c) QUS of the tibia and heel. We obtained 26 proximal femurs and intact lower limbs from 16 female and 10 male cadavers, with a mean age of 81+/-12 years. Bone mineral density (BMD, g/cm2) of the proximal femur and tibia were assessed using dual-energy x-ray absorptiometry, and BMD (g/cm) of the heel was measured using single-energy x-ray absorptiometry. Ultrasound velocity at the mid-tibia was determined using a contact, gel-coupled ultrasound device. Broadband ultrasound attenuation (BUA) and speed of sound (SOS) of the heel were determined using a transmission ultrasound device with water-based coupling. The femurs were tested to failure in a configuration designed to simulate a fall to the side with impact to the greater trochanter. As in previous studies, the strength of the proximal femur was very strongly correlated with femoral BMD and heel BMD (r2 = 0.78-0.92, p < .0001 for all). BUA and SOS of the heel were also strongly correlated to femoral strength (r2 = 0.70 and 0.67, respectively, p < 0.0001 for both), whereas tibia SOS was only weakly correlated (r2 = 0.19, p = 0.03). The average coefficient of variation for triplicate tibial SOS measurements was 0.50%. This study indicates that, although tibial SOS measurements are precise, they are not strongly correlated with femoral BMD or strength. In contrast, heel QUS measurements are strongly correlated with the strength of the proximal femur. These findings imply that tibial SOS may be of limited use for assessing hip fracture risk. Prospective fracture risk data are needed to define further the clinical utility of tibia ultrasound measurements.

Absorptiometry, Photon↗
PubMed1997

Precision and accuracy of computed digital absorptiometry for assessment of bone density of the hand.

Widespread osteoporosis testing and diagnosis are currently limited due to the high capital cost and reduced portability of many existing bone densitometry techniques. In this study we evaluated an inexpensive, low radiation, X-ray-based technique for assessing bone density of the middle phalanx. The technique, termed computed digital absorptiometry (CDA), is similar to radiographic absorptiometry (RA), using a single-energy X-ray source, an aluminum alloy step-wedge, and a charge-coupled device (CCD) detector system to automatically compute bone mineral content (BMC, g) and bone mineral density (BMD, g/cm2) in the middle phalanx of the third finger. The potential advantage of CDA over current RA techniques is that by using a filmless detector system, no off-site processing of radiographs is required and bone density results are obtained immediately after the test. Using human cadaveric specimens we determined the accuracy and short-term precision of CDA as well as its correlation with other hand and forearm bone densitometry methods. We obtained 26 cadaveric forearms (50% female, mean age 78 years, range 52-96 years). BMC and BMD of the middle phalanx of the third finger were determined using CDA and using RA. We assessed forearm BMC and BMD using single-energy and dualenergy X-ray absorptiometry (SXA and DXA). Precision of CDA was assessed by measuring ten of the specimens five times each with repositioning between measurements. Finally, the middle phalanx was dissected and incinerated to determine ash weight. BMC estimates from CDA and from RA were strongly correlated with ash weight (r = 0.89, p < 0.001 and r = 0.93, p < 0.001, respectively). The mean coefficients of variation using CDA were 1.36% and 0.70% for phalanx BMC and BMD, respectively. BMC and BMD measured by CDA were strongly correlated with hand and forearm bone mineral measurements performed by SXA, DXA and RA (r = 0.74-0.91). These results indicate that CDA accurately and precisely predicts BMC of the middle phalanx. Thus, with further clinical verification, this technique may prove to be a useful tool for the widespread testing and assessment of osteoporotic fracture risk.

Absorptiometry, Photon↗
PubMed1997

Tibial ultrasound velocity measured in situ predicts the material properties of tibial cortical bone.

Quantitative ultrasound (QUS) is currently being investigated as a possible alternative or adjunct to X-ray-based methods for assessing osteoporosis and fracture risk. It has been proposed that QUS may allow measurement of bone "quality," such as bone architecture or material properties. In this study, we used human cadaveric specimens to evaluate whether ultrasound velocity measurements performed in situ at the midtibia were correlated with the mechanical properties of tibial cortical bone. We obtained 26 human lower limbs (10 men and 16 women) with a mean (+/-SD) age of 81 +/- 12 and range of 53-98 years. The longitudinal ultrasound velocity of the cortical bone at the anteromedial midtibia (tUV, meters per second) was assessed in the intact legs (SoundScan 2000, Myriad Ultrasound, Rehovot, Israel). Then a cylinder of cortical bone was removed from the anterior tibia at the site of QUS scanning, scanned using peripheral quantitative computed tomography to determine bone density, and mechanically tested in tension to failure. We found that tUV of the intact legs correlated strongly with bone density of the cortical bone specimens (r2 = 0.74, p < 0.0001). Both bone density (r2 = 0.89, p < 0.0001) and tUV (r2 = 0.84, p < 0.0001) were very strongly correlated with the cortical bone elastic modulus. In addition, both tUV (r2 = 0.75) and bone density (r2 = 0.80) were highly correlated with the ultimate strength of the cortical bone specimens. In summary, tibial ultrasound velocity measured in situ correlated with the material properties of tibial cortical bone nearly as strongly as did bone density. (Bone 21:119-125; 1997).

Aged↗
PubMed1997

Quantitative ultrasound of the calcaneus reflects the mechanical properties of calcaneal trabecular bone.

To provide new information about the potential role of quantitative ultrasound (QUS) in fracture risk prediction, we assessed whether QUS and densitometric variables derived from measurements of intact cadaveric feet were associated with the mechanical properties of calcaneal trabecular bone. We obtained 31 intact cadaveric feet from the local anatomic gifts program, including 13 men and 18 women, with a mean age of 77 years (range 50-91 years). Broadband ultrasound attenuation (BUA) and ultrasound transit velocity (SOS) were assessed in the intact cadaveric feet using a water-based ultrasound system. In addition, we measured the bone mineral density (BMD) of the posterior calcaneus using dual-energy X-ray absorptiometry. Cubes of trabecular bone were then removed from the calcaneus at approximately the same location as the QUS measurements were obtained, and the elastic modulus and ultimate strength of the trabecular bone specimens were measured by compressing them in the mediolateral direction. We found that QUS variables were moderately to strongly correlated with the mechanical properties of calcaneal trabecular bone (r2 = 0.48-0.63, p < 0.001 for all). However, the strongest associations with the mechanical properties trabecular bone were provided by calcaneus BMD and trabecular bone apparent density (r2 = 0.66-0.88). BUA and densitometric measurements were independently associated with elastic modulus, but not with ultimate strength. Our results indicate that QUS measurements of the intact heel are associated with the mechanical properties of calcaneal trabecular bone and, in some cases, provide information in addition to that provided by BMD or density measurements.

Absorptiometry, Photon↗
PubMed1997

Precision and discriminatory ability of calcaneal bone assessment technologies.

To determine if measuring skeletal status at the calcaneus is a potentially valuable technique for diagnosing osteoporosis, we examined five calcaneal assessment techniques in 53 young normal women and 108 postmenopausal women with osteoporosis and compared these measurements to dual-energy X-ray absorptiometry (DEXA) at the calcaneus, hip, and spine. The five instruments, including single-energy X-ray absorptiometry (SEXA) and four quantitative ultrasound (QUS) instruments, were evaluated for precision, ability to discriminate osteoporotic from young normal subjects, and correlation to the other instruments. The coefficient of variation (%CV) for instrument, positioning, interobserver, and short-term precision of the five calcaneal instruments ranged from 1.34-7.76%, 1.63-7.00%, 1.84-9.44%, and 1.99-7.04%, respectively. The %CVs for positioning, interobserver, and short-term precision were similar for calcaneal DEXA, calcaneal SEXA, and stiffness (as measured by Achilles). The %CVs for instruments precision were similar between calcaneal DEXA and SEXA. The ability of the five calcaneal instruments to discriminate osteoporotic from young normal subjects was similar based on the analysis of area under the receiver operating characteristic curves (range 0.88-0.93) and equivalent to DEXA of the calcaneus and hip (0.88-0.93). The correlations between the measurements of five calcaneal instruments were strong (0.80 < or = r < or = 0.91, p < 0.001). These data suggest that although the precision is variable, the calcaneal QUS and SEXA instruments can discriminate between osteoporotic patients and young normal controls and appear to be a useful technique for assessment of osteoporosis.

Absorptiometry, Photon↗
PubMed1996

Impact direction from a fall influences the failure load of the proximal femur as much as age-related bone loss.

Recent studies have shown that factors related to fall biomechanics may play as important a role in the etiology of hip fracture as age-related bone loss. Motivated by finite element analyses that showed failure of the proximal femur to be sensitive to loading direction, our objective with the current investigation was to determine experimentally if changes in impact direction affect the failure load of the elderly proximal femur. Thirty-three cadaveric femurs were assigned randomly to three groups of 11 and tested at one of three loading angles, 0 degree, 15 degrees, or 30 degrees, representing a fall on the hip rolled slightly forward, to the side, or rolled slightly backwards, respectively. Femurs were scanned using dual-energy X-ray absorptiometry (DXA) to assess bone mineral density (BMD) and tested to failure in a fall loading configuration at a displacement rate of 100 mm/second. Using an analysis of covariance to adjust for total hip BMD, we found that failure load decreased by 24% as the loading angle changed from 0 degree to 30 degrees. This reduction in failure load is comparable to that associated with about 25 years of age-related bone loss after the age of 65. Therefore, the impact direction associated primarily with a fall is a critical determinant of hip fracture risk that is both independent of bone density and associated with fall biomechanics.

Accidental Falls↗
PubMed1995

Ultrasound and densitometry of the calcaneus correlate with the failure loads of cadaveric femurs.

We assessed the bone mineral density (BMD) of 16 matched sets of cadaveric proximal femurs and feet using dual-energy x-ray absorptiometry (DXA). We also estimated the femoral neck length from the DXA scans. Quantitative ultrasound densitometry was used to measure the velocity of sound and broadband ultrasound attenuation (BUA) in the calcaneus of each foot. The proximal femurs were then tested to failure in a loading configuration designed to simulate a fall with impact to the greater trochanter. Femoral neck BMD and trochanteric BMD were strongly associated with the femoral failure load (r2 = 0.79 and 0.81, respectively; P < 0.001), whereas femoral neck length was modestly correlated with femoral failure load (r2 = 0.27, P = 0.04). Calcaneal BMD (r2 = 0.63, P < 0.001) and BUA (r2 = 0.51, P = 0.002) were also significantly associated with femoral failure load. Given the small sample size, we were unable to detect differences in the strength of the correlations between the independent parameters and femoral failure load. Using linear multiple regression analyses, the strongest predictor of femoral failure load was a combination of femoral neck BMD and femoral neck length (R2 = 0.85, P < 0.001). Thus, it appears that both femoral and calcaneal bone mineral properties may be useful for identifying those persons at greatest risk for hip fracture.

Absorptiometry, Photon↗
PubMed1995

Failure load of thoracic vertebrae correlates with lumbar bone mineral density measured by DXA.

Fractures of the thoracic spine account for a large portion of vertebral fractures in the elderly, yet noninvasive measurements of bone mineral properties are limited to the L2-L4 vertebral bodies. The purpose of this investigation was to determine whether bone mineral properties of the lumbar spine correlate with the failure properties of thoracic vertebrae. Cadaveric lumbar segments were scanned using dual-energy x-ray absorptiometry (DXA) from both the lateral and anteroposterior projections. Three-body segments L1-L3 and T10-T12 were then compressed to create crush fractures in the L2 and T11 vertebral bodies, and linear correlation analyses were performed to compare each DXA measure with the failure properties of L2 and T11. Lumbar BMD from the lateral view correlated significantly with T11 ultimate load (r = 0.94, P < 0.001), as did lumbar BMD from the anteroposterior projection (r = 0.83, P = 0.001). Significant correlations were also found between both lumbar BMD and BMC and the stiffness and energy to failure of T11. Furthermore, BMD and BMC measured at L2 correlated significantly with L2 ultimate load, stiffness, and energy to failure. We conclude that bone mineral properties measured at the lumbar spine provide a valid assessment of the compressive strength of both thoracic and lumbar vertebrae. Lumbar BMD may therefore be used to derive an index for the prediction of thoracolumbar fractures to aid in the early intervention of vertebral fractures.

Absorptiometry, Photon↗
PubMed1994

Age-related differences in cross-sectional geometry of the forearm bones in healthy women.

Men exhibit age-related adaptive changes in long bone geometry, namely, endosteal resorption and periosteal apposition of bone, that help to preserve bone strength. It is not clear whether women undergo similar adaptive responses. To address this question, we assessed the bone mineral density and cross-sectional geometry of the radius and ulna at the one-third distal site by single photon absorptiometry and computed tomography (CT) in healthy young (n = 21, age 20-30 years) and older (n = 22, age 63-84 years) women. We used the CT data to compute the total subperiosteal, medullary, and cortical areas, as well as the maximum, minimum, and polar moments of inertia. We normalized the geometric parameters for bone length and performed comparisons using both the original and size-corrected data. Radial and ulnar bone mineral content and density were 20-30% lower in the older women (P < 0.0001). Ulnar width, total area, medullary area, and maximum and polar moment of inertia were greater in the older than in the younger women. Although we observed similar trends when we examined the radius data that were corrected for bone size, age-related differences in radial geometry were less pronounced and were not significant. We conclude that women undergo endosteal resorption and periosteal apposition of the ulna with age, thereby exhibiting an adaptive pattern that helps to preserve bone strength. The different behavior of these two bones suggests that local, rather than systemic, factors underlie this adaptation.

Adult↗
PubMed1992

New approaches for interpreting projected bone densitometry data.

Bone densitometry using dual-photon absorptiometry (DPA) or dual-energy x-ray absorptiometry (DXA) has become a standard method for assessing bone mineral content in the spine and other skeletal regions. A projected areal density, referred to as bone mineral density (BMD,g/cm2), is normally calculated to assess regional bone density and strength. We demonstrate that this measure can be misleading when used to compare bones of different sizes due to inherent biases caused by bone thickness differences. For example, assuming that volumetric bone density remains constant and bony linear dimensions are proportional to height, a 20% increase in height would result in a 20% increase in both the thickness and the BMD of any bone. We describe new analysis methods to reduce the confounding effect of bone size, and we introduce a parameter, bone mineral apparent density (BMAD, g/cm3), that better reflects bone apparent density. Using this parameter, we calculate a quantity that serves as an index of bone strength (IBS, g2/cm4) for whole vertebral bodies. These analyses were applied to lumbar spine (L2-4) DXA measurements in a population of women 17-40 years old and appear to offer advantages to conventional techniques.

Absorptiometry, Photon↗
PubMed1992

Effects of resistance and endurance exercise on bone mineral status of young women: a randomized exercise intervention trial.

A substantial body of cross-sectional data and a smaller number of intervention trials generally justify optimism that regular physical activity benefits the skeleton. We conducted an 8 month controlled exercise trial in a group of healthy college women (mean age = 19.9 years) who were randomly assigned to a control group or to progressive training in jogging or weight lifting. We measured the following variables: bone mineral density (BMD) of the spine (L2-4) and right proximal femur using dual-energy x-ray absorptiometry, dynamic muscle strength using the 1-RM method, and endurance performance using the 1.5 mile walk/run field test. A total of 31 women completed the 8 month study. For women completing the study, compliance, defined as the percentage of workout sessions attended, was 97% for the runners (range 90-100%) and 92% (range 88-100%) for the weight trainers. Body weight increased by approximately 2 kg in all groups (p less than 0.05). Weight training was associated with significant increases (p less than 0.01) in muscle strength in all muscle groups. Improvement ranged from 10% for the deep back to 54% for the leg. No significant changes in strength scores were observed in the control or running groups. Aerobic performance improved only in the running group (16%, p less than 0.01). Lumbar BMD increased (p less than 0.05) in both runners (1.3 +/- 1.6%) and weight trainers (1.2 +/- 1.8%). These results did not differ from each other but were both significantly greater than results in control subjects, in whom bone mineral did not change.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗