Spine and femur BMD by DXA in patients with varying severity spinal osteoporosis

Failure of human cervical endplates: a cadaveric experimental model

STUDY DESIGN

An in vitro biomechanical study using a servohydraulic testing machine on cadaveric endplates.

OBJECTIVES

To characterize the effects of bone mineral density, endplate geometry, and preparation technique on endplate failure load.

SUMMARY OF BACKGROUND DATA

The effects of endplate preparation methods on failure loads are only partly characterized in the literature. Endplate burring has been recommended to increase fusion rates. However, graft subsidence may complicate anterior reconstruction procedures.

METHODS

After radiographic screening, 21 cadaveric cervical spines underwent dual-energy x-ray absorptiometry scanning to quantify mineral content. Endplate geometry was calculated in 55 randomly selected endplates from the inferior C2 to the superior T1 levels. These vertebrae were embedded in polyester resin and randomly left intact, perforated, or burred. The cervical endplates were loaded at a rate of 0.2 mm/s on an Instron materials tester with an attached 9 mm diameter polycarbonate rod (an area of 64 mm2). A stepwise, univariate linear regression was used to compare the point of endplate failure with the vertebral level, endplate area, gender, age, bone mineral density, and preparation technique.

RESULTS

Mean bone mineral density, as measured by dual-energy x-ray absorptiometry, was 0.713 g/cm2 (+/- 0.173 g/cm2). Mean endplate area was calculated at 323 mm2. A mean compressive force of 754 N (+/- 445 N) was required before endplate failure. Trends toward increasing compressive loads were noted with decreasing endplate area and increasing bone mineral density. Increasing age (P = 0.0203), caudal vertebral level (P < 0.0001), endplate burring (P = 0.0068), and female gender (P = 0.0452) were associated with significantly lower endplate fracture loads in compression.

CONCLUSIONS

Bone quality was predictive of endplate compressive failure loads. Intact endplates failed at significantly higher loads than their perforated or burred counterparts.

Inverse relation between osteoporosis and spondylosis in postmenopausal women as evaluated by bone mineral density and semiquantitative scoring of spinal degeneration

STUDY DESIGN

The relation between bone mineral density and severity of spondylosis was evaluated in postmenopausal women.

OBJECTIVE

To examine the possible inverse relation between osteoporosis and spondylosis by evaluating the association between bone mineral density and osteophyte formation or intervertebral disc narrowing using a semiquantitative scoring system.

SUMMARY OF BACKGROUND DATA

The literature contains studies demonstrating an inverse relation between osteoporosis and spondylosis as well as those documenting insufficient support for such a relation. However, in these studies, only limited-range grading systems (e.g., Grades 1-4) were used to evaluate the severity of spondylosis.

METHODS

In this study, 104 postmenopausal women older than 60 years underwent bone mineral density measurement of the lumbar spine (anteroposterior, lateral, and midlateral) and proximal femur (femoral neck, trochanter, and Ward's triangle) using dual-energy x-ray absorptiometry. Raw data representing the semiquantitative osteophyte score and disc score as well as the number of vertebral fractures were obtained using spinal radiograph. Correlations between bone mineral density and the radiographic variable were then analyzed.

RESULTS

Significant negative correlations were found between all bone mineral density data and the number of vertebral fractures (-0.524 < or r= r < or = -0.347; P < 0.05). Marginal/moderate positive correlations were observed between the osteophyte score and the bone mineral density data (0.263 < or = r < or = 0.580, P < 0.05), and between the disc score and the bone mineral density data (0.233 < or = r < or = 0.570, P < 0.05).CONCLUSIONS On the basis of the finding that spondylotic changes in postmenopausal women exhibit positive correlations not only with the lumbar bone mineral density, but also with the remote-site bone mineral density, this study supports the view that osteoporosis has an inverse relation with spondylosis.

Measurement of bone mineral density at the spine and proximal femur by volumetric quantitative computed tomography and dual-energy X-ray absorptiometry in elderly women with and without vertebral fractures

The goal of this study was to determine the effect of vertebral fracture status on trabecular bone mineral density (BMD) measurements obtained in the proximal femur and spine by helical volumetric quantitative computed tomography (vQCT). The study population consisted of 71 Italian women (average age 73 +/- 6) years. This group included 26 subjects with radiographically confirmed atraumatic vertebral fractures and 45 controls. The subjects received helical CT scans of the L1 and L2 vertebral bodies and the hip. The three-dimensional CT images were processed using specialized image analysis algorithms to extract measurements of trabecular, cortical, and integral BMD in the spine and hip. To compare the vQCT results with the most widely used clinical BMD measurement, dual X-ray absorptiometry (DXA) scans of the anteroposterior (AP) spine and proximal femur were also obtained. The difference between the subjects with vertebral fractures and the age-matched controls was computed for each BMD measure. All BMD measurements showed statistically significant differences, which ranged from 7% to 22% between subjects with fractures and controls. Although, given our small sample size, we could not detect statistically significant differences in discriminatory power between BMD techniques, integral BMD of the spine measured by vQCT and DXA tended to show stronger associations with fracture status (0.001 < p < 0.004). Measurements by QCT and DXA at the hip were also associated with vertebral fracture status, although the association of DXA BMD with fracture status was explained largely by differences in body weight between subjects with vertebral fractures and controls.

Which central dual X-ray absorptiometry skeletal sites and regions of interest should be used to determine the diagnosis of osteoporosis?

Although central measurement of bone mass by dual X-ray absorptiometry (DXA) is viewed by many as the "gold standard" for the diagnosis of osteoporosis in patients without previous fragility fracture, controversy remains on how best to use central DXA as a tool for diagnosis. Questions concerning the measurement of bone mass of the central skeleton were addressed at the International Society for Clinical Densitometry Position Development Conference. An expert panel agreed on the following positions: First, the diagnosis of osteoporosis should be based on the lowest T-score of either the PA spine or hip. Second, both the PA spine and hip should be measured. Third, whenever possible, bone mineral density (BMD) of the first four lumbar vertebrae should be measured. Fourth, DXA manufacturers should use L1-L4 as the default region of interest for their printouts. Fifth, BMD of either hip may be measured. Sixth, the lowest T-score of the three sites total hip, femoral neck, or trochanter should be considered. Seventh, Ward's area should not be used for diagnostic purposes; DXA manufacturers should not include this region in the default printout. Eighth, BMD of the forearm should be measured if the hip or spine cannot be accurately measured. Finally, lateral spine BMD should not be used to diagnose osteoporosis.

Cross-sectional study of osteopenia with quantitative MR imaging and bone densitometry

PURPOSE

To evaluation the cancellous bone-induced intravoxel spin dephasing rate (R2') and its relationship to bone mineral density and marrow fat and to examine these parameters as predictors of vertebral fracture status.

MATERIALS AND METHODS

R2' and R2, the rate constants for reversible and irreversible spin dephasing, and marrow fat fraction were measured in the lumbar vertebrae and proximal femur. One hundred thirty-nine subjects (mean age, 62.4 years +/- 11.4 [SD]; 33 men, 106 women) had spinal dual-energy x-ray absorptiometric bone mineral density (BMD) T scores ranging from +3 to -5. R2', BMD, and bone marrow composition as determinants of vertebral fracture status were examined.

RESULTS

Strongest single predictors of fracture status for BMD and R2' were the Ward triangle (r(2) = 0.48) and trochanter (r(2) = 0.37), respectively. Combined, the two parameters and sites increased fracture prediction (r(2) = 0. 62), whereas the combination of multiple BMD sites did not. Multivariate regression involving marrow fat fraction further improved fracture status prediction. R2' was correlated with BMD at all sites, although slopes differed by a factor of up to 2.5, which reflected differences in trabecular orientation relative to the static field. R2, the true transverse relaxation rate, was negatively correlated with marrow fat fraction. A non-age-related increase in marrow fat fraction in osteoporosis parallels earlier findings in animal models.

CONCLUSION

Cancellous bone marrow R2' measured in the proximal femur provides information, which, with BMD, improves prediction of vertebral fracture status.

Posterior-anterior and lateral dual-energy x-ray absorptiometry for the assessment of vertebral osteoporosis and bone loss among older men

Lateral spine dual-energy x-ray absorptiometry (DXA) selectively measures the trabecular-rich vertebral bodies without the contributions of the cortical-rich posterior elements of the spine and is less affected by spinal degenerative disease than posterior-anterior DXA. We tested whether lateral DXA detects vertebral osteoporosis more often and is more sensitive to age-related bone loss than posterior-anterior DXA in 193 healthy, community-dwelling men aged 51-81 years (mean +/- SD; 67 +/- 8 years). All men had supine lateral, posterior-anterior, and proximal femur DXA scans on a Hologic QDR 2000 densitometer. A subset (n = 102) had repeat scans after 4 years to determine annualized rates of change in bone mineral density (BMD). Age was inversely and significantly associated with BMD in the midlateral (r = -0.27) and lateral (r = -0.24) but not posterior-anterior (r = 0.04) projections. Midlateral (-1.43 +/- 3.48% per year; p = 0.0001), lateral (-0.27 +/- 1.68% per year; p = 0.12), and hip (-0.19 +/- 1.02% per year; p = 0.06) BMD decreased, whereas posterior-anterior BMD increased (0.73 +/- 1.11% per year; p = 0.0001) during follow-up. When compared with normal values in 43 men aged 21-42 years, mean T scores were significantly lower with lateral (-1.47 +/- 1.32) and midlateral (-1.57 +/- 1.36) than posterior-anterior (-0.12 +/- 1.30; p < 0.0001) DXA. Only 2.6% of the older men were considered osteoporotic (T score < or = -2.5) at the posterior-anterior spine, whereas 11.0% were osteoporotic at the femoral neck, 22.5% at the lateral spine, and 24.6% were osteoporotic at the midlateral spine. We conclude that supine lateral DXA identifies considerably more men as osteoporotic and is more sensitive to age-related bone loss than posterior-anterior DXA. Spinal osteoporosis may represent a substantially greater health problem among older men than previously recognized.

Individual smallest detectable difference in bone mineral density measurements

Bone mineral density (BMD) measurement is a major outcome measure in osteoporosis. The BMD changes observed must exceed the variability inherent in the measurement process to be considered related to disease progression. The objective of the study was to estimate short-term variability of BMD measurement and to propose a cut-off value for the smallest detectable BMD changes for an individual. To estimate the short-term variability, 70 healthy postmenopausal women aged 53 +/- 4 years (group 1) and 57 elderly osteoporotic postmenopausal women aged 80 +/- 6 years (group 2) had two repeated BMD measurements of the lumbar spine (L2-L4) and the proximal femur with dual-energy X-ray absorptiometry, with complete repositioning within 1 h. Cut-offs derived from short-term variability were either estimated from the coefficient of variation (CV) (which is a function of the measured value) or from the standard deviation (SD), and applied to 330 postmenopausal women (group 3) who had BMD measurements at baseline and 2 years later. The short-term intrasubject variability was greater at the lumbar spine in group 2 versus group 1 (0.0123 vs. 0.0059 g/cm2, p < 10-4), whereas it was not at the femoral neck (0.0098 vs. 0.0076 g/cm2, p = 0.28). There was no statistically significant correlation between short-term intrasubject variability (SD) and BMD as demonstrated with an analysis of covariance (p values ranging from 0.17 to 0.90). Cut-offs estimated with SD and CV were individually applied to group 3 patients. Using these two cut-offs, discrepancies in assessment of progression were observed in 1.7-8.6% of cases. Short-term BMD variability is constant in a wide range of BMD values. Consequently, to determine cut-off values for the smallest detectable differences in BMD at the individual level, precision errors should be based on SD (expressed in absolute units) rather than on CV (expressed in percentage).

Biomechanical analysis of bone mineral density, insertion technique, screw torque, and holding strength of anterior cervical plate screws

✓ The bone mineral density (BMD) of 99 cadaveric cervical vertebral bodies (C3–7) was determined using dual x-ray absorptiometry. The vertebral bodies were randomly assigned to receive either a unicortical (51 bodies) or bicortical (48 bodies) Caspar cervical plating screw. The initial insertion torque was measured using a digital electronic torque wrench, and the force required to withdraw the screw from the vertebral body was determined. The mean BMD for the total group of 99 was 0.787 ± 0.154 g/cm2, the mean insertion torque was 0.367 ± 0.243 newton-meters, and the mean pullout force was 210.4 ± 158.1 newtons. A significant correlation was noted between BMD and torque (p < 0.0001, r = 0.42), BMD and pullout force (p < 0.0001, r = 0.54), and torque and pullout force (p < 0.0001, r = 0.88). Although the BMD of the unicortical and bicortical groups was equivalent (p = 0.92), the insertion torque and pullout force differed significantly (p = 0.02 and p = 0.008, respectively) for the unicortical and bicortical groups. A holding index for each screw and insertion technique was defined as the product of the BMD and insertion torque. The calculated holding index and resultant pullout force were significantly correlated for both techniques of screw insertion (r = 0.92), and a significant difference in holding index was observed with unicortical versus bicortical screw placement (p = 0.04). The determination of BMD and measurement of insertion torque to create a unique holding index provides an assessment of bone—screw interaction and holding strength of the screw, both of which impact on the resultant stability of cervical instrumentation. As the number of cervical plating systems increases, the determination of a holding index for various screws and insertion techniques may assist in the comparison of cervical instrumentation.

Postmenopausal bone loss in Japanese women

OBJECTIVES

Our purpose was to detect anatomic variations in postmenopausal bone loss and to determine the risk factors most affecting bone mass in Japanese women.

METHODS

One hundred sixty-six Japanese women (54 premenopausal and 112 postmenopausal), aged 40-68 years, were enrolled in the study. Bone mineral densities (BMD) of the lumbar spine (L2-4) and total body were measured by dual energy X-ray absorptiometry and the results were subjected to statistical analysis.

RESULTS

Among the various sites studied, the lumbar spine (L2-4) showed the fastest bone loss after menopause. Multiple regression analysis indicated that two factors, number of years since the menopause and body mass index (BMI), affected lumbar spine (L2-4) BMD.

CONCLUSION

Measurement of lumbar spine (L2-4) BMD is suitable for evaluating postmenopausal osteoporosis. The risk factors for postmenopausal bone loss were a long period after menopause and a low BMI.

A comparison of bone densitometry measurements of the central skeleton in post-menopausal women with and without vertebral fracture

The purpose of this investigation was to compare the ability of two different bone densitometry techniques (quantitative computed tomography and dual X-ray absorptiometry) to discriminate subjects without any vertebral fracture from those with definite vertebral fractures. Bone mineral density (BMD) was determined in 112 post-menopausal women. 83 women were classified free of vertebral fracture and 29 were considered to have definite vertebral fractures. Quantitative computed tomography (QCT) was performed using three different spinal regions of interest. Dual X-ray absorptiometry (DXA) was measured at the spine (both in posteroanterior (PA) and lateral (L-DXA) projection, and at hip (total, neck and Ward regions). An additional estimated volumetric BMD was derived from the PA and L-DXA spine scans. Individuals with definite vertebral fractures had lower bone mineral density for each of the methods and regions of interest (ROI). Spinal QCT results, total and Ward hip DXA results showed the greatest percentage decrement. Odds ratio estimates revealed a significant relationship between BMD and fracture with spinal QCT, hip, and volumetric spinal DXA. The greatest areas under the receiver operating characteristic (ROC) curves were found with results of spinal QCT, total and Ward hip DXA, and volumetric spinal DXA measurements. It is concluded that spinal QCT and femoral total DXA measurement may be preferred to PA and lateral L3 DXA measurements.

Accurate assessment of precision errors: how to measure the reproducibility of bone densitometry techniques

Assessment of precision errors in bone mineral densitometry is important for characterization of a technique's ability to detect longitudinal skeletal changes. Short-term and long-term precision errors should be calculated as root-mean-square (RMS) averages of standard deviations of repeated measurements (SD) and standard errors of the estimate of changes in bone density with time (SEE), respectively. Inadequate adjustment for degrees of freedom and use of arithmetic means instead of RMS averages may cause underestimation of true imprecision by up to 41% and 25% (for duplicate measurements), respectively. Calculation of confidence intervals of precision errors based on the number of repeated measurements and the number of subjects assessed serves to characterize limitations of precision error assessments. Provided that precision error are comparable across subjects, examinations with a total of 27 degrees of freedom result in an upper 90% confidence limit of +30% of the mean precision error, a level considered sufficient for characterizing technique imprecision. We recommend three (or four) repeated measurements per individual in a subject group of at least 14 individuals to characterize short-term (or long-term) precision of a technique.