Does bone mineral density affect hip fracture severity?

The association between hip fracture and reduced bone mineral density is well documented, with reduced bone mineral density predisposing to fracture. However, it is unknown whether an association exists between the magnitude of bone density lost and the severity of the hip fracture sustained. One hundred forty-two patients (96 women, 46 men) with a mean age of 74 years (range, 49-92 years) who sustained a hip fracture following a simple ground-level fall and were treated for this injury were reviewed. All patients had undergone dual-energy x-ray absorptiometry bone scanning of the contralateral hip and lumbar spine. Fractures were classified as intra- or extracapsular or subtrochanteric and then subclassified by degree of severity as simple (stable) or multifragmentary (unstable) fracture patterns.Although a low hip bone mineral density (T- or Z score <2.5) was associated with an increased risk of extracapsular fracture (P=.025) compared with other fracture types, no association existed between bone mineral density and the severity of the resultant hip fracture. Although an association exists between bone mineral density and the risk of fragility fractures, the results of the current study suggest that the severity of hip fractures does not follow this correlation. Therefore, no assumption can be made about bone mineral density of the proximal femur based on the severity of the fracture observed on plain radiographs.     

High prevalence of spine–femur bone mineral density discordance and comparison of vertebral fracture risk assessment using femoral neck and lumbar spine bone density in Korean patients

The aim of this study was to evaluate the prevalence of spine–femur discordance, and to compare the effectiveness of femoral neck (FN) and lumbar spine (LS) bone mineral density (BMD) for estimation of the risk of vertebral fractures. Women who were evaluated with dual energy X-ray absorptiometry between January 2001 and December 2005 were enrolled in this study. Vertebral fracture risk was calculated using initial FN and LS BMD. The follow-up vertebral X-rays from all subjects were reviewed, and the calculated estimated risk using the Fracture Risk Assessment Tool (FRAX^®) was compared with the actual prevalence of vertebral fractures during the follow-up period. Among a total of 443 women with a mean age of 58.5 years, 130 women (29.3 %) demonstrated femur–spine discordance (i.e., a difference between FN and LS BMD of >1 SD). Most subjects having discordance showed lower LS BMD (73.1 %) compared to FN BMD. During the mean 7-year follow-up period, 12 (2.7 %) vertebral fractures occurred. In cases with high estimated fracture risk (>20 % for estimated fracture risk), using LS BMD significantly reflected the actual vertebral fracture in total subjects [odds ratio (OR) 19.29, 95 % confidence interval (CI) 4.21–88.46], in subjects with spine–femur discordance (OR 16.00, 95 % CI 1.91–134.16), and in subjects with spine–femur discordance having lower LS BMD (OR 20.67, 95 % CI 1.63–262.71). In comparison, the estimated risk using FN BMD did not reflect the actual occurrence of vertebral fractures. In conclusion, a significant number of Korean subjects exhibited spine–femur discordance, and LS BMD might be more appropriate for estimation of vertebral fracture risk.     

Degenerative changes at the lumbar spine—implications for bone mineral density measurement in elderly women

Summary

Degenerative changes of the lumbar spine may lead to misinterpretation of bone mineral density (BMD) measurements and cause underdiagnosis of osteoporosis. This longitudinal study of 1,044 women, 75 years at inclusion and followed for 10 years, shows that identification of apparent degenerative changes on the dual energy X-ray absorptiometry (DXA) scan can increase the proportion diagnosed.

Introduction

In the elderly, degenerative manifestations in the lumbar spine may result in falsely elevated BMD values, consequently missing a large proportion of those with osteoporosis. Our aim was to determine the distribution and impact of degenerative changes on lumbar spine DXA over time and its clinical implications.

Methods

Participants were 1,044 women from the population-based Osteoporosis Risk Assessment cohort. All women were 75 years old at invitation and followed up after 5 years (n?=?715) and 10 years (n?=?382). Degenerative changes were evaluated visually on the DXA image for each vertebra L1 to L4 (intraobserver precision kappa values of 0.66–0.70).

Results

At baseline, apparent degenerative changes were more frequent in the inferior segments of the lumbar spine [5 % (L1), 15 % (L2), 26 % (L3), and 36 % (L4)] and increased over time. At 10 years, the prevalences were 20 % (L1), 39 % (L2), 59 % (L3), 72 % (L4), resulting in a significant increase in overall BMD. In women without apparent degenerative changes, BMD remained stable between 75 and 85 rather than an expected bone loss. At baseline, 37 % had osteoporosis (BMD?<??2.5) at L1–L4; exclusion of women with apparent degenerative changes increased this proportion to 47 %. Using L1–L2, which was less prone to degenerative changes, 46 % of women were classified as osteoporotic regardless of degenerative changes.

Conclusion

Degenerative changes were very common in elderly women, accelerated disproportionately over time, were increasingly frequent from vertebrae L1 to L4, and had significant impact on diagnosing osteoporosis. This suggests that routine reporting of spine BMD at L1–L2 would add valuable information for reassessment and monitoring.     

What happens to femoral neck bone mineral density after hip resurfacing surgery?

The major advantage of hip resurfacing is the decreased amount of bone resection compared with a standard total hip replacement. Fracture of the femoral neck is the most common early complication and poor bone quality is a major risk factor. We undertook a prospective consecutive case control study examining the effect of bone mineral density changes in patients undergoing hip resurfacing surgery. A total of 423 patients were recruited with a mean age of 54 years (24 to 87). Recruitment for this study was dependent on pre-operative bilateral femoral bone mineral density results not being osteoporotic. The operated and non-operated hips were assessed. Bone mineral density studies were repeated over a two-year period. The results showed no significant deterioration in the bone mineral density in the superolateral region in the femoral neck, during that period. These findings were in the presence of a markedly increased level of physical activity, as measured by the short-form 36 health survey physical function score.     

Hip structural geometry and incidence of hip fracture in postmenopausal women: what does it add to conventional bone mineral density?

Summary

Hip geometry measurements of outer diameter and buckling ratio at the intertrochanter and shaft of the hip dual energy X-ray absorptiometry (DXA) scan predicted incident hip fracture in postmenopausal women. These associations, independent of age, body size, clinical risk factors, and conventional areal bone mineral density, suggest hip geometry plays a role in fracture etiology and may aid in improving identification of older women at high fracture risk.

Introduction

This study examined whether hip geometry parameters predicted hip fracture independent of body size, clinical risk factors, and conventional femoral neck bone mineral density (aBMD) and whether summary factors could be identified to predict hip fracture.

Methods

We studied 10,290 postmenopausal women from the Women's Health Initiative. Eight thousand eight hundred forty-three remained fracture free during follow-up to 11 years of follow-up, while 147 fractured their hip, and 1,300 had other clinical fractures. Hip structural analysis software measured bone cross-sectional area, outer diameter, section modulus, average cortical thickness, and buckling ratio on archived DXA scans in three hip regions: narrow neck, intertrochanter, and shaft. Hazard ratios were estimated using Cox proportional hazards models for individual parameters and for composite factors extracted from principal components analysis from all 15 parameters.

Results

After adjustment for age, body size, clinical risk factors, and aBMD, intertrochanter and shaft outer diameter measurements remained independent predictors of hip fracture with hazard ratios for a one standard deviation increase of 1.61 (95% confidence interval (CI), 1.25–2.08) for the intertrochanter and 1.36 (95% CI, 1.06–1.76) for the shaft. Average buckling ratios also independently predicted incident hip fracture with hazard ratios of 1.43 (95% CI, 1.10–1.87) at the intertrochanter and 1.24 (95% CI, 1.00–1.55) at the shaft. Although two composite factors were extracted from principal components analysis, neither was superior to these individual measurements at predicting incident hip fracture.

Conclusions

Two hip geometry parameters, intertrochanter outer diameter and buckling ratio, predict incident hip fracture after accounting for clinical risk factors and aBMD.     

Congenital hip dysplasia and bone mineral density of the hip--a new risk factor for osteoporotic fracture?

Decreased bone mineral density (BMD) at the hip is an important risk factor for hip fractures, which are a major socioeconomic problem in the elderly. The incidence of congenital hip dysplasia (CHD) is about 7-13% in the Middle European population. We assessed the question of whether a conservatively treated CHD may be a risk factor for low BMD at the hip in adult women. We evaluated prospectively 240 premenopausal women (33 +/- 7 years). Past medical history was recorded including the presence or absence of CHD. Lumbar and femoral BMD using dual-energy X-ray absorptiometry (DXA) and biochemical parameters of bone metabolism were measured. X-rays of the pelvis were performed in CHD patients. Thirty-one (12.9%) of the patients had a history of conservatively treated CHD, four (1.2%) had undergone surgery; all other patients served as control group. Patients and controls were comparable for anthropometric data, lifestyle factors, and hip axis length. BMD in CHD patients was significantly lower at the hip (difference by 1 STD) but comparable at the spine. OC was significantly higher in patients with CHD than in controls. In a logistic regression model, CHD was associated with a 6.3-fold increased risk for low BMD at the hip. We therefore conclude that a history of conservatively treated CHD may be a major risk factor for low BMD at the hip in about 1 out of 10 women. Whether this translates into an increased risk for future hip fractures will have to be assessed in further prospective studies.     

HDL cholesterol and bone mineral density: is there a genetic link?

Overwhelming evidence has linked cardiovascular disease and osteoporosis, but the shared root cause of these two diseases of the elderly remains unknown. Low levels of high density lipoprotein cholesterol (HDL) and bone mineral density (BMD) are risk factors for cardiovascular disease and osteoporosis respectively. A number of correlation studies have attempted to determine if there is a relationship between serum HDL and BMD but these studies are confounded by a number of variables including age, diet, genetic background, gender and hormonal status. Collectively, these data suggest that there is a relationship between these two phenotypes, but that the nature of this relationship is context specific. Studies in mice plainly demonstrate that genetic loci for BMD and HDL co-map and transgenic mouse models have been used to show that a single gene can affect both serum HDL and BMD. Work completed to date has demonstrated that HDL can interact directly with both osteoblasts and osteoclasts, but no direct evidence links bone back to the regulation of HDL levels. Understanding the genetic relationship between BMD and HDL has huge implications for understanding the clinical relationship between CVD and osteoporosis and for the development of safe treatment options for both diseases.     

Weight and body mass index predict bone mineral density and fractures in women aged 40 to 59 years

Summary  Weight and body mass index are associated with low bone mineral density and fractures in older women. This retrospective cohort study confirms a similar relationship in women aged 40 to 59 years. Introduction  Risk factors for the prediction of osteoporosis and fractures have been less thoroughly studied in younger women. We evaluated the associations between weight, body mass index (BMI), the Osteoporosis Self-Assessment Tool (OST), bone mineral density (BMD) and fracture risk in women aged 40 to 59 years. Methods  Using administrative health management databases, we conducted a retrospective cohort study in 8,254 women aged 40–59 years who had baseline BMD testing. Linear regression and Cox proportional multivariate models were created to examine the associations with weight, BMI, OST, BMD, and subsequent fractures throughout a 3.3-year follow-up. Results  Body weight, BMI, and OST had a similar overall performance in their ability to classify women with femoral neck T-score ≤ −2.5. Throughout 27,256 person years of observation, 225 women experienced one or more fractures. After adjustment for age, prevalent fractures, and use of corticosteroids, each standard deviation decrease in weight was associated with a 19% increase in the risk of incident fracture (95% CI: 1.01–1.35). Femoral neck BMD and the presence of prevalent fractures were also associated with the risk of incident fractures. Conclusions  Low weight and BMI predict osteoporosis and are associated with increased fracture risk in younger women. The negative impact of low body weight on bone health should be more widely recognized. On behalf of the Manitoba Bone Density Program.     

Is vascular calcification associated with bone mineral density and osteoporotic fractures in ambulatory,elderly women?

Summary  

We analyzed the relationship between aortic calcification and two osteoporotic parameters (bone mineral density (BMD) and incident osteoporotic fractures) in 667 ambulatory, elderly women from the Epidemiology of Osteoporosis (EPIDOS) cohort (mean age, 80 years; range, 72–94 years). We did not find any correlation between the aortic calcification score and BMD or osteoporotic fractures.     

Hypocitraturia: a risk factor for reduced bone mineral density in idiopathic hypercalciuria?

The association between idiopathic hypercalciuria (IH) and reduced bone mineral density (BMD) has been described in adults and children. Frequently, hypocitraturia (HC) is an associated condition. To determine the effect that HC may have on bone metabolism of these patients, we studied 88 children with IH at diagnosis, divided into the following groups: group 1 - 44 (50%) patients with associated HC; group 2 - 44 (50%) patients without HC; group 3 (29 subjects), a healthy control group. Urinary and blood electrolytes, as long as urinary N-telopeptide, were measured. Lumbar spine (L2–L4) and femoral neck bone mineral density (BMD) and bone mineral content (BMC) were measured by dual energy X-ray absorptiometry. There was no difference in age between the three groups (P=0.80), but weight, height, body mass index, and bone age were lower (P<0.01) and serum intact parathyroid hormone (iPTH) was higher (P<0.05) in group 1 than in groups 2 and 3. N-telopeptide, measured in urine, did not differ between groups. The following bone densitometry parameters: lumbar spine BMC, BMC adjusted for height (BMCh), BMC adjusted for width of vertebrae (BMCw) and BMD, as well as femoral neck BMD, were significantly lower in group 1 than in groups 2 and 3 (P<0.01). When we corrected densitometry parameters for height, BMC was lower in group 1 and not in group 2 when compared with controls. Conclusions: Children with IH and associated HC may have a higher risk of bone mass loss and consequent osteopenia. Further studies are needed to assess the role that hypocitraturia may have in this form of bone disease.     

Does body size account for gender differences in femur bone density and geometry?

The extent to which greater bone strength in men is caused by proportionately greater bone mass versus bigger bone size is not clear, primarily because the larger overall body size of men has made direct comparisons of skeletal measures difficult. We examined gender differences in femur neck (FN) areal bone mineral density (BMD) values collected from 5,623 non-Hispanic whites aged 20+ years in the third National Health and Nutrition Examination Survey (NHANES III, 1988-1994) before and after correction for measured height and weight. We supplemented the conventional areal BMD data (Hologic QDR 1000) with measurements of areal BMD and geometric properties (subperiosteal width, section modulus, and cortical thickness) made at narrow "cross-sectional" regions traversing the FN and the proximal shaft using a structural analysis program. Before body size adjustment, men had significantly higher values than women for all variables at the three measurement sites (p < 0.0001). Adjustment for body size reduced the differences between the sexes for all variables but had a greater effect on BMD (1-8% higher in men) than on geometry (5-17% higher in men). When examined by age, the sex discrepancy was significantly greater in the older group for all variables except subperiosteal widths. We conclude that although body size difference may account for most of the areal BMD difference between men and women, male bones are still bigger in ways that suggest greater bone strength. These differences may contribute importantly to lower fracture risk in men.     

Pelvic incidence–lumbar lordosis mismatch results in increased segmental joint loads in the unfused and fused lumbar spine

Purpose

Symptomatic adjacent segment disease (ASD) has been reported to occur in up to 27 % of lumbar fusion patients. A previous study identified patients at risk according to the difference of pelvic incidence and lordosis. Patients with a difference between pelvic incidence and lumbar lordosis >15° have been found to have a 20 times higher risk for ASD. Therefore, it was the aim of the present study to investigate forces acting on the adjacent segment in relation to pelvic incidence–lumbar lordosis (PILL) mismatch as a measure of spino-pelvic alignment using rigid body modeling to decipher the underlying forces as potential contributors to degeneration of the adjacent segment.

Methods

Sagittal configurations of 81 subjects were reconstructed in a musculoskeletal simulation environment. Lumbar spine height was normalized, and body and segmental mass properties were kept constant throughout the population to isolate the effect of sagittal alignment. A uniform forward/backward flexion movement (0°–30°–0°) was simulated for all subjects. Intervertebral joint loads at lumbar level L3–L4 and L4–L5 were determined before and after simulated fusion.

Results

In the unfused state, an approximately linear relationship between sagittal alignment and intervertebral loads could be established (shear: 0° flexion r = 0.36, p < 0.001, 30° flexion r = 0.48, p < 0.001; compression: 0° flexion r = 0.29, p < 0.01, 30° flexion r = 0.40, p < 0.001). Additionally, shear changes during the transition from upright to 30° flexed posture were on average 32 % higher at level L3–L4 and 14 % higher at level L4–L5 in alignments that were clinically observed to be prone to ASD. Simulated fusion affected shear forces at the level L3–L4 by 15 % (L4–L5 fusion) and 23 % (L4–S1 fusion) more for alignments at risk for ASD.

Conclusion

Higher adjacent segment shear forces in alignments at risk for ASD already prior to fusion provide a mechanistic explanation for the clinically observed correlation between PILL mismatch and rate of adjacent segment degeneration.     

Evaluation of dual-energy X-ray absorptiometry bone mineral measurement—comparison of a single-beam and fan-beam design: The effect of osteophytic calcification on spine bone mineral density

Dual energy X-ray absorptiometry (DXA) using a single-beam (SB) design is a well-established procedure for measuring bone mineral area density (BMD). Recently, fan beam (FB) techniques have become available to measure BMD. We evaluated the QDR1000 and QDR2000 densitometers with regard to precision and cross-compared values using single beam (SB) and FB techniques. To study the effect of osteoarthritic changes on bone measurement (BMC in g) and bone mineral area density (BMD in g/cm²), both parameters were measured in patients with and without osteophytic calcifications (OC) of the lumbar spine. Precision errors for BMD in vitro over 1 and 6 months using the QDR2000 were 0.4% and 0.6% for SB and 0.5% and 0.7% for the three FB modes. For QDR1000 only SB is available. Using this scan mode, the BMD difference (=0.1%) in vitro between QDR1000 and QDR2000 was not significant. The short-term (same day) reproducibility of BMD in vivo was 0.85% for SB mode and 1.1% for FB scan mode (n=33). The midterm (1 month) precision errors were 0.9% for SB and 1.5% for FB (n=11). The spine BMD of 751 patients from our outpatient clinic and department of rheumatology was 1.7% lower with FB than with SB (0.878±0.137 versus 0.888±0.146 g/cm²). Lower (1.8%) BMD values were also found in the hip with FB compared to SB (0.805±0.111 versus 0.821±0.111 g/cm²). There was a highly significant (P<0.00001) correlation between SB and FB on the spine (r =0.99) and hip (r=0.98) using the QDR2000. Correlations found QDR1000 and QDR2000 were lower on the spine (r=0.97) hip (r=0.93). In contrast to hip BMD, spine BMD was significantly higher in women (n=78) with OC (FB: 0.894±0.134 g/cm², SB: 0.900±0.140 g/cm²) than in normals (n=148) (FB: 0.844±0.130 g/cm², SB: 0.865±0.140 mals (n=148) (FB: 0.844±0.130 g/cm², SB: 0.865±0.140 g/cm²) (P<0.05). The FB mode provides reproducible data in vitro and in vivo, though not as precise as SB. FB results in vivo are 1–2% lower than FB results, even with identical results in vitro. Women with OC present with higher BMD values in spine scans than normals.     

Effects of 1α-hydroxyvitamin D3 on lumbar bone mineral density and vertebral fractures in patients with postmenopausal osteoporosis

The effects of 1-hydroxyvitamin D₃ [1(OH)D₃] on bone mineral density, fracture incidence, and bone metabolism were evaluated by a double-blind, placebo-controlled study. Eighty postmenopausal osteoporotic Japanese women (71.9±7.3 years, mean±SD) were randomly assigned to 1 g of 1(OH)D₃ daily or inactive placebo for 1 year. All patients were given supplemental calcium (300 mg of elemental calcium daily). Lumbar (L2–L4) bone mineral density (BMD) determined by dual energy X-ray absorptiometry increased 0.65% with 1(OH)D₃ treatment and decreased 1.14% with placebo (P=0.037). BMD in both the femoral neck and Ward's triangle did not yield any significant differences between the two groups, whereas trochanter BMD in the 1(OH)D₃-treated group increased 4.20% and decreased 2.37% with placebo (P=0.055). X-ray analysis demonstrated that new vertebral fractures occurred in two patients with 1(OH)D₃ and in seven patients with placebo. The vertebral fracture rate in the treated group was significantly less (75/1000 patient years) than in the control group (277/1000 patient years; P=0.029). Hypercalcemia (12.1 mg/100 ml) occurred in one patient receiving 1(OH)D₃; however, the serum calcium level in this patient promptly decreased to the reference range after cessation of the treatment. There were no significant changes in serum creatinine level in either group. A significant increase in urinary excretion of calcium was found but there was no significant change in urinary excretion of hydroxyproline in the treated group. The serum level of bone-derived alkaline phosphatase activity significantly decreased by–26±26 (mU/ml) after the treatment (P=0.003). These results indicate that 1(OH)D₃ treatment is effective for maintaining trabecular bone mass and prevents further vertebral fractures without any serious adverse effects in postmenopausal osteoporosis.     

Is a change in bone mineral density a sensitive and specific surrogate of anti-fracture efficacy?

Anti-resorptive agents perturb steady state remodeling; they suppress, but do not abolish, the birth rate of new basic multicellular units (BMUs). In doing so, remodeling goes to completion with bone formation in the many BMUs created before treatment but now with fewer resorption cavities appearing concurrently. As a result, cortical porosity and trabecular stress concentrators decrease reducing bone fragility. From this improved bone strength, steady state is re-established at a slower remodeling rate that again produces bone fragility but more slowly as fewer new BMUs, each with a less negative BMU balance, produce cortical thinning and porosity, trabecular thinning and loss of connectivity while bone fragility progresses rapidly in controls. Thus, the fracture risk reduction--the incidence of fractures in patients treated with an anti-resorptive agent relative to the incidence in controls--is the net effect of the slowing or partial reversal of fragility and then reduced progression of structural abnormalities in treated patients and continued structural decay in controls. Although some morphological features in treated patients and controls may be captured in the bone mineral density (BMD) measurement, many are not. The early increase in BMD is largely determined by the pre-treatment remodeling rate whereas the later and more modest BMD increase is a function of the degree of suppression of remodeling and secondary mineralization. When pre-treatment remodeling rate is low, the increase in BMD is small but the fracture risk reduction (relative to controls with comparable baseline characteristics) is no different to that in patients with high baseline remodeling (relative to their controls) and a greater BMD increase. Therefore, a small increase in BMD does not mean treatment has failed and a large increase in BMD is not indicative of a greater fracture risk reduction.