Proceedings of the 2015 Santa Fe Bone Symposium: Clinical Applications of Scientific Advances in Osteoporosis and Metabolic Bone Disease

The 2015 Santa Fe Bone Symposium was a venue for healthcare professionals and clinical researchers to present and discuss the clinical relevance of recent advances in the science of skeletal disorders, with a focus on osteoporosis and metabolic bone disease. Symposium topics included new developments in the translation of basic bone science to improved patient care, osteoporosis treatment duration, pediatric bone disease, update of fracture risk assessment, cancer treatment-related bone loss, fracture liaison services, a review of the most significant studies of the past year, and the use of telementoring with Bone Health Extension for Community Healthcare Outcomes, a force multiplier to improve the care of osteoporosis in underserved communities.

Quantification of skeletal growth, modeling, and remodeling by in vivo micro computed tomography

In this study we established an image analysis scheme for the investigation of cortical and trabecular bone development during skeletal growth and tested this concept on in vivo μCT images of rats. To evaluate its efficacy, we applied the technique to young (1-month-old) and adult (3-month-old) rat tibiae with vehicle (Veh) or intermittent parathyroid hormone (PTH) treatment. By overlaying 2 sequential scans based on their distinct trabecular microarchitecture, we calculated the linear growth rate of young rats to be 0.31 mm/day at the proximal tibia. Due to rapid growth (3.7 mm in 12 days), the scanned bone region at day 12 had no overlap with the bone tissue scanned at day 0. Instead, the imaged bone region at day 12 represented newly generated bone tissue from the growth plate. The new bone of the PTH-treated rats had significantly greater trabecular bone volume fraction, number, and thickness than those of the Veh-treated rats, indicating PTH's anabolic effect on bone modeling. In contrast, the effect of PTH on adult rat trabecular bone was found to be caused by PTH's anabolic effect on bone remodeling. The cortical bone at the proximal tibia of young rats also thickened more in the PTH group (23%) than the Veh group (14%). This was primarily driven by endosteal bone formation and coalescence of trabecular bone into the cortex. This process can be visualized by aligning the local bone structural changes using image registration. As a result, the cortex after PTH treatment was 31% less porous, and had a 22% greater polar moment of inertia compared to the Veh group. Lastly, we monitored the longitudinal bone growth in adult rats by measuring the distance of bone flow away from the proximal tibial growth plate from 3 months to 19 months of age and discovered a total of 3.5mm growth in 16 months. It was demonstrated that this image analysis scheme can efficiently evaluate bone growth, bone modeling, and bone remodeling, and is ready to be translated into a clinical imaging platform.

Increased risk of hip fracture associated with dually treated HIV/hepatitis B virus coinfection

HIV and hepatitis B virus (HBV) infections are each associated with reduced bone mineral density, but it is unclear whether HIV/HBV coinfection is associated with an increased risk of fracture. We determined whether dually treated HIV/HBV patients had a higher incidence of hip fracture compared to treated HBV-monoinfected, antiretroviral therapy (ART)-treated HIV-monoinfected and HIV/HBV-uninfected patients. We conducted a cohort study among 4156 dually treated HIV/HBV-coinfected, 2053 treated HBV-monoinfected, 96,253 ART-treated HIV-monoinfected, and 746,794 randomly sampled uninfected persons within the US Medicaid populations of California, Florida, New York, Ohio and Pennsylvania (1999-2007). Coinfected patients were matched on propensity score to persons in each comparator cohort. Weighted survival models accounting for competing risks were used to estimate cumulative incidences and hazard ratios (HRs) with 95% confidence intervals (CIs) of incident hip fracture for dually treated coinfected patients compared to (i) HBV-monoinfected receiving nucleos(t)ide analogue or interferon alfa therapy, (ii) HIV-monoinfected on ART and (iii) uninfected persons. Dually treated coinfected patients had a higher cumulative incidence of hip fracture compared to ART-treated HIV-monoinfected (at 5 years: 1.70% vs 1.24%; adjusted HR, 1.37 [95% CI, 1.03-1.83]) and uninfected (at 5 years: 1.64% vs 1.22%; adjusted HR, 1.35 [95% CI, 1.03-1.84]) persons. The cumulative incidence of hip fracture was higher among coinfected than treated HBV-monoinfected patients (at 5 years: 0.70% vs 0.27%), but this difference was not statistically significant in competing risk analysis (adjusted HR, 2.62 [95% CI, 0.92-7.51]). Among Medicaid enrollees, the risk of hip fracture was higher among dually treated HIV/HBV-coinfected patients than ART-treated HIV-monoinfected and uninfected persons.

Type 1 diabetes is associated with an increased risk of fracture across the life span: a population-based cohort study using The Health Improvement Network (THIN)

OBJECTIVE

This study was conducted to determine if type 1 diabetes is associated with an increased risk of fracture across the life span.

RESEARCH DESIGN AND METHODS

This population-based cohort study used data from The Health Improvement Network (THIN) in the U.K. (data from 1994 to 2012), in which 30,394 participants aged 0-89 years with type 1 diabetes were compared with 303,872 randomly selected age-, sex-, and practice-matched participants without diabetes. Cox regression analysis was used to determine hazard ratios (HRs) for incident fracture in participants with type 1 diabetes.

RESULTS

A total of 334,266 participants, median age 34 years, were monitored for 1.9 million person-years. HR were lowest in males and females age <20 years, with HR 1.14 (95% CI 1.01-1.29) and 1.35 (95% CI 1.12-1.63), respectively. Risk was highest in men 60-69 years (HR 2.18 [95% CI 1.79-2.65]), and in women 40-49 years (HR 2.03 [95% CI 1.73-2.39]). Lower extremity fractures comprised a higher proportion of incident fractures in participants with versus those without type 1 diabetes (31.1% vs. 25.1% in males, 39.3% vs. 32% in females; P < 0.001). Secondary analyses for incident hip fractures identified the highest HR of 5.64 (95% CI 3.55-8.97) in men 60-69 years and the highest HR of 5.63 (95% CI 2.25-14.11) in women 30-39 years.

CONCLUSIONS

Type 1 diabetes was associated with increased risk of incident fracture that began in childhood and extended across the life span. Participants with type 1 diabetes sustained a disproportionately greater number of lower extremity fractures. These findings have important public health implications, given the increasing prevalence of type 1 diabetes and the morbidity and mortality associated with hip fractures.

Bone Mineral Accrual Is Associated With Parathyroid Hormone and 1,25-Dihydroxyvitamin D Levels in Children and Adolescents

CONTEXT

Rapid bone accrual and calcium demands during puberty may result in compensatory increases in PTH and 1,25-dihydroxyvitamin D [1,25(OH)2D] levels; however, these relations have not been established in longitudinal studies.

OBJECTIVE

To determine whether greater bone accrual velocity is associated with greater PTH and 1,25(OH)2D levels in healthy children and adolescents.

DESIGN

Prospective cohort study with baseline PTH, 25-hydroxyvitamin D [25(OH)D], and 1,25(OH)2D levels and dual-energy x-ray absorptiometry whole-body bone mineral content (BMC) accrual over 12 months. Secondary analyses examined bone biomarkers and tibia quantitative computed tomography midshaft cortical-BMC.

PARTICIPANTS

A total of 594 healthy participants, ages 5-21 years, with longitudinal measures in a subset of 145 participants.

MAIN OUTCOME MEASURES

PTH and 1,25(OH)2D levels.

RESULTS

PTH levels were higher during Tanner stages 3 and 4 compared to Tanner 1 (P < .05) in males and females and were inversely and significantly associated with 25(OH)D levels and dietary calcium intake. In multivariable analyses, greater bone accrual [measured directly as change in dual-energy x-ray absorptiometry-BMC (P < .001) or quantitative computed tomography-BMC (P < .05), or indirectly as growth velocity (P < .05) or greater bone-formation biomarker level (P < .01)] was associated with higher PTH levels, independent of 25(OH)D level and dietary calcium intake. Similar associations were observed between these direct and indirect indices of bone accrual and 1,25(OH)2D levels.

CONCLUSIONS

PTH levels rise in midpuberty, in association with multiple measures of bone accrual. This is consistent with compensatory increases in PTH to drive 1,25(OH)2D production and calcium absorption during periods of increased calcium demands. Additional studies are needed to address PTH effects on bone modeling and remodeling during growth and development.

Use of proton pump inhibitors is associated with fractures in young adults: a population-based study

Proton pump inhibitors (PPIs) are associated with risk for fracture in osteoporotic adults. In this population-based study, we found a significant association between PPIs and fracture in young adults, with evidence of a dose-response effect. Young adults who use PPIs should be cautioned regarding risk for fracture.

INTRODUCTION

Proton pump inhibitors (PPIs) are associated with fracture in adults with osteoporosis. Because PPI therapy may interfere with bone accrual and attainment of peak bone mineral density, we studied the association between use of PPIs and fracture in children and young adults.

METHODS

We conducted a population-based, case-control study nested within records from general medical practices from 1994 to 2013. Participants were 4-29 years old with ≥ 1 year of follow-up who lacked chronic conditions associated with use of long-term acid suppression. Cases of fracture were defined as the first incident fracture at any site. Using incidence density sampling, cases were matched with up to five controls by age, sex, medical practice, and start of follow-up. PPI exposure was defined as 180 or more cumulative doses of PPIs. Conditional logistic regression was used to estimate the odds ratio and confidence interval for use of PPIs and fracture.

RESULTS

We identified 124,799 cases and 605,643 controls. The adjusted odds ratio for the risk of fracture associated with PPI exposure was 1.13 (95% CI 0.92 to 1.39) among children aged < 18 years old and 1.39 (95% CI 1.26 to 1.53) among young adults aged 18-29 years old. In young adults but not children, we observed a dose-response effect with increased total exposure to PPIs (p for trend <0.001).

CONCLUSIONS

PPI use was associated with fracture in young adults, but overall evidence did not support a PPI-fracture relationship in children. Young adults who use PPIs should be cautioned regarding potentially increased risk for fracture, even if they lack traditional fracture risk factors.

Insulin-like Growth Factor 1 and Adiponectin and Associations with Muscle Deficits, Disease Characteristics, and Treatments in Rheumatoid Arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is associated with low muscle mass and density. The objective of our study was to evaluate associations between 2 serum biomarkers [insulin-like growth factor 1 (IGF-1) and adiponectin] and skeletal muscle in RA.

METHODS

Whole-body dual energy X-ray absorptiometry measures of the appendicular lean mass index (ALMI; kg/m(2)) and total fat mass index (kg/m(2)), as well as the peripheral quantitative computed tomography measures of the lower leg muscle and fat cross-sectional area (CSA; cm(2)) and muscle density (an index of fat infiltration) were obtained from 50 participants with RA, ages 18-70 years. Multivariable linear regression analyses evaluated associations between body composition and levels of adiponectin and IGF-1, adjusted for age, sex, and adiposity.

RESULTS

Greater age was associated with higher adiponectin (p = 0.06) and lower IGF-1 (p = 0.004). Eight subjects had IGF-1 levels below the reference range for their age and sex. These subjects had significantly lower ALMI and muscle CSA in multivariable models. Lower IGF-1 levels were associated with greater clinical disease activity and severity, as well as low ALMI, muscle CSA, and muscle density (defined as 1 SD below normative mean). After adjusting for age and sex, greater adiponectin levels were associated with lower BMI (p = 0.02) as well as lower ALMI, and lower muscle CSA, independent of adiposity (p < 0.05). Only greater Health Assessment Questionnaire scores were significantly associated with lower adiponectin levels.

CONCLUSION

Low IGF-1 and greater adiponectin levels are associated with lower muscle mass in RA. Lower IGF-1 levels were seen in subjects with greater disease activity and severity.

Adverse Fat Depots and Marrow Adiposity Are Associated With Skeletal Deficits and Insulin Resistance in Long-Term Survivors of Pediatric Hematopoietic Stem Cell Transplantation

Allogeneic hematopoietic stem-cell transplantation (alloHSCT) survivors treated with total body irradiation (TBI) exhibit bone deficits and excess adiposity, potentially related to altered mesenchymal stem cell differentiation into osteoblasts or adipocytes. We examined associations among fat distribution, bone microarchitecture, and insulin resistance in alloHSCT survivors after TBI. This was a cross-sectional observational study of 25 alloHSCT survivors (aged 12 to 25 years) a median of 9.7 (4.3 to 19.3) years after alloHSCT compared to 25 age-, race-, and sex-matched healthy controls. Vertebral MR spectroscopic imaging and tibia micro-MRI were used to quantify marrow adipose tissue (MAT) and trabecular microarchitecture. Additional measures included DXA whole-body fat mass (WB-FM), leg lean mass (Leg-LM), trunk visceral adipose tissue (VAT), and CT calf muscle density. Insulin resistance in alloHSCT survivors was estimated by HOMA-IR. AlloHSCT survivors had lower Leg-LM (p < 0.001) and greater VAT (p < 0.01), MAT (p < 0.001), and fat infiltration of muscle (p = 0.04) independent of WB-FM, versus matched controls; BMI did not differ. Survivors had lower bone volume fraction and abnormal microarchitecture including greater erosion and more rod-like structure versus controls (all p = 0.04); 14 had vertebral deformities and two had compression fractures. Greater WB-FM, VAT, MAT, and muscle fat infiltration were associated with abnormal trabecular microarchitecture (p < 0.04 for all). AlloHSCT HOMA-IR was elevated, associated with younger age at transplantation (p < 0.01), and positively correlated with WB-FM and VAT (both p < 0.01). In conclusion, the markedly increased marrow adiposity, abnormal bone microarchitecture, and abnormal fat distribution highlight the risks of long-term treatment-related morbidity and mortality in alloHSCT recipients after TBI. Trabecular deterioration was associated with marrow and visceral adiposity. Furthermore, long-term survivors demonstrated sarcopenic obesity, insulin resistance, and vertebral deformities. Future studies are needed to identify strategies to prevent and treat metabolic and skeletal complications in this growing population of childhood alloHSCT survivors.

Deficits in bone density and structure in children and young adults following Fontan palliation

BACKGROUND

Survival of patients with congenital heart disease has improved such that there are now more adults than children living with these conditions. Complex single ventricle congenital heart disease requiring Fontan palliation is associated with multiple risk factors for impaired bone accrual. Bone density and structure have not been characterized in these patients.

METHODS

Tibia peripheral quantitative computed tomography (pQCT) was used to assess trabecular and cortical volumetric bone mineral density (vBMD), cortical dimensions, and calf muscle area in 43 Fontan participants (5-33 years old), a median of 10 years following Fontan palliation. pQCT outcomes were converted to sex- and race-specific Z-scores relative to age based on >700 healthy reference participants. Cortical dimensions and muscle area were further adjusted for tibia length.

RESULTS

Height Z-scores were lower in Fontan compared to reference participants (mean ± SD: -0.29 ± 1.00 vs. 0.25 ± 0.93, p < 0.001); BMI Z-scores were similar (0.16 ± 0.88 vs. 0.35 ± 1.02, p = 0.1). Fontan participants had lower trabecular vBMD Z-scores (-0.85 ± 0.96 vs. 0.01 ± 1.02, p < 0.001); cortical vBMD Z-scores were similar (-0.17 ± 0.98 vs. 0.00 ± 1.00, p = 0.27). Cortical dimensions were reduced with lower cortical area (-0.59 ± 0.84 vs. 0.00 ± 0.88, p<0.001) and periosteal circumference (-0.50 ± 0.82 vs. 0.00 ± 0.84, p < 0.001) Z-scores, compared to reference participants. Calf muscle area Z-scores were lower in the Fontan participants (-0.45 ± 0.98 vs. 0.00 ± 0.96, p = 0.003) and lower calf muscle area Z-scores were associated with smaller periosteal circumference Z-scores (R = 0.62, p < 0.001). Musculoskeletal deficits were not associated with age, Fontan characteristics, parathyroid hormone or vitamin D levels.

CONCLUSIONS

Children and young adults demonstrate low trabecular vBMD, cortical structure and muscle area following Fontan. Muscle deficits were associated with smaller periosteal dimensions. Future studies should determine the fracture implications of these deficits and identify interventions to promote musculoskeletal development.

Fractures on bisphosphonates in osteoporosis pseudoglioma syndrome (OPPG): pQCT shows poor bone density and structure

Osteoporosis pseudoglioma syndrome (OPPG) is a rare autosomal recessive disorder of childhood osteoporosis and blindness due to inactivating mutations in LDL receptor-like protein 5 (LRP5). We and others have reported improvement in areal bone mineral density (aBMD) by DXA in OPPG on short term bisphosphonates. Long-term data on bisphosphonate use in OPPG and measures of volumetric BMD (vBMD) and cortical structure are not available. In addition, no long-term DXA data on untreated OPPG is available. The aims of this study were to: (1) record low trauma fractures and longitudinal aBMD by DXA in 5 OPPG patients on chronic bisphosphonate treatment, and in 4 OPPG patients never treated (2) to perform tibia peripheral quantitative CT (pQCT) to evaluate volumetric bone mineral density (vBMD), cortical structure and calf muscle area in 6 OPPG patients and 14 unaffected first degree family members. pQCT results were converted to sex-specific Z-scores for age and adjusted for tibia length based on data in >700 reference participants. We observed 4 fractures (3 femoral shafts) in 3 OPPG patients while on bisphosphonates, after each achieved significant improvement in aBMD. OPPG participants had significantly lower mean trabecular vBMD (-1.51 vs. 0.17, p = 0.002), cortical area (-2.36 vs. 0.37; p < 0.001) and periosteal circumference (-1.86 vs. -0.31, p = 0.001) Z-scores, compared with unaffected participants and had a trend toward lower muscle area Z-score (-0.69 vs. 0.47, p = 0.12). These data demonstrate substantial bone fragility despite improvements in aBMD. The pQCT data provide insight into the fragility with substantial deficits in trabecular vBMD and cortical dimensions, consistent with OPPG effects of bone formation. Treatment that improves bone quality is needed to reduce fractures in OPPG.

Fracture Burden and Risk Factors in Childhood CKD: Results from the CKiD Cohort Study

Childhood chronic kidney disease (CHD) poses multiple threats to bone accrual; however, the associated fracture risk is not well characterized. This prospective cohort study included 537 CKD in Children (CKiD) participants. Fracture histories were obtained at baseline, at years 1, 3, and 5 through November 1, 2009, and annually thereafter. We used Cox regression analysis of first incident fracture to evaluate potential correlates of fracture risk. At enrollment, median age was 11 years, and 16% of patients reported a prior fracture. Over a median of 3.9 years, 43 males and 24 females sustained incident fractures, corresponding to 395 (95% confidence interval [95% CI], 293-533) and 323 (95% CI, 216-481) fractures per 10,000 person-years, respectively. These rates were 2- to 3-fold higher than published general population rates. The only gender difference in fracture risk was a 2.6-fold higher risk in males aged ≥15 years (570/10,000 person-years, adjusted P=0.04). In multivariable analysis, advanced pubertal stage, greater height Z-score, difficulty walking, and higher average log-transformed parathyroid hormone level were independently associated with greater fracture risk (all P≤0.04). Phosphate binder treatment (predominantly calcium-based) was associated with lower fracture risk (hazard ratio, 0.37; 95% CI, 0.15-0.91; P=0.03). Participation in more than one team sport was associated with higher risk (hazard ratio, 4.87; 95% CI, 2.21-10.75; P<0.001). In conclusion, children with CKD have a high burden of fracture. Regarding modifiable factors, higher average parathyroid hormone level was associated with greater risk of fracture, whereas phosphate binder use was protective in this cohort.

Improvements in Bone Density and Structure during Anti-TNF-α Therapy in Pediatric Crohn's Disease

CONTEXT

Pediatric Crohn's Disease (CD) is associated with deficits in trabecular bone mineral density (BMD) and cortical structure, potentially related to TNF-α effects to decrease bone formation and promote bone resorption.

OBJECTIVE

This study aimed to examine changes in bone density and structure in children and adolescents with CD following initiation of anti-TNF-α therapy.

DESIGN AND PARTICIPANTS

Participants (n = 74; age 5-21 years) with CD completed a 12-month prospective cohort study.

MAIN OUTCOME MEASURES

Tibia peripheral quantitative computed tomography scans were obtained at initiation of anti-TNF-α therapy and 12 months later. Musculoskeletal outcomes were expressed as sex-and race-specific z scores relative to age, based on >650 reference participants.

RESULTS

At baseline, CD participants had lower height, trabecular BMD, cortical area (due to smaller periosteal and larger endocortical circumferences), and muscle area z scores, compared with reference participants (all P < .01). Pediatric CD activity index decreased during the 10-week induction (P < .001), in association with subsequent gains in height, trabecular BMD, cortical area (due to recovery of endocortical bone), and muscle area z scores over 12 months (height P < .05; others P < .001). Bone-specific alkaline phosphatase levels, a biomarker of bone formation, increased a median of 75% (P < .001) during induction with associated 12-month improvements in trabecular BMD and cortical area z scores (both P < .001). Younger age was associated with greater increases in trabecular BMD z scores (P < .001) and greater linear growth with greater recovery of cortical area (P < .001).

CONCLUSIONS

Anti-TNF-α therapy was associated with improvements in trabecular BMD and cortical structure. Improvements were greater in younger and growing participants, suggesting a window of opportunity for treatment of bone deficits.

Are men at greater risk of lean mass deficits in rheumatoid arthritis?

OBJECTIVE

We aimed to determine if there were sex differences in lean body mass (LBM) in patients with rheumatoid arthritis (RA) when compared with sex- and race-specific National Health and Nutrition Examination Survey (NHANES) reference data, and to investigate the impact of sex differences in risk factors for LBM deficits.

METHODS

Dual x-ray absorptiometry measures of whole body LBM and appendicular LBM (arms and legs, appendicular lean mass [ALM]) were obtained on a total of 190 subjects from 2 independent cohorts (141 from San Francisco [SF], 49 from Philadelphia [PA]), expressed as indices adjusted for height (LBM index and ALM index, kg/m(2) ), and converted to sex- and race-specific Z scores relative to age and based on NHANES data. Sarcopenia was defined using 4 different sex-specific definitions. Multivariable linear and logistic regression analyses adjusted for disease activity, disease duration, physical activity, anti-cyclic citrullinated peptide seropositivity, fat mass index, and glucocorticoid use.

RESULTS

While there were significant differences between the 2 cohorts, ALM index Z scores were significantly lower in men compared to women in both (SF: -1.43 versus -0.43, P < 0.0001; PA: -0.83 versus -0.06, P = 0.03). Observed sex differences were significant after adjustment in multivariable analyses within both cohorts. Odds of sarcopenia were 3 to 8 times greater in men in the SF cohort. Men in the PA cohort also had a higher, but nonsignificant, risk of sarcopenia.

CONCLUSION

RA is associated with significant LBM deficits, with greater deficits observed in men. Future study may help elucidate the mechanisms driving greater deficits among men.

Tibia and radius bone geometry and volumetric density in obese compared to non-obese adolescents

Childhood obesity is associated with biologic and behavioral characteristics that may impact bone mineral density (BMD) and structure. The objective was to determine the association between obesity and bone outcomes, independent of sexual and skeletal maturity, muscle area and strength, physical activity, calcium intake, biomarkers of inflammation, and vitamin D status. Tibia and radius peripheral quantitative CT scans were obtained in 91 obese (BMI>97th percentile) and 51 non-obese adolescents (BMI>5th and <85th percentiles). Results were converted to sex- and race-specific Z-scores relative to age. Cortical structure, muscle area and muscle strength (by dynamometry) Z-scores were further adjusted for bone length. Obese participants had greater height Z-scores (p<0.001), and advanced skeletal maturity (p<0.0001), compared with non-obese participants. Tibia cortical section modulus and calf muscle area Z-scores were greater in obese participants (1.07 and 1.63, respectively, both p<0.0001). Tibia and radius trabecular and cortical volumetric BMD did not differ significantly between groups. Calf muscle area and strength Z-scores, advanced skeletal maturity, and physical activity (by accelerometry) were positively associated with tibia cortical section modulus Z-scores (all p<0.01). Adjustment for muscle area Z-score attenuated differences in tibia section modulus Z-scores between obese and non-obese participants from 1.07 to 0.28. After multivariate adjustment for greater calf muscle area and strength Z-scores, advanced maturity, and less moderate to vigorous physical activity, tibia section modulus Z-scores were 0.32 (95% CI -0.18, 0.43, p=0.06) greater in obese, vs. non-obese participants. Radius cortical section modulus Z-scores were 0.45 greater (p=0.08) in obese vs. non-obese participants; this difference was attenuated to 0.14 with adjustment for advanced maturity. These findings suggest that greater tibia cortical section modulus in obese adolescents is attributable to advanced skeletal maturation and greater muscle area and strength, while less moderate to vigorous physical activities offset the positive effects of these covariates. The impact of obesity on cortical structure was greater at weight bearing sites.

Usefulness of insulin like growth factor 1 as a marker of heart failure in children and young adults after the Fontan palliation procedure

Growth hormone and its mediator, insulinlike growth factor 1 (IGF-1), are key determinants of growth in children and young adults. As patients with Fontan physiology often experience diminished longitudinal growth, we sought to describe IGF-1 levels in this population and to identify factors associated with IGF-1 deficiency. Forty-one Fontan subjects ≥5 years were evaluated in this cross-sectional study. Age- and gender-specific height Z scores were generated using national data. Laboratory testing included IGF-1 and brain natriuretic peptide (BNP) levels. IGF-1 levels were converted to age-, gender-, and Tanner stage-specific Z scores. BNP levels were log transformed to achieve a normal distribution (log-BNP). Medical records were reviewed for pertinent clinical variables. Predictors of IGF-1 Z score were assessed through the Student t test and Pearson's correlation. Median age was 11.1 years (range 5.1 to 33.5 years), and time from Fontan was 8.2 years (1.1 to 26.7). Mean height Z score was -0.2 ± 0.9 with a mean IGF-1 Z score of -0.1 ± 1.3. There was no association between IGF-1 Z score and height Z score. Longer interval since Fontan (R = -0.32, p = 0.04), higher log-BNP (R = -0.40; p = 0.01), and lower indexed systemic flow on cardiac magnetic resonance (R = 0.55, p = 0.02) were associated with lower IGF-1 Z scores. In conclusion, in this cohort with Fontan physiology, higher BNP and lower systemic flow were associated with lower IGF-1 Z score. Longitudinal studies are needed to determine if these relations represent a mechanistic explanation for diminished growth in children with this physiology and with other forms of congenital heart disease.

Structural Bone Deficits in HIV/HCV-Coinfected, HCV-Monoinfected, and HIV-Monoinfected Women

BACKGROUND

Coinfection with human immunodeficiency virus (HIV) and hepatitis C virus (HCV) is associated with reduced bone mineral density (BMD) and increased fracture rates, particularly in women. The structural underpinnings for skeletal fragility in coinfected women have not been characterized. We used tibial peripheral quantitative computed tomography to evaluate skeletal parameters in women, by HIV/HCV status.

METHODS

We conducted a cross-sectional study among 50 HIV/HCV-coinfected, 51 HCV-monoinfected, and 50 HIV-monoinfected women. Tibial volumetric BMD and cortical dimensions were determined with peripheral quantitative computed tomography. Race-specific z scores for age were generated using 263 female reference participants without HIV infection or liver disease.

RESULTS

Coinfected participants had lower mean z scores for trabecular volumetric BMD (-0.85), cortical volumetric BMD (-0.67), cortical area (-0.61), and cortical thickness (-0.77) than reference participants (all P < .001). The smaller cortical dimensions were due to greater mean z scores for endosteal circumference (+0.67; P < .001) and comparable z scores for periosteal circumference (+0.04; P = .87). Trabecular volumetric BMD was lower in coinfected than in HCV- or HIV-monoinfected participants. HCV-infected women with stage 3-4 liver fibrosis had lower mean z scores for trabecular volumetric BMD, cortical thickness, and total hip BMD those with stage 0-2 fibrosis.

CONCLUSIONS

Compared with healthy reference patients, HIV/HCV-coinfected women had decreased tibial trabecular volumetric BMD, diminished cortical dimensions, and significant endocortical bone loss.

Muscle torque relative to cross-sectional area and the functional muscle-bone unit in children and adolescents with chronic disease

Measures of muscle mass or size are often used as surrogates of forces acting on bone. However, chronic diseases may be associated with abnormal muscle force relative to muscle size. The muscle-bone unit was examined in 64 children and adolescents with new-onset Crohn's disease (CD), 54 with chronic kidney disease (CKD), 51 treated with glucocorticoids for nephrotic syndrome (NS), and 264 healthy controls. Muscle torque was assessed by isometric ankle dynamometry. Calf muscle cross-sectional area (CSA) and tibia cortical section modulus (Zp) were assessed by quantitative CT. Log-linear regression was used to determine the relations among muscle CSA, muscle torque, and Zp, adjusted for tibia length, age, Tanner stage, sex, and race. Muscle CSA and muscle torque-relative-to-muscle CSA were significantly lower than controls in advanced CKD (CSA -8.7%, p = 0.01; torque -22.9%, p < 0.001) and moderate-to-severe CD (CSA -14.1%, p < 0.001; torque -7.6%, p = 0.05), but not in NS. Zp was 11.5% lower in advanced CKD (p = 0.005) compared to controls, and this deficit was attenuated to 6.7% (p = 0.05) with adjustment for muscle CSA. With additional adjustment for muscle torque and body weight, Zp was 5.9% lower and the difference with controls was no longer significant (p = 0.09). In participants with moderate-to-severe CD, Zp was 6.8% greater than predicted (p = 0.01) given muscle CSA and torque deficits (R(2)  = 0.92), likely due to acute muscle loss in newly-diagnosed patients. Zp did not differ in NS, compared with controls. In conclusion, muscle torque relative to muscle CSA was significantly lower in CKD and CD, compared with controls, and was independently associated with Zp. Future studies are needed to determine if abnormal muscle strength contributes to progressive bone deficits in chronic disease, independent of muscle area. © 2014 American Society for Bone and Mineral Research.

Deficits in muscle mass, muscle density, and modified associations with fat in rheumatoid arthritis

OBJECTIVE

To quantify muscle outcomes, independent of fat mass, in rheumatoid arthritis (RA) patients compared to healthy controls.

METHODS

Quantitative computed tomography scans measured calf muscle and fat cross-sectional area (CSA) and muscle density (an index of intramuscular adipose tissue), and isometric dynamometry was used to measure ankle muscle strength in 50 participants with RA ages 18-70 years and 500 healthy controls. Multivariable linear regression models assessed muscle deficits in RA after adjusting for group differences in adiposity and assessing for an altered muscle-fat association. Associations between RA disease characteristics and fat-adjusted muscle outcomes were also assessed.

RESULTS

Compared to controls, RA subjects had significantly greater body mass index (BMI) and fat area, and lower muscle area, muscle density, and muscle strength (P < 0.001 for all). Strength deficits were eliminated with adjustment for the smaller muscle area. The magnitude of muscle deficits, relative to controls, was significantly greater (P < 0.03 for interaction) in participants with lower fat area and BMI. Among those in the lower tertiles of adiposity, RA subjects demonstrated more significant deficits compared to controls with similar adiposity. In contrast, among those in the highest tertile for adiposity, RA was not associated with muscle deficits. Among RA, greater Sharp/van der Heijde scores were associated with lower muscle CSA and muscle density. Greater disease activity and disability were associated with low muscle density.

CONCLUSION

Deficits in muscle area and muscle density are present in RA patients compared to controls and are most pronounced in subjects with low fat mass. Greater joint destruction is associated with greater muscle deficits.

Urinary creatinine excretion, bioelectrical impedance analysis, and clinical outcomes in patients with CKD: the CRIC study

BACKGROUND AND OBJECTIVES

Previous studies in chronic disease states have demonstrated an association between lower urinary creatinine excretion (UCr) and increased mortality, a finding presumed to reflect the effect of low muscle mass on clinical outcomes. Little is known about the relationship between UCr and other measures of body composition in terms of the ability to predict outcomes of interest.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Using data from the Chronic Renal Insufficiency Cohort (CRIC), the relationship between UCr, fat free mass (FFM) as estimated by bioelectrical impedance analysis, and (in a subpopulation) whole-body dual-energy x-ray absorptiometry assessment of appendicular lean mass were characterized. The associations of UCr and FFM with mortality and ESRD were compared using Cox proportional hazards models.

RESULTS

A total of 3604 CRIC participants (91% of the full CRIC cohort) with both a baseline UCr and FFM measurement were included; of these, 232 had contemporaneous dual-energy x-ray absorptiometry measurements. Participants were recruited between July 2003 and March 2007. UCr and FFM were modestly correlated (rho=0.50; P<0.001), while FFM and appendicular lean mass were highly correlated (rho=0.91; P<0.001). Higher urinary urea nitrogen, black race, younger age, and lower serum cystatin C level were all significantly associated with higher UCr. Over a median (interquartile range) of 4.2 (3.1-5.0) years of follow-up, 336 (9.3%) participants died and 510 (14.2%) reached ESRD. Lower UCr was associated with death and ESRD even after adjustment for FFM (adjusted hazard ratio for death per 1 SD higher level of UCr, 0.63 [95% confidence interval, 0.56 to 0.72]; adjusted hazard ratio for ESRD per 1 SD higher level of UCr, 0.70 [95% confidence interval, 0.63 to 0.75]).

CONCLUSIONS

Among a cohort of individuals with CKD, lower UCr is associated with death and ESRD independent of FFM as assessed by bioelectrical impedance analysis.

Obesity is associated with greater valgus knee alignment in pubertal children, and higher body mass index is associated with greater variability in knee alignment in girls

OBJECTIVE

In adults, osteoarthritis (OA) is associated with obesity and knee alignment. Whether knee alignment differences develop during childhood and are associated with obesity is unknown. We assessed the distribution of knee alignment in children and adolescents, and determined how knee alignment differs between obese and nonobese children.

METHODS

This cross-sectional study examined knee alignment in 155 healthy weight and 165 obese subjects. Knee alignment [metaphyseal-diaphyseal angle (MDA) and anterior tibiofemoral angle (ATFA)] and fat mass were measured using whole body dual-energy X-ray absorptiometry (DEXA). National reference data were used to generate age- and sex-specific body mass index (BMI, kg/m(2)) Z-scores. Multivariable linear regression was used to identify independent factors associated with ATFA and MDA.

RESULTS

The mean MDA and ATFA were similar between obese and nonobese subjects. In stratified analyses, females had greater variability in MDA and ATFA values (p < 0.001 and p = 0.04, respectively) at higher BMI Z-scores. Compared with healthy weight controls, obese subjects had less valgus of the MDA prior to the onset of puberty (+ 2.0°, p = 0.001), but had greater valgus at later pubertal stages (-1.9°, p = 0.01).

CONCLUSION

We found significantly greater variability in knee alignment among females at higher BMI Z-scores, and greater valgus alignment in obese adolescents in late puberty. The major limitation is the use of DEXA for assessment of alignment, which needs validation against longstanding radiographs. Longitudinal studies are needed to determine whether childhood obesity is a risk factor for progressive malalignment that may predispose to pain and risk of early osteoarthritis.

Risk of fracture in urolithiasis: a population-based cohort study using the health improvement network

BACKGROUND AND OBJECTIVES

Studies have shown decreased bone mineral density in individuals with urolithiasis, but their burden of fracture remains unclear. This study sought to determine whether urolithiasis is associated with increased fracture risk across the lifespan and to delineate sex effects.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A population-based retrospective cohort study using The Health Improvement Network was performed. The median calendar year for the start of the observation period was 2004 (1994-2012). This study identified 51,785 participants with ≥1 of 87 diagnostic codes for urolithiasis and 517,267 randomly selected age-, sex-, and practice-matched participants. Cox regression was used to estimate the hazard ratio (HR) for first fracture. Fractures identified using diagnostic codes were classified by anatomic site.

RESULTS

Median age was 53 years, and 67% of participants were men, confirming their greater urolithiasis burden. Median time from urolithiasis diagnosis to fracture was 10 years. The HR for fracture associated with urolithiasis differed by sex and age (P for interactions, P≤0.003). In men, the adjusted HR was greatest in adolescence (1.55; 95% confidence interval [95% CI], 1.07 to 2.25) with an overall HR of 1.10 (95% CI, 1.05 to 1.16). Urolithiasis was associated with higher fracture risk in women aged 30-79 years (HR, 1.17-1.52), and was highest in women aged 30-39 years (HR, 1.52; 95% CI, 1.23 to 1.87). Peak background fracture rates were highest in boys aged 10-19 years and in women aged 70-79 years. The incidence per 10,000 person-years in participants with versus without urolithiasis was 392 versus 258 in male participants aged 10-19 years, and 263 versus 218 in women aged 70-79 years. Distribution of fracture site within sex did not differ between participants with versus without urolithiasis.

CONCLUSIONS

Urolithiasis was associated with higher incident fracture risk. The significantly higher risk at times of peak background fracture incidence in adolescent boys and elderly women has profound public health implications.

Abstract B29: Increased vertebral marrow adiposity in long-term survivors of pediatric allogeneic hematopoietic stem cell transplant is associated with deficits in trabecular microarchitecture

Background: As treatment-related mortality following allogeneic hematopoietic stem-cell transplantation (alloHSCT) declines, a major unmet need is the identification and prevention of late effects. Long-term survivors of hematologic malignancies requiring alloHSCT show impaired bone density and structure with excess whole body adiposity (Mostoufi-Moab, JBMR, 2012). Marrow adipocytes share common mesenchymal stem cells (MSC) with bone-forming osteoblasts, with an inverse relation between MSC differentiation into osteoblasts or adipocytes. The impact of alloHSCT and total body irradiation (TBI) on marrow adipose tissue (MAT) and trabecular bone microarchitecture (TBA) has not been addressed.

Methods: Magnetic resonance spectroscopic imaging (MRSI) and high-resolution structural imaging were used to quantify vertebral MAT and distal tibia TBA on a 1.5 Tesla magnet. Twenty-five alloHSCT recipients with underlying diagnosis of acute leukemia, ages 12-24 years, were enrolled, a median of 11 years (range 5-19) after alloHSCT and TBI, and compared with age-, sex- and race-matched healthy controls.

Results: AlloHSCT survivors had lower height Z-scores (-1.39 ± 0.98 vs. -0.04 ± 0.98; p &lt; 0.001), compared with controls, while BMI Z-scores did not differ. Overall, greater MAT was associated with lower bone volume fraction (BVF), R = -0.57, p &lt; 0.001. AlloHSCT was associated with higher mean (± SD) vertebral fat fraction (59.0 ± 11.3 vs. 29.3 ± 9.9; p &lt; 0.001) and trabecular deficits including lower bone volume fraction (β -0.01; 95% CI -0.12, -0.00; p=0.02) and evidence of abnormal microarchitecture [greater erosion (p=0.01) with a more rod like structure (p=0.02)], vs. controls. TBA deficits were more pronounced in female alloHSCT recipients. Growth hormone deficiency was not associated with MAT or bone deficits.

Conclusion: Survivors of childhood alloHSCT after TBI demonstrate marked increases in vertebral MAT combined with abnormal trabecular bone microarchitecture. Future studies are needed to determine the metabolic effects and fracture implications of excess MAT, and to identify therapies for improved bone accrual following childhood alloHSCT.

Citation Format: Sogol Mostoufi-Moab, Wenli Sun, Jeremy Magland, Elizabeth Isaacoff, Nancy J. Bunin, Jill P. Ginsberg, Felix Wehrli, Justine Shults, Mary B. Leonard. Increased vertebral marrow adiposity in long-term survivors of pediatric allogeneic hematopoietic stem cell transplant is associated with deficits in trabecular microarchitecture. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr B29.