Abnormalities in Cortical Bone, Trabecular Plates, and Stiffness in Postmenopausal Women Treated...

Abnormalities in Cortical Bone, Trabecular Plates, andStiffness in Postmenopausal Women Treated WithGlucocorticoids

Stephanie Sutter, Kyle K. Nishiyama, Anna Kepley, Bin Zhou, Ji Wang,Donald J. McMahon, X. Edward Guo, and Emily M. Stein

Department of Medicine (S.S., K.K.N., A.K., D.J.M., E.M.S.), Columbia University College of Physiciansand Surgeons, New York, New York 10032; and Bone Bioengineering Laboratory (B.Z., J.W., X.E.G.),Department of Biomedical Engineering, Columbia University, New York, New York 10027

Context: The mechanisms by which glucocorticoids (GCs) increase skeletal fragility are not wellunderstood.

Objective: The objective of the study was to evaluate the microarchitecture, trabecular morphol-ogy, and biomechanical properties of bone in postmenopausal women treated with GCs.

Design: This was a case-control study.

Setting: The study was conducted at a university hospital outpatient facility.

Patients: Postmenopausal women treated with oral GCs for longer than 3 months (n � 30) andage/race-matched controls (n � 60) participated in the study.

Main Outcome Measures: Areal bone mineral density aBMD (BMD) by dual-energy x-ray absorpti-ometry (DXA) was measured. Trabecular and cortical volumetric BMD (vBMD) and microarchitecturebyhigh-resolutionperipheral computedtomographyofthedistal radiusandtibiawerealsomeasured.Whole-bone stiffness was estimated by finite element analysis. A novel technique, individual trabeculasegmentation, was used to evaluate trabecular type (as plate or rod), orientation, and connectivity.

Results: DXA T-scores did not differ significantly at any site. GC subjects had significantly lowertotal, cortical, and trabecular vBMD and thinner cortices, fewer, thinner, more widely, and irreg-ularly spaced trabeculae. They had fewer trabecular plates, fewer axially aligned trabeculae, andlower trabecular connectivity. Differences ranged from 4% to 65% for these trabecular measuresand 5% to 17% for the cortical measures. Whole-bone stiffness was significantly lower (11%–16%)in GC subjects. Markers of bone formation (osteocalcin and amino-terminal propeptide of type Iprocollagen) and resorption (C-telopeptide) were lower in the GC subjects.

Conclusions: Despite similar areal BMD by DXA, GC-treated women had abnormal cortical andtrabecular vBMD and microarchitecture at both the radius and tibia, including fewer trabecularplates, a less axially aligned trabecular network, lower trabecular connectivity, thinner cortices,and lower whole-bone stiffness. Further research into these abnormalities as mechanisms forfracture in GC-treated women is warranted. (J Clin Endocrinol Metab 99: 4231–4240, 2014)

Osteoporosis is a major complication of glucocorticoid(GC) therapy (1, 2). The risk of vertebral, hip, and

other nonvertebral fractures increases within 3 months ofdrug exposure (3–5). Bone loss and fracture risk are di-

rectly associated with dose and duration of GCs (4). Pa-tients treated with GCs have a higher risk of fracture thanuntreated patients with similar areal bone mineral densi-ties (aBMD) measured by dual-energy x-ray absorptiom-

ISSN Print 0021-972X ISSN Online 1945-7197Printed in U.S.A.Copyright © 2014 by the Endocrine SocietyReceived April 25, 2014. Accepted August 7, 2014.First Published Online August 15, 2014

Abbreviations: aBMD, areal BMD; BMD, bone mineral density; BMI, body mass index; CTX,C-telopeptide; CV, coefficient of variation; DXA, dual-energy x-ray absorptiometry; FEA, finiteelement analysis; GC, glucocorticoid; HR-pQCT, high-resolution peripheral quantitative com-puted tomography; HRT, hormone replacement therapy; ITS, individual trabecula segmenta-tion; P1NP, amino-terminal propeptide of type I procollagen; vBMD, volumetric BMD.

O R I G I N A L A R T I C L E

E n d o c r i n e R e s e a r c h

doi: 10.1210/jc.2014-2177 J Clin Endocrinol Metab, November 2014, 99(11):4231–4240 jcem.endojournals.org 4231

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etry (DXA) (6), suggesting that factors distinct fromaBMD contribute to the increased fracture risk in thesepatients. Bone microarchitecture is an important determi-nant of bone strength that contributes to fracture suscep-tibility, independent of areal BMD (7). Differences in bonemicroarchitecture might therefore contribute to skeletalfragility in patients using GCs.

Histomorphometry of iliac crest bone biopsies hasdemonstrated lower trabecular bone volume, thinner tra-beculae, a more fragmented trabecular network, lowerbone formation, and higher bone resorption (8, 9) as wellas increased cortical porosity (10) in patients with long-termglucocorticoid use. High-resolution peripheral quantitativecomputed tomography (HR-pQCT) is a noninvasive, three-dimensional imaging technique, which measures volumetricBMD of the distal radius and tibia, can distinguish be-tween cortical and trabecular bone and visualize fine de-tails of trabecular microarchitecture. HR-pQCT scans canbe computationally modeled by microstructural finite el-ement analysis (FEA) to assess bone stiffness, a surrogatemeasure of strength. HR-pQCT has been used to evaluatestructural abnormalities underlying fragility in many dif-ferent populations (11–15).

We have developed a novel technique based upon HR-pQCT data, individual trabecula segmentation (ITS)-based morphological analysis that provides additional in-sight into the microstructural mechanisms of skeletalfragility. This three-dimensional, model-independenttechnique directly measures individual trabeculae, char-acterizing trabecular type (plate vs. rod), orientation, andconnectivity. Trabecular plates and rods of different ori-entations have distinct roles in mechanical properties andfailure mechanisms of trabecular bone (16, 17). We haveshown that disparities in plate and rod structure explaindifferences in bone strength between postmenopausalwomen with and without fractures (18, 19).

We performed this study to determine whether post-menopausal women with a history of GC use have differ-ences in cortical and trabecular microarchitecture and bio-mechanical properties of bone compared with controls.We sought to build upon current knowledge by using ITSto evaluate the plate and rod microstructure of trabecularbone in women using GCs, hypothesizing that these noveltechniques would reveal skeletal abnormalities that weremore pronounced than suggested by DXA. Specifically,based on histomorphometric findings of biopsy studies,we hypothesized that women treated with GCs wouldhave worse microarchitecture, lower volumetric BMD,and lower stiffness compared with controls, althoughDXA might not differ in the 2 groups. Furthermore,women using GCs would have fewer, thinner trabecular

plates and less connectivity between plates and rods byITS.

Materials and Methods

PatientsPostmenopausal women, over the age of 55 years or more

than 5 years after menopause, were recruited at Columbia Uni-versity Medical Center (New York, New York) by advertisementor self- or physician referral. Cases were women who had at least3 months of oral glucocorticoid use with a minimum daily doseof 5 mg of prednisone (or the equivalent). Control subjects hadno history of glucocorticoid use. Due to standard practice pat-terns, it was not possible to find controls with the same medicalproblems as cases who were not being treated with glucocorti-coids. Therefore, patients in our clinic population with variouschronic diseases were used as controls. Potential cases and con-trols were excluded if they had endocrinopathies (eg, untreatedhyperthyroidism, Cushing’s syndrome, prolactinoma), celiac orother gastrointestinal diseases, abnormal mineral metabolism(eg, osteomalacia, primary hyperparathyroidism), or malig-nancy (except for skin cancer). Hormone replacement therapyand raloxifene were permitted in both groups. Subjects and con-trols with current or past teriparatide use were excluded. Casesubjects with current or prior history of bisphosphonates wereincluded, given the prevalence of bisphosphonate use in this pop-ulation, and ethical concerns about not treating postmenopausalwomen using chronic steroids. Control subjects were recruited aspart of an ongoing cohort study in which cumulative bisphos-phonate use was limited to less than 1 year. At the study visit,medical history, reproductive history, and medication use wereassessed. A physical examination was performed includingheight by Harpenden stadiometer and weight, and body massindex (BMI) was calculated. Physical activity was assessed usingthe Physical Activity Scale for the Elderly questionnaire, a vali-dated tool for older populations (20). All subjects provided writ-ten informed consent, and the Institutional Review Board ofColumbia University Medical Center approved this study.

BiochemistriesSerum calcium, albumin, and creatinine were measured using

automated techniques. Serum 25-hydroxyvitamin D2 and D3

were measured by ultraperformance liquid chromatographycombined with tandem mass spectrometry using a 1290 ultrap-erformance liquid chromatography and a 6410 tandem massspectrometer (Agilent). The interassay coefficient of variation(CV) is 2.9% for 25-hydroxyvitamin D2 and 5.4% for 25-hy-droxyvitamin D3. Intact PTH was measured by an immunora-diometric assay (Scantibodies Laboratories; CV 6.8%). SerumC-telopeptide (CTX) was measured by an ELISA (Immunodiag-nostics Systems; CV � 10%). Osteocalcin was measured by anELISA (Immunodiagnostic Systems; CV 2.7%). Amino-terminalpropeptide of type I procollagen (P1NP) was measured by a RIA(Orion Diagnostica; CV 7.0%). Sclerostin was measured by anELISA (TECO Medical Group; CV 9.4%). Serum was archivedat �80°C and analyzed in one batch after all visits werecompleted.

4232 Sutter et al Glucocorticoids and Microarchitecture J Clin Endocrinol Metab, November 2014, 99(11):4231–4240


Areal bone mineral densityAreal BMD was measured by DXA (QDR-4500; Hologic Inc)

at the lumbar spine (L1–4), total hip, femoral neck, one thirdradius, and ultradistal radius. Lumbar vertebrae with significantdeformity, osteosclerosis, osteophytes, or degenerative diseasewere excluded from the analysis. T-scores compared subjects andcontrols with young-normal populations of the same race andsex, as provided by the manufacturer.

HR-pQCT and image-based microstructural FEA ofthe distal radius and tibia

HR-pQCT (XtremeCT; Scanco Medical AG) was performedby immobilizing the nondominant forearm and ipsilateral tibiain a carbon fiber shell and scanning as we have described in priorpublications (11, 21–23). The European Forearm Phantom wasscanned daily for quality control. All scans were acquired by thesame highly experienced technician. The standard patientthresholding procedure was used to segment the mineralizedphase. In addition to standard cortical and trabecular measure-ments of volumetric BMD, cortical thickness and trabecular mi-croarchitecture, HR-pQCT data were used to calculate whole-bone stiffness, a measure of bone’s resistance to force.

Cortical porosityTo evaluate the cortical bone structure, a validated autoseg-

mentation method (24) was applied to separate the cortical andtrabecular compartments and to measure cortical porosity (per-centage). This method has been validated for accuracy (25) andreproducibility (26), and it is distributed by the manufacturer(Scanco Medical).

ITS-based morphological analyses of HR-pQCTimages

The trabecular bone compartment of each HR-pQCT imagewas extracted from cortex using the autosegmentation methodthat could accurately separate trabecular bone from corticalbone (24, 25). Trabecular bone images were then subjected toITS-based morphological analyses. A complete volumetric de-composition technique was applied to segment the trabecularnetwork into individual plates and rods. Detailed methods de-scribing this technique and ITS-based measurements can befound in our prior publications (16, 17, 27). Based on the three-dimensional evaluations of each individual trabecular plate androd, bone volume, and plate and rod number were evaluated byplate and rod bone volume fraction as well as plate and rodnumber densities (1 per millimeter). Intactness of trabecular net-work was characterized by plate-plate, plate-rod, and rod-rodjunction density (1 per cubic millimeter), calculated as the totalnumber of junctions between trabecular plates and rods normal-ized by the bulk volume. Orientation of trabecular bone networkwas characterized by axial bone volume fraction, defined as ax-ially aligned bone volume divided by the bulk volume.

Statistical methodsAnalyses were conducted with STATA version 11.0 (Stata

Corp) and SAS version 9.1 (SAS Institute Inc). Normality testing(Shapiro Wilk) was performed and variables that were not nor-mally distributed were logarithmically transformed prior togroup comparisons. Satterthwaite adjustment was performed inthe case of unequal variance between the groups. Two-sided

values of P � .05 were considered to indicate statistical signifi-cance. Descriptive data are presented as mean � SD and groupcomparisons as mean � SEM. The differences between GC andcontrol subjects were assessed by a Student’s t test or �2. Rela-tionships between dose and duration of GC use with microarchi-tecture were assessed using Pearson correlations.

Results

Thirty postmenopausal women with a history of 3 or moremonths of oral GC use were enrolled and matched one totwo by age (�3 y) and race/ethnicity to a control groupwith no GC exposure. The mean age of enrolled subjectswas 68 � 8 years. The majority (67%) was Caucasian andthe rest were Latina. The mean daily GC dose was 8.4 �

7.2 mg (median dose 5 mg). The mean duration of use was2.9 � 3.4 years, with a mean cumulative dose of 49 � 12 g(median 9 g). Most patients were using glucocorticoids forrheumatological conditions. These included polymyalgiarheumatica/giant cell arteritis (n � 6), polymyositis (n �

2), lupus (n � 5), rheumatoid arthritis (n � 4), and otherinflammatory arthritis (n � 3). Other indications weregastrointestinal [Crohn’s disease (n � 2) and ulcerativecolitis (n � 1)]; pulmonary, [asthma (n � 4) and interstitiallung disease (n � 1)]; and renal, [minimal change disease(n � 1), focal segmental glomerulosclerosis (n � 1), andglomerulomephritis (n � 1)].

GC subjects and controls did not differ on the basis ofheight, weight, or time since menopause (Table 1). Con-trol subjects reported greater alcohol use (P � .03), al-though only three subjects had more than 2 U/d. Tobaccouse and a family history of osteoporosis did not differ. GCsubjects were more likely to be using bisphosphonates(P � .01) and tended to use more hormone replacementtherapy (HRT) (P � .10). Calcium intake from supple-ments was greater among GC subjects (895 vs 525 mgdaily; P � .01). Mean vitamin D intake was similar be-tween groups and above the recommended daily allow-ance, although there was a wide range of intakes amongthe subjects. The prevalence of chronic medical problemsin both groups is detailed in Table 1. Fewer GC-treatedpatients had diabetes (P � .03), but more had hyperlip-idemia (P � .01). Sixteen of the GC-treated women hadprevalent fractures, and the most common sites were ver-tebral (44%), ankle (19%), and forearm (13%). As perprotocol specifications, there were no fractures among thecontrol group. Physical activity, assessed by the PhysicalActivity Scale for the Elderly questionnaire, was variableamong the subjects on average and not significantly dif-ferent between groups (105 � 78 in controls and 96 � 65in GC subjects; P � .56). Values in both groups were

doi: 10.1210/jc.2014-2177 jcem.endojournals.org 4233


similar to the mean (and median) values from the generalpopulation [103 (90)].

Bone turnover markers were significantly lower in GCpatients than in controls (Table 2). Bone formation mark-ers, osteocalcin and P1NP, were 33% lower (P � .05) and28% lower (P � .051), respectively, in GC patients, andthe bone resorption maker CTX was 39% lower (P � .01).Sclerostin was also 29% lower in GC subjects than con-trols (P � .01). PTH was within the normal range. Themean serum 25-hydroxyvitamin D concentrations were inthe sufficient range (�30 ng/mL) and did not significantlydiffer between groups.

The prevalence of osteoporosis (47% in GC subjectsand 37% in controls) and osteopenia (43% in GC subjectsand 50% in controls) did not differ significantly betweengroups. Mean DXA T-scores were similar between groupsat all sites, except at the total hip, in which they tended tobe lower in women using GCs (P � .08; Figure 1).

Volumetric BMD, cortical and trabecular microarchi-tecture by HR-pQCT, and whole-bone stiffness by FEAdiffered markedly between GC and control subjects (Fig-ure 2). At the radius, bone size, measured as total cross-sectional area, did not differ. GC subjects had significantlysmaller cortical area (�15.8%; P � .002) and tended tohave a larger trabecular area (10%; P � .07). Total densitywas lower (�17.6%; P � .001). Cortical density (�4.7%;P � .02) and cortical thickness (�16.6%; P � .002) weresignificantly lower in the GC subjects. Trabecular densitywas significantly lower (�20.4%; P � .005) and trabec-ular microarchitecture was worse, with lower trabecularnumber (�27.5%; P � .04) and thickness (�9.3%; P �

.03) and greater separation (30.7%; P � .03) in the GCsubjects. Network heterogeneity, a measure of how irreg-ularly spaced the trabeculae are, was greater (64.8%; P �

.04). Whole-bone stiffness was significantly lower among

Table 1. Characteristics of the Study Population (Mean � SD)

GC(n � 30)

Control(n � 60) P Value

Age, y 68 � 9 67 � 7 .58Race, % Caucasian 67 67 1.00Height, cm 159 � 8 160 � 7 .63Weight, kg 71 � 19 71 � 16 .82BMI, kg/m2 28 � 8 28 � 6 .65Years since menopause 21 � 10 19 � 10 .47Family history of osteoporosis by BMD, % 40 46 .58Family history of fracture, % 37 33 .77Tobacco use

Never, % 43 50 .14Former, % 50 50Current, % 7 0

Alcohol use, beverages per day 0.2 � 0.3 0.7 � 1.1 .03Calcium supplements, total daily dose, mg 895 � 569 524 � 461 .01Vitamin D supplements, total daily dose, IU 1374 � 1552 1129 � 1768 .54Bisphosphonates, current use, % 30 7 .01HRT, % 13 4 .10Raloxifene, % 3 2 .65T4, % 13 25 .21Thiazide diuretics, % 14 17 .78GC use

Duration, y 2.9 � 3.4 n/aCurrent dose, mg/d 8.4 � 7.2 n/aCumulative dose, g 49 � 12 n/a

Abbreviation: n/a, not available. Bold values indicate significance.

Table 2. Biochemistries in GC and Control Subjects (Mean � SD)

GC Control P Value

Osteocalcin, 8.4–33.9 ng/mL 14.6 � 10.8 21.9 � 15.0 �.02P1NP, 16–96 �g/L 41.3 � 34.4 57.7 � 33.6 �.05CTX, 0.11–0.74 ng/mL 0.31 � 0.20 0.50 � 0.26 �.001Sclerostin, mean 0.69 � 0.26 ng/mL 0.63 � 0.23 0.88 � 0.37 �.00125-Hydroxyvitamin D, 30–80 ng/mL 39.3 � 12.5 34.6 � 11.3 .13PTH, 14–66 pg/mL 46.7 � 30.0 51.1 � 39.7 .57



the GC subjects (�15.7%; P � .005), as was failure load(�14.6%; P � .007).

At the tibia, the total cross-sectional area did not differ.However, GC subjects tended to have a smaller corticalarea (�11.4%; P � .08) and a greater trabecular area(9.3%; P � .07). The total density (�17.0%; P � .0001),trabecular density (�18.4; P � .002), and cortical density(�5.5%; P � .02) were lower among the GC subjects andof the same magnitude as the radial differences. Corticalthickness tended to be lower (�12.8%; P � .056). Thetrabecular thickness was lower (�13.4; P � .002). Thetrabecular number did not differ. The trabecular separa-

tion tended to be greater among theGC subjects (11.2%; P � .09), andnetwork heterogeneity was signifi-cantly greater (33.3%; P � .02).Whole-bone stiffness was loweramong the GC subjects (�10.5%;P � .02). Failure load tended to belower (�9%; P � .59). Cortical po-rosity did not differ at either site (ra-dius: GC 2.8% � 0.2% vs control2.6% � 0.1%, P � .58; tibia: GC,7.4 � 0.3, vs control, 7.3 � 0.2, P �.80).

Current GC dose tended to be as-sociated with more heterogeneity ofthe trabecular network at the tibia

(0.33; P � .07) but was not associated with other micro-architectural parameters. We did not find an associationbetween cumulative GC dose, or treatment duration, andmicroarchitecture or stiffness.

Using ITS at the radius, GC subjects had significantlylower, directly measured bone volume fraction (�12.6;P � .03) and fewer trabecular plates (�6.9%; P � .03) andtended to have fewer trabecular rods (�3.7%; P � .08).They had significantly fewer axially aligned trabeculae(�16.0%; P � .03). They had lower connectivity betweenplates (�18.9%; P � .02) and between plates and rods(�17.4%; P � .02). There was no difference in connec-

tivity between rods. At the tibia,women using GCs tended to havelower bone volume fraction (�8.0%;P � .052), had significantly fewertrabecular plates (�5.7%; P � .02),had fewer axially aligned trabeculae(�14; P � .01), and had less connec-tivity between plates (�14%; P �

.02). They tended to have less con-nectivity between plates and rods(�10.3%; P � .06). There was nodifference in rod number or connec-tivity between the rods (Figure 3).Representative HR-pQCT and ITSimages are shown in Figure 4.

Analyses were repeated, exclud-ing women receiving bisphospho-nates (21 GC treated women and 54controls remained). Results weresimilar to those in the entire cohort.Bone resorption remained lower inGC-treated subjects. At the radius,differences in total density, trabecu-lar density, trabecular number sepa-

Figure 1. Comparison of T-scores (mean � SEM) by DXA in postmenopausal women using GCs(striped bars) and controls (white bars) at the lumbar spine (LS), total hip (TH), femoral neck (FN),one third radius (1/3R), and ultradistal radius (UDR). No significant difference was found at anysite, although GC subjects tended to have lower T-scores at the total hip (TH) (P � .08).

Figure 2. Comparison of the percent difference � SEM in vBMD and microarchitecture by HR-pQCT and whole-bone stiffness by FEA in GC-treated and control subjects at the radius (blackbars) and tibia (gray bars). *, P � .05; **, P � .01. Ct.Th, cortical thickness; Ct.vBMD, corticaldensity; Tb.Number, trabecular number; Tb.Separation, trabecular separation; Tb.Thickness,trabecular thickness; Tb.vBMD, trabecular density; Total vBMD, total density.



ration and heterogeneity, cortical thickness, and whole-bone stiffness remained significant. The differences incortical density (P � .10) and trabecular thickness (P �.07) were no longer significant. At the tibia, the differencein total density, cortical density, trabecular density, andtrabecular thickness and network heterogeneity remained

significant. The difference in whole-bone stiffness became a trend (P �.055). As in the entire cohort, therewas no significant difference in cor-tical thickness (P � .23) or trabecu-lar separation (P � .12). All differ-ences in the ITS measures remainedsignificant. In this subgroup, therewas no difference in cortical porosityat either site according to GCtreatment.

Discussion

In this study, we found that post-menopausal women using GCs hadcortical and trabecular abnormali-ties and lower stiffness comparedwith age- and ethnicity-matchedcontrols and extend previous reports

by describing pronounced abnormalities at both the ra-dius and tibia as well as new abnormalities in trabecularmicrostructure. In contrast to the differences in volumetricBMD (vBMD) and microarchitecture, we did not detectany significant differences in aBMD by DXA between the2 groups. Although it is possible that our sample size pre-cluded our detection of significant differences in aBMD,this finding is consistent with studies demonstrating anincreased fracture risk in GC-treated subjects despite sim-ilar aBMD to controls (6) as well as reports of microarchi-tectural abnormalities in women with fragility fracturescompared with controls despite the similar areal bone den-sity results (11, 21, 22, 28, 29).

To date, only one study has used HR-pQCT to compareGC-treated patients and controls. Tang et al (15) foundthat a group of pre- and postmenopausal Chinese womenusing GCs had lower total and cortical vBMD, lower cor-tical thickness, higher cortical porosity, and lower stiffnessat the radius compared with a group of healthy controls.They found no significant differences in the trabecularvariables. Measurements at the tibia were not obtained.More GC-treated patients were postmenopausal and hadlower BMI than the controls, which may have influencedtheir results. Racial differences in study populations mayalso have contributed to the disparate findings betweentheir study and ours because significant microarchitec-tural and strength differences exist between Chinese andCaucasian women (30). Because we included only post-menopausal women and our controls had other chronicdiseases common in this age group, we may have been able

Figure 3. Comparison of plate and rod structure and connectivity by ITS-based morphologicalanalysis between GC-treated and control subjects. A, Percentage differences � SEM shown.*, P � .05; **, P � .01. aBV/TV, axial bone volume fraction; BV/TV, total bone volume fraction;PP Junc.D, plate-plate junction density; P-R Junc.D, plate-rod junction pTb.N, plate trabecularnumber; rTb.N, rod trabecular number; density.

Figure 4. A, HR-pQCT scans of the distal radius (above) and tibia(below) from a GC-treated subject and control matched for age andrace/ethnicity demonstrate the lower trabecular number, increasedtrabecular separation, and heterogeneity found in the GC subjects. B,ITS images (plates in green, rods in red) at the radius illustrating fewertrabecular plates in the GC-treated subject.



to discern more specific effects of GC treatment at both theradius and tibia.

Our findings of lower trabecular number, thickness,greater separation, and network heterogeneity in GC-treated women are consistent with prior histomorphomet-ric studies showing that patients using GCs have decreasedtrabecular bone volume, thinner trabeculae, a more frag-mented trabecular network, lower bone formation, andhigher bone resorption (8, 9, 31). This is the first study touse ITS to evaluate trabecular characteristics and connec-tivity in woman treated with GCs. With this higher-orderimaging, we found that women using GCs had fewer tra-becular plates, fewer axially aligned trabeculae, and lessconnectivity between trabeculae, all features that havebeen associated with decreased strength (16, 17). Trabec-ular differences were somewhat less pronounced at thetibia than the radius, suggestive of a protective effect ofweight bearing on trabecular bone at that site. We havereported similar discrepancies between the radius andtibia in osteopenic women with fractures (19) and womenwith hyperparathyroidism (23) compared with controls.

Although bone biopsy studies have predominantly re-ported abnormalities in the trabecular bone (8, 31), ouruse of HR-pQCT enabled us to discern abnormalities incortical density and thickness as well. We did not detect anincrease in cortical porosity, which has been previouslyreported (10, 15). This difference may be related to meth-odology because one of these studies was based on tran-siliac crest bone biopsies. GC-treated women in our studymay have had differences in fine porosity or primarilyendocortical porosity, as opposed to coalesced osteons, ormacropores, that were not detectable by the resolution ofour technique. This idea is supported by the fact that wedid detect differences in cortical density. Our analyseswere based on images thresholded by the global thresholdtechnique provided by the HR-pQCT manufacturer,which may overestimate trabecular bone parameters, par-ticularly in patients who have cortical thinning and in-creased endosteal porosity (32). The study by Tang et al(15) using HR-pQCT, did not report PTH levels, but it isconceivable that higher levels of PTH among those sub-jects may have contributed to increased cortical porosityin that cohort. The magnitude of trabecular differenceswas greater than seen in cortical bone, consistent withstudies from our group and others of both women withosteoporotic fractures and hyperparathyroidism (11, 12,14, 23) and likely related to the higher rate of turnover ofthis skeletal compartment. The largest difference was inthe measure of network heterogeneity. This may be animportant feature of skeletal deterioration in GC-treatedpatients and may reflect uncoupling due to profound sup-

pression bone formation by osteoblasts, ultimately result-ing in trabecular dropout.

Whole-bone stiffness was markedly lower at both theradius and tibia in women treated with GCs, which may beassociated with the increased fracture risk reported in GC-treated subjects (33). Other authors have reported lowerstiffness with central and peripheral FEA (13, 34, 35). Weare the first to report equivalently lower stiffness at boththe radius and tibia. Although vertebrae are the most com-mon site of GC-related fractures (36, 37), as opposed toperipheral locations, we have previously reported that tib-ial microstructure and strength is closely associated withthe presence of vertebral fractures (21). Studies using cen-tral quantitative computed tomography have reportedlower cortical and trabecular vBMD of the spine and hip(38) and lower stiffness by FEA at the hip in patients usingoral GCs than controls (39).

In our study, the GC and control groups were wellmatched on age, race, BMI, years since menopause, andchronic diseases. The significantly higher use of bisphos-phonates in GC subjects compared with controls may havebiased the results toward the null and masked an evengreater effect of GCs on bone quality. Our results do notsuggest that a difference in physical activity played a sub-stantial role in the difference in skeletal structure andstrength that we found between GC-treated women andcontrols. This may be because the activity levels in bothgroups were fairly robust. In an older population, we mayhave detected more of an effect of GCs on muscle weak-ness and, subsequently, activity. It is also important tonote that scores were higher in controls and therefore con-ceivable that with a larger sample, we might have observedsignificant differences.

Although we found a small association between currentGC dose and trabecular heterogeneity, we did not observea relationship between the current dose and other micro-architectural parameters, nor did we find an associationbetween the cumulative GC dose or treatment durationand microarchitecture or stiffness. This may have been dueto several factors. The structural differences we observedmay have occurred shortly after the initiation of GC treat-ment and be less related to effects of long-term treatment.Some women, because of the influence of genetics andlifestyle on bone, may have had a greater detrimental re-sponse to the initiation of treatment, something we couldnot detect with our study design. Our small sample sizemay have also precluded detecting an effect.

The structural abnormalities we observed in the GC-treated patients may reflect the cellular effects of thesemedications. GCs decrease osteoblast number and func-tion by inhibiting replication of osteoblastic lineage cells,thus reducing the pool of mature osteoblasts (40). GCs



also inhibit osteoblast differentiation by interfering withsignaling between wnt and �-catenin (41). An antiapop-totic effect on osteoclasts may also result in an early tran-sient increase in bone resorption (42). This uncoupling ofbone turnover may result decreased ability to repair on-going age-related losses and subsequently the markedstructural abnormalities that we observed. GCs also re-duce osteocyte viability (41) and may adversely affect theirfunction by increasing the size of osteocyte lacunae anddecreasing mineralization and strength of the surroundingbone (43). We observed that both formation and resorp-tion markers were lower in GC subjects. This may havereflected the suppressive effects of long-term glucocorti-coids on bone turnover (2); the initial, transient increase inbone resorption was not seen because most patients hadbeen on treatment for extended periods.

Our finding could also be due to greater bisphospho-nate and HRT use among GC-treated women. It is notablethat after restricting our analysis to women not on anti-resorptive treatment, the results did not significantlychange. Variability in the levels of bone turnover markersmay have accounted for the lack of an association withturnover markers and microarchitecture. Another poten-tial explanation is that perturbations in turnover were as-sociated with early microarchitectural changes and thatthe microstructural abnormalities we observed reflectedlong-term GC use. Lower levels of sclerostin in the GCgroup likely reflect the destructive effects of GCs on os-teocytes. Although the inhibition of the wnt pathway isconsidered to play an important role in GC suppression ofbone formation, studies measuring sclerostin in GC-treated patients have found conflicting results (28, 44).Differences may relate to dose, duration, and indicationfor treatment.

Our findings have several significant implications.They demonstrate a structural basis, distinct from aBMD,which may account for skeletal fragility among postmeno-pausal women on glucocorticoids. They highlight thatboth cortical and trabecular bone abnormalities are foundin women using GCs and that there are substantial ab-normalities in trabecular plate structure, alignment, con-nectivity, and whole-bone stiffness.

This study has both unique strengths and importantlimitations. This is the first study to use FEA and ITS toevaluate trabecular bone in patients using GCs and tocompare postmenopausal women treated with GCs andcontrols with chronic illnesses. By assessing both the ra-dius and tibia, we were able to evaluate the effects of thesemedications at multiple skeletal sites and determine themodifying effectsofweightbearing.Althoughwe includeda control population with similar rates of chronic diseases,we were not able to compare subjects with a control group

with the same diseases for which they were receiving GCsbecause GC treatment of these patients is part of routineclinical care. Important limitations are our sample size andthe cross-sectional study design, which prevented us fromdetermining whether microarchitectural abnormalities re-flect ongoing losses or effects that occurred early after theinitiation of GC treatment. This study was not designed toevaluate fracture as an outcome. We did not measurevBMD at the spine, the site most commonly affected byGC associated fractures. Bisphosphonate use by many ofthe women in the GC group, appropriate clinically giventheir fracture risk, may have contributed to the suppres-sion of their bone turnover markers. There are also severalpotential measurement limitations, which may have pre-cluded our ability to detect differences in porosity, as sum-marized earlier in the Discussion. Studies in men and pre-menopausal women would be helpful in determiningwhether these findings are specific to postmenopausalwomen. Longitudinal studies will be critical to better de-lineate a mechanism for the structural deficits that we ob-served and to better investigate the relationship betweenthe duration of therapy and structural abnormalities.

In conclusion, this study demonstrated several novelstructural abnormalities in postmenopausal women usingglucocorticoids. With ITS, we found that women usingGCs have fewer trabecular plates, a less axially alignedtrabecular network, and less trabecular connectivity.Women treated with GCs had marked trabecular and cor-tical abnormalities and lower stiffness at both the radiusand tibia. Our work suggests new mechanisms for biome-chanical compromise in women treated with chronic GCsand provides the basis for future studies of fracture in thispopulation.

Acknowledgments

WethankElizabethShane forherguidancewith studydesignandmanuscript preparation.

Address all correspondence and requests for reprints to:Emily M. Stein, MD, MS, Assistant Professor of Medicine, Colum-bia University College of Physicians and Surgeons, 630 West168th Street, PH8 West 864, New York, NY 10032. E-mail:[email protected].

This work was supported by the Junior Faculty OsteoporosisResearch Award from the American Society for Bone and Min-eral Research (to E.M.S.), National Institutes of Health GrantNIHK23 DK084337 (to E.M.S.), National Institutes of HealthGrant R01 AR051376 (to X.E.G.), National Institutes of HealthGrant R01 AR058004 (to X.E.G. and Elizabeth Shane), and theThomas L. Kempner and Katheryn C. Patterson Foundation.

Disclosure Summary: The authors have no conflicts ofinterest.



mailto:[email protected]

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