Iliac crest biopsy: Representativity for the amount of mineralized bone

Bone, 7, 427-430 (1986) Printed in the USA. All rights reserved.

8756-3282186 $3.00 + .OO 0 1986 Pergamon Journals Ltd.

Copyright

Iliac Crest Biopsy: Representativity for the Amount of Mineralized Bone J. P0DENPHANT, Departments Address

A. GOTFREDSEN,

of Clirucal Chemistry

for correspondence

L. NILAS,

and Pathology,

H. N0RGAARD,

Glostrup Hospital,

and 0. BRIENDSTRUP

Unwers/ty of Copenhagen,

and reprints:: Jan Pmdenphant, Department of Clinical Chemistry,

Denmark. Glostrup Hospital,

University

of

Copenhagen, DK-2600 Glostrup, Denmark.

Abstract

crest biopsies with densities in the lumbar spine and distal forearm, two sites frequently used to measure bone mineral content (BMC) and predilection locations for osteoporotic fractures.

The aim of the study was to evaluate the representativity of iliac crest biopsy for the amount of mineralized trabecular and cortical bone in the skeleton. The following data were obtained on bone from 14 necropsies: right sided iliac crest biopsy, lumbar spine biopsy, dry fat free weight of lumbar spine, bone mineral density @MD) in the lumbar spine and dry fat free weight of cortical and trabecular bone from the left distal forearm. The amount of mineralized cortical and trabecular bone from various sites was compared by linear regression analysis. The results confirm iliac crest biopsy as a good predictor of the amount of trabecular bone, but not of cortical bone. Furthermore, iliac crest biopsy is a better estimate of the amount of trabecular bone in the lumbar spine than spinal BMD.

Materials and Methods Bone tissue was obtained at 14 necropsies, 12 routine and 2 medicolegal, comprising 5 men and 9 women (age range 25-90, X = 68.3, SD = 18.9). Necropsies with malignant bone disease or bone metastases were excluded from the investigation. Bone was removed from the following sites: iliac crest, lumbar spine, and left distal forearm (Fig. 1). Forearm bone was obtained from 13 of the necropsies. Iliac crest

specimens

Iliac crest specimens were taken on the right side with a Bordler trephine 8 mm internal diameter, 2 cm behind the antenor superior iliac spine and 2 cm below the summit of the iliac crest. The specimens were fixed in 70% ethanol The undecalcified specimens were prestained by the Villanueva method before plastic embedding (Villanueva, 1974) The sections were cut by a Jung Universal microtome 1150iautocut Histomorphometric analysis was done on all trabecular and cortical bone in one section, using a Morphomat 30 (Zeiss, West Germany) digitizing analyzer The cortical-trabecular junction was arbitrarily fixed as the distance of one trabecular width from the endosteal cortex The total trabecular area averaged 42.2 mm2 and the total cortical area averaged 5 6 mm*. The following variables were measured and calculated. Mineralized trabecular bone volume (TBV) as percentage of total tissue volume; mean trabecular plate thickness (MTPT) tn pm as

Key words: Iliac crest biopsy-Representativity.

Introduction Iliac crest biopsy is a widely used procedure for evaluation of metabolic bone disease. Among other variables, it provides information on the thickness and porosity of cortical bone and the density of trabecular bone. Thus the method presumably has the potential for diagnosis of osteopenic conditions. The question is, however, whether the amount of bone in an iliac crest biopsy is representative of the amount of bone in the rest of the skeleton. This question has been amplified by several investigations which have indicated variations in the rate of postmenopausal bone loss in various parts of the skeleton, and the concept that loss of mineralized_trabecular bone takes place earlier than loss of cortical bone (Mazess, 1982; Nordin et al., 1980; Riggs et al., 1980). A number of methodological studies have dealt with the subject and several quantitative and qualitative correlations between bone from the iliac crest and bone from the spine have been established by comparing ash weights, compressive strengths, and the amount of trabecular bone in the two regions (Bell et al., 1967; Chalmers et al., 1966; Melsen et al., 1977; Meunier et al., 1973). In the present study we have compared the densities-of cortical and trabecular bone in iliac

mean trabecular

(trabecular

bone area) x 2

trabecular

bone perimeter

plate density (MTPD) per mm as TBVll 00 MTPTil 000’

and mean trabecular

plate separation

1 x 1000 ___ MTPD 427

(MTPS) in Frn as

MTPT

J Podenphant

428

et al.: Bone biopsy as estimate of amount of bone

TBV

Volume + weight

Weight volume Fia. 1. Schematic depiction of measuring sites and measuring cortical width corrected for soft tissue _

procedures

(Parfitt et al., 1983, Kleerekoper et al., 1985) MTPD and MTPS are estimates of the density and coherence of trabeculae (Parfrtt et al., 1983). Corrected cortical width (CW) mm was calculated as

L

= lumbar vertebra, TBV = trabecular bone volume, CW =

(cm3)] by displacement of millet seeds in 500 and 1000 cm3 graduated cylinders (Trotter et al., 1960).

Processing (area of cortical trssue) -

(area of cortical soft tissue)

total cortical length and cortical porosity (car por) % as (area of cortical tissue) - (area of cortical soft tissue x 100) area of cortical tissue Cortical soft tissue is consrdered unmineralized tical bone (i e marrow + osteoid)

tissue in the cor-

Lumbar spine specimen Lumbar spine specimens were removed from the anterior central part of the first lumbar vertebra (L,) using an electrrc rotary saw In shape and srze the specimen was approxrmately a cube with a side length of 1 3 cm (Fig. 1). The histotechnical procedure employed was as described for the iliac crest biopsy Histomorphometric analysrs In one section was done on all corttcal bone and all trabecular bone wrthin a distance of 8 mm from the cortex. The cortical-trabecular junction was fixed as described. The total trabecular area averaged 58 7 mm* and the total cortical area averaged 3 0 mm2 Histomorphometric variables were calculated as described.

Processing

of bone tissue from the lumbar spine

The lumbar spine was taken out in one piece (Fig 1) Soft tissue was removed, first mechanically and then by exposure of the bone to the following solutions, (a) antiformin 5% for 18 hr, (b) sodium carbonate 2% for 12 hr, and (c) ether/acetone 50%/50% vol/vol for 24 hr (Romeis, 1968). After removal of pedicles and spinous processes vertebrae LPI L, and L, were weighed in a dry fat-free state Volumes were determined [in cubic centimeters

of bone tissue from the distal forearm

The distal third of the radius and ulna was removed from the left forearm (Fig 1). Before removal the point on the forearm where the radius and ulna are separated at a distance of 8 mm was marked. This point represents the borderline between proxrmal and distal scans with the scanning procedure currently used In our laboratory (Nrlas et al., 1985). Wtth this location as the distal point sections 8 mm long were cut from both the radius and ulna The average composition of bone in these sections was 30% tram becular and 70% cortical This composition makes it possible to preserve the integrity of cortical bone during separation from trabecular bone Soft tissue was removed as described for the lumbar spine Dry fat-free weight of the two bone sectrons was determined on a Mettler weight. Trabecular bone was removed using a small drill and the weight of the cortical bone alone was determined. The weight of the trabecular bone was calculated as Table I. Mean values and standard estimates of bone density.

TBV iliac crest CW iliac crest car por iliac crest TBV spine CW spine car por spine BMD spine Density L, + L, + LAa Density trab bone forearma Densrty tort. bone forearmb a Dry weight per unit volume b Dry weight per unit area

deviations

% mm % % mm % glcm’ g/cm3 glcm3 g/cm*

of various

T7

SD

15 1 0 53 89 7 81 0 33 94 9 0 91 0 31 0 32 0 23

52 0 15 71 41 0 25 42 0 27 0 08 0 14 0 08

J. P0denphant

et al.: Bone biopsy as estimate of amount of bone

Table II. Correlations

between various estimates of bone density tn “trabecular”

TBV,,,,, W) r = 0.86c I = 0.39 r = 0.6gb r = 0.62”

TBV,,,,, W) BMD,,,,, W) Density L, + L3 + LGd (gicm3) Density trab. boned forearms (g/cm”) a p < 0 05.

429

bp < 0.01.

=p < 0 001.

bone

TBV,,,“, W)

Density L, + L, f L,d

BMDW!,, (g/cm?

r = 0.59= r = 0 76c r = 0.5@

(g/cm?

r = 0.83c r = 0.46

r = 0.5?

dDry weight per unit volume,

total bone minus cortical bone. The approximate voiumes of the trabecular bone spaces were determined by measuring both the proximal and distal vertrcal and horizontal diameters and combining the area formula for an ellipse with the volume formula of a truncated cone (Documenta Geigy, 1970). In the same manner the total inner areas of the cortical bone “cones” were calculated Finally, we calculated the average weight per unit volume of trabecular bone and the average weight per square centimeier of cortical bone

Bone mineral density (BMD) measuring

procedure

Before necropsy BMD was measured on a Lunar ffadiation Corporation DP-3 spine scanner using dual photon absorptiometry @PA) and a 1CYs3 Gd source. This scanner operates over the lumbar portion of the spine in a maximum scan area of 28 x 20 cm. The transverse speed is 2 5 mmisec and the 40 nonoverlapping longitudinal steps are 4 5 mm each. The counting intervals are 0.5 set yielding a pixel size of 1.25 x 4.5 mm BMD is calculated from BMC by divrding BMC by the projected bone area. BMD therefore represents an area denstty. Lumbar spine BMD (g/cmz) is calculated as an average of the sum of values obtained from L,. I, and 4, including intervertebral disks.

Statistics To describe

the relationship between various variables we used the simple linear regression analysis. The correlation coefficient was used to summarize the degree of correlation between vanTBVSL

l

15

ables and compare the strength of various relationshlps. Significance of r-values was tested by Student’s f-test.

Results Table I shows mean values and standard deviations

of the various variables of bone density measured in the study. Table II shows the correlations between estimates of trabecular bone density. TBV iliac crest shows significant correlations to the amount of trabecular bone both in the spine and the distal forearm. The highest coefficient of correlation was between TBV,,iac and TBV,,,,, (r = 0.86). The amount of bone in all pairs was higher in iliac bone than in spinal bone. The correlation is shown in Figure 2. Furthermore, TBV,,,,, correlated with the density of vertebrae L2 f L3 + L4 expressed in g/cm3. This variable is made out of both cortical and trabecular bone of the vertebrae minus pedicles and spinous processes. An alternative measurement of bone density is dual photon absorptiometry. DPA-BMD,,,,, correlated significantly with the above-mentioned density of L2 + L, + L, and a significant correlation was found between DPAcoefficient (r = BMD,,,,, and TBV,,,,,. The correlation 0.59) however, was appreciably lower than the correlation coeffrcrent between TBV,,,,, and TBV,,,,, (r = 0.86). Furthermore, the correlation coefficients of the cortical width of the iliac crest with the cortical width of the lumbar spine and the cortical density of the distal forearm were nonsignificant (r = 0.39 in each case). Finally, no significant correlation was found between cortical porosity of iliac crest and lumbar spine (r = 0.28). Table Ill shows mean values, standard deviations and correlation coefficients between estimates of trabecular microstructure of iliac crest and spine. Significant correlations were found for MTPT and MTPS while MTPD was insignificant.

70

Discussion The value of iliac crest biopsy in predicting the amount of mineralized trabecular bone in the skeleton has been suby=5.67x-1.96 r =4.86 p<0.01 Sb-_O.ll SEE=2.13

5

l

.

Table Ill. Mean values standard

deviations and coefficients correlation between estimates of trabecular microstructure. Iliac crest

I

10

1

1.5

1

20

I

25

I

30

b

TBvi1ir.x crest %

Fig. 2. Correlation between TBV iliac crest and TBV spine. The equation of the line is given in the figure as well as the coefficient of correlation (r), the significance of the correlation, the standard error of the regression coefficrent (S,) and the standard error of the estimate (SEE)

MTPT pm MTPD per mm MTPS pm a p < 0.05.

of

Spine

si

Sd

X

SD

r

134 1.14 785

32 0.22 181

106 0 75 1433

27 0 28 651

0.58= 0.46 0 538

J Podenphant

stantiated. The results are in agreement with those found by others investigating the amount and quality of bone in the iliac crest versus spine (Bell et al., 1967; Chalmers et al., 1966; Melsen et al., 1977; Meunier et al., 1973). Furthermore, two of the three indices of trabecular microstructure showed significant correlations corroborating the value of iliac crest biopsy as an estimate of biomechanical competence of the spine (Kleerekoper et al., 1985). Values of TBV for all pairs were lower in the spine than in the iliac crest and the trabecular microstructure was reduced in the spine compared to the iliac crest (Table Ill), Finally, we have established a correlation between the amount of trabecular bone in the iliac crest and the distal forearm. Amount of bone in the distal forearm was measured immediately proximal to the point where the radius and ulna are separated by 8 mm. More distally the amount of trabecular bone increases and scanning procedures of the forearm use this site as an estimate of trabecular bone (Nilas et al., 1985). With the technique used we, however, were not able to separate trabecular from cortical bone in this clinically even more relevant area. The study also enabled an evaluation of DPA-BMD,,,,, for estimation of trabecular bone mass. When TBV,,,,, is used as the key answer, it appears that iliac crest biopsy is superior to BMDspine for evaluation of trabecular bone status. The main reason for this observation is probably that DPA-BMD~~i”~ determinations include cortical bone. The amount of trabecular bone in whole lumbar vertebrae, including pedicles and spinous processes, has been found to be 66% (Johnson, 1964). The correlation coefficients presented in Table I give an indication of the advantage of invasive over noninvasive methods. With regard to the amount of cortical bone iliac crest biopsy did not have any predictive value. This suggests that it is not possible to predict the amount of cortical bone in one part of the skeleton from an investigation carried out in another part by means of histomorphometry. However, other studies, in which photon absorptiometry was used, have found a high correlation between different regions with predominantly cortical bone (Gotfredsen et al., 1986). We conclude that iliac crest biopsy is a good measurement of the amount of trabecular bone in the skeleton, but is unable to predict the amount of cortical bone. Iliac crest biopsy is superior to DPA-BMD,,,,, for evaluation of the amount of trabecular bone in the spine.

Acknowledgment; We thank Professor Jorgen A. Voigt, Department of Forensic Medicine, University of Copenhagen, for supplying bone from medicolegal autopsies The investigation was

et al

Bone biopsy as estimate of amount of bone

supported by the Danish Hospital Foundation for Medical Research, region of Copenhagen, the Faroe Islands, and Greenland

References Bell G H and Dunbar 0 : Variations in strength of vertebrae with age and their relation to osteoporosis Calc Tiss. Res.‘l 75-86. 1967 Chalmers J. and Weaver J.K Cancellous bone. Its strength and changes with aging and an evaluation of some methods for measunng its mineral content J. f3one Joint Surg. 48A(2) 299-308, 1966 Documenta Geigy, henthc Tab/es. K Diem and C Lenther, eds CubaGeigy Ltd Basle. Switzerland 1970, pp 142-143 Gotfredsen A, Borg J., Nilas L , Tleilesen L. and Christlansen C Representativlty of regional to total bone mineral in healthy subjects and “anticonvulsive treated” epileptic patients Measurements by smgle and dual photon absorptiometry. Eur. J, CXn /west 16:198--203, 1986 Johnson L C Morphologic analyses In pathology In Bone B,odynamics H M Frost, ed. Little, Brown and Co., Boston, MA, 1964, pp 543-654 Kleerekoper M., Villanueva A.R , Stancia J , Sudhaker R D and Parfitt A M The role of three-dimensional ?rabecular microstructure In the pathogenesis of vertebral compression fractures C&if. Tissue hf. 37 593597, 1985 Mazess R B. On aging bone loss C/in. Orthop. 165:239-252, 1982 Melsen F., Vlidik A, Melsen B and Mosekilde L: Some relations between bone strength, ash weight and histomorphometry In Bone Hkstomorphometry Second internabonal Workshop. P J Meunier, ed Armour Montagu, Paris, 1977, pp 89-95. Meunier P , Courpron P , Edouard C.. Bernard J , Bringuier J and Vignon G.: Physiological senile involution and pathologIca rarefaction of bone Units Endow/no/. Metab. 2(2) 239-256. 1973 Nilas L Borg J., Gotfredsen A. and ChrIstIansen C Comparison of singleand dual-photon absorptlometry in postmenopausal bone mineral loss J Nuci. Med 26.1257- 1262, 1985 Nordin B.E.C Heyburn P J.%Peacock M., Horsman A., Aaron J,. Marshall D and Cr#y R.G In Ciinics in ~~docr/no/, and Metab. metabolic bone djsease. L.V. Aviol! and L.G. Ralsz. eds W B. Saunders Company ild London, 1980. Vol. 9, pp 177-205 Parfitt A M., Mathews C H E Villanueva A.R Kleerekoper M , Frame B and Rao D.S. RelatIonships between surface volume and thickness of iliac trabecular bone in agtng and osteoporosis J. C/in. invest 72: 1396- 1409, 1983 Riggs B L., Wahner H.W , Dunn W L., Mazess RB , Offord K P. and Melton Ill L J: Differential changes in bone mineral density of the appendicular and axial skeleton wtth aging J Chn /west 67.328..-335, 1980 Romeis B Mikroskop,sche Jechnik R Oldenbourg Verlag Munchen, Wren, 1968. p 215. Trotter M.. Broman G E and Peterson R R.: Densittes of bones of white and negro skeletons. J. Bone Joint Surg. 42A(l):50-58. 1960. Villanueva A.R A bone slain for osteoid seams in fresh unembedded mlneralized bone. Stain Technoi. 49.1-8, 1974

Received February 27, 1986 Reused Apnt 28, 1986 Accepted May 16, 1986