X-RAY DENSITY CHANGES IN THE HUMAN HEEL DURING BED REST*

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1 JULY, 1969 X-RAY DENSITY HANGES IN THE HUMAN HEEL DURING BED REST* OENTGENOGRAPHI By GEORGE P. VOSE, M.S.,f and LEWIS M. HURXTHAL, M.D4 densitometry DENTON, has been used to estimate bone mineral losses during weightlessness oforbital space flight2 and during anti-gravity simulation by extended bed rest of volunteer subjects. 4 Bone mass losses have been reported in both instances, with a greater magnitude of loss during actual weightlessness than in its bed rest simulation. The computing apparatus used in these studies is capable of highly accurate measurements of changes in x-ray absorption by bone,5 6 and it is probable that the reported changes in bone mass by the method of densitometry used reflect real variations in bone mineral or matrix. However, it is also possible that the observed changes were partly a consequence of changes in quality or quantity of surrounding soft tissues, which was an uncorrected variable in both the space flight and bed rest studies, e.g., the tissue thickness at the os calcis site will vary as a result of the state of hydration, venous pooling, or changes in muscle mass. Although the mass x-ray absorption coefficient by bone at 6o ky. is approximately 1.4 times greater than that of soft tissue (.34 and.25, respectively), and the volume of overlying soft tissue is small in comparison with bone volume, it is probable that rather small changes in tissue mass are detectable roentgenographically. In fact, we have determined that a io per cent change in x-ray absorption will occur when the tissue thickness at the os calcis site is increased or decreased by 5 mm. The effect of gravity on venous pooling and its effect upon roentgenographic density of the os calcis has been measured in a TEXAS * From the Research Institute, Texas Woman s University, Denton, Texas. FIG. i. (A and B) Variations in x-ray density of the os calcis as a result of venous pooling. simple experiment (Fig. i). Three successive roentgenograms were taken of an adult foot with the subject in the normal vertical position, and 3 roentgenograms were taken after the subject s leg had been elevated at a 45#{176} angle for i minutes. It was found that the os calcis site in the elevated position absorbed 5 per cent less x- radiation than with the leg in the vertical position. It is apparent, therefore, that venous pooling in the extremities is an important factor to be considered in the interpretation of apparent bone density changes by x-ray densitometry. Supported by NASA Grant NGR t The Research Institute, Texas Woman s University, Denton, Texas. The Lahey linic Foundation, Boston, Massachusetts. 486

$\OL. io6, No.$ days and i subject was retamed as an ambulatory control. Efforts were made to duplicate as closely as possible the conditions reported in the other bed rest studies.

days and i subject was retamed as an ambulatory control. Efforts were made to duplicate as closely as possible the conditions reported in the other bed rest studies.

2 \OL. io6, No. 3 X-Ray Density hanges in the Human Heel 487 MATERIAL AND METHOD Four healthy young adult male volunteers participated in a bed rest study in which 3 subjects underwent complete recumbency for 14 days and i subject was retamed as an ambulatory control. Efforts were made to duplicate as closely as possible the conditions reported in the other bed rest studies. 4 Roentgenograms of the left foot and hand adjacent to an aluminum alloy calibration wedge were made at the same time each day. The same mobile x-ray unit was used throughout the study, and a standard absorber having a mass similar to that of the os calcis was roentgenographed daily to detect spurious variations which might contribute to erroneous density interpretation. Eastman Type AA fine grain x-ray film was used and double-loaded into cardboard exposure holders. One of the films was developed immediately for quality check, and the second film was retained for the simultaneous development of all films at the termination of the study. Exact reproducibility in alignment was accomplished by marking the center of the os calcis with a permanent dye target, and the foot was superimposed each day upon the photographic print of the subject s original roentgenogram (Fig. 2, ii and B). All roentgenograms were evaluated 2 times with the bone density computer at Texas Woman s University. If the values varied by less than 2 per cent, the average value was used. If a deviation greater than 2 per cent resulted, one or more additional evaluations were made. Routinely, the instrument can be expected to produce reevaluations of a single roentgenogram well within the 2 per cent limit regardless of the time factor between evaluations. Tissue thickness was measured by caliper at the dyed target site immediately prior to the x-ray exposure. RESULTS AND DISUSSION All subjects exhibited rather marked daily variations in os calcis x-ray absorption throughout the study. Hegsted has I--- - I A B * v/f L./ FIG. 2. (A) Footholder and aligning photograph used to assure reproducible x-ray positioning during os calcis densitometry. (B) 1 oot in position for densitometry. suggested that such short-term changes are a normal biologic variable and cautions that they may have no significance in reflecting real changes in bone density. However, when the os calcis aluminum equivalency values for the entire 2 week period were plotted and analyed by the method of least squares (Fig. 3), a gradual increase in roentgenographic density occurred in the 3 bed rest subjects in contrast to flo change in the control subject (who served as a daytime orderly). The largest increase occurred in bed rest subject D.. (7.2 per cent) followed b\- increases of 6.3 per cent and 5.7 per cent in subjects N.M. and T.B., respectively. The os calcis density change in control subject J.W. was less than i per cent. The correlation coefficients for each of the bed rest subjects were significant: subject D..: P= o.o6 (r=o.oo5); subject N.M.: P=o.488

488 George P. Vose and Lewis M. Hurxthal JULY, 1969 4 -.4 I) 39 BED REST SUBJET..39 BED REST SUBJET NM E 38 E 37.36 >- 35 U &1 -J 34 U c.31.3 #{176} 29.28... SLOPE 1.

3 488 George P. Vose and Lewis M. Hurxthal JULY, I) 39 BED REST SUBJET..39 BED REST SUBJET NM E 38 E >- 35 U &1 -J 34 U c.31.3 #{176} SLOPE 1.78 I I I I I I I BED REST SUBJET TB. SLOPE.8 22 I I I I I I I I B 332 D -.31 x SLOPE a I I I O E.34 o.32 w -J.33 ONTROL SUBJET J.W #{149}31.. I1J.3 D.29 I I 1 1 I I SLOPEa Fio. 3. Os calcis density patterns preceding and during bed rest for the 3 experimental subjects and i control subject. (r=o.o5); and subject T.B.: P=o.36o (r =.1 o). The correlation coefficient, P, for control subject J. W. was o.o6o (r=n.s.). The slopes for the os calcis of all subjects are shown in Figure 3. The second phalanx of the right hand and the distal epiphysis of the radius were analyed in the same manner and no significant change occurred during the course of the study. aliper thicknesses at the os calcis site during early and final periods of bed rest (Days 1-3 and Days 13-14) indicated that the mean tissue thickness increased among

N5= not significant. Subjects Bed Rest D.. N.M. T.B. Over-all Thickness at the Os alcis Site (cm.) Values of t l)ays 1-3 I)ays 13-14 t P 5.3 (SD=.15) 5.33 (SD=.7) 5.5 (SD=.17) 5.9 (SD=.14).6o (SD=.

4 VOL. io6, No. 3 X-Ray Density hanges in the Human Heel 489 TABLE I THIKNESS AT THE OS ALIS SITE (BONE AND OVERLYING TISSUE) DURING THE FIRST 3 DAYS AND THE FINAL 2 DAYS OF 1H E STUDY SD= standard deviation. N5= not significant. Subjects Bed Rest D.. N.M. T.B. Over-all Thickness at the Os alcis Site (cm.) Values of t l)ays 1-3 I)ays t P 5.3 (SD=.15) 5.33 (SD=.7) 5.5 (SD=.17) 5.9 (SD=.14).6o (SD=.2) 5.7 (SD=o) (3 subjects) ontrol J.W (SD=.o7) 5.io(SD=o).767 NS all 3 experimental subjects as the bed rest progressed, but there was no significant change in the control subject. The average tissue thickness for each subject and the t- test probability values between Days 1-3 and Days are given in Table 1. The increases varied between 2 mm. and 6 mm. among the bed rest subjects, while the ambulant control subject, J. W., changed by only.3 mm. Since an increase or decrease in tissue thickness of i mm. will produce an x-ray absorption change of 2 per cent, the observed variations in tissue thickness could account for changes in x-ray absorption of 4 per cent to 12 per cent (and variations of this magnitude occurred during the study). Some of the previous studies reported losses in x-ray density as a result of bed rest,3 4 while the current study indicates that a slight gain occurred. In considering the magnitude of change in x-ray absorption observed in other studies (without regard to actual increase or decrease per se), it is important to notice that the changes in tissue thickness observed in the current study could readily explain the variations in bone density reported in the other studies involving bed rest-and reports of those studies do not indicate that tissue thickness was measured. In fact, the changes in tissue absorption which we observed could easily mask the slight changes in bone absorption normally expected to be associated with bed rest. For this reason, one must not condude from x-ray densitometry alone that bone mass losses occurred in the earlier studies because the method of densitometry used did not differentiate between bone and tissue absorption. It is obvious that an adequate soft tissue correction factor must be applied in future studies of the effects of bed rest and weightlessness upon skeletal density. A method now being used in this laboratory consists of encompassing both the body part and wedge in a tissue-simulating medium, lead shielding of the calibration wedge and body part from undercut scatter, and use of a scatter-reducing grid. This method has demonstrated greatly improved reproducibility in serial roentgenograms and higher precision in quantitating x-ray absorption to actual bone mineral content. SUMMARY In a study of the effects of recumbency on bone density, 3 young adult males participated in a study involving 14 days of complete bed rest, and i subject was retained as an ambulatory control. A slight but significant increase in x-ray density at the os calcis site was noted among the bed rest subjects as the study progressed, but the increase was not evident in the control subject. No significant density variations occurred in the hand phalanx or distal radius,

5 49 George P. Vose and Lewis M. Hurxthal JULY, 1969 Periodic caliper measurements of the heel indicated that increased tissue thickness (luring the latter phases of bed rest may have accounted for the apparent gain in x-ray density of the os calcis. Such an increase in tissue thickness may be a result of venous pooling in the limbs with immobiliation. An adequate soft tissue orrection factor must be applied in future studies of the effects of bed rest and weightlessness upon skeletal density. George P. Vose, M.S. Research Institute Texas Woman s University Denton, Texas 7624 The authors wish to acknowledge the valuable technical assistance of Ted Roach, Richard McMahan, James Silcox, and Bruce Obermeyer. REFERENES I. HEGSTED, D. M. Mineral intake and bone loss. Fed. Proc., 1967, 26, MAK, P. B., LAHANE, P. A., VOSE, G. P., and VGT, F. B. Bone demineraliation of foot and hand of Gemini-Titan IV, V, and VII astronauts during orbital flight. AM. J. ROENT- GENOL., RAD. THERAPY & NULEAR MED., 3967, 1, MAK, P. B., KLAPPER, E. A., PYKE, R. E., ALFORD, B. B., and GAULDIN, R. Fourth Semi- Annual Report to the National Aeronautics and Space Administration. Texas Woman s University, Denton, Texas, March 31, MAK, P. B., KLAPPER, E. A., PYKE, R. E., AL- FORD, B. B., and GAULDIN, R. Fifth Semi-Annual Report to the National Aeronautics and Space Administration. Texas Woman s University, Denton, Texas, September 3, VOSE, G. P., HOERSTER, S. A., and MAK, P. B. New technic for radiographic assessment of vertebral density. Am. 7. Med. Electronics, 1964, 3, VosE, G. P., and PYKE, R. E. ompositional factors affecting vertebral x-ray absorption. Invest. Radiol., 1966, I,

6 This article has been cited by: 1. W. Kalender, K. Engelke, T. P. Fuerst, - Glüer, P. Laugier, J. Shepherd. 29. References. Journal of the IRU 9:1, [rossref] 2. A. Horsman, M. Simpson, F. Armes A left/right comparison of sequential bone loss from the metacarpals of postmenopausal women. American Journal of Physical Anthropology 54:4, [rossref] 3. Harry J. Griffiths, Robert E. Zimmerman The clinical application of bone mineral analysis. Skeletal Radiology 3:1, 1-9. [rossref] 4. harles L. Donaldson, Stephen B. Hulley, John M. Vogel, Robert S. Hattner, Jon H. Bayers, Donald E. McMillan Effect of prolonged bed rest on bone mineral. Metabolism 19:12, [rossref]

RADIOGRAPHY OF THE HAND, FINGERS & THUMB

RADIOGRAPHY OF THE HAND, FINGERS & THUMB FINGERS (2nd 5th) - PA Projection Patient Position: Seated; hand ; elbow on IR table top Part Position: Fingers centered to IR unless protocol is Central Ray: Perpendicular