Evaluation of bone density with peripheral quantitative computed tomography in healthy premenopausal, perimenopausal, and postmenopausal women

Age and Ageing, Sept, 1995 by E.R. Hernandez, C. Seco-Durban, M. Revilla, J. Gonzalez-Riola, H. Rico

Introduction

Single-photon absorptiometry measurements in the forearm, and both dual-photon absorptiometry and quantitative computed tomography in the spine indicate a premenopausal loss of bone mass [1-3] that becomes slightly more accentuated in the perimenopausal period [4]. In the distal forearm, as in the femur, there is some premenopausal bone loss followed by a menopausal bone loss of lesser magnitude than in the spine [5]. However, techniques such as dual-energy X-ray absorptiometry (DXA) do not disclose any loss of bone mass in the axial and peripheral skeleton in premenopausal women [6, 7].

Another technique for measuring bone mass is peripheral quantitative computed tomography (pQCT) [8], which is precise [9] and allows separate measurement of cortical and trabecular bone [10]. This is advantageous because these two types of bone are heterogeneous [11] and have distinct temporal remodelling characteristics [12] that reflect differences in metabolic activity [13]. Moreover, pQCT measurements of cortical and trabecular bone mass in the upper limbs differ significantly as a result of greater activity in the dominant limb [14]. We determined the possible influence of the perimenopausal state on cortical bone mass and trabecular bone mass measured by pQCT.

Materials and Methods

Subjects: Altogether 167 women were studied. Seventy-two were postmenopausal [mean age (SD) 65.4 (5.7) years], defined as the natural absence of menstruation for at least 12 months [15]. Thirty-one [mean age 51.0 (2.5) years] were considered perimenopausal, defined as 3-6 missed menstruations in the last year with menstrual cycles of widely varying length [16, 17]. Sixty-four healthy premenopausal women [mean age 34.0 (9.6) years] were also studied. In all the premenopausal women, menstrual histories indicated both current and prior menstrual regularity (11-13 cycles/year). All the women were from the health district of the Principe de Asturias University Hospital (Alcala de Henares, Madrid, Spain), and had visited the clinic of the Rheumatology Department for nonspecific pain for which no organic cause was found. All were considered normal after clinical and analytic studies. Normality was established on the basis of an interview and biochemical measurements of blood glucose, transaminases, GGT, creatinine, calcium, phosphorus, total proteins, bilirubin, alkaline phosphatase, tartrate-resistant acid phosphatase (TRAP), gonadal hormones, gonadotropins, and a coagulation study. In all cases calcium was corrected for proteins. A biochemical study was made of 24-hour urine to confirm the normality of calcium excretion and tubular phosphate resorption. Radiological study of the thoracic and lumbar spine excluded vertebral deformities involving loss of more than 25% of the height of the anterior, middle, or posterior vertebral body.

None of the women smoked or was taking oral contraceptives. Assessment of dietary intake over a 7-day period revealed that the calcium intake of all subjects was more than 800 mg per day. None of them practised sports assiduously. The subjects' economic status was similar and they all were from Alcala de Henares (Madrid, Spain), an industrial city. All subjects gave written informed consent. The investigation was approved by the Office for Protection from Research Risks of the Alcala de Henares Medical School. The group characteristics are shown in the Table.

Table. Number, characteristics, and cortical, trabecular, and
total bone density measured by pQCT in premenopausal
(Pre), perimenopausal (Peri), and postmenopausal (Post)
women
                           Menopausal status
                           Pre          Peri           Post
No.                        64           31             72
Age (years)                34.0 (9.6)   51.0 (2.5)     65.4 (5.7)
Height (m)                 1.62 (0.06)  1.57 (0.04)    1.57 (0.06)
Weight (kg)                60.0 (8.0)   61.7 (7.4)     62.4 (9.1)
BMI (kg/[m.sup.2]          22.6 (3.1)   24.8 (3.0)     25.2 (3.5)
Cortical (mg/cm.sup.3]     524 (98)     502 (73)       465 (83)(a)
Trabecular (mg/[cm.sup.3]  159 (49)     138 (40)(b)    121 (28)(c)
Total (mg/[cm.sup.3])      360 (67)     343 (61)       316 (55)(d)
BMI = Body mass index.
(a) p < 0.0001 vs. pre and p < 0.05 vs. peri, (b) p < 0.05 vs. pre,
(c) p < 0.005 vs. pre and p < 0.05 vs. peri, (d) p < .0061 vs. pre
and
p < 0.05 vs. peri, according to ANOVA test.

pQCT studies: Determinations were made using the pQCT Stratec XCT 900 (GmBH, Birkefeld, Germany). After scanning the distal part of the arm, the lower part of the cubital base was marked and a tomogram was made automatically at a distance corresponding to 4% of cubital length, thus differentiating the radius from the cubitus. Radial measurements then were made automatically. The instrument's computer program gave measurements in mg/ [cm.sup.3]. Our coefficient of variation (CV) for this method is 1.1% as calculated from five measurements on five individuals made at intervals of 2-3 weeks. The XCT 900 was calibrated daily with a calibrator (bone simulation standard) supplied by GmBH.