Kemerovo State Medical Academy, 

Kemerovo, Russia

 

Osteoporosis is one of the most common metabolic disorders of bone tissue and it presents a serious medical, social and economic problem. The important feature of this pathology is decrease in bone mineral density (BMD). The relationship has been found between the level of BMD and the rate of fractures [1, 2].    

Most studies review osteoporosis from the point of involutional, hormonal metabolic changes (postmenopausal, senile osteoporosis) [3, 4]. At the same time it is known that decreasing bone mass appears since before menopause [5, 6].

Radial techniques are leading in diagnostics of osteoporosis: dual-energy X-ray absorptiometry (DXA) and quantitative computer tomography (QCT) [7]. DXA evaluates two-dimensional mineral density of bone tissue, QCT – three-dimensional. The advantages of QCT include the ability to examine dimensional BMD of trabecular and cortical bone individually with simultaneous prevention of different overlapping of surrounding tissues. DXA differs in terms of less financial costs and less radial load in comparison with QCT. There is a small amount of the studies comparing DXA and QCT according to evaluation of bone mineral density, mainly in women in postmenopausal period [8, 9, 10]. Therefore, there is an unfinished discussion about advantages of one or another radial technique for osteoporosis, and the relevance is related to comparison of DXA and QCT results for women of different age.

Objective – to conduct the comprehensive assessment of bone mineral density in women of different ages by means of dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT).

 

MATERIALS AND METHODS

The study included 261 women. The patients were distributed into 5 groups depending on their age: the group I (40-49 years, n = 51), the group II (50-59 years, n=73), the group III (60-69 years, n = 58), the group IV (70-79 years, n = 53), the group V (80 years and older, n = 26), all patients received osteodensimetry by means of dual-energy X-ray absorptiometry and quantitative computer tomography.

The study was approved by the ethical committee of Kemerovo State Medical Academy, and it corresponded to the ethical standards of Helsinki Declaration of World Medical Association – Ethical Principles for Medical Research with Human Participation 2000, and the Rules for Clinical Practice in Russian Federation confirmed by the Order of Russian Ministry of Health, 19.06.2003, #266.

Dual-energy X-ray absorptiometry was conducted with the densitometer Lunar-DPX-NT (GE Healthcare, Great Britain), QCT-densitometry – with the computer tomographic scanner Somatom Emotion (Siemens, Germany) with Osteo mode. L2-L4 vertebrae were examined.

The statistical preparation of the data was performed with Microsoft Office Excel и Statistica 6.1. The normalcy of distribution of empirical measures was estimated with Kolmogorov-Smirnov test. The strength of relationship between results of DXA and QCT was examined with correlation technique – the correlation ratio was calculated. Consistency between DXA and QCT results was defined with Blend-Altman test [11]. For testing the statistical hypotheses the critical level of significance was 0.05 (p = 0.05).

 

RESULTS AND DISCUSSION

The results of densitometry with use of DXA and QCT demonstrated normal distribution that allowed using parametric statistical techniques.

 Z-score was used for estimation of consistency of BMD values between dual-energy X-ray absorptiometry and quantitative computer tomography in the women at the age < 50. Z-score presents the amount of standard deviations (SD) from values of bone mineral density which correspond to the respective age. For the women at the age of 50 and older T-score was used – the amount of standard deviations from the mean value of peak bone mass in young women. The table 1 shows distribution of mean values of Z- and T-tests.                         

 There were no significant differences after comparison of identified cases of osteoporosis with use of DXA and QCT in the women in the group of 50-59 years (p = 0.01); the results of DXA and QCT differed beginning from the age of 60 (table 1). The rate of identified osteoporosis was higher for QCT. The level of significance was as indicated below: p = 0.001 in the group of 60-69 years, p = 0.03 in the group of 70-79, p = 0.01 in the group of 80 years and older.          

Blend-Altman test was used for estimation of consistency of results of DXA and QCT. It was found that results of Z- and T-scores were within the limits of two standard deviations (2 SD) for difference of the values (Fig. 1). It testified that DXA and QCT stand together in terms of estimating bone mineral density.

The positive correlation was found after examination of the relationship between results of dual-energy X-ray absorptiometry and quantitative computer tomography in the women of the general sample (Fig. 2).

Estimation of the correlation in the different groups found the trend to decreasing strength of the relationship with increasing age (table 3). The identified change of the correlation strength (age-dependent) is possibly related to the overstated rates of bone mineral density which was estimated with dual-energy X-ray absorptiometry in the women with age-associated involutional dystrophic processes in the spine.

The findings correspond to the results of some studies. According to the literature data [12], lumbar spinal osteochondrosis associating with boundary osteophytes and subcartilaginous osteosclerosis result in increasing bone mineral density by 5.5-14.5 %, and compression vertebral fractures result in increasing by 6-29 %.

 

CONCLUSION

The number of cases of diagnosed osteoporosis in women older 60 is significantly higher after quantitative computer tomography in comparison with dual-energy X-ray absorptiometry. All age groups showed consistency in the results of two examination techniques. The significant positive relationship was found between DXA and QCT. The strength of the relationship decreased with increasing age.