Osteoporosis is a metabolic disease that bone fragility increases due to bone mass loss and osseous structure change [21]. Osteoporosis posts a great concern since it is often associated with lumbago that brings disability to who suffer from it and huge socioeconomic burden to the healthcare system. Unfortunately, osteoporosis has recently become increasingly common since the population grows old as the birth rate slowing down [22]. The osteoporosis usually is known when a bone fracture occurs to the patient secondary to a low-energy trauma, for example, a fall from ground. And the risk of fragility fracture often depends on bone mass, as well as BMD. Specifically, fractures at femur neck and distal radius present two common types of fractures in the aged people with osteoporosis, and the reason can largely attribute to that osteoporosis is not diagnosed timely and thus no treatment is given.
Osteopenia, the early stage of bone mass loss, could be prevented from developing into its subsequent stage, osteoporosis, by changing lifestyle such as balanced diet and exercise. Therefore, trying to notify bone mass loss at its early stage is of great clinical relevance that reduce the risk of osteoporosis associated bone fractures.
The BMF content can be used as a predictor of bone mass change. Previous studies [23-25] proved that the alternation in bone marrow composition of vertebra that characterized by decreased BMD and increased BMF content was strongly correlated with osteoporosis. Furthermore, a study in healthy adults had demonstrated a significantly negative correlation between the BMF content and the BMD value [10, 11]. Studies by Griffith et al. [26, 27] showed the similar finding that the patients with osteoporosis possessed significantly higher BMF content than the healthy individuals.
Double-echo CSI used in the present study holds advantages in measuring BMF content, comparing to the magnetic resonance spectroscopy (MRS) previously used by many studies [27-29]. Although MRS can precisely detect the fat content in the minor volume of tissue [30], however, its application in measuring BMF content is limited because it has low spatial resolution and fat is not evenly distributed within the bone marrow [31, 32]. The double-echo CSI has the advantages of higher spatial resolution, which is valuable especially in areas with heterogeneous marrow fat distribution that can overcome such limitation [32].
In accordance with present study, we demonstrated patients who had lower BMD values (abnormal bone mass group) obtained significantly lower CSR values (0.578±0.145 vs. 0.634±0.136, P = 0.008), suggesting higher BMF content in the lumbar vertebrae. And, we also found the positive correlation between the CSR value and the T-value. These findings inclusively allow using the CSR value to predict osteoporosis in aged patients with lumbago. To note, Gokhan G et al. [33] claimed that the vertebral BMF content calculated from chemical-shift MRI is not reliable for predicting BMD in female patients aged between 50 and 65 years. The difference between their work and our study could be explained from two aspects: one is our study included both males and females but the subjects of them were only females; another one is the subjects in our study had a varied interval of age (aged from 60 to 70), and the median age of subjects in our study was 65.5 but that of their work was 55.9.
The relationship between diabetes and osteoporosis has been consistently confirmed. Increasing evidences support the association between type 2 diabetes increased fracture risk [34, 35]. Diabetic osteoporosis refers to metabolic bone disease secondary to diabetes mellitus, including bone loss, bone microstructure damage, bone brittleness increases and fracture-prone [36]. The present study verified that patients with a history of type 2 diabetes were more easily to have bone mass change (P < 0.001), and such finding is corroborative with previous studies[37, 38]. Futhermore, the risk of fracture increases with the progressing type 2 diabetes [39]. Therefore, early monitoring of bone mass change in patients with diabetes is needful for timely and effective clinical intervention.
The vertebral BMF content increases sharply in postmenopausal females [40]. Although both androgen and estrogen levels fall in later years, estrogen levels decline particularly sharply in postmenopausal females, which promotes greater fat deposition [41]. Females over 65 years have 10% greater BMF content than males even for the same age [42]. The pathogenesis of osteoporosis in postmenopausal females is closely related to the reduction of estrogen levels [43]. The decrease of estrogen levels weakens the excitability and activity of osteoblasts because estrogen receptors existing on the surface of osteoblasts [44]. Hence, the dynamic balance between osteoblasts and osteoclasts is lost, and the reabsorption capacity of osteoclasts is enhanced, resulting in bone loss. Females of the present study were postmenopausal, and the results showed that females were more prone to have abnormal bone mass than males.
BMF content is continuously increasing with age [45, 46]. BMF in the vertebrae body is approximately 20-25% in the 11-20-year group and rises to 65-75% in the 81-90-year group [45]. Nevertheless, our study found no association between the bone mass change and age. This difference can be explained as the present pilot study included the subjects aged from 60 to 70, no younger subjects were enrolled for comparison. Age-related bone loss indicates the risk of fragility fracture in the aged population. Double-echo CSI can provide a more economical way to detect bone mass change, which is beneficial for early treatment in aged patients to prevent the occurrence of osteoporosis-related fractures.
This study still holds many limitations. Firstly, this study consisted of only elderly patients (aged from 60 to 70) with lumbago from one community and lacked data of other age groups from broader area. A larger sample size and more age groups are intended in the subsequent study. Secondly, the present study is preliminary and had no healthy control. Hence, the findings may be generalizable only to patients with lumbago, and this should be noted when other study quote our results. Also, the BMF content was not directly measured but indirectly related by the CSR value.