There are different theoretical assumptions for the diagnosis and understanding of OP in China. Modern medical research has confirmed that bone loss is one of the main causes of OP4, with genetics, amenorrhea, weight, abnormal hormone metabolism, nutritional status, and lifestyle as important related factors. Furthermore, OP has become an important health problem for people over 50 years of age in China, especially for middle-aged and older women3. It has been reported that by 2050, the global population of patients with fractures due to OP is expected to reach 21 million, which would have a huge impact on the health and quality of life of the population9–11. Existing studies have also confirmed that bone loss is one of the main causes of OP4,12. Trabecular bone is an extension of the cortical bone in cancellous bones (i.e., trabecular bone is connected with cortical bone), and it has an irregular three-dimensional network structure in the bone marrow cavity (mostly sponge or honeycomb), which supports the bone. Trabecular bone is characterized by unevenness according to position, with differences in tension and pressure. Trabecular bone is widely distributed throughout the human body and constitutes 80% of the BS. It is the "base" for a variety of metabolic processes and plays a key role in the structure of human bone tissue.
The distribution pattern and morphological characteristics on Micro-CT have become the "gold standard" for evaluating bone morphology and microstructure5. Micro-CT is currently used widely in the fields of bone tissue such as for finite element analysis13,14, tissue engineering15, transgenic animals16, oral implantation and repair17, soft tissue, blood vessels4, and biomaterials. Micro-CT and its related analysis software can be used to accurately calculate the metrological and morphological parameters of the trabecular bone in a region of interest 18,19.
The current study focused on the morphological characteristics and distribution of the trabecular bone of the uncinate process in the uncinate vertebral joint. The proliferation of the clinical uncinate process occurs is mainly due to the degeneration of the intervertebral disc and related to factors such as age or trauma, which renders the intervertebral space narrow. As the stress on the uncinate process increases and the repeated stimulation eventually induces bone hyperplasia, it finally protrudes to the adjacent uncinate joint and compresses the surrounding structures, resulting in a series of clinical syndromes of cervical spondylosis. From the shape and arrangement of the trabecular bone within the uncinate process, the trend of the internal bone trabecula was found to be consistent with the trend of the trabecular bone in the vertebral body, and the overall arrangement was longitudinal.
In the current study, BV/TV, BS/BV, Tb.N and Tb.Pf (trabecular bone model factors) showed downward trends, and Tb.Th and Tb.Sp showed upward trends, with the increase in vertebral sequence number, whereas SMI and DA did not show any obvious change. Additionally, there were no significant differences in trabecular parameters between the left and right sides; however, the resolution of the Micro-CT scan may have had an impact on this observation20. found that with changes in scan resolution parameters, the lower the resolution, the smaller is the bone size. The beam parameters also change accordingly. Furthermore, it has been reported that Tb.Pf is more sensitive to the resolution than other parameters are, and the most suitable resolution of the other parameters is 20 µm. Perilli, Parkinson and Reynolds21studied the human lumbar vertebral body at resolutions of 17 µm, 34 µm, and 68 µm. Comparison of the BV/TV, Tb.Th, Tb.Sp, Tb.N, and SMI revealed that as the resolution decreased, the loss of trabecular bone also increased, with differences between vertebrae, which was similar to the report by Guoqiang et al.20.Perilli et al. 21evaluated morphological parameters at a resolution of 68 µm and reported the BV/TV as 4.2 ± 1.5, Tb.Th as 203 ± 11, Tb.Sp as 1,477 ± 382, Tb.N as 0.21 ± 0.08, and SMI as 2.01 ± 0.25. In this study, the overall scan resolution of the cervical vertebrae is 70 µm. There is a big difference between the measured trabecular parameters of the uncinate process and the results documented by Perilli et al., which may be due to the small proportion of the uncinate process in the vertebral body. At the same time, the entire vertebral body is scanned. Therefore, there is a loss of trabecular bone to a certain extent, but it still meets the needs of this research. In the current study, the overall scanning resolution of the cervical vertebrae was 70 µm. The measured parameters of the trabecular bone in the uncinate process in this study were very different from those reported by Perilli et al. 21possibly due to the small proportion of the uncinate process in the vertebral body. Therefore, there was a certain degree of trabecular bone loss in the vertebral body scan, but the needs of this research were still met.
Studying the morphometric parameters and change laws of trabecular bone can not only improve our understanding of the current trabecular bone state but also aid in determining the reasons for its changes, providing a theoretical basis for subsequent prevention, diagnosis, and treatment 22. By selecting an area of interest (i.e., uncinate process) after Micro-CT scanning, the TV, BV, BS, BS/BV, BV/TV, and BS/TV indicators of the area and trabecular bone in the uncinate process can be calculated. Overall, our study revealed that, except for BS, morphological parameter values did not significantly differ between the left and right sides, indicating that the overall distribution and quantity of trabecular bone in the uncinate process is not asymmetrical.
Furthermore, the basic morphological parameters of trabecular bone, Tb.Th, Tb.Sp, Tb.N, can directly reflect the change characteristics of trabecular bone 23. The current study found that the basic morphological parameters of trabecular bone in the uncinate process do not show significant differences between sides and between vertebral bodies, suggesting that the morphological characteristics of the trabecular bone in the uncinate process of each vertebra are relatively stable. Additionally, Eu.N, Conn, DA, and other parameters can better explain the state of the trabecular bone. Jing et al. 24studied the bone microstructure of the hip fracture area and found that the interconnected structure of trabecular bone ensures smooth arrival of bone marrow, blood, and other components. Each part of the bone satisfies the body's metabolic growth requirements.
Another important mechanism behind OP is the change in the shape of the trabecular bone (i.e., from plate-like to rod-like) 25. SMI reflects the degree of plate-like and rod-like trabeculae. The normal range for SMI is 0–3, with values closer to 0 indicating that the trabecular bone has mainly a plate-like structure, and values closer to 3 indicating that the rod-like structure is predominant. When OP occurs, the trabecular bone tends to transform from plate-like to rod-like shape, and the SMI increases. The SMI of the uncinate process in this study was about 2.0, suggesting that the trabecular bone in the uncinate process tends toward that seen with OP; accordingly, the distribution of trabecular bones decreases and the gap becomes wider.
4.1 Prospects and shortcomings
Although Micro-CT has the characteristics of high-precision and high-resolution, it cannot scan the dynamic structure of large animals or humans due to limitations in its coil. Micro-CT can only scan small, isolated specimens or living rats under anesthesia. Additionally, this study focused only on the metrological and morphological parameters of the uncinate trabeculae. There was no uniform comparison standard, and there were no comparisons between the donor’s age and sex and different parts of the same vertebral body, which will be the focus of our continued exploration.
4.2 Conclusions
Micro-CT can be used to observe the arrangement, metrology, and morphological parameters of the trabecular bone in the uncinate process of the cervical spine. The parameters of the trabecular bone in the uncinate process do not significantly differ between the left and right sides and between cervical vertebrae and indicate a trend towards OP. The present results provide a theoretical basis for prevention, diagnosis and treatment.