
==== Front
Med Sci Monit
Med Sci Monit
Medical Science Monitor
Medical Science Monitor : International Medical Journal of Experimental and Clinical Research
1234-1010
1643-3750
International Scientific Literature, Inc.

39205372
10.12659/MSM.944963
944963
Clinical Research
Identification of Risk Factors for Primary Osteoporosis: The Role of Cervical Ligament Ossification
Wang Dongping 1AB
Yang Jiamin 1E
Li Haishan 1E
Chen Yuxian 1EF
Lin Wei 1BC
Lei Shenglin 2BC
You Yawen 3BCD
Liu Chang 1CD
Lin Yuewei 1D
Guo Huizhi 45D
Mo Guoye 45D
Tang Yongchao 45E
Yuan Kai 45E
Deng Wei 1F
Liu Teng 1D
Gu Guoning 1D
Mai Bin 1F
Zhang Zhen 1A
Zhang Shuncong 45ABCG
Li Yongxian 45ABC
1 The First Clinical Medical School of Guangzhou University of Chinese Medicine, Guangzhou, Guangdong, PR China
2 The Shenzhen Clinical College of Medicine of Guangzhou University of Chinese Medicine, Shenzhen, Guangdong, PR China
3 The Fifth Clinical Medical School of Guangzhou University of Chinese Medicine, Guangzhou, Guangdong, PR China
4 Department of Orthopedics, The First Affiliated Hospital of Guangzhou University of Chinese Medicine, Guangzhou, Guangdong, PR China
5 Guangdong Clinical Research Academy of Chinese Medicine, Guangzhou, Guangdong, PR China
Corresponding Authors: Yongxian Li, e-mail: Spinelyx@126.com, Shuncong Zhang, e-mail: 18172886263@163.com
A Study Design

B Data Collection

C Statistical Analysis

D Data Interpretation

E Manuscript Preparation

F Literature Search

G Funds Collection

2024
29 8 2024
30 7 2024
30 e944963-1e944963-10
26 4 2024
11 7 2024
© Med Sci Monit, 2024
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ This work is licensed under Creative Common Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)
Background

Long-term clinical practice has suggested a possible association between ossification of cervical ligament (OCL) and primary osteoporosis (POP). However, there is a lack of relevant research data. This study aimed to clarify the potential relationship between OCL and POP, and propose new strategies for preventing the onset of POP.

Material/Methods

The study involved 107 patients. The patients’ diagnosis included OCL (ossification of the posterior longitudinal ligament, ossification of the ligamentum flavum, and ossification of the nuchal ligament) and POP. Bone mineral density (BMD), types of OCL, types of ossification of posterior longitudinal ligament, age, sex, serum calcium, serum phosphorus, alkaline phosphatase, type I collagen amino-terminal extension peptide, type I collagen degradation products, osteocalcin N-terminal molecular fragments, 25-hydroxyvitamin D, and history of taking steroid drugs were collected. SPSS24.0 and GraphPad Prism 8 were used to obtain the risk factors for POP.

Results

One-way analysis of variance found that OCL, ossification of posterior longitudinal ligament, alkaline phosphatase, and osteocalcin N-terminal molecular fragments had statistical significance on BMD of the femoral neck (P<0.05). The independent sample t test showed that patient sex had statistical significant effect on BMD (femoral neck) (P=0.036). Incorporating the above factors into multiple linear regression analysis, it was found that OCL, alkaline phosphatase, and osteocalcin N-terminal molecular fragments were risk factors affecting BMD of femoral neck (P<0.05).

Conclusions

OCL, osteocalcin N-terminal molecular fragments, and alkaline phosphatase are risk factors for POP.

Osteoporosis
Ossification, Heterotopic
Ossification of Posterior Longitudinal Ligament
Ossification of the Posterior Longitudinal Ligament of the Spine
Natural Science Foundation of Guangdong Province, China2021A1515012168 Administration of Traditional Chinese Medicine of Guangdong Province, China20221146; 20241091; 20203004 Basic and Applied Basic Research Fund Project in Guangdong Province, China2020A1515110948 Basic and Applied Basic Research in Jointly Funded Projects of City Schools (Institutes) Projects, China202201020295 Project of Guangzhou Science and Technology Department, China202102021040; 202201020533 Application and Foundation Research Project of Guangzhou, China 202201020500; 202201020295 Guangzhou Science and Technology Plan Project, China2023B03J0379 Chinese Society of Traditional Chinese Medicine Youth Talent Lifting Project2022-QNRC2-B11 Hospital of Guangzhou University of Traditional Chinese Medicine2023.10
==== Body
pmcIntroduction

Osteoporosis (OP) is an age-related disease that mostly affects postmenopausal women and middle-aged and elderly people [1,2]. It is a systemic metabolic disorder characterized by bone loss, bone microstructural destruction, and bone strength loss, making bones prone to fractures [3]. Primary osteoporosis (POP) is a high-conversion type of OP, and patients usually present with symptoms such as hunchback, height loss, and chronic pain. Fracture is one of the most serious complications of POP and one of the important risk factors for patient death [4,5]. Because bone fragility increases when patients develop POP, fractures can occur under the action of daily minor external forces, placing a heavy burden on patients and medical systems [6,7]. The World Health Organization attaches great importance to the prevention of POP and lists POP as one of the common diseases that endangers the health of the elderly, especially postmenopausal women [8,9].

Ossification of cervical ligament (OCL) refers to the hyperplasia and ossification of the posterior longitudinal ligament, ligamentum flavum, and nuchal ligament [10,11]. OCL is difficult to detect in the budding stage, without the assistance of radiological equipment, and hard to treat in the advanced stage. OCL was initially identified by Tsukimoto through autopsy findings and was subsequently formalized by Terayama. In 1975, a research society focused on OCL was founded in Japan, leading to extensive basic research. Epidemiological studies indicate that OCL predominantly affects the East Asian yellow race, particularly Japanese individuals, whereas its prevalence is lower in Europe and the United States. The highest incidence rate among those over 30 years old is observed in Japan, ranging from 1.9% to 4.3%, followed by China at 1.6% to 1.8%, and South Korea at 3.6% [12–14]. In the early stage of the disease, most patients have no obvious clinical symptoms. As the disease progresses, neurological symptoms gradually worsen and limb sensory and motor dysfunction occur [15–17]. OCL is the result of the combined action of multiple pathological factors. Local vascular tissue and spindle cells infiltrate within the ligament, which leads to fibroblast proliferation. The cervical ligament becomes hypertrophic or calcified, transforming into bone tissue, to form plate-like bone [18,19]. Some studies have suggested that OCL is related to genetic and environmental factors. The pathological and physiological mechanisms, however, are still unclear but may be similar to that of diffuse idiopathic osteohypertrophy [10,20]. From a biomechanical perspective, during the degeneration process of the cervical spine, segmental instability and mechanical stress distribution imbalance activate ossification pathways and upregulate the expression levels of osteogenic markers such as alkaline phosphatase and osteocalcin [15,19]. From a genomic perspective, there is a familial genetic tendency of ossification of the posterior longitudinal ligament. A study reported that the rs199772854A site of the IL17RC gene may be one of the potential pathogenic genes for posterior longitudinal ligament ossification [21]. In addition, long-term poor posture, strenuous exercise, fatigue, and abnormal hormone secretion levels are risk factors for OCL [22,23].

Both POP and OCL are age-related diseases and are the result of multiple factors. However, the correlation between the two remains controversial. In this article, we study and discuss the correlation between the POP and OCL.

Material and Methods

Study Design and Participants

This was a clinical retrospective study based on the medical record system of the First Affiliated Hospital of Guangzhou University of Traditional Chinese Medicine. The discharge time was set from January 2014 to January 2024. The first diagnostic setting was “ossification of cervical ligament (ossification of posterior longitudinal ligament, ossification of ligamentum flavum, and ossification of nuchal ligament)”. The bone mineral density (BMD), OCL, ossification of posterior longitudinal ligament, age, sex, serum calcium, serum phosphorus, alkaline phosphatase, type I collagen amino-terminal extension peptide, type I collagen degradation products, osteocalcin N-terminal molecular fragments, 25-hydroxyvitamin D, and history of taking steroid drugs of all included patients were recorded. This study was conducted in accordance with the Declaration of Helsinki. Medical record information obtained from previous diagnoses and treatments were used to conduct an accidental application for informed consent. The study was approved by the ethics committee of the regional hospital (ID: JY2024-032).

Inclusion and Exclusion Criteria

The inclusion criteria were as follows: (1) patients whose radiological examination clearly showed OCL (ossification of posterior longitudinal ligament, ossification of ligamentum flavum, and ossification of nuchal ligament); (2) patients who accepted dual-energy X-ray method to detect BMD [1,4]; (3) patients who had complete basic information; and (4) patients who had no history of cervical surgery.

The exclusion criteria were as follows: (1) unnatural menopause; (2) secondary hypertension; (3) diabetes and abnormal glucose tolerance; (4) severe damage to heart, lung, liver, and kidney functions; (5) gonadal disease, adrenal gland disease, parathyroid disease, thyroid disease, and pituitary disease; (6) a history of immune deficiency diseases, cancer, malignant tumors, autoimmune diseases, serious cardiovascular diseases, or other diseases that might significantly reduce life expectancy; (7) participation in any drug clinical trials within 6 months before the screening examination; and (8) patients who were judged by the researcher to be unfit to participate in this study.

Research Approaches

The dual-energy X-ray absorptiometry (Lunar-Prodigy, General Electric, USA) was used to measure the BMD of the patient’s lumbar spine, femoral neck, and hip joint for classification of POP. Instrument quality control was performed daily, and the coefficient of variation was ≤1.2%.

Based on X-ray and computed tomography examination, according to the location of the patient’s OCL, it was divided into ossification of the posterior longitudinal ligament, ossification of the ligamentum flavum, and ossification of the nuchal ligament. Ossification of posterior longitudinal ligament was divided into type focal, type segmental, type continuous, and type hybrid according to the shape and extent of ossification lesions. Type focal meant that it straddled the upper and lower posterior edges of 2 adjacent vertebral bodies, that is, it occurred at the intervertebral disc plane; type segmental meant that ossification blocks existed in the form of clouds on the posterior edge of each vertebral body, and several ossification lesions could be split separately; type continuous meant that the ossification was in the shape of a cord and spanned several vertebral bodies continuously; and type hybrid meant that there were continuous ossification and segmental ossification blocks.

Age, sex, serum calcium, serum phosphorus, alkaline phosphatase, type I collagen amino-terminal extension peptide, type I collagen degradation products, osteocalcin N-terminal molecular fragments, 25-hydroxyvitamin D, and history of taking steroid drugs were carefully and accurately documented based on the medical record system (Jiahe electronic medical record editing system, China) and hematological testing system (Huiqiao testing system, China).

Statistical Analysis

SPSS24.0 software (IBM Corp, Armonk, NY, USA) was used in the study, and the data are presented in the form of mean±standard deviation. Graphing was performed using GraphPad Prism 8 (GraphPad Software Inc, USA). BMD (lumbar spine, femoral neck, and hip joint), OCL, ossification of posterior longitudinal ligament, age, sex, serum calcium, serum phosphorus, alkaline phosphatase, type I collagen amino-terminal extension peptide, type I collagen degradation products, osteocalcin N-terminal molecular fragments, 25-hydroxyvitamin D, and history of taking steroid drugs were analyzed using the independent sample t test, one-way analysis of variance, or Pearson correlation analysis. For differences between groups, the Dunnett T3 test was used when the variances were different; the least significant difference method was used when the variances were uniform. After data analysis, if it was suggested that the variables were potential influencing factors (P<0.10), multiple linear regression analysis of each influencing factor and BMD was performed. P<0.05 was considered to indicate a statistical difference. Finally, the correlation between the influencing factors and BMD was judged by the size of the analysis coefficient value.

Results

A total of 107 cases were included in the study. The detailed process of patient collection is shown in Figure 1. Demographic characteristics are detailed in Table 1. Representative radiological images of patients with OCL are shown in Figure 2.

The dependent variable was POP. One-way analysis of variance was used to evaluate the effect of OCL, ossification of posterior longitudinal ligament, age, serum calcium, serum phosphorus, alkaline phosphatase, type I collagen amino-terminal extension peptide, type I collagen degradation products, osteocalcin N-terminal molecular fragments, and 25-hydroxyvitamin D on BMD (lumbar spine, femoral neck, and hip joint). The results suggested that OCL, ossification of posterior longitudinal ligament, alkaline phosphatase, and osteocalcin N-terminal molecular fragments had statistical significance on BMD (femoral neck) (P=0.018, P=0.035, P=0.045, P=0.010, respectively). The above 4 factors might be potential influencing factors leading to BMD (femoral neck) abnormalities, which were planned to be included in multiple linear regression analysis. More details are shown in Figures 3, 4, and Table 2.

The independent sample t test was used to evaluate the effect of patient sex and history of taking steroid drugs on BMD (lumbar spine, femoral neck, and hip joint). The results showed that sex had statistically significant effect on BMD (femoral neck) (P=0.036). The correlation between history of taking steroid drugs and BMD (femoral neck) was not significant (P=0.991). Therefore, sex might be a potential influencing factor leading to BMD (femoral neck) abnormalities. It was included in multiple linear regression analysis. More details are shown in Figures 3D and 4F.

Multiple linear regression analysis was conducted with OCL, ossification of posterior longitudinal ligament, alkaline phosphatase, sex, and osteocalcin N-terminal molecular fragments as independent variables and BMD (femoral neck) as the dependent variable. In the original goodness-of-fit test table, R2 was 0.198; after adjustment, R2 became 0.158. In the significance F test, F=4.984 and P=0.000, there was statistical significance. In the t test, OCL, alkaline phosphatase, and osteocalcin N-terminal molecular fragments were risk factors affecting BMD (femoral neck) (P=0.005, P=0.015, P=0.025, respectively). However, ossification of posterior longitudinal ligament and sex were not risk factors (P=0.830, P=0.092, respectively). According to the standardized coefficient, the variables that affected BMD were sorted from large to small, as follows: osteocalcin N-terminal molecular fragments, alkaline phosphatase, and ossification of cervical ligament. More details are shown in Table 3.

Discussion

POP has become an important health problem affecting people over 50 years old [1,3]. According to the results of the epidemiological survey of OP among Chinese residents in 2018, the prevalence of OP among people aged 40 to 49 years old is 3.2%, but the prevalence rate among people over 50 years old reaches 19.2%. The prevalence rate among the above 65-year-old group is as high as 32%, of which women account for the majority. The prevalence rate for women over 50 years old is 32.1%, and for women over 65 years old is 51.6%. Its incidence rate cannot be ignored [24].

A study found that OCL was an influencing factor leading to abnormal BMD [25]. One-way analysis of variance was used to evaluate the effects of different types of OCL on the BMD of the lumbar spine, femoral neck, and hip joints. It was found that OCL had a statistically significant effect on the BMD of the lumbar spine, femoral neck, and hip joints (P=0.002, P=0.018, P=0.000, respectively). In multiple linear regression analysis, OCL was found to be a risk factor affecting BMD (femoral neck) (P=0.005). Hirai et al found that the BMD of type continuous and hybrid of cervical posterior longitudinal ligament ossification was higher than that of type segmental, and the BMD of patients with OCL was higher than that of those without spinal ligament ossification [26]. It can be seen that BMD can reflect the tendency of ligament ossification. However, some studies had found that patients with OCL had reduced BMD, especially of the trabecular bone. The reason might be that the ossified site required mineral supply from other sites. During the progression of OCL, the cortical bone remained unaltered while the quantity of cancellous bone diminished. This might be attributed to the fact that cancellous bone possesses a greater blood supply than does cortical bone. Consequently, when the ossification growth factor is secreted and enters the bloodstream, it initially encounters the cancellous bone, instigating mineral transformation. Due to this mineral transfer, BMD decreases, which induces OP [27,28]. Osteocalcin N-terminal molecular fragments are the degradation products of osteocalcin. Their content in the blood is more stable than osteocalcin and can better reflect bone formation [29,30]. When OP occurs, human bone metabolism and bone turnover rate are significantly enhanced, and the level of osteocalcin N-terminal molecular fragments is elevated [31,32]. Studies have shown that when physiological or pathological bone resorption is enhanced, osteocalcin N-terminal molecular fragments are at a lower level in the blood of patients. Clinical studies have shown that BMD values are correlated with the level of osteocalcin N-terminal molecular fragments, which increased sequentially in the normal bone mass group, osteopenia group, and OP group [33,34]. This is consistent with the conclusions of the present study. Alkaline phosphatase is released by osteoblasts and has the effect of promoting bone formation and bone matrix mineralization. The number of bone trabeculae decreases, and the body’s compensatory bone formation increases, causing the level of alkaline phosphatase to increase. The increase in the level of alkaline phosphatase reflects the rising in bone formation, which also means higher bone turnover, accelerated osteoblast apoptosis, and continuous reduction in bone volume [6,35]. Upon identifying pertinent risk factors, clinicians should educate potential high-risk groups on these risks and disseminate relevant knowledge. Once patients understand the dangers associated with these risk factors, they should be advised to implement suitable preventive strategies. Lifestyle significantly influences the development of POP. The emergence of risk factors can be mitigated through interventions such as a calcium-rich diet and exercise of appropriate intensity. Regular health assessments facilitate early detection of potential risk factors. Individuals at high risk can then adopt suitable therapeutic measures to inhibit further escalation of these risk factors.

OCL is a pathological heterotopic ossification disease of spinal ligaments, whose pathogenic mechanism remains unclear [16,27,28,36]. From the perspective of genetic susceptibility, epidemiological studies have shown that OCL mainly occurs in Asian populations and has a familial genetic tendency [37–40]. Runx2 is a key factor required for osteoblast differentiation. Runx2 regulates the osteogenic differentiation of osteoblasts and promotes bone tissue formation and reconstruction. Two loci in Runx2, RS1321075 and RS12333172, are different between OCL patients and controls: one of the haplotype loci is associated with an increased incidence of OCL [41,42]. Bone morphogenetic protein (BMP) is a multifunctional growth factor that plays a vital regulatory role in the osteogenesis process [43,44]. The BMP family has more than 10 subtypes, among which the genes related to OCL include BMP-2, BMP-4, and other subtypes [18]. The expression level of BMP-2 in ligamentum flavum cells is found to be significantly increased under cyclic mechanical stress, indicating that BMP may be involved in promoting endochondral osteogenesis at the ectopic ossification site of OCL, and the ossification activity of OCL continues to exist [17,45]. Fibroblast growth factor (FGF) and its receptor FGFR play a fundamental role in bone development, regulating osteoblast proliferation, differentiation and apoptosis, among which FGF-2 is an important regulator of bone and cartilage differentiation. The direct sequencing method was used to conduct a comparative study on the relationship between FGF-2, FGFR-1, FGFR-2 and single nucleotide polymorphisms in patients and controls. The results showed that the rs1476217 polymorphism site of FGF-2 was associated with OCL [46,47].

This study had several limitations. First, the patients in the study came from the same medical institution, resulting in underrepresentation and selection bias. This limited the generalizability of the study. Second, the number of included samples was not large enough, which might affect the statistical analysis and reduce the credibility of extending the results to the general population. Third, we reported a rare ligament ossification disease, and the number of references worldwide is currently low. Our study was biased toward exploratory research and unable to refer to past clinical studies. Lack of data or previous studies can result in insufficient study hypotheses or inability to compare and verify.

Conclusions

OCL, osteocalcin N-terminal molecular fragments, and alkaline phosphatase are risk factors for POP. Considering the huge medical burden caused by POP, identifying the risk factors of POP, providing health education, and conducting early diagnosis can help prevent the occurrence of POP earlier and bring important health benefits.

Acknowledgements

We are highly grateful to the contribution from all the doctors and nurses.

Figure 1 Patient flow diagram.

Figure 2 Representative radiologic images of patients with ossification of cervical ligament. (A) Lateral X-ray of the cervical spine; (B) sagittal view of the cervical spine computed tomography: (C) C2/3; (D) back of the C4 vertebral body; (E) C5/6.

Figure 3 Statistical analysis results. (A) Types of ossification of cervical ligament and bone mineral density (BMD); (B) types of ossification of posterior longitudinal ligament and BMD; (C) age and BMD; (D) sex and BMD; (E) serum calcium and BMD; (F) serum phosphorus and BMD.

Figure 4 Statistical analysis results. (A) Alkaline phosphatase and bone mineral density (BMD); (B) type I collagen amino-terminal extension peptide and BMD; (C) type I collagen degradation products and BMD; (D) osteocalcin N-terminal molecular fragments and BMD; (E) 25-hydroxyvitamin D and BMD; (F) history of taking steroid drugs and BMD.

Table 1 Demographic characteristics.

Characteristic	Value	
Sex (Male/Female)	48 (44.86%)/ 59 (55.14%)	
Age (years)	61.66±10.42	
Height (m)	1.61±0.07	
Weight (kg)	61.51±12.50	
Body mass index (kg/m2)	23.61±4.29	
Systolic blood pressure (mm Hg)	133.50±16.75	
Diastolic blood pressure (mm Hg)	81.27±11.43	
Blood sugar (mmol/L)	5.39±1.37	
Bone mineral density (femoral neck)	−1.90±1.10	
Serum calcium (mmol/L)	2.25±0.10	
Serum phosphorus (mmol/L)	1.24±0.18	
Alkaline phosphatase (U/L)	70.91±21.42	
Type I collagen amino-terminal extension peptide (pg/L)	55.49±27.76	
Type I collagen degradation products (pg/L)	0.73±0.39	
Osteocalcin N-terminal fragment (ug/L)	16.53±7.35	
25-Hydroxyvitamin D (pg/L)	29.71±9.01	
History of taking steroid drugs	72 (67.29%)	

Table 2 The significant variables before the regression analysis.

Variable	P	
Sex	0.036	
Ossification of cervical ligament	0.018	
Ossification of posterior Longitudinal ligament	0.035	
Alkaline phosphatase	0.045	
Osteocalcin N-terminal molecular fragments	0.010	

Table 3 The results of multiple linear regression analysis.

Model	Unstandardized coefficient	Standardized coefficient	t	P	
B	Std. error	Beta	
1	(Constant)	0.717	0.629		1.141	0.257	
Sex	−0.348	0.204	−0.158	−1.704	0.092	
Ossification of cervical ligament	−0.280	0.097	−0.272	−2.900	0.005	
Ossification of posterior longitudinal ligament	−0.023	0.106	−0.020	−0.216	0.830	
Alkaline phosphatase	−0.291	0.118	−0.221	−2.465	0.015	
Osteocalcin N-terminal molecular fragments	−0.271	0.119	−0.205	−2.283	0.025	

Conflict of interest: None declared

Ethics Statement: The study was approved by the First Affiliated Hospital of Guangzhou University of Chinese Medicine (ID: JY2024-032).

Declaration of Figures’ Authenticity: All figures submitted have been created by the authors, who confirm that the images are original with no duplication and have not been previously published in whole or in part.

Financial support: This work was supported by the Natural Science Foundation of Guangdong Province, China (number: 2021A1515012168), Administration of Traditional Chinese Medicine of Guangdong Province, China (number: 20221146; 20241091; 20203004), Basic and Applied Basic Research Fund Project in Guangdong Province, China (number: 2020A1515110948), Basic and Applied Basic Research in Jointly Funded Projects of City Schools (Institutes) Projects, China (number: 202201020295), Project of Guangzhou Science and Technology Department, China (number: 202102021040; 202201020533), Application and Foundation Research Project of Guangzhou, China (number: 202201020500; 202201020295), Guangzhou Science and Technology Plan Project, China (number: 2023B03J0379), Chinese Society of Traditional Chinese Medicine Youth Talent Lifting Project (number: 2022-QNRC2-B11), and The Hospital Young and Middle Aged Key Talent Cultivation Project of The First Affiliated Hospital of Guangzhou University of Traditional Chinese Medicine (2023.10)
==== Refs
References

1 Walker M Shane E Postmenopausal osteoporosis N Engl J Med 2023 389 21 1979 91 37991856
2 LeBoff M Greenspan S Insogna K The clinician’s guide to prevention and treatment of osteoporosis Osteoporosis Int 2022 33 10 2049 102
3 Gielen E Dupont J Dejaeger M Laurent M Sarcopenia, osteoporosis and frailty Metab 2023 145 155638
4 Aibar-Almazán A Voltes-Martínez A Castellote-Caballero Y Current status of the diagnosis and management of osteoporosis Int J Mol Sci 2022 23 16 9465 36012730
5 Ayers C Kansagara D Lazur B Effectiveness and safety of treatments to prevent fractures in people with low bone mass or primary osteoporosis: A living systematic review and network meta-analysis for the American college of physicians Ann Intern Med 2023 176 2 182 95 36592455
6 Ginsberg C Ix J Diagnosis and management of osteoporosis in advanced kidney disease: A review Am J Kidney Dis 2022 79 3 427 36 34419519
7 Gosset A Pouillès J Trémollieres F Menopausal hormone therapy for the management of osteoporosis Best Pract Res Clin Endoc Metab 2021 35 6 101551
8 Reid I Billington E Drug therapy for osteoporosis in older adults Lancet 2022 399 10329 1080 92 35279261
9 Foessl I Dimai H Obermayer-Pietsch B Long-term and sequential treatment for osteoporosis Nat Rev Endocrinol 2023 19 9 520 33 37464088
10 Abiola R Rubery P Mesfin A Ossification of the posterior longitudinal ligament: Etiology, diagnosis, and outcomes of nonoperative and operative management Glob Spine J 2016 6 2 195 204
11 Yoshii T Sakai K Machino M Furuya T Choice of surgical procedure for cervical ossification of the posterior longitudinal ligament J Clin Med 2022 11 18 5396 36143041
12 Koike Y Takahata M Nakajima M Genetic insights into ossification of the posterior longitudinal ligament of the spine eLife 2023 12 e86514 37461309
13 Le H Wick J Van B Klineberg E Ossification of the posterior longitudinal ligament: Pathophysiology, diagnosis, and management J Am Acad Orthop Surg 2022 30 17 820 30 35587949
14 Tamai K Terai H Hoshino M A deep learning algorithm to identify cervical ossification of posterior longitudinal ligaments on radiography Sci Rep 2022 12 1 2113 35136170
15 Iwasawa T Iwasaki K Sawada T Pathophysiological role of endothelin in ectopic ossification of human spinal ligaments induced by mechanical stress Calcif Tissue Int 2006 79 6 422 30 17160579
16 Guo J Luk K Karppinen J Prevalence, distribution, and morphology of ossification of the ligamentum flavum: A population study of one thousand seven hundred thirty-six magnetic resonance imaging scans Spine 2010 35 1 51 56 20042956
17 Ning S Chen Z Fan D Genetic differences in osteogenic differentiation potency in the thoracic ossification of the ligamentum flavum under cyclic mechanical stress Int J Mol Med 2017 39 1 135 43 28004120
18 Matsumoto M Toyama Y Chikuda H Outcomes of fusion surgery for ossification of the posterior longitudinal ligament of the thoracic spine: A multicenter retrospective survey J Neurosurg-Spine 2011 15 4 380 85 21740130
19 Yang H Lu X Chen D Mechanical strain induces Cx43 expression in spinal ligament fibroblasts derived from patients presenting ossification of the posterior longitudinal ligament Eur Spine J 2011 20 9 1459 65 21442291
20 Niu C Lin S Yuan L Correlation of blood bone turnover biomarkers and Wnt signaling antagonists with AS, DISH, OPLL, and OYL BMC Musculoskelet Disord 2017 18 1 61 28153008
21 Wang P Liu X Liu X IL17RC affects the predisposition to thoracic ossification of the posterior longitudinal ligament J Orthop Surg Res 2019 14 1 210 31291973
22 Endo T Takahata M Koike Y Association between obesity and ossification of spinal ligaments in 622 asymptomatic subjects: A cross-sectional study J Bone Miner Metab 2022 40 2 337 47 35034211
23 He Z Tung N Makino H Assessment of cervical myelopathy risk in ossification of the posterior longitudinal ligament patients with spinal cord compression based on segmental dynamic versus static factors Neurospine 2023 20 2 651 61 37401084
24 Epidemiological survey of osteoporosis in China and results of the “Healthy Bones” special action Chinese J Osteoporosis and Bone Miner Diseases 2019 12 4 317 18
25 Gurban C Balas M Vlad M Bone turnover markers in postmenopausal osteoporosis and their correlation with bone mineral density and menopause duration Rom J Morphol Embryol 2019 60 4 1127 35 32239087
26 Hirai N Ikata T Murase M Bone mineral density of the lumbar spine in patients with ossification of the posterior longitudinal ligament of the cervical spine J Spinal Disord 1995 8 5 337 41 8563152
27 Liu J Chen Y Shan X Wang H Investigation of the biomarkers involved in ectopic ossification: The shared mechanism in ossification of the spinal ligament Front Genet 2022 13 991834 36276940
28 Kishimoto H Clinical study on bone mineral mass in metabolic bone disorders – I-125 photon absorptiometry Nihon Seikeigeka Gakkai Zasshi 1983 57 11 1699 715 [in Japanese] 6676388
29 Liu K Tan G Sun W Percutaneous kyphoplasty combined with zoledronic acid for the treatment of primary osteoporotic vertebral compression fracture: A prospective, multicenter study Arch Orthop Trauma Surg 2023 143 7 3699 706 35933563
30 Deng L Yao F Tian F Influence of iguratimod on bone metabolism in patients with rheumatoid arthritis: A meta-analysis Int J Clin Pract 2022 2022 5684293 35936067
31 Xiong L Chen Q Cheng Y The relationship between coronary artery calcification and bone metabolic markers in maintenance hemodialysis patients BMC Nephrol 2023 24 1 238 37582785
32 Gong M Xu C Wen S The effects of obesity on bone turnover markers in diabetic patients with diabetic ketosis or ketoacidosis Endocr 2023 23 13 1660 67
33 Ning W Changes of bone metabolism markers in the healing stage of hip fracture in the elderly of different genders J Lab Clin Med 2018 15 1329 31
34 An N Ji L Meng H Study on the correlation of N-MID and β-CTX with BMD with bone mineral density in patients with type 2 diabetes mellitus Chinese J Osteoporosis Bone Miner Diseases 2018 24 12 1591 95 1605
35 Schini M Vilaca T Gossiel F Bone turnover markers: Basic biology to clinical applications Endocr Rev 2023 44 3 417 73 36510335
36 Furuya T Sakai K Yoshii T Machino M Conservative treatment and surgical indication of cervical ossification of the posterior longitudinal ligament J Clin Med 2023 12 17 5719 37685786
37 Maigne J Ayral X Guérin-Surville H Frequency and size of ossifications in the caudal attachments of the ligamentum flavum of the thoracic spine. Role of rotatory strains in their development. An anatomic study of 121 spines Surg Radiol Anat 1992 14 2 119 24 1641735
38 Qu X Chen Z Fan D Two novel BMP-2 variants identified in patients with thoracic ossification of the ligamentum flavum Eur J Hum Genet 2017 25 5 565 71 28145426
39 Kong Q Ma X Li F COL6A1 polymorphisms associated with ossification of the ligamentum flavum and ossification of the posterior longitudinal ligament Spine 2007 32 25 2834 38 18246005
40 Elkon R Agami R Characterization of noncoding regulatory DNA in the human genome Nat Biotechnol 2017 35 25 732 46 28787426
41 Liu Y Zhao Y Chen Y Runx2 polymorphisms associated with OPLL and OLF in the Han population Clin Orthop Rel Res 2010 468 12 3333 41
42 Kishiya M Sawada T Kanemaru K A functional RNAi screen for Runx2-regulated genes associated with ectopic bone formation in human spinal ligaments J Pharmacol Sci 2008 106 3 404 14 18319563
43 Chen G Deng C Li Y TGF-β and BMP signaling in osteoblast differentiation and bone formation Int J Biol Sci 2012 8 2 272 88 22298955
44 Siamwala J Rajendran S Chatterjee S Strategies of manipulating BMP signaling in microgravity to prevent bone loss Vitam Horm 2015 99 249 72 26279379
45 Hayashi K Ishidou Y Yonemori K Expression and localization of bone morphogenetic proteins (BMPs) and BMP receptors in ossification of the ligamentum flavum Bone 1997 21 1 23 30 9213004
46 Ornitz D Marie P Fibroblast growth factor signaling in skeletal development and disease Genes Dev 2015 29 14 1463 86 26220993
47 Jun J Kim S Association study of fibroblast growth factor 2 and fibroblast growth factor receptors gene polymorphism in korean ossification of the posterior longitudinal ligament patients J Korean Neurosurg Soc 2012 52 1 7 13 22993671
