Ossification of the posterior longitudinal ligament (OPLL) is a well-known cause of myelopathy in East Asian populations.1 OPLL commonly develops in the cervical spine and less commonly in the thoracic spine.2–5 An epidemiological study showed that patients with symptomatic thoracic OPLL (T-OPLL) are likely to have multiple ossified lesions over the entire spine, early onset of symptoms, and morbid obesity compared with patients with cervical OPLL (C-OPLL).2 This indicates that patients with symptomatic T-OPLL have a higher risk of progression of OPLL, not only in the thoracic spine but also in other regions of the spine, and have different risk factors for progression compared with patients with C-OPLL.
Although the progression of OPLL in the cervical spine has been investigated in several studies,6–13 information regarding the incidence and risk factors for progression of OPLL in the thoracic spine is scarce. The incidence of radiographic progression of OPLL in patients with asymptomatic C-OPLL was reported to be 18.3% over a mean follow-up period of 7 years (at least 5 years).7 Recognized risk factors for the progression of C-OPLL include young age, mixed or continuous types, and C2–3 involvement.6,7,9,10,12 Laminoplasty or laminectomy has also been reported as a risk factor for the progression of C-OPLL, with a reported incidence of 3.3% to 74.5%.8,9,13
The main motivation of this study comes from our earlier observation that patients with symptomatic T-OPLL have a high prevalence of coexisting OPLL in the cervical spine (71.5%) and in the lumbar spine (45.2%).2 Thus, it is of great interest whether patients with symptomatic T-OPLL have an increase in lesion size or develop new ossified lesions of the spinal ligaments in regions in addition to the thoracic spine. Recent investigations of OPLL using whole-spine CT have highlighted the usefulness of assessing the severity and distribution of OPLL over the entire spine.1,3,4,7,14,15 Nevertheless, few studies have assessed the progression of OPLL in the whole spine. To the best of our knowledge, only one study has conducted a longitudinal observation of OPLL using repeat whole-spine CT; however, the study included only patients who were asymptomatic, with most (97.2%) having the maximum OPLL mass in the cervical spine.7
The objective of the present study was to elucidate the difference in the radiographic progression pattern of OPLL and its risk factors between C-OPLL and T-OPLL among patients who were symptomatic, using repeated whole-spine CT scans over an interval of at least 3 years. This study may provide important insights that will lead to the early detection or prediction of developing paralysis due to OPLL and provide early treatment opportunities.
Methods
Study Design
In accordance with the Declaration of Helsinki (1964), we conducted a retrospective longitudinal study of patients with symptomatic OPLL who underwent CT imaging evaluations of the entire spine twice, with an interval of at least 3 years between scans, between May 2009 and September 2019. This study was approved by our institutional ethics review board, and the need for patient-informed consent was waived due to the retrospective nature of the study and the de-identified data used.
Patients
In total, 123 patients with symptomatic OPLL, ranging in age from 31 to 93 years, who regularly visited our hospitals and underwent repeated whole-spine CT examinations at an interval between scans of at least 3 years were included.
Since 2013, we have developed a new patient follow-up protocol, which involves baseline initial whole-spine CT scanning and repeat whole-spine CT scanning at 3- to 5-year intervals to assess for progression of ossification of lesions and the appearance of new lesions over the entire spine; this protocol is based on previous reports describing the utility of whole-spine CT examination.14,15 Therefore, we have proposed a follow-up protocol for patients with symptomatic OPLL who regularly visit hospitals for postoperative follow-up or for conservative treatment for sustained symptoms. We provided patients with information regarding the risks and benefits of repeat CT scanning, including the potential risk of radiation exposure. Patients who agreed to the follow-up protocol underwent repeat whole-spine CT examinations.
Included patients were classified into C-OPLL (n = 68) and T-OPLL (n = 55) groups, based on the region that included the main OPLL, which was defined as the region primarily responsible for myelopathic symptoms at the initial examination (basically identical to the region of maximum OPLL). The findings from the neurological examination were used to diagnose the lesion responsible for myelopathy. In cases in which the responsible lesion was difficult to determine because of mild symptoms or myelopathy in patients with multiregional OPLL, the region with the larger OPLL was diagnosed as the main region.
Demographics, Comorbidities, and Distribution of OPLL
The following data were collected from each patient: BMI, sex, age at the onset of OPLL symptoms, age at the initial CT scan, duration from the onset of symptoms to the initial CT scan, family history of OPLL, and comorbidities (hypertension, diabetes, hyperlipidemia, ischemic heart disease, hyperuricemia, renal disease, and cancer). The history of spinal surgery for OPLL was also assessed. The distribution of OPLL (cervical, thoracic, or lumbar spine) at the time of the initial CT scan was evaluated using sagittal reconstructed CT images of the entire spine. OPLL was defined as an ossified lesion with a thickness of 2 mm or more on sagittal reconstructed CT images. Whole-spine CT scans were obtained using the Aquilion ONE/GENESIS Edition system (Canon Medical Systems Corp.).
Assessment of OPLL Progression
Progression of OPLL was defined as an increase of more than 2 mm in the sagittal thickness and/or the longitudinal distance of the ossified mass, which is the most commonly used criterion for OPLL progression.6,7,15 The sagittal thickness and longitudinal distance between the proximal and distal margins of the OPLL mass were digitally measured on sagittal CT reconstructed images of the spine. All images were assessed independently by three board-certified spine surgeons, and the progression of OPLL was determined based on agreement between at least two of them. The interobserver intraclass correlation coefficient (ICC) was 0.92, and the 95% confidence interval (CI) was 0.90 to 0.94, indicating high interobserver agreement. The regions of OPLL progression (cervical, thoracic, and lumbar) were also assessed in each case. Based on these findings, we subdivide the patients into four groups: C-OPLL nonprogression (C-OPLL-NP), C-OPLL progression (C-OPLL-P), T-OPLL nonprogression (T-OPLL-NP), and T-OPLL progression (T-OPLL-P).
To elucidate whether the type of OPLL was related to the progression risk of OPLL, we analyzed whether the OPLL lesions, which were confirmed to have progressed on the second CT scan, were or were not at the unfused intervertebral disc level at the initial CT scan. This was done in accordance with the study by Yang et al.16 We then compared the proportion of unfused-type OPLL in the progressive OPLL lesions between the C-OPLL-P and T-OPLL-P groups.
Assessment of Severity of Ossification of the Spinal Ligaments
The severity of ossification of the spinal ligaments, including ossification of the anterior longitudinal ligament (OALL), ossification of the ligamentum flavum (OLF), and OPLL, was evaluated using the ossification index, which is defined as the sum of the presence of ossification at each vertebral body and intervertebral level, with slight modification.14,17 To reflect both the size and extent of ossification throughout the spine, massive ossification (thickness ≥ 5 mm) was scored twice at each level.
Statistical Analysis
Statistical analyses were performed using JMP statistical software version 14 (SAS Institute Inc.). Normality of data was tested using the Shapiro-Wilk test. The differences in continuous variables between the two groups were evaluated with the Student t-test (for normally distributed data) or Mann-Whitney U-test (for nonnormally distributed data). Results are presented as mean ± standard deviation for parametric variables (normally distributed data) or median (minimum, maximum) for nonparametric variables (nonnormally distributed data). The differences in proportions between two groups were evaluated using the Fisher exact test. The relationship between factors affecting the progression of OPLL was analyzed using multivariate logistic regression analysis. The selection of a priori variables was based on previous literature and its clinical importance. The ICC was analyzed using a two-way mixed-effects model. Statistical significance was set at p < 0.05.
Results
Baseline Characteristics of Patients at the Time of the Initial CT Scan
The demographic data of the study participants are shown in Table 1. The follow-up period from the initial CT scan ranged from 3 to 10 years, and an average of 2.4 CT scans were obtained per patient. Compared with the C-OPLL group, the T-OPLL group had a significant male predominance, younger age at the initial CT scan, younger age at symptom onset, higher BMI and proportion of severe obesity (BMI > 35.0 kg/m2), and higher proportion of comorbid hyperlipidemia. There was no significant difference in the prevalence of comorbidities other than hyperlipidemia between the C-OPLL and T-OPLL groups.
Demographic data of study patients stratified according to the location of the main OPLL lesion at the initial CT scan
| Variable | C-OPLL Group (n = 68) | T-OPLL Group (n = 55) | p Value |
|---|---|---|---|
| Median age, yrs (range) | 62 (40–79) | 60 (28–79) | 0.003 |
| Age at onset <50 yrs, % | 17.6 | 43.6 | 0.001 |
| Median age at Sx onset, yrs (range) | 61 (36–79) | 55 (25–77) | 0.006 |
| Mean duration from Sx onset to initial CT scan, yrs | 2.6 ± 4.6 | 4.1 ± 6.6 | 0.03 |
| Male sex, % | 17.6 | 43.6 | 0.001 |
| Mean BMI, kg/m2 | 25.9 ± 3.8 | 31.2 ± 5.6 | <0.001 |
| BMI >35.0 kg/m2, % | 2.9 | 30.9 | <0.001 |
| Comorbidity, % | |||
| Hypertension | 41.4 | 58.4 | 0.37 |
| Hyperlipidemia | 18.6 | 37.7 | 0.03 |
| Diabetes mellitus | 31.4 | 37.7 | 0.56 |
| Myocardial infarction | 8.6 | 3.8 | 0.76 |
| Renal disease | 1.4 | 3.8 | 0.11 |
| Gout | 3.8 | 3.8 | 0.81 |
| Cancer | 1.9 | 1.9 | 0.35 |
Sx = symptom.
Mean values are presented as the mean ± SD, for normally distributed variables, and median values are presented as median (range), for nonnormally distributed variables.
The presence of OPLL in other regions of the spinal column (i.e., cervical and/or lumbar spine in the T-OPLL group, and thoracic and/or lumbar spine in the C-OPLL group) was 61.5% in the T-OPLL group, which was higher than the 33.8% in the C-OPLL group (Fig. 1).
Pie charts showing the distribution of OPLL over the entire spine, evaluated using whole-spine CT, in the C-OPLL (A) and T-OPLL (B) groups at the initial examination. C = cervical; L = lumbar; T = thoracic.
Difference in the Progression Pattern of Ossification Between C-OPLL and T-OPLL
Of the 123 patients with symptomatic OPLL, 31 (25.2%) showed progression of OPLL 3 years or more from baseline. The incidence of OPLL progression was comparable between the T-OPLL group (29.1%) and C-OPLL group (22.1%) (p = 0.671) (Fig. 2). Next, we compared the regions of OPLL progression between the two groups. In the C-OPLL group, the majority of patients exhibited OPLL progression in only the cervical spine, while in the T-OPLL group, most patients exhibited OPLL progression in multiple regions of the spinal column.
Bar graphs showing the difference in the OPLL progression pattern between the C-OPLL and T-OPLL groups, and the prevalence (upper) and regions (lower) of OPLL progression between the initial and second CT scans in the C-OPLL (A) and T-OPLL (B) groups, respectively.
To confirm the diffuse progression pattern of OPLL in the T-OPLL group, we compared the surgical history of OPLL between the C-OPLL and T-OPLL groups. The proportions of patients who received surgical treatment for OPLL before the second CT scan were 82.9% and 81.1% in the C-OPLL and T-OPLL groups, respectively. Among the patients with a surgical history, the proportion of patients who underwent multiple surgeries (additional surgeries for OPLL in regions other than the main region) in the T-OPLL group was 37.8%, which was significantly higher than the 15.8% in the C-OPLL group (p = 0.001) (Supplemental Table 1). There were three revision surgeries in the T-OPLL group, all of which were an extension of instrumented fusion for adjacent-segment disc disease, distal junctional vertebral fracture, and OLF.
Comparison of Characteristics Between the OPLL-P and OPLL-NP Groups
Then, we compared the characteristics of the patients with and without progression in the C-OPLL and T-OPLL groups, respectively (Table 2). The C-OPLL-P group had a significantly younger age, younger age at symptom onset, shorter duration from symptom onset to the initial CT scan, and a lower prevalence of hypertension than the C-OPLL-NP group. There was no significant difference between the C-OPLL-P and C-OPLL-NP groups with respect to sex, BMI, and comorbidities other than hypertension. The T-OPLL-P group had a significantly younger age, younger age at symptom onset, shorter duration from the onset of symptoms to the initial CT scan, greater proportion of male patients, and higher mean BMI than the T-OPLL-NP group. There was no significant difference in comorbidities between the T-OPLL-P and T-OPLL-NP groups.
Comparison of characteristic features of patients exhibiting OPLL progression between the C-OPLL and T-OPLL groups
| Variable | C-OPLL Group (n = 68) | T-OPLL Group (n = 55) | ||||
|---|---|---|---|---|---|---|
| P (n = 16) | NP (n = 52) | p Value | P (n = 17) | NP (n = 38) | p Value | |
| Median age, yrs (range) | 56 (40–72) | 62 (42–79) | 0.004 | 42 (28–66) | 62 (29–79) | <0.001 |
| Median age at Sx onset, yrs (range) | 56 (36–70) | 62 (40–79) | 0.01 | 42 (25–66) | 57 (29–77) | 0.001 |
| Mean duration from Sx onset to initial CT scan, yrs | 1.0 ± 2.0 | 3.1 ± 5.0 | 0.01 | 2.0 ± 3.2 | 3.5 ± 5.4 | 0.06 |
| Age at onset <50 yrs, % | 43.8 | 9.6 | 0.001 | 62.5 | 26.3 | 0.02 |
| Male sex, % | 68.6 | 63.4 | 0.69 | 52.9 | 18.9 | 0.01 |
| Mean BMI, kg/m2 | 26.3 ± 1.3 | 25.8 ± 5.6 | 0.69 | 36.7 ± 6.1 | 28.5 ± 6.3 | <0.001 |
| BMI >35.0 kg/m2, % | 0 | 3.8 | 0.42 | 56.2 | 18.4 | 0.001 |
| Comorbidity, % | ||||||
| Hypertension | 25.0 | 55.8 | 0.03 | 58.4 | 47.3 | 0.65 |
| Hyperlipidemia | 12.5 | 25.0 | 0.26 | 37.7 | 26.7 | 0.52 |
| Diabetes mellitus | 18.6 | 42.3 | 0.08 | 37.7 | 32.3 | 0.54 |
| Myocardial infarction | 6.3 | 9.6 | 0.67 | 3.8 | 7.3 | 0.32 |
| Renal disease | 0 | 0 | NA | 3.8 | 1.8 | 0.57 |
| Gout | 0 | 3.8 | 0.42 | 3.8 | 5.3 | 0.3 |
| Cancer | 0 | 1.9 | 0.57 | 0 | 0 | NA |
NA = not applicable.
Mean values are presented as the mean ± SD, for normally distributed variables, and median values are presented as median (range), for nonnormally distributed variables.
Regarding the correlation between the type of OPLL and progression of OPLL, 78.1% of the progressive OPLL lesions in the C-OPLL-P group were at the unfused intervertebral disc level on the initial CT scan, compared with 64.4% of those in the T-OPLL-P group. In the remaining progressive lesions, progression of OPLL was seen at the fused intervertebral disc level or vertebral body level.
We also quantified and compared the severity of OALL, OLF, and OPLL using the OALL index, OLF index, OPLL index, and total ossification index between progression cases and nonprogression cases in the C-OPLL and T-OPLL groups, respectively (Supplemental Table 2). There was no significant difference in the ossification indices between the C-OPLL-P and C-OPLL-NP groups, while the T-OPLL index in the T-OPLL-P group was significantly higher than that in the T-OPLL-NP group (p = 0.001).
Surgical Procedures and the Rate of Progression of OPLL at the Surgical Site
We evaluated the association between surgical procedures and the rate of progression of OPLL at the surgical site and compared them between the C-OPLL and T-OPLL groups (Supplemental Table 3). There was no significant difference in the progression rate of C-OPLL between laminoplasty and conservative treatment (30.3% vs 56.3%), while the progression rate of T-OPLL in patients who underwent laminectomy was significantly higher than in those treated conservatively (100% vs 29.4%). There was only one patient in whom OPLL progressed within the instrumented spinal segments in both C-OPLL and T-OPLL.
Risk Factors for Progression of C-OPLL and T-OPLL
We evaluated the risk factors associated with the progression of OPLL in the C-OPLL and T-OPLL groups using multiple logistic regression analysis. Only age at the initial CT scan was identified as a significant risk factor for OPLL progression in the C-OPLL group (Table 3), while male sex, BMI, age at the initial CT scan, and T-OPLL index were identified as significant risk factors for OPLL progression in the T-OPLL group (Table 4).
Results of multivariable logistic regression analysis for C-OPLL progression
| Independent Variable | Adjusted OR | 95% CI | p Value |
|---|---|---|---|
| Male sex | 1.07 | 0.38–4.20 | 0.69 |
| BMI, kg/m2 | 1.11 | 0.75–5.29 | 0.45 |
| Age at initial CT scan, yrs | 1.23 | 1.19–21.87 | 0.005 |
Results of multivariable logistic regression analysis for T-OPLL progression
| Independent Variable | Adjusted OR | 95% CI | p Value |
|---|---|---|---|
| Male sex | 10.5 | 1.39–81.94 | 0.02 |
| BMI, kg/m2 | 1.19 | 1.03–1.37 | 0.006 |
| Age at initial CT scan, yrs | 1.11 | 1.04–1.19 | 0.04 |
| T-OPLL index | 1.24 | 1.16–1.45 | 0.001 |
Relationship Between Age or Obesity and OPLL Progression
Finally, we compared the proportion of OPLL progression by age group and BMI in the C-OPLL and T-OPLL groups (Fig. 3). The proportion of patients exhibiting progression was consistent (approximately 20%) in the C-OPLL group, regardless of age. In the T-OPLL group, progression was highest (80%) in their 30s and subsequently declined with age. The proportion of patients with OPLL progression tended to increase as the BMI increased in both the C-OPLL and T-OPLL groups. In the T-OPLL group, this tendency was notable in patients with morbid obesity (BMI > 35 kg/m2).
Bar graphs showing the proportion of patients who exhibited OPLL progression, stratified according to the decade of age (A and B) and BMI (C and D) at the initial CT scan in the C-OPLL (A and C) and T-OPLL (B and D) groups.
Illustrative Case From the C-OPLL Group
A 64-year-old man who presented with cervical myelopathy was found to have C-OPLL that compressed the spinal cord at the C4–6 levels, based on the initial whole-spine CT scan (Supplemental Fig. 1). The patient had a history of hypertension and a BMI of 19.2 kg/m2. He underwent laminoplasty at the C3–6 levels. The myelopathy recovered postoperatively and did not worsen thereafter, although the second CT scan showed that the C-OPLL had progressed 10 years after baseline.
Illustrative Case From the T-OPLL Group
A 46-year-old woman who presented with thoracic myelopathy was found to have T-OPLL that compressed the spinal cord (Fig. 4). The patient had a history of hypertension and hyperlipidemia and a BMI of 34.3 kg/m2. The initial whole-spine CT scan showed that she also had asymptomatic cervical and lumbar OPLL. She underwent posterior decompression and instrumented fusion at the T1–L1 level for T-OPLL. Soon after thoracic spinal surgery, the patient developed paralysis of the upper limb and was diagnosed with cervical myelopathy caused by C-OPLL. Then, she underwent cervical laminoplasty 3 months after thoracic spinal surgery. The second CT scan showed that the cervical and lumbar OPLL had progressed vertically and horizontally. There was no change in the size or extent of the T-OPLL, and trabeculation was observed in the ossified lesion in the thoracic spine 7 years after baseline.
Representative case from the T-OPLL group. Sagittal reconstructed CT images of the spine obtained in a 41-year-old woman at initial CT (A, B, E, and H), and 1 year (C, F, and I) and 4 years (D, G, and J) after initial CT. OPLL progression is visible in the cervical and lumbar spine (white arrowheads). A: Whole spine. B–D: Cervical spine. E–G: Thoracic spine (T11–L1). H–J: Lumbar spine. Over the course of 4 years, tabularization has occurred (black arrowheads).
Discussion
Recent investigations of whole-spine CT have revealed considerable diversity in the severity, distribution, and precise prevalence of OPLL.3,4,7,15 However, to our knowledge, only one study has conducted a longitudinal whole-spine CT study of OPLL progression in 109 patients who were asymptomatic, of whom 97.2% had C-OPLL and only 2.8% had T-OPLL.7 Therefore, our data on OPLL progression patterns and risk factors based on longitudinal whole-spine CT performed in patients with symptomatic OPLL, especially T-OPLL, provide important information for clinical practice.
Our data showed that patients with T-OPLL had a predisposition toward diffuse progression of OPLL over the entire spine, whereas those with C-OPLL were likely to have progression in only the cervical spine. This idea was supported by the higher incidence of multiregional OPLL progression as well as a more diffuse distribution of OPLL in the T-OPLL group than in the C-OPLL group. More importantly, this observation is strengthened by the fact that patients with T-OPLL had a history of multiple surgeries at multiple spinal regions compared with those with C-OPLL. The prevalence of multiple regional OPLL in patients with C-OPLL was lower than that reported in a multicenter study in Japan (56.2%),3 possibly because the patients in the present study were younger than those in the multicenter study, and some cervical patients with OPLL whose main lesion or preceding lesion was in the thoracic spine were classified as having T-OPLL in our study.
Our study results demonstrated that young age was a common risk factor for OPLL progression regardless of the region in which the main OPLL was located. This is consistent with findings of several earlier studies of C-OPLL, demonstrating that young age is the most significant predictor of OPLL progression in both the postoperative course and the natural course.7,9,10,12,13 Of note, this trend is more obvious in patients with T-OPLL than in those with C-OPLL. The incidence of OPLL progression in patients with T-OPLL in their 30s was 80%, and it steadily decreased with age. While Katsumi et al. speculated that the annual rate of lesion increase was negatively correlated with age,10 our data suggest that OPLL robustly progresses in the 4th decade of life and decelerates its progression after 40 years of age, although it remains unclear at what age OPLL initially appears.
Another important finding is that obesity is an independent risk factor for the progression of OPLL in patients with T-OPLL but not in those with C-OPLL. This is not surprising as morbid obesity and early onset of symptoms are distinct features of patients with symptomatic T-OPLL.2 Thus, the reason obesity is not detected as a risk factor for progression of OPLL in patients with C-OPLL may be due to the milder degree of obesity in patients with C-OPLL. Katsumi et al. showed that obesity seemed to be related to OPLL progression in univariate analysis; however, multivariate analysis did not confirm this relationship in patients with C-OPLL,10 indicating that there may be a weak association between obesity and progression in patients with C-OPLL.
Our study also demonstrated that the effects of surgical treatment on OPLL progression differed between the C-OPLL and T-OPLL groups. Although it is inconclusive whether laminoplasty or laminectomy accelerates OPLL progression,6,13 our data showed that laminoplasty or laminectomy may not have a significant effect on the progression of C-OPLL and yet is likely to promote ossification of T-OPLL. That the 56.3% progression rate in patients with C-OPLL who underwent conservative treatment was relatively high compared with that in previous studies is notable.6,18 This may be due to the inclusion of patients in the T-OPLL group, who have a strong tendency to diffuse ossification. The results of the present study also showed that instrumented spinal fusion surgery could suppress progression of both C-OPLL and T-OPLL. Similar to our data, recent studies have shown a possible suppressant effect of posterior instrumented fusion surgery on the progression of C-OPLL;19,20 however, it is inconclusive whether posterior instrumented fusion suppresses the progression of T-OPLL.16,21,22 Further studies with a larger number of patients are warranted to confirm whether laminoplasty promotes OPLL progression and whether instrumented spinal fixation can slow OPLL progression.
Our study has several limitations. First, this study had selection bias due to the focus on patients with symptomatic OPLL who regularly visited the hospital for checkups to see whether their symptoms or paralysis worsened during the postoperative course. This means that the patients in this study are probably at high risk of OPLL progression; therefore, the incidence of OPLL progression determined in this study cannot be applied to all patients with OPLL. Second, although there is a possibility that patients with T-OPLL are less likely to be symptomatic or more likely to be detected later in the disease course and, therefore, show a different progression pattern compared with patients with C-OPLL, this retrospective study of symptomatic OPLL cannot answer the question. Third, the degree of canal stenosis is much more important than the size of OPLL in terms of the risk of myelopathy. Unfortunately, we were unable to assess the change in the degree of canal stenosis in most patients with symptomatic OPLL because they underwent canal expansive laminoplasty or laminectomy. Lastly, the interval between the initial and second CT scans was not controlled, as this was not a prospective longitudinal study; a longer interval might increase the risk of OPLL progression, although the interval between CT scans was not detected as a risk factor for OPLL progression.
Conclusions
Patients with T-OPLL are predisposed to diffuse progression of OPLL over the entire spine, whereas those with C-OPLL are likely to have progression in only the cervical spine. Young age is a common risk factor for OPLL progression, regardless of the region in which the main OPLL is located. Obesity, male sex, and multilevel, severe T-OPLL are also independent risk factors for OPLL progression in patients with T-OPLL. Thus, our study highlights the need for continued follow-up in patients with T-OPLL, especially young patients and those with obesity, for early detection of spinal cord and cauda equina symptoms due to the progression of OPLL throughout the spine.
Acknowledgments
We would like to thank Editage for English-language editing.
Disclosures
The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.
Author Contributions
Conception and design: Takahata. Acquisition of data: Takahata, Hisada, Kanayama, Suzuki, Fujita, Yamada, Iwata, Hasebe, Sudo. Analysis and interpretation of data: Takahata, Hisada, Endo, Koike, Kanayama, Suzuki, Fujita, Yamada, Iwata, Hasebe, Sudo. Drafting the article: Takahata, Hisada, Endo. Critically revising the article: Takahata, Kanayama, Sudo. Reviewed submitted version of manuscript: Takahata, Hisada, Endo, Koike, Kanayama, Suzuki, Fujita, Yamada, Iwata, Hasebe, Iwasaki. Approved the final version of the manuscript on behalf of all authors: Takahata. Statistical analysis: Hisada, Endo, Koike. Study supervision: Iwasaki.
Supplemental Information
Online-Only Content
Supplemental material is available with the online version of the article.
Supplemental Tables and Figure. https://thejns.org/doi/suppl/10.3171/2022.1.SPINE211010.
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