Background: Heterotopic ossification of tendons and ligaments (HOTL) is a common clinical condition characterized by the absence of discernible features and a lack of effective treatment. In vitro experiments have demonstrated that mechanical stimulation can induce cell differentiation toward osteogenesis, thereby promoting heterotopic ossification. Currently, there are few experimental designs aimed at inducing ligament stretching in mice, and the mechanism of heterotopic ossification may not entirely mirror that observed in clinical cases. Therefore, there is an urgent imperative to develop a novel and feasible animal model. Methods: In this study, all the Enpp1 gene deficiency mice (a mouse model with heterotopic ossification of multiple ligaments) were divided into three groups: the control group, the spinal brake group, and the hyperactive group (treadmill training group). An external spinal fixation device was designed to restrict mice\'s spinal flexion and extension at 6 weeks of age. The brace was adjusted weekly according to the changes in the size of the mice. Additionally, treadmill training was used to increase activity in the spinal ligaments and Achilles tendons of the mice. Micro-CT scanning and HE staining were performed at 12, 20, and 28 W to evaluate the degree of ossification in the spinal ligament and Achilles tendon. What\'s more, As one of the mechanical stimulation transduction signals, YAP plays a crucial role in promoting osteogenic differentiation of cells. Immunofluorescence was utilized to assess YAP expression levels for the purpose of determining the extent of mechanical stimulation in tissues. Results: Our findings showed that a few ossification lesions were detected behind the vertebral space of mice at 8 weeks of age. Spinal immobilization effectively restricts the flexion and extension of cervical and thoracic vertebrae in mice, delaying spinal ligament ossification and reducing chronic secondary spinal cord injury. Running exercises not only enhance the ossification area of the posterior longitudinal ligament (PLL) and Achilles tendons but also exacerbate secondary spinal cord injury. Further immunofluorescence results revealed a notable increase in YAP expression levels in tissues with severe ossification, suggesting that these tissues may be subjected to higher mechanical stimulation. Conclusion: Mechanical stimulation plays a pivotal role in the process of heterotopic ossification in tissues. Our study provided valid animal models to further explore the pathological mechanism of mechanical stimulation in HOTL development.

UNASSIGNED: Postoperative C5 palsy is a common complication of laminoplasty for cervical ossification of the posterior longitudinal ligament (C-OPLL), although there are several hypotheses regarding its etiology, the exact pathomechanism for this undesirable event remain unclear. The aim of this study was to review clinical and imaging findings in patients with C5 palsy and to propose potential risk factors for this complication.
UNASSIGNED: A total of 220 consecutive patients who had undergone posterior spinal process-splitting laminoplasty (pSPSL) for C-OPLL between January 2018 and December 2019 were included in this study. Postoperative C5 palsy was defined as deltoid muscle weakness of a grade ≤3 in manual muscle test (MMT). These patients were divided into two groups based on the postoperative development of C5 palsy: patients with C5 palsy (group A) and those without C5 palsy (group B). The clinical and imaging covariates evaluated were age, sex, OPLL type, K-line, foraminal stenosis, gutter malposition, and preoperative spinal cord signal change. Logistic regression was used to analyze the independent risk factors for C5 palsy.
UNASSIGNED: In total, 211 patients (18 in group A and 193 in group B) were enrolled in this study, and the incidence of C5 palsy was 8.53%. Sixteen patients had a MMT of grade 3 and two had an MMT of grade ≤2. During the follow-up period (mean duration: 25.10±6.67 months), the MMT grade rose to 5 in 16 patients, 4 in one patient, and 3 in one patient. Multivariate analysis revealed that malposition of the bony gutter [odds ratio (OR) 11.073, 95% confidence interval (CI): 3.411, 35.948; P<0.001] and C4/5 intervertebral foramen stenosis (OR 8.455, 95% CI: 2.559, 27.936; P<0.001) were independent risk factors for C5 palsy.
UNASSIGNED: The incidence of C5 palsy was 8.53% among patients undergoing pSPSL for C-OPLL. Gutter malposition and C4/5 intervertebral foramen stenosis were identified as risk factors for this complication.

UNASSIGNED: The surgical outcomes of individual patient with ossification of the posterior longitudinal ligament (OPLL) can vary depending on various patient-related factors. Japanese Orthopaedic Association Cervical Myelopathy Evaluation Questionnaire (JOACMEQ) is a well-developed tool for outcome measurement and considers both disease-specific and general health aspects. This study aimed to investigate the reliability, validity, and responsiveness of the JOACMEQ in patients with OPLL in mainland China and to compare post-operative outcomes of OPLL patients between mainland China and Japan.
UNASSIGNED: This multicenter trial was performed between July 2009 and June 2019. The procedure for the JOACMEQ translation followed Beaton\'s guidelines. All patients enrolled were diagnosed with OPLL and had completed the JOACMEQ, the modified Japanese Orthopaedic Association (mJOA) scale, and the 36-Item Short Form Health Survey (SF-36) before and after surgery. The reliability (Cronbach\'s α and Pearson\'s correlation), construct validity (factor analysis), concurrent validity (Spearman\'s correlation with SF-36) and responsiveness (effect sizes) of JOACMEQ were evaluated. A mixed-model analytic approach was used to analyze differences in postoperative outcomes between the 2 countries.
UNASSIGNED: Ninety-one patients from mainland China and ninety-one patients from Japan were recruited. JOACMEQ showed satisfactory internal consistency (Cronbach\'s α=0.75). In test-retest reliability evaluation, except for the bladder function domain, the JOACMEQ domains had good test-retest reliability (0.89-0.96). In factor analysis, most of the items (19/24) were well clustered. Regarding clinical validity, all 5 domains were found to have moderate correlations with the physical component summary (PCS) of SF-36 (r=0.25-0.50), and the bladder function and quality of life domains also had moderate correlations (r=0.25-0.50) with the mental component summary (MCS) of SF-36. JOACMEQ showed a variable responsiveness in different domains (effect size =0.17-0.84; standardized response means =0.15-0.85). Regarding postoperative improvements in the JOACMEQ score, mixed-model analysis revealed a significant difference in the quality of life domain between Chinese and Japanese patients (16.0±18.7 vs. 7.8±17.7, P<0.05).
UNASSIGNED: JOACMEQ generally shows good reliability, good validity and mild responsiveness, and can identify the post-operative improvements in patients with OPLL in mainland China. Chinese OPLL patients showed a significantly larger improvement in postoperative quality of life compared to their Japanese counterparts.

UNASSIGNED: Cervical ossification of the posterior longitudinal ligament (OPLL) causes spinal cord compression, which can lead to myelopathy or radiculopathy. Non-surgical treatments have little effect on this condition. Current OPLL classification systems offer little guidance on the selection of an appropriate operating procedure. In this study, we developed a modified axial computed tomography classification (MACTC) scheme. We then examined the usefulness of the MACTC scheme and two other existing classification schemes in guiding OPLL operation choice.
UNASSIGNED: Following screening in which a defined exclusion criteria was used, a total of 91 patients with OPLL participated in the study. Patients\' follow-up data for at least 2 years were obtained. The recovery rate of the Japanese Orthopaedic Association (JOA) scores was compared to two other classification schemes.
UNASSIGNED: According to the MACTC, central-sharp-type OPLL had a lower recovery rate of the JOA score than that of central-gentle-type OPLL (36.05±32.38 vs. 83.90±23.52, P≤0.05). The recovery rate of the JOA scores in the ipsilateral open-door OPLL group was significantly lower than that in the contralateral group of the lateral-steep type (36.67±41.5 vs. 88.89±17.21, P=0.04), but not of that in the lateral-gentle type. There was no significant difference in the recovery rates of the JOA scores between groups when using either existing classification scheme (P>0.05).
UNASSIGNED: The MACTC scheme can assist surgeons to choose the most appropriate operating procedure, and provide an accurate prognosis. If operations on central-sharp-type OPLL are not performed using both the posterior and anterior approaches, prognosis will be poor. The contralateral side should be the first choice for door opening in laminoplasty, especially for patients with lateral-steep-type OPLL. Severe OPLL may not be an absolute contraindication for the posterior approach.

OBJECTIVE: To compare the clinical outcomes of anterior controllable antedisplacement fusion (ACAF), a new surgical technique, with laminoplasty for the treatment of multilevel severe cervical ossification of the posterior longitudinal ligament (OPLL) based on a 2-year follow-up.
METHODS: Clinical data of 53 patients (21 by ACAF and 32 by laminoplasty) who have accepted surgery for treatment of cervical myelopathy caused by multilevel severe OPLL (occupying rate ≥ 50%) from March 2015 to March 2017 were retrospectively reviewed and compared between ACAF group and laminoplasty group. Operative time, blood loss, and complications of the two groups were recorded. Radiographic parameters were evaluated pre- and postoperatively: cervical lordosis on X-ray, space available for the cord (SAC) and the occupying ratio (OR) on computed tomography (CT), and the anteroposterior (AP) diameter of the spinal cord at the narrowest level and the spinal cord curvature on magnetic resonance imaging (MRI). Japanese Orthopaedic Association (JOA) scoring was used to evaluate neurologic recovery. Statistical analysis was conducted to analyze the differences between two groups. The Mann-Whitney U test and chi square test were used to compare categorical variables. unpaired t test was used to compare continuous data.
RESULTS: All patients were followed up for at least 24 months. The operative time was longer in ACAF group (286.5 vs 178.2 min, P < 0.05). The blood loss showed no significant difference (291.6 vs 318.3 mL, P > 0.05). Less complications were observed in ACAF group than in laminoplasty group (one case [4.7%] of C5 palsy and one case [4.7%] of cerebrospinal fluid [CSF] leakage in ACAF group; four cases [12.5%] of C5 palsy, two cases [6.3%] of CSF leakage, and four cases [12.5%] of axial symptoms in laminoplasty group). The mean JOA score at last follow-up (14.6 vs 12.8, P < 0.05) and the improvement rate (IR) (63.8% vs 47.8%, P < 0.05) in ACAF group were superior to those in laminoplasty group significantly. The postoperative OR (16.7% vs 40.9%, P < 0.05), SAC (150.8 vs 110.5 mm2 , P < 0.05), AP spinal cord diameter (5.5 vs 4.2 mm, P < 0.05), and cervical lordosis (12.7° vs 4.7°, P < 0.05) were improved more considerably in ACAF group, with significant differences between two groups. Notably, the spinal cord on MRI showed a better curvature in ACAF group.
CONCLUSIONS: This study showed that ACAF is considered superior to laminoplasty for the treatment of multilevel severe OPLL as anterior direct decompression and better curvature of the spinal cord led to satisfactory neurologic outcomes and low complication rate.

Long non-coding RNAs (lncRNAs) play an important role in the development of bone-related diseases. This study was conducted to investigate the role and mechanism of lncRNA X inactive specific transcript (XIST) in the occurrence of cervical ossification of the posterior longitudinal ligament (OPLL). Here, primary human ligament fibroblasts cells (LFCs) were isolated from 30 cases of OPLL and 30 normal cervical posterior longitudinal ligament (non-OPLL) tissues to perform the qPCR and Western blot assay. We found that the mRNA level of lncRNA XIST was significantly increased in OPLL LFCs compared to non-OPLL LFCs. By bioinformatics analysis, we found that lncRNA XIST has four binding sites for miR-17-5p and found that the mRNA level of miR-17-5p was also significantly decreased in OPLL LFCs compared to non-OPLL LFCs. Since AHNAK is the target gene of miR-17-5p, we further found that the expression of AHNAK was significantly reduced in non-OPLL LFCs after being transfected with miR-17-5p mimic. The qPCR results showed that the mRNA expressions of BMP2 and Runx2 were significantly decreased. After being transfected with lncRNA XIST siRNA in the non-OPLL LFCs, the mRNA levels of lncRNA XIST, AHNAK, BMP2, and Runx2 were significantly decreased and the phosphorylated protein of Smad1/5/8 was reduced. After being cultured by mechanical vibration, the mRNA levels of lncRNA XIST, AHNAK, BMP2, Runx2, COL1, OC, OPN, and Phospho1 were significantly increased, but the mRNA expression of miR-17-5p was significantly decreased. The expression of phosphorylated Smad1/5/8 protein was also significantly increased. Together, this study was the first to determine that XIST gene inhibition plays an important role in the occurrence of cervical OPLL, through the mechanism of regulation of miR-17-5P/AHNAK/BMP2 signaling pathway. Thus, XIST may be a potential target that could be modulated for the treatment of cervical OPLL.

We have introduced a novel surgery technique named anterior controllable antedisplacement and fusion (ACAF) for the treatment of ossification of the posterior longitudinal ligament. As reported, the satisfactory postoperative outcome can be attributed to the larger decompression width. However, it may associate with high prevalence of vertebral artery injury (VAI) theoretically. Thus, assessment of the vulnerability of vertebral artery in ACAF is of great importance.
Computed tomographic scan data of 28 patients were retrospectively studied. Seven radiographic parameters were evaluated: uncinate process (UP) tips distance, transverse foramen (TF)-UP tips distance, TF-LWL (the ipsilateral limited wedging line) distance, the limited distance of lateral decompression, the maximum oblique angle of LWL, TF-LWG (the lateral wall of groove) distance, and width of groove. Eleven fresh cadaveric spines undergoing ACAF surgery were also studied. Two anatomic parameters were evaluated: width of groove and LWG-TF distance.
The UP tips distance increased from C3 to C6 and tended to be larger in males. The UP tip-TF distance and LWL-TF distance were smallest at C4, but both were larger than 2 mm. Maximum oblique angle decreased from C3 to C6. Postoperatively, both radiographic and cadaveric measurements showed the width of groove was larger than UP tips distance, but LWG-TF distance was larger than 2 mm in all levels.
UP can be used as anatomical landmarks to avoid VAI during ACAF surgery. Radiographic and cadaveric measurements verified the safety of ACAF surgery, even for those cases with wedging and lateral slotting.

BACKGROUND: The aim of this study was to compare the clinical efficacy and radiological outcomes of skip corpectomy and fusion (SCF) with anterior controllable antedisplacement and fusion (ACAF) for treating multilevel ossification of the posterior longitudinal ligament (OPLL).
METHODS: 62 patients with multilevel OPLL who had undergone SCF or ACAF were analyzed retrospectively. Types of OPLL, occupying ratio (OR), Japanese Orthopaedic Association (JOA) score, Recovery Rate (RR), Neck Disability Index (NDI) score, Cobb\'s angles of C2-C7, operation time, blood loss, hospital stay, ratings for fusion assessment and complications were recorded and assessed.
RESULTS: Postoperative C2-C7 Cobb\'s angle (11.1 ± 3.2° vs. 13.7 ± 2.5°; P < 0.05), NDI scores at final follow-up (14.3 ± 1.6 vs. 13.3 ± 1.3; P < 0.05), and rate of cerebral fluid (CSF) leakage (5, 16.7% vs. 0,0%; P < 0.05) were significantly better in the ACAF group. At 6 months, bone graft fusion rate was significantly greater in the ACAF group (24.75% vs. 15.50%; P < 0.05).
CONCLUSIONS: Surgical treatment of multilevel OPLL by SCF or ACAF showed no significant differences in clinical outcomes, with the exception of better NDI scores at final follow-up in ACAF. In addition, ACAF is better than SCF in terms of early bone graft fusion rate, lordotic curvature improvement, risk of CSF leakage.

To compare the incidence rate of cerebrospinal fluid (CSF) leakage between anterior controllable antedisplacement fusion (ACAF) and anterior cervical corpectomy and fusion (ACCF) in the treatment of ossification of the posterior longitudinal ligament (OPLL) with dura ossification (DO).
In the period from June 2015 to June 2017, ACAF and ACCF were performed on patients with OPLL with DO. Double-layer sign was observed on axial bone window of CT images. The operation duration, blood loss, and hospital stay were measured. Radiologic assessment included occupying rate, type and extent of OPLL, decompression width, postoperative area of the spinal canal, and anteroposterior diameter of the spinal cord. The JOA scoring system was used to evaluate the neurological status. Surgery-related complications such as CSF leakage and spinal cord or nerve injury were all recorded.
There were 28 patients in ACAF group and 31 in ACCF group. On cross-sectional CT, decompression width and postoperative spinal canal area were both significantly larger in the ACAF group than that in the ACCF group (P < 0.01). The anteroposterior diameter of the spinal cord was significantly larger in the ACAF group (P < 0.05). Mean JOA score was better in the ACAF group (P < 0.05). In the ACCF group, seven (22.6%) patients had CSF leakage. However, only one (3.6%) presented with CSF leakage in the ACAF group. The difference of incidence rate of CSF leakage was significant (P < 0.01).
ACAF, which can significantly reduce CSF leakage and achieve good neurological recovery, is a good option to treat cervical OPLL with DO. These slides can be retrieved under Electronic Supplementary Material.

Posterior surgery has been widely used as an initial surgery for cervical ossification of the posterior longitudinal ligament (OPLL). However, some patients require revision surgery because of failure of symptom relief or late neurological deterioration after posterior surgery. The aim of this study is to retrospectively investigated the surgical results and complications of anterior controllable antedisplacement fusion (ACAF) as a revision surgical technique after initial posterior surgery for OPLL. The present study concluded 13 patients. The operation duration, blood loss and hospital stay was estimated. Radiologic assessment included type and extent of OPLL, decompression width and antero-posterior (AP) diameter of the spinal cord. The JOA scoring system was used to evaluate the neurological status. Surgery- and implant-related complications such as cerebrospinal fluid (CSF) leakage, spinal cord or nerve injury, subsidence and pseudoarthrosis were all recorded. The results showed that nine patients undergoing revision ACAF because of residual stenosis after initial posterior surgery, two because of OPLL progression, one because of lamina closure, one because of a blind man requiring better neurological function of both hands. The mean decompression width and AP diameter of the spinal cord was 20.3 ± 2.1 mm and 5.8 ± 1.1 mm respectively. The mean postoperative JOA score at last follow-up was significantly better than preoperation (14.8 ± 2.5 vs. 8.5 ± 2.7 points, P < 0.01), with a mean improvement rate of 75.3% ± 12.2%. No complication such as CSF leakage, spinal cord or nerve injury, subsidence and pseudoarthrosis occurred. In conclusion, ACAF is a well choice for revision surgery after initial posterior surgery for OPLL.