Atlantoaxial dislocation is a pathological anatomical condition caused by the loss of stability between the atlantoaxial joints, which is a serious disabling disease in spine surgery, and may even endanger the patient's life. The causes of atlantoaxial dislocation include traumatic, congenital, inflammatory, degenerative, tumor, and other factors. Since the symptoms and signs are not specific in clinic, imaging examination is particularly important. Atlantoaxial dislocation is mainly classified according to the etiology, the relative position of atlas and axis, and the difficulty of reduction. Accurate classification is of great significance for the selection of treatment options. There is no popular guideline for surgical indications of atlantoaxial dislocation. Patients presenting with related symptoms or spinal cord dysfunction are generally recognized surgical indications in clinical practice. With the continuous improvement and optimization of atlantoaxial screw placement, reduction and fusion technology, supplemented by new equipment in spine surgery, the surgery-related risks and complications have been greatly reduced, and the surgical treatment of atlantoaxial dislocation can obtain good reduction and fusion results. This tutorial summariz the etiology, diagnosis, classification, treatment, complications, and prognosis of atlantoaxial dislocation, in order to provide a more complete and refined reference for clinical diagnosis and treatment.

Axial pedicle screw fixation technique, as a classic posterior fixation technique, is the first choice and gold standard of posterior axial screw fixation. Since it can pass through the whole vertebrae and play the role of three-column fixation, it has excellent biomechanical properties and is widely used in cervical spine surgery. However, with the deepening of clinical research, some scholars found that the application of axial pedicle screws was limited in patients with pedicle hypoplasia, high-riding vertebral artery and irreducible atlantoaxial dislocation. At the same time, in order to expose bone markers during screw placement, the muscle dissection of pedicle screws is wider compared with that of isthmus screws. Isthmus screw fixation, as a complementary technique for pedicle screw technique, has gradually attracted the attention of scholars in recent years and has been applied in the surgical treatment of various types of cervical spine diseases. The entry point of axial isthmus screw is closer to the midline of the spine and the inferior facet joint than pedicle screw, to avoid extensive muscle dissection during the operation, so that the paravertebral muscles can be protected, which make the surgery more minimally invasive and the invasion of the operation further reduced. At the same time, compared with the lateral mass or pedicle screw of the atlas combined with axial pedicle screw fixation, the lateral mass or pedicle screw of the atlas combined with axial isthmus screw fixation can increase the anteroposterior and vertical distance between the heads of C 1 and C 2 screws due to the change of screw entry points, which can provide a wider operative space for the three dimensional reduction of atlantoaxial dislocation. However, since the axis is a transitional vertebra between the upper and lower cervical spine which has complexity and variability in anatomical structure, many scholars have limited understanding of this new technique. There are no unified standards for screw placement and surgical details, which are mostly based on the personal experience of clinicians. Meanwhile, the biomechanical properties, surgical complications and long-term efficacy of this technique have received little attention and concern, resulting in the limitation of clinical application and promotion for this technique. This review evaluates the relative advantages of axial isthmus screws according to existing literature reports, and analyzes the anatomy, biomechanics, clinical applications and surgical complications of axial isthmus screw fixation technique, aiming to provide a reference for the safety and feasibility of axial isthmus screw placement.

Objective:To explore the value of the Pfirrmann grading standard for disc degeneration in the quantification of heterotopic ossification (HO) after artificial cervical disc replacement (ACDR).Methods:Data of 120 patients who underwent ACDR from January 2009 to December 2016 were retrospectively analyzed. There were 88 males and 32 females with an average age of 43.86±8.69 (range, 27-67) years old. There were 100 single-level replacements (9 Hybrid cases) and 20 double-level replacements (3 Hybrid cases). The occurrence of HO was observed by lateral radiographs of the cervical spine. The HO severity was assessed using the McAfee rating system. Degeneration degrees of cervical intervertebral discs were evaluated by the Pfirrmann grading standard based on the preoperative cervical MRI. The weighted Kappa test was used to analyze the consistency of evaluations between different observers of the Pfirrmann scoring system and the McAfee grading system. Pfirrmann scores for preoperative disc degeneration in the HO and non-HO groups were compared using the t-test. The chi-square test was used to analyze the effect of the Pfirrmann score on the incidence of postoperative segmental HO. The correlation between Pfirrmann score and McAfee grade, as well as postoperative ROM of HO group were analyzed by the Spearman rank-sum test. Quantitative indicators for risks of HO after ACDR surgery were proposed based on the incidence of segment HO in different Pfirrmann score groups. Results:One hundred and twenty patients were followed up for an average of 74.08±28.05 (range, 31-125) months. Based on statistics of cases 2 years after surgery, the overall HO incidence was 31.67% (38/120). The HO incidence was 27% (27/100) and 55% (11/20) for single-level and double-level replacements, respectively. There were 46 replacement segments in the HO group and 94 replacement segments in the non-HO group. The Pfirrmann score of HO group (3.17±1.08) was 25.80% significantly higher than that of the non-HO group (2.52±0.98) ( t=3.46, P=0.01). The incidence of HO in the replacement segment increased significantly with the preoperative Pfirrmann score ( χ2=12.44, P=0.01). The Pfirrmann score of the intervertebral disc in the HO group had a significant positive correlation with the McAfee grade ( R=0.54, P=0.01) and a significant negative correlation with the ROM ( R=-0.75, P=0.01). At 2 years after the operation, when the Pfirrmann score of the intervertebral disc was less than 3, the incidence of HO in the replacement segment was 20.55%(15/73); when the Pfirrmann score was equal to 3, the incidence of HO was 38.46% (10/26); when the Pfirrmann score was greater than 3, HO incidence was 51.22% (21/41). Conclusion:The Pfirrmann score of cervical disc degeneration was significantly related to the incidence of HO, McAfee grade, and ROM in the postoperative replacement segment. The Pfirrmann score of cervical disc degeneration can be used as a quantitativeindicator of HO risk in ACDR.

Objective To investigate the imaging characteristics and pathogenic manifestations of thoracic ossification of the ligamentum flavum complicated with dural ossification.Methods CT and MRI imaging data of 62 segments from 29 patients with thoracic ossification of the ligamentum flavum (TOLF) treated with "en bloc resection of lamina and ossified mass" were retrospectively analyzed.There were 19 males and 10 females,aged 54.9±10.25 years (36-77 years),16 segments in 11 cases with dural ossification (DO) and 46 segments in 18 cases without DO.The ossified mass shape,the relationship between ossified mas and dura mater on cross section of CT bone window and MRI T2WI,and the ossified mass occupational rate (OR) of the spinal canal were investigated.Pathologic features of TOLF-DO from 2 patients were analyzed by H&E staining.Results The shape of ossified mass was as followed,in 16 segments with DO,7 segments (43.8％) by CT and 2 segments (12.5％) by MRI showing ossification layer on the dural sac side of ligamentum flavum;1 segment (6.3％) by CT and 2 segments (12.5％) by MRI showing typical Tram track sign.The relationship between ossified mass and dura mater was that 7 segments (43.8％) by CT and 7 segments (43.8％) by MRI with "C" sign and 7 segments (43.8％) by CT and 8 segments (50.0％) by MRI with "V" sign.The ossified mass OR was 60.5％± 13.0％ in the group with DO and 42.2％± 12.3％ in the group without DO.There was a significant difference between the two groups (t=5.192,P＜0.001).Among the 16 segments with DO,the ossified mass OR of 7 segments with "C" sign was 68.8％± 12.8％ and that of the other 9 segments without "C" sign was 54.39％±9.9％.There was significant difference between the two groups (t=2.45,P=-0.028).Histological examination showed that there were two pathological phenomena in the dura tissue adjacent to ossified mass.The one,there were fibrocartilage,cartilage and osteogenesis in the dura mater.The other,the unossified dura mater fused with the ossified mass but with clear histological demarcation,while the dura mater on the ventral side of the ossified ligamentum flavum atrophies or disappeared.Conclusion The occurrence of dural sac ossification is associated with the ossification of ligamentum flavum beginning at the side of the dural sac and the persistent thickening of the ossified mass.The pathological manifestations of DO are ossification of dural tissue or fusion of dural with ligamentum flavum ossification.

Ossification of spinal ligament (OSL) is a common clinical disease associated with many factors while its etiology is unknown. It is characterized by heterotopic ossification of spinal ligament, which leaded to narrowing of spinal canal diameter, followed by spinal cord and nerve root lesions in varying degrees, including ossification of posterior longitudinal ligament (OPLL) and ossification of flavum ligament (OLF). At present, surgical intervention of ossification of spinal ligament is the only effective treatment method, while the clinical effect is not very satisfactory. Therefore, understanding the etiology and pathogenesis of the ossification of the spinal ligament has important clinical significance for the prevention and treatment of ossification of the ligament. The pathogenesis of ossification of spinal ligament is complex. An ideal animal model is of great significance in studying its etiology and pathogenesis. In this paper, the modeling methods of various animal models of spinal ligament ossification in recent years were reviewed, which could provide reference for the selection of animal models for future experiments.

Objective To evaluate theclinical efficacy and safety of anterior cervical ossified posterior longitudinal ligament en bloc resection (ACOE),and analyze the advantages of ACOE compared to the traditionally anterior cervical surgery.Methods The clinical datawith more than one year follow-up of 96 patients suffered from cervical ossification of the posterior longitudinal ligament(OPLL) from April 2010 to March 2017 was retrospectively analyzed,including 57 males and 39 females,aged 32-69 years,average 54.6±8.7 years.There were 29 cases of nodular type (30.2％),48 cases of segmental type (50.0％),5 cases of continuous type(5.2％),and 14 cases of mixed type (14.6％).The neurological function assessments before and after operation were performed using the Japanese Orthopaedic Association (JOA) scoring system and the visual analogue scale (VAS) scoring system.The effect of ossified mass resection was observed by three-dimensional reconstruction CT scan.The spinal cord decompression was evaluated by MRI.The cervical curvature was compared before and after surgery by cervical lateral radiograph.The operation time,intraoperative blood loss,recovery rates of the JOA scores and complication rates of this group were compared with the cases of anterior cervical ossified posterior longitudinal ligament piecemeal resection (ACOP) reported by the recent literature to analyze the clinical efficacy,safety and advantages of ACOE.Results All the surgeries of 96 cases were successfully performed,including 57 cases (59.4％) with subtotal resectionof single vertebra,31 cases (32.3％) with subtotal resectionof doublevertebras,1 case (1.0％) with expanded intervertebral decompression,4 cases (4.2％) with "vertebra + semi-vertebra" subtotal resection,1 case (1.0％) with "semi-vertebra + vertebra + semi-vertebra" subtotal resection,2 cases with "double vertebras + semi-vertebra" subtotal resection (2.1％).Ninty-six cases were followed up for 12 to 78 months,with an average of 28.0±9.3 months.The preoperative JOA score with (11.38±2.80) scores was increased to 15.32± 1.62 scores at the last follow-up,and the recovery rate of JOA score was 74.63％±13.18％.The preoperative VAS score with 6.00±1.41 scores was reduced to 2.35±1.11 scores at the last follow-up.The cervical curvature increased from 10.4°±9.0° before surgery to 15.8°±8.1° at the last follow-up.CT showed that the ossified masses of the surgical segments were completely excised without residue;MRI showed that the compressionsof spinal cords and dural sacs were completely relieved,with nice morphology recovery.There was no neurological deterioration in this group.There were 6cases of cerebrospinal fluid leakage (CSFL),3 cases of C5 nerve palsy,1 case of Hornersyndrome,2 cases of dysphagia and hoarseness,1 case of titanium mesh subsidence with screw loosing.At the final followups,except one case of occasional throat foreign body sensation,the above complications were all remittedat different followup periods.Compared with the cases of ACOP reported by the recent meta-analysis,the operation time,the intraoperative blood loss,the complication rate of dysphagia with hoarseness and neurological deterioration were lower than those reported in the literature.The recovery rate of JOA scorewas higher than which reported in the literature.Conclusion ACOE is safe and effective for the treatment of cervical OPLL,which may be superior to traditional anterior cervical surgery in terms of surgical safe-ty,controllability of cerebrospinal fluid leakage and improvement of neurological function.

Cervical ossification of posterior longitudinal ligament (OPLL) is common in peopleover 50 years old.It can lead to compression myelopathy,which may end in paralysis when it's severe enough.It has quite a high prevalence in Asian,especially in Japan-cohort,while lower in other districts or races relatively.There have been many surgical methods aiming at cervical OPLL and all of them show satisfied short-term efficacy.However,there hasn't been a comprehensive discussion about disease evolution in natural circumstances as Well as its long-term prognosis up till now,which means that clinicians haven't got direct understanding.In that case it does make sense to ensure patients' natural progression and long-term post-surgical prognosis,from which summarized their rules in different cases with cervical OPLL.It is possible to analyze the long-term prognosis and provide suggestions to clinicians,with collection of papers about cervical OPLL's progression after conservative or surgical treatment and summing up cervical OPLL's radiological and clinical course either in natural circumstance or after surgical intervention.According to the review,ossified sites' axial length grows about 2 mm per year,while its thickness grows 0.2 mm per year.Young age and ossified sites of continuous/mixed types are its risk factors.Compared with natural course,laminectomy with fusion and all kinds of anterior approaches can inhibit ossification site's progression,while laminectomy and laminoplasty will speed it up.Young age and continuous/mixed type still contribute to the post-surgical progress of ossification sites.Symptoms of spinal cord are partly determined by the worsen of ossified site,which in the meantime is related to rate of occupation,range of motion,age and trauma history.Current surgical approaches are all able to eliminate symptoms,though anterior approaches undertake more intraoperative complications as well as better long-term prognosis than posterior ones.

Ossification of the posterior longitudinal ligament (OPLL) is a degenerative disease with a series of clinical manifestations caused by compression of the spinal cord and nerve roots.The disease is prevalent in East Asian countries,and the average prevalence rate of Chinese people is 3.08％.Disease progression can lead to paraplegia,but there is no effective prevention and cure.The pathogenesis of OPLL is still unclear.Most scholars suggest it may be related to genes,hormones,environment,lifestyle and other factors,but all stay in the stage of hypothesis and theory.In this paper,we searched Pubmed,Embase,CNKI and Wanfang database.According to the included literatures,the pathogenesis of OPLL was divided into the following parts:extracellular microenvironment,intracellular cytokines,genetic factors,biomechanical factors,and endocrine and living habits.We summarized and analyzed these literatures.These existing studies independently elucidated the possible mechanisms of OPLL from different angles.Different pathogenic factors promote mesenchymal stem cells to differentiate into osteoblasts through corresponding molecular pathways,initiate osteogenesis,and lead to the formation of ectopic ossification.However,none of these studies have clarified the complete pathogenesis of OPLL.Most of the studies focused on the field of genetics.In recent years,a large number of susceptible genes or loci related to the pathogenesis of OPLL have been screened,but they have shortcomings such as insufficient sample size,ethnic regional differences,and poor reproducibility.

Objective To investigate the clinical effect of anterior controllable antedisplacement and fusion (ACAF) for the treatment of ossification of the posterior longitudinal ligament (OPLL) of the cervical spine.Methods The data of 45 cases with cervical posterior longitudinal ligament ossification treated by ACAF from March 2017 to October 2017 were retrospectively analyzed,including 25 males and 20 females,age 45-68 years,average 57.5 years.There were 18 cases involving C3 vertebral body,30 cases involving C4 vertebral body,40 cases involving C5 vertebral body,34 cases involving C6 vertebral body,and 7 cases involving C7 vertebral body.The function of the neural function was evaluated by the Japanese Orthopaedic Association (JOA) scoring system at preoperation and latest follow-up.The curvature of the cervical spine was measured on the lateral X-ray film of the cervical spine,the maximum occupying ratio of the spinal canal was measured on the cross section of the CT scan,and compression of the cervical spinal cord was evaluated by the cervical MRI.Results Patients were followed up for 3 to 6 months (average,3.9 months).The improvement of neurological function was obtained in all the patients.The JOA score improvement rate at the latest follow-up was 71.3％±9.6％.The cervical lordosis was improved from preoperative 4.5°±3.8° to 10.3°±4.8° at the latest follow-up.The canal stenosis ratio was decreased from preoperative 54.3％±8.2％ to 12.5％±5.3％ at the latest follow-up.MRI showed that the cervical spinal cord was adequately decompressed in situ.No specific complications were identified that were associated with this technique.Conclusion The present study elaborates the surgical tips and demonstrates the satisfactory outcome of ACAF for the treatment of OPLL.This novel technique has the potential to serve as an alternative surgical technique for the treatment of cervical OPLL.

BACKGROUND:The pathogenesis of ligamentum flavum hypertrophy remains poorly understood, and the expression of transforming growth factor beta1 (TGF-β1) is increased notably. Reactive oxygen species (ROS) accumulation is associated with tissue degeneration, which may accelerate the progression of ligamentum flavum hypertrophy by upregulating TGF-β1 expression. OBJECTIVE:To clarify the effect and significance of ROS H2O2-mediated up-regulation of TGF-β1 and collagen type Ⅰ in the progress of ligamentum flavum hypertrophy. METHODS:Ligamentum flavum was removed from a case of acquired lumbar disc herniation with normal ligamentum flavum during lumbar posterior decompression surgery, and then separated and cultured in vitro to the 4-6 generations, followed by exposure to H2O2 at various concentrations (0, 50, 100, 150, 200μmol/L) for 72 hours. The mRNA and protein expression levels of TGF-β1 and collagen type Ⅰ were detected by real-time PCR and western blot assay, respectively. RESULTS AND CONCLUSION:Real-time quantitative PCR showed that the mRNA expression level of TGF-β1 was significantly increased in the 150 and 200μmol/L groups (P<0.05). The mRNA expression level of collagen type Ⅰ was significantly higher in the experimental groups than that in the control group, especially in the 200μmol/L group (P<0.05). Western blot assay revealed that the protein expression levels of TGF-β1 and collagen type Ⅰ were significantly increased in a dose-dependent manner (P<0.05). These findings indicate that H2O2 may accelerate the progression of ligamentum flavum hypertrophy by up-regulating the expression levels of TGF-β1 and collagen type Ⅰ.