Development and Preliminary Clinical Application of a Novel Posterior Atlantoaxial auto Anti-Rotation Reduction Rod (PAAR)

Development and Preliminary Clinical Application of a Novel Posterior Atlantoaxial auto Anti-Rotation Reduction Rod (PAAR) | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Development and Preliminary Clinical Application of a Novel Posterior Atlantoaxial auto Anti-Rotation Reduction Rod (PAAR) Xiangyang Ma, Junlin Chen, Xiaobao Zou, Mandi Cai, Haozhi Yang, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6848247/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background: Atlantoaxial dislocation (AAD) is a common upper cervical spine disorder caused by various factors, including trauma, congenital anomalies, and inflammation, which can lead to spinal cord compression and neurological dysfunction. The posterior atlantoaxial screw-rod (PASR) system, though widely used for reduction and fixation, has limitations such as insufficient reduction force and potential spinal cord injury due to rod rotation. This study aimed to evaluate a novel posterior atlantoaxial reduction (PAAR) system with enhanced reduction capabilities and an auto anti-rotation feature. Methods: This was a retrospective study involving 11 patients who underwent posterior atlantoaxial surgery using the PAAR system. The patients' demographic data, dislocation types, surgical time, and blood loss were recorded. Pre- and post-operative measurements of the atlantodental interval (ADI), rotational angle (RA), neurological function, and occipital cervical pain were assessed. Statistical analysis was performed using paired t-test and Wilcoxon ranks test to evaluate significant differences between preoperative and postoperative outcomes. Results: The PAAR system demonstrated excellent reduction capabilities in all patients, with satisfactory outcomes for anterior, posterior, and rotational dislocations. The average surgical time was 110.5 minutes, and the average blood loss was 75 ml. Significant improvements were observed in the Japanese Orthopaedic Association (JOA) scores, Visual Analog Scale (VAS) scores for occipital cervical pain, ADI, and RA (P < 0.05). Additionally, MRI and CT scans showed complete decompression and stable fixation without complications. Conclusions: The novel PAAR system provides effective reduction and fixation for various types of atlantoaxial dislocations. Its auto anti-rotation function and versatile design overcome the limitations of traditional PASR systems, offering a safe and efficient treatment option for patients with atlantoaxial dislocation. This approach may help improve clinical outcomes and reduce surgical complications. Atlantoaxial dislocation Posterior atlantoaxial reduction Auto anti-rotation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Background Atlantoaxial dislocation is a common disorder of the upper cervical spine with various pathological factors such as congenital anomalies, trauma, inflammation, and tumors. This condition often leads to the spinal cord compression at the corresponding segment and produces symptoms of neurological dysfunction. More severely, it can be life-threatening and usually requires surgical treatment aimed at reduction, decompression, and stability reconstruction 1 . By confining the fixation segment only within the atlantoaxial joint, posterior atlantoaxial screw-rod systems (PASR) can provide a rigid fixation without sacrificing the motion of occipitocervical junction. In addition, the inherent reduction function of PASR, which can further improve the reduction efficacy for atlantoaxial dislocation, makes it become the mainstream technique for posterior atlantoaxial reduction and fixation and the golden standard procedure for atlantoaxial dislocation 2 – 6 . However, common PASR have limited reduction capabilities, and the rod is prone to rotation during the reducing process, leading to insufficient reduction force transmission. Meantime, the potential for spinal cord injuries increases due to the need for additional tools to adjust rods. Moreover, for posterior or rotational atlantoaxial dislocations, common PASR fail to achieve effective reduction. To solve these problems, we designed a novel PAAR with multi-gradient reduction function and auto anti-rotation feature. This study aimed to characterize this novel rod and to evaluate its preliminary clinical efficacy. Methods Design of the PAAR The structure of the PAAR is designed as a "Z" shape and consists of three parts. One end of the rod is 15 mm long with a "D" shaped cross-section for anti-rotation (Fig. 1 A), and the other end is 35mm long with an "O" shaped cross-section that can be cut as needed during surgery (Fig. 1 B). The two ends are connected by a vertical connector available in various lengths from 0 to 8 mm (Fig. 1 C). Clinical Data A total of 11 patients (7 male and 4 female) with a mean age of 32.4 (4–55) years who underwent posterior atlantoaxial surgery using PAAR were retrospectively reviewed (Table 1 ). Of the 11 cases, 8 cases were anterior atlantoaxial dislocation, 1 case was posterior atlantoaxial dislocation and 2 cases were rotational atlantoaxial dislocation. Six patients reported occipitocervical pain and five patients had neurological impairment symptoms at different degrees including numbness and weakness of limbs. The compression of spinal cord at C1-C2 level was revealed in 6 cases by preoperative MRI. Table 1 Data of 11 patients who underwent posterior atlantoaxial reduction, fixation and fusion using PAAR. Case Gender Age (yrs) Surgical time (mins) BL (ml) Follow up duration (months) Direction of dislocation 1 M 9 120 100 15 anterior 2 F 4 90 50 16 anterior 3 F 47 125 80 17 anterior 4 M 55 95 90 16 anterior 5 M 31 105 100 15 anterior 6 F 53 115 130 18 anterior 7 M 41 120 50 9 anterior 8 M 39 110 45 11 anterior 9 M 57 127 120 10 posterior 10 F 4 115 30 10 rotatory 11 M 41 110 75 14 rotatory Mean 34.6 ± 20.1 `112 ± 11.7 79.1 ± 32.5 13.7 ± 3.2 BL, blood loss. Surgical Procedure After general anesthesia, appropriate weight skull traction was performed and maintained during the surgery, the patient was placed in a prone position with proper cervical flexion. A median longitudinal incision of 6-8cm was made from the occipital eminence to the C2 spinous process. Subperiosteal dissection exposed occipital bone, C1 posterior arch and C2 lateral mass. Retain the attachment of the cervical semispinalis muscle to the C2 spinous process. C1 and C2 preferred pedicle screws, lateral mass screws could be replaced when preoperative imaging evaluation finding it difficult or not safe to place pedicle screws. Two PAARs with the suitable gradients were selected and cut to the appropriate length for placements. For anterior dislocation, placed the "D" end into the C2 screw slot and the "O" end into the C1 screw slot. First tightened the C2 screw nut, then tightened the C1 screw nut and pulled C1 to complete the reduction (Fig. 2 A, Fig. 3 ). For posterior dislocation, put the "D" end into the C1 screw slot and the "O" end into the C2 screw slot. First tightened the C1 screw nut, and then tightened the C2 screw nut to complete the reduction as this push C1 forward (Fig. 2 B, Fig. 5 ). For rotational dislocation, the reduction procedure of the anterior rotation side was the same as that of the anterior dislocation, and the reduction procedure of the posterior rotation side was also same as that of the posterior dislocation (Fig. 2 C, Fig. 4 ). If the reduction was not ideal, replaced a larger gradient rod until obtaining ideal result. Grinding drill was used to grind the posterior arch of atlas and axial lamina to prepare the bone graft bed, and took autogenous iliac cancellous bone for grafting (non-fusion surgery does not need this procedure). Placed negative pressure drainage tube and suture the wound layer by layer. Observed indexes and Follow-up The surgical time and blood loss (BL) were recorded. Atlantodental interval (ADI) were measured before and after surgery to assess reduction of anterior and posterior dislocation. Rotational angle (RA) was measured before and after surgery to evaluate reduction of rotational dislocation. Japanese Orthopaedic Association (JOA) scores was used to assess neurological function. And the Visual analog scale (VAS) was used to assess the degree of occipital neck pain. Patients were followed up at 3, 6, 9 and 12 months, then once per year or as needed. Surgical complications were documented after surgery and during the follow-up. Cervical X-rays and CT scans were performed at each follow-up for assessment of internal fixations failure, stability, and bone fusion. Statistical Analysis Normality of numeric data was assessed by Shapiro-Wilk test. For numeric data with normal distribution, paired t test was used to compare pre- and post-operative change. Wilcoxon ranks test was used to compare difference for numeric data without normality. All statistical analyses were performed by SPSS 26.0 (IBM, Armonk, NY) and P<0.05 meant statistically significant difference. Results All patients successfully underwent posterior reduction and fixation surgery with PAAR, including 5 cases with non-fusion surgery and 6 cases with fusion surgery. The average surgery time was 110.5 minutes (ranged 90.0-120.0 minutes), with an average blood loss (BL) of 75 ml (ranged 30.0-130.0 ml). No spinal cord or vertebral artery injuries occurred during surgery. Postoperative X-rays and CT scans showed satisfactory reduction in all 11 cases, and MRI revealed complete decompression in 6 patients with preoperative spinal cord compression. Neurological symptoms and occipital cervical pain improved in all patients. At the last follow-up, JOA scores improved significantly from an average of 12.4 (range 6–16) preoperatively to 15.9 (range 13–17), occipital cervical VAS scores significantly reduced from an average of 3.8 (range 2–6) preoperatively to 0.8 (range 0–2) and the atlantodental interval (ADI) decreased from an average of 5.9 mm (range 2.3–15.4 mm) preoperatively to 1.8 mm (range 1.0-2.5 mm); Besides, Rotational angle (RA) decreased from an average of 40° preoperatively to 4°(Table 2 ). CT scans during the follow-up showed bone graft fusion in all 6 patients underwent fusion surgeries, and 5 cases with odontoid fractures achieved fracture healing. No fixation loosening or re-dislocation was observed in X-rays and CT scans during the follow-up period. All 11 patients had remarkable clinical benefit after surgery without internal fixation failure confirmed by radiological outcomes, which shows PAAR is safe and effective for the treatment of atlantoaxial dislocation. Table 2 Comparison of outcomes before and after operation. Case Cervical JOA score Occipitocervical VAS ADI(mm)/RA(°) Pre-op F/U IR (%) Pre-op F/U IR (%) Pre-op F/U 1 16 17 100 6 1 83.3 4.3 1.5 2 15 17 100 2 0 100 2.3 1.0 3 12 15 60.0 3 0 100 6.8 2.3 4 15 17 100 6 1 83.3 5.4 1.6 5 12 16 80.0 4 1 75.0 5.1 1.2 6 6 13 63.6 5 2 60.0 7.7 2.1 7 12 16 80.0 5 2 60.0 5.5 2.5 8 10 16 85.7 4 1 75.0 15.4 1.4 9 16 17 100 1 0 100 -6.2 -1.4 10 10 15 71.4 2 0 100 14.1 1.3 11 12 17 100 4 0 100 45.2 5.1 Mean 12.4 ± 3.2 15.9 ± 1.3 84.1 ± 15.7 3.8 ± 1.8 0.8 ± 0.8 83.7 ± 16.1 P 0.005* 0.004* 0.005* JOA, Japanese Orthopsedic Association; VAS, visual analog scale; ADI, atlanto-dental interval; RA, mutual C1-C2 rotational angle.Pre-op, pre-operation; F/U, the last follow up; IR, improvement rate; *Wilcoxon ranks test, and p<0.05 means statistically significant difference. Discussion The C1/C2 transarticular screw fixation, also known as the Magerl technique, was once considered the gold standard for treating atlantoaxial dislocation due to its rigid fixation capabilities before the emergence of posterior atlantoaxial screw-rod systems 7 , 8 . However, the Magerl technique lacks the ability to reduce dislocations and requires anatomical reduction of the atlantoaxial joint before screw insertion. In addition, it is difficult to place transarticular screw during surgery, and intraoperative X-ray fluoroscopy is needed repeatedly in the preparation process of the screw path. Therefore, Magerl technique is gradually replaced by the PASR (also known as Goel-Harms technique) 9 – 11 . With its capability for reduction, the PASR is now widely used in the treatment of atlantoaxial dislocation 12 – 18 . The common posterior atlantoaxial screw-rod system's capability for reduction is based on the height difference between the C1 and C2 screws in the sagittal plane. The reduction is achieved by connecting the C1 and C2 screws with a rod to eliminate this height drop and generate reverse forces. While increasing the rod's curvature can enhance the reduction forces by increasing the height difference, but the rod cannot be bent indefinitely. Meantime, excessive curvature will cause the rod to rotate easily and make it difficult to place. Conversely, insufficient curvature can result in failed reduction. These all reflect the limited reduction capacity of the existing screw-rod system. The PAAR overcomes these limitations by determining the height difference through the length of the vertically connecting part (Fig. 1 C), allowing for the required height difference without bending. Theoretically, the length of the connector is unlimited, completely overcoming the issue of finite bending of common rods. Regardless of the specification, the two ends of the PAAR remain parallel that will not increase the difficulty of placements. Different specifications of PAAR can provide varying reduction forces, allowing surgeons to choose the appropriate rod based on intraoperative X-ray. PAAR effectively reduces the time of repeatedly adjusting the rod curvature and fluoroscopy times. If the reduction is insufficient, a new rod with a larger height difference could be replaced for a stronger reduction force. For over-reduction, replacing a smaller height difference rod or reversing the rod direction can eliminate the extra reduction. Common rods are prone to rotation during the placement that requiring auxiliary instruments to secure and maintain their orientation. However, the surgical area for atlantoaxial surgeries is narrow, and without bony structures protecting the spinal cord between C1 and C2. These make the use of auxiliary instruments likely to accidentally injury the spinal cord during surgery. The "D" shaped design at one end of the PAAR has an automatic anti-rotation function. Compared to the common rods' "O" shaped cross-section, the "D" shaped end can fully match with the nut and screw slot (Fig. 1 -b). When tightening the nut at the "D" shaped end, there is no need for auxiliary instruments, and the rod will not rotate, allowing it to be fixed at the predetermined position. The design of the "D" shaped end not only simplifies the rod placement process but also enhances the safety of posterior atlantoaxial reduction process. Considering that the C1 and C2 screws are usually not on the same sagittal plane, the other end of the rod remains "O" shape to facilitate insertion into the screw slot. Moreover, the "O" shaped end of this PAAR is long enough to be cut as needed. The common PASR is primarily used to treat anterior atlantoaxial dislocation and achieves reduction by using the C2 screw as a fulcrum, tightening the C1 and C2 screws in sequence to pull the atlas backward. However, for posterior or rotational dislocations requiring reverse movement of the atlas, common rods cannot provide the necessary corresponding height difference. This issue is resolved by reversing the placement direction of the PAAR which creating an opposite height difference for forward movement capability. For posterior dislocation, reversing the rod enables forward movement of C1 to achieve reduction. As for rotational dislocation, the reduction steps for the anterior rotation side are the same as for anterior dislocation, while those for the posterior rotation side are the same as for posterior dislocation. Therefore, the PAAR is applicable not only for common anterior dislocations but also for various types of dislocations. In the practice of clinical PAAR applications, it was found that C1 was prone to rotation during the reduction process if lamina screws were used for C2, which is related to the large distance between C2 lamina screw and C1 screw in sagittal plane. So the C2 lamina screw cannot serve as a fulcrum for PAAR but only as auxiliary fixation after reduction. For the surgical treatment of atlantoaxial dislocations, the C2 pedicle screw should be the first choice. When pedicle screws are not appropriate, lateral mass screws or pars screws may be used instead. Conclusions In this study, we describe a specially designed PAAR and successfully explored the primary clinical effect of this rod for atlantoaxial dislocation. The PAAR, with satisfactory reduction capabilities and auto anti-rotation function, is safe and effective for treating atlantoaxial dislocation and overcomes the limitations of common existing rods. In addition, this new rod is suitable for the surgical treatments of various types of atlantoaxial dislocation. Abbreviations Atlantoaxial dislocation (AAD), Posterior AtlantoAxial Reduction (PAAR), AtlantoDental Interval (ADI), Rotational Angle (RA), Japanese Orthopaedic Association (JOA) scores, Visual Analog Scale (VAS), Posterior Atlantoaxial Screw-Rod (PASR) Declarations Ethics approval and consent to participate Our institution certifies that this clinical retrospective study entitled “Development and Preliminary Clinical Application of a Novel Posterior Atlantoaxial auto Anti-Rotation Reduction Rod (PAAR)”, performed by Xiangyang Ma, Junlin Chen, Xiaobao Zou, Mandi Cai et al, had been examined by Ethical Review Committee of General Hospital of Southern Theatre Command of PLA, People’s Republic of China. All investigations were conducted in conformity with ethical principles of research. The informed consent for participation in the study was obtained. Details that might disclose the identity of the subjects under study were omitted. This study had been performed in accordance with the ethical standards in the 1964 Declaration of Helsinki. Consent for publication In accordance with ethical standards, consent for publication was obtained from all patients whose data, images, or videos are included in this manuscript. For patients under the age of 18, consent was obtained from their parent or legal guardian. The identities of the patients have been anonymized to ensure privacy and confidentiality. Competing interests The authors declare that they have no competing interests. Funding This work was supported by fund of the Guangzhou Municipal Science and Technology Project (No.2024A03J0635) and the National Natural Science Foundation of China (No.82272582). Author Contribution Xiangyang Ma conceptualized and designed the study, supervised the surgical procedures, and performed the surgical procedures was responsible for data interpretation and analysis. Junlin Chen contributed to the collection, and prepared figures analysis of clinical data. Xiaobao Zou prepared tables and drafting of the manuscript. Mandi Cai, Haozhi Yang, Rencai Ma, Zexing Chen contributed to the statistical analysis. All authors read and approved the final manuscript. Acknowledgements Not applicable. Availability of data and materials The datasets used and analysed during the current study are available from the corresponding author on reasonable request. References Yin QS, Wang JH. Current Trends in Management of Atlantoaxial Dislocation. Orthop Surg. 2015;7:189–99. Elliott RE, Tanweer O, Boah A, et al. Outcome comparison of atlantoaxial fusion with transarticular screws and screw-rod constructs: meta-analysis and review of literature. J Spin Disord Tech. 2014;27:11–28. Guan J, Chen Z, Wu H, et al. Effectiveness of posterior reduction and fixation in atlantoaxial dislocation: a retrospective cohort study of 135 patients with a treatment algorithm proposal. European spine journal: official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical. Spine Res Soc. 2019;28:1053–63. Stulik J, Vyskocil T, Sebesta P, et al. Atlantoaxial fixation using the polyaxial screw-rod system. European spine journal: official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical. Spine Res Soc. 2007;16:479–84. Guo SL, Zhou DB, Yu XG, et al. Posterior C1-C2 screw and rod instrument for reduction and fixation of basilar invagination with atlantoaxial dislocation. European spine journal: official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine. Res Soc. 2014;23:1666–72. Huang DG, Hao DJ, He BR, et al. Posterior atlantoaxial fixation: a review of all techniques. spine journal: official J North Am Spine Soc. 2015;15:2271–81. Jeanneret B, Magerl F. Primary posterior fusion C1/2 in odontoid fractures: indications, technique, and results of transarticular screw fixation. J Spinal Disord. 1992;5:464–75. Suchomel P, Stulík J, Klézl Z, et al. Transarticular fixation of C1-C2: a multicenter retrospective study. Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca. 2004;71:6–12. Goel A, Laheri V. Plate and screw fixation for atlanto-axial subluxation. Acta Neurochir. 1994;129:47–53. Goel A, Achawal S. The surgical treatment of Chiari malformation association with atlantoaxial dislocation. Br J Neurosurg. 1995;9:67–72. Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine. 2001;26:2467–71. Ma XY, Yin QS, Wu ZH, et al. Anatomic considerations for the pedicle screw placement in the first cervical vertebra. Spine. 2005;30:1519–23. Ma XY, Yin QS, Wu ZH et al. Biomechanical evaluation of four different posterior atlantoaxial screw-rod fixation techniques. Chin J Spine Spinal Cord 2008:464–8. Sinha AK, Goyal S. Myoarchitectonic advancement of the C2 spinous process for C1-C2 posterior fusion: A novel technique. J neurosciences rural Pract. 2015;6:267–71. Eshra MA. C2 pars/pedicle screws in management of craniocervical and upper cervical instability. Asian spine J. 2014;8:156–60. Davidson CT, Bergin PF, Varney ET, et al. Planning C2 pedicle screw placement with multiplanar reformatted cervical spine computed tomography. J craniovertebral junction spine. 2019;10:46–50. Wright NM. Posterior C2 fixation using bilateral, crossing C2 laminar screws: case series and technical note. J Spin Disord Tech. 2004;17:158–62. Ma XY, Yin QS, Wu ZH, et al. The clinical combination of multi C1-C2 screw-rods fixation techniques in atlantoaxial instabilit. Chin J Clin Basic Orthop Res. 2010;2:12–6. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6848247","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":485181530,"identity":"f8c2d3a3-60eb-4a7e-b442-610967e9c54f","order_by":0,"name":"Xiangyang Ma","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAu0lEQVRIiWNgGAWjYLCCBAMJHn5m5oMPiNfyoMJGRrKdLdmAaB2MD86k2Ric5zETIEq5bvsZM4nEtsM8xocZzBgYamyiCWoxO5OWBtZidpgh7QHDsbTcBoJaDiQfg2k5bsDYcJgILecftkEc1szYJkGclhtAWxLOpPEYMDOzEavlWbJFQoUNj8RhNmaDBKL8cj7H8OYPAwl7/v7zHx98qLEhrAUIWCTgzAQilIMA8wciFY6CUTAKRsFIBQB3ej9jS7tMwQAAAABJRU5ErkJggg==","orcid":"","institution":"General Hospital of Southern Theatre Command","correspondingAuthor":true,"prefix":"","firstName":"Xiangyang","middleName":"","lastName":"Ma","suffix":""},{"id":485181531,"identity":"6b209607-ea04-4eb6-93b9-6b85bac0879f","order_by":1,"name":"Junlin Chen","email":"","orcid":"","institution":"General Hospital of Southern Theatre Command","correspondingAuthor":false,"prefix":"","firstName":"Junlin","middleName":"","lastName":"Chen","suffix":""},{"id":485181532,"identity":"7d1dff26-17fd-4b97-9412-ea35047bec50","order_by":2,"name":"Xiaobao Zou","email":"","orcid":"","institution":"General Hospital of Southern Theatre Command","correspondingAuthor":false,"prefix":"","firstName":"Xiaobao","middleName":"","lastName":"Zou","suffix":""},{"id":485181533,"identity":"4561ba4b-bd04-4860-a761-6ae5f1d50d8c","order_by":3,"name":"Mandi Cai","email":"","orcid":"","institution":"General Hospital of Southern Theatre Command","correspondingAuthor":false,"prefix":"","firstName":"Mandi","middleName":"","lastName":"Cai","suffix":""},{"id":485181534,"identity":"9ff43b80-55ef-4caa-b0a1-fcfca7fef8f4","order_by":4,"name":"Haozhi Yang","email":"","orcid":"","institution":"General Hospital of Southern Theatre Command","correspondingAuthor":false,"prefix":"","firstName":"Haozhi","middleName":"","lastName":"Yang","suffix":""},{"id":485181535,"identity":"326788eb-1bec-45e1-8622-653d2a1d60d5","order_by":5,"name":"Rencai Ma","email":"","orcid":"","institution":"General Hospital of Southern Theatre Command","correspondingAuthor":false,"prefix":"","firstName":"Rencai","middleName":"","lastName":"Ma","suffix":""},{"id":485181536,"identity":"b5e61c9e-2741-4e97-88a7-5572c13f1656","order_by":6,"name":"Zexing Chen","email":"","orcid":"","institution":"General Hospital of Southern Theatre Command","correspondingAuthor":false,"prefix":"","firstName":"Zexing","middleName":"","lastName":"Chen","suffix":""}],"badges":[],"createdAt":"2025-06-08 15:08:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6848247/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6848247/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":87036619,"identity":"722378d4-b00b-4041-abab-050a196fb37b","added_by":"auto","created_at":"2025-07-18 13:21:36","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":946704,"visible":true,"origin":"","legend":"\u003cp\u003eComparison between the common rod and PAAR.\u003cstrong\u003e (a) Ⅰ. \u003c/strong\u003eCommon rod. \u003cstrong\u003eⅡ-Ⅵ\u003c/strong\u003e. Different specifications of PAAR, with different height intervals of 2mm from 0 to 8mm in sequence (A is “D” shaped, B is “O” shaped, and C is conjunction part). \u003cstrong\u003e(b) \u003c/strong\u003eComparison between the common rods' \"O\" shaped and PAARs' \"D\" shaped cross-section. PAARs' \"D\" shaped can fully match with the nut and screw slot.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6848247/v1/8129fc16ab1d0dbab011dec9.png"},{"id":87036620,"identity":"bee7e4dc-2163-4287-b9dc-cc1ebc0e8289","added_by":"auto","created_at":"2025-07-18 13:21:36","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1037675,"visible":true,"origin":"","legend":"\u003cp\u003eAtlantoaxial anterior dislocation reduction process (A), Atlantoaxial posterior dislocation reduction process(B), Atlantoaxial rotation dislocation reduction process(C)\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6848247/v1/bd080e4da7c2ad7854c07fd1.png"},{"id":87036631,"identity":"4bee2f78-b377-4ebb-b46f-8af80ffa5de5","added_by":"auto","created_at":"2025-07-18 13:21:36","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":842107,"visible":true,"origin":"","legend":"\u003cp\u003eCase 1,\u003cstrong\u003e \u003c/strong\u003ea 55-year-old male with single anterioratlantoaxial dislocation underwent posterior atlantoaxial reduction and fusion fixation. \u003cstrong\u003e(a, b)\u003c/strong\u003e The preoperative X-rays showed atlantoaxial dislocation. \u003cstrong\u003e(c, d) \u003c/strong\u003eSagittal CT scan and MRI showed atlantoaxial dislocation with lightly compression of the spinal cord. \u003cstrong\u003e(e, f) \u003c/strong\u003eThe \"Z\" shaped reduction and fixation rod was used for intraoperative reduction (see arrow) and obtained ideal reduction. \u003cstrong\u003e(g, h, i, j) \u003c/strong\u003ePostoperative X-ray, CT and MRI showed satisfying sequence and spinal cord decompression.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6848247/v1/620ae83a3070facc94c2de99.png"},{"id":87036623,"identity":"aaf3c41e-2923-4a50-bda3-6a8be2b4e873","added_by":"auto","created_at":"2025-07-18 13:21:36","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":684029,"visible":true,"origin":"","legend":"\u003cp\u003eCase 2,\u003cstrong\u003e \u003c/strong\u003ea 4-year-old female with single rotatory atlantoaxial dislocation underwent posterior atlantoaxial reduction and temporary fixation without fusion . \u003cstrong\u003e(a, b)\u003c/strong\u003e The preoperative X-rays showed atlantoaxial dislocation. \u003cstrong\u003e(c, d) \u003c/strong\u003eAxial and Sagittal CT scan showed atlantoaxial dislocation. \u003cstrong\u003e(e, f) \u003c/strong\u003eThe \"Z\" shaped reduction and fixation rod was used for intraoperative reduction (see arrow) and obtained ideal reduction. \u003cstrong\u003e(g, h, i, j) \u003c/strong\u003ePostoperative X-ray and CT showed satisfying sequence .\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6848247/v1/405d293394f57f28e1214629.png"},{"id":87038523,"identity":"1e83e554-3550-43f5-8619-c2bbaf0c9d79","added_by":"auto","created_at":"2025-07-18 13:29:36","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":2061941,"visible":true,"origin":"","legend":"\u003cp\u003eCase 3,\u003cstrong\u003e \u003c/strong\u003ea 51-year-old disorder of consciousness male with type III fresh odontoid fracture and posterior atlantoaxial dislocation underwent posterior atlantoaxial reduction and non-fusion fixation. \u003cstrong\u003e(a, b)\u003c/strong\u003e The preoperative X-rays and Sagittal CT scan showed odontoid fracture and atlantoaxial dislocation. \u003cstrong\u003e(c, d, e) \u003c/strong\u003eThe \"Z\" shaped reduction and fixation rod was used for intraoperative reduction (see arrow) and obtained ideal reduction. \u003cstrong\u003e(f, g, h) \u003c/strong\u003ePostoperative X-ray and CT showed satisfying sequence.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6848247/v1/311ae39b8ebbcfe5db4a7096.png"},{"id":87041004,"identity":"9c669383-ef5d-48fd-88f3-01ce6e497ec9","added_by":"auto","created_at":"2025-07-18 13:53:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8375373,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6848247/v1/09e43ba5-db9b-4b36-a082-1252b23b38ce.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Development and Preliminary Clinical Application of a Novel Posterior Atlantoaxial auto Anti-Rotation Reduction Rod (PAAR)","fulltext":[{"header":"Background","content":"\u003cp\u003eAtlantoaxial dislocation is a common disorder of the upper cervical spine with various pathological factors such as congenital anomalies, trauma, inflammation, and tumors. This condition often leads to the spinal cord compression at the corresponding segment and produces symptoms of neurological dysfunction. More severely, it can be life-threatening and usually requires surgical treatment aimed at reduction, decompression, and stability reconstruction\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. By confining the fixation segment only within the atlantoaxial joint, posterior atlantoaxial screw-rod systems (PASR) can provide a rigid fixation without sacrificing the motion of occipitocervical junction. In addition, the inherent reduction function of PASR, which can further improve the reduction efficacy for atlantoaxial dislocation, makes it become the mainstream technique for posterior atlantoaxial reduction and fixation and the golden standard procedure for atlantoaxial dislocation\u003csup\u003e\u003cspan additionalcitationids=\"CR3 CR4 CR5\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. However, common PASR have limited reduction capabilities, and the rod is prone to rotation during the reducing process, leading to insufficient reduction force transmission. Meantime, the potential for spinal cord injuries increases due to the need for additional tools to adjust rods. Moreover, for posterior or rotational atlantoaxial dislocations, common PASR fail to achieve effective reduction. To solve these problems, we designed a novel PAAR with multi-gradient reduction function and auto anti-rotation feature. This study aimed to characterize this novel rod and to evaluate its preliminary clinical efficacy.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eDesign of the PAAR\u003c/h2\u003e\u003cp\u003eThe structure of the PAAR is designed as a \"Z\" shape and consists of three parts. One end of the rod is 15 mm long with a \"D\" shaped cross-section for anti-rotation (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA), and the other end is 35mm long with an \"O\" shaped cross-section that can be cut as needed during surgery (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). The two ends are connected by a vertical connector available in various lengths from 0 to 8 mm (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eClinical Data\u003c/h3\u003e\n\u003cp\u003eA total of 11 patients (7 male and 4 female) with a mean age of 32.4 (4\u0026ndash;55) years who underwent posterior atlantoaxial surgery using PAAR were retrospectively reviewed (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Of the 11 cases, 8 cases were anterior atlantoaxial dislocation, 1 case was posterior atlantoaxial dislocation and 2 cases were rotational atlantoaxial dislocation. Six patients reported occipitocervical pain and five patients had neurological impairment symptoms at different degrees including numbness and weakness of limbs. The compression of spinal cord at C1-C2 level was revealed in 6 cases by preoperative MRI.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eData of 11 patients who underwent posterior atlantoaxial reduction, fixation and fusion using PAAR.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"7\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCase\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eGender\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eAge\u003c/p\u003e\u003cp\u003e(yrs)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSurgical time\u003c/p\u003e\u003cp\u003e(mins)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eBL\u003c/p\u003e\u003cp\u003e(ml)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eFollow up duration (months)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eDirection of dislocation\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e120\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003eanterior\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003eanterior\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e47\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e125\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003eanterior\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e55\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e95\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003eanterior\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e105\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003eanterior\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e53\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e115\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e130\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003eanterior\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e41\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e120\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003eanterior\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e39\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e110\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003eanterior\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e127\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e120\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003eposterior\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e115\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003erotatory\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e41\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e110\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e75\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003erotatory\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eMean\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e34.6\u0026thinsp;\u0026plusmn;\u0026thinsp;20.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e`112\u0026thinsp;\u0026plusmn;\u0026thinsp;11.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e79.1\u0026thinsp;\u0026plusmn;\u0026thinsp;32.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e13.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"7\" nameend=\"c7\" namest=\"c1\"\u003e\u003cp\u003eBL, blood loss.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\n\u003ch3\u003eSurgical Procedure\u003c/h3\u003e\n\u003cp\u003eAfter general anesthesia, appropriate weight skull traction was performed and maintained during the surgery, the patient was placed in a prone position with proper cervical flexion. A median longitudinal incision of 6-8cm was made from the occipital eminence to the C2 spinous process. Subperiosteal dissection exposed occipital bone, C1 posterior arch and C2 lateral mass. Retain the attachment of the cervical semispinalis muscle to the C2 spinous process. C1 and C2 preferred pedicle screws, lateral mass screws could be replaced when preoperative imaging evaluation finding it difficult or not safe to place pedicle screws.\u003c/p\u003e\u003cp\u003eTwo PAARs with the suitable gradients were selected and cut to the appropriate length for placements. For anterior dislocation, placed the \"D\" end into the C2 screw slot and the \"O\" end into the C1 screw slot. First tightened the C2 screw nut, then tightened the C1 screw nut and pulled C1 to complete the reduction (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). For posterior dislocation, put the \"D\" end into the C1 screw slot and the \"O\" end into the C2 screw slot. First tightened the C1 screw nut, and then tightened the C2 screw nut to complete the reduction as this push C1 forward (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). For rotational dislocation, the reduction procedure of the anterior rotation side was the same as that of the anterior dislocation, and the reduction procedure of the posterior rotation side was also same as that of the posterior dislocation (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). If the reduction was not ideal, replaced a larger gradient rod until obtaining ideal result. Grinding drill was used to grind the posterior arch of atlas and axial lamina to prepare the bone graft bed, and took autogenous iliac cancellous bone for grafting (non-fusion surgery does not need this procedure). Placed negative pressure drainage tube and suture the wound layer by layer.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\n\u003ch3\u003eObserved indexes and Follow-up\u003c/h3\u003e\n\u003cp\u003eThe surgical time and blood loss (BL) were recorded. Atlantodental interval (ADI) were measured before and after surgery to assess reduction of anterior and posterior dislocation. Rotational angle (RA) was measured before and after surgery to evaluate reduction of rotational dislocation. Japanese Orthopaedic Association (JOA) scores was used to assess neurological function. And the Visual analog scale (VAS) was used to assess the degree of occipital neck pain. Patients were followed up at 3, 6, 9 and 12 months, then once per year or as needed. Surgical complications were documented after surgery and during the follow-up. Cervical X-rays and CT scans were performed at each follow-up for assessment of internal fixations failure, stability, and bone fusion.\u003c/p\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003eStatistical Analysis\u003c/h2\u003e\u003cp\u003eNormality of numeric data was assessed by Shapiro-Wilk test. For numeric data with normal distribution, paired t test was used to compare pre- and post-operative change. Wilcoxon ranks test was used to compare difference for numeric data without normality. All statistical analyses were performed by SPSS 26.0 (IBM, Armonk, NY) and P\u0026lt;0.05 meant statistically significant difference.\u003c/p\u003e\u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eAll patients successfully underwent posterior reduction and fixation surgery with PAAR, including 5 cases with non-fusion surgery and 6 cases with fusion surgery. The average surgery time was 110.5 minutes (ranged 90.0-120.0 minutes), with an average blood loss (BL) of 75 ml (ranged 30.0-130.0 ml). No spinal cord or vertebral artery injuries occurred during surgery. Postoperative X-rays and CT scans showed satisfactory reduction in all 11 cases, and MRI revealed complete decompression in 6 patients with preoperative spinal cord compression. Neurological symptoms and occipital cervical pain improved in all patients. At the last follow-up, JOA scores improved significantly from an average of 12.4 (range 6\u0026ndash;16) preoperatively to 15.9 (range 13\u0026ndash;17), occipital cervical VAS scores significantly reduced from an average of 3.8 (range 2\u0026ndash;6) preoperatively to 0.8 (range 0\u0026ndash;2) and the atlantodental interval (ADI) decreased from an average of 5.9 mm (range 2.3\u0026ndash;15.4 mm) preoperatively to 1.8 mm (range 1.0-2.5 mm); Besides, Rotational angle (RA) decreased from an average of 40\u0026deg; preoperatively to 4\u0026deg;(Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). CT scans during the follow-up showed bone graft fusion in all 6 patients underwent fusion surgeries, and 5 cases with odontoid fractures achieved fracture healing. No fixation loosening or re-dislocation was observed in X-rays and CT scans during the follow-up period. All 11 patients had remarkable clinical benefit after surgery without internal fixation failure confirmed by radiological outcomes, which shows PAAR is safe and effective for the treatment of atlantoaxial dislocation.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eComparison of outcomes before and after operation.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"9\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eCase\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e\u003cp\u003eCervical JOA score\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e\u003cp\u003eOccipitocervical VAS\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003eADI(mm)/RA(\u0026deg;)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePre-op\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eF/U\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eIR (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003ePre-op\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eF/U\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eIR (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003ePre-op\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eF/U\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e83.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e4.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e2.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e60.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e6.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e2.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e83.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e5.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1.6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e80.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e75.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e5.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1.2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e63.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e60.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e7.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e2.1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e80.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e60.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e5.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e2.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e85.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e75.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e15.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1.4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e-6.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e-1.4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e71.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e14.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e45.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e5.1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eMean\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e12.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e15.9\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e84.1\u0026thinsp;\u0026plusmn;\u0026thinsp;15.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e3.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e83.7\u0026thinsp;\u0026plusmn;\u0026thinsp;16.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eP\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e\u003cp\u003e0.005*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e\u003cp\u003e0.004*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e0.005*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"9\" nameend=\"c9\" namest=\"c1\"\u003e\u003cp\u003eJOA, Japanese Orthopsedic Association; VAS, visual analog scale; ADI, atlanto-dental interval; RA, mutual C1-C2 rotational angle.Pre-op, pre-operation; F/U, the last follow up; IR, improvement rate;\u003c/p\u003e\u003cp\u003e*Wilcoxon ranks test, and p\u0026lt;0.05 means statistically significant difference.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe C1/C2 transarticular screw fixation, also known as the Magerl technique, was once considered the gold standard for treating atlantoaxial dislocation due to its rigid fixation capabilities before the emergence of posterior atlantoaxial screw-rod systems\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. However, the Magerl technique lacks the ability to reduce dislocations and requires anatomical reduction of the atlantoaxial joint before screw insertion. In addition, it is difficult to place transarticular screw during surgery, and intraoperative X-ray fluoroscopy is needed repeatedly in the preparation process of the screw path. Therefore, Magerl technique is gradually replaced by the PASR (also known as Goel-Harms technique)\u003csup\u003e\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. With its capability for reduction, the PASR is now widely used in the treatment of atlantoaxial dislocation\u003csup\u003e\u003cspan additionalcitationids=\"CR13 CR14 CR15 CR16 CR17\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThe common posterior atlantoaxial screw-rod system's capability for reduction is based on the height difference between the C1 and C2 screws in the sagittal plane. The reduction is achieved by connecting the C1 and C2 screws with a rod to eliminate this height drop and generate reverse forces. While increasing the rod's curvature can enhance the reduction forces by increasing the height difference, but the rod cannot be bent indefinitely. Meantime, excessive curvature will cause the rod to rotate easily and make it difficult to place. Conversely, insufficient curvature can result in failed reduction. These all reflect the limited reduction capacity of the existing screw-rod system.\u003c/p\u003e\u003cp\u003eThe PAAR overcomes these limitations by determining the height difference through the length of the vertically connecting part (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC), allowing for the required height difference without bending. Theoretically, the length of the connector is unlimited, completely overcoming the issue of finite bending of common rods. Regardless of the specification, the two ends of the PAAR remain parallel that will not increase the difficulty of placements. Different specifications of PAAR can provide varying reduction forces, allowing surgeons to choose the appropriate rod based on intraoperative X-ray. PAAR effectively reduces the time of repeatedly adjusting the rod curvature and fluoroscopy times. If the reduction is insufficient, a new rod with a larger height difference could be replaced for a stronger reduction force. For over-reduction, replacing a smaller height difference rod or reversing the rod direction can eliminate the extra reduction.\u003c/p\u003e\u003cp\u003eCommon rods are prone to rotation during the placement that requiring auxiliary instruments to secure and maintain their orientation. However, the surgical area for atlantoaxial surgeries is narrow, and without bony structures protecting the spinal cord between C1 and C2. These make the use of auxiliary instruments likely to accidentally injury the spinal cord during surgery. The \"D\" shaped design at one end of the PAAR has an automatic anti-rotation function. Compared to the common rods' \"O\" shaped cross-section, the \"D\" shaped end can fully match with the nut and screw slot (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e-b). When tightening the nut at the \"D\" shaped end, there is no need for auxiliary instruments, and the rod will not rotate, allowing it to be fixed at the predetermined position. The design of the \"D\" shaped end not only simplifies the rod placement process but also enhances the safety of posterior atlantoaxial reduction process. Considering that the C1 and C2 screws are usually not on the same sagittal plane, the other end of the rod remains \"O\" shape to facilitate insertion into the screw slot. Moreover, the \"O\" shaped end of this PAAR is long enough to be cut as needed.\u003c/p\u003e\u003cp\u003eThe common PASR is primarily used to treat anterior atlantoaxial dislocation and achieves reduction by using the C2 screw as a fulcrum, tightening the C1 and C2 screws in sequence to pull the atlas backward. However, for posterior or rotational dislocations requiring reverse movement of the atlas, common rods cannot provide the necessary corresponding height difference. This issue is resolved by reversing the placement direction of the PAAR which creating an opposite height difference for forward movement capability. For posterior dislocation, reversing the rod enables forward movement of C1 to achieve reduction. As for rotational dislocation, the reduction steps for the anterior rotation side are the same as for anterior dislocation, while those for the posterior rotation side are the same as for posterior dislocation. Therefore, the PAAR is applicable not only for common anterior dislocations but also for various types of dislocations.\u003c/p\u003e\u003cp\u003eIn the practice of clinical PAAR applications, it was found that C1 was prone to rotation during the reduction process if lamina screws were used for C2, which is related to the large distance between C2 lamina screw and C1 screw in sagittal plane. So the C2 lamina screw cannot serve as a fulcrum for PAAR but only as auxiliary fixation after reduction. For the surgical treatment of atlantoaxial dislocations, the C2 pedicle screw should be the first choice. When pedicle screws are not appropriate, lateral mass screws or pars screws may be used instead.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn this study, we describe a specially designed PAAR and successfully explored the primary clinical effect of this rod for atlantoaxial dislocation. The PAAR, with satisfactory reduction capabilities and auto anti-rotation function, is safe and effective for treating atlantoaxial dislocation and overcomes the limitations of common existing rods. In addition, this new rod is suitable for the surgical treatments of various types of atlantoaxial dislocation.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eAtlantoaxial dislocation (AAD), Posterior AtlantoAxial Reduction (PAAR), AtlantoDental Interval (ADI), Rotational Angle (RA), Japanese Orthopaedic Association (JOA) scores, Visual Analog Scale (VAS), Posterior Atlantoaxial Screw-Rod (PASR)\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003cp\u003e Our institution certifies that this clinical retrospective study entitled \u0026ldquo;Development and Preliminary Clinical Application of a Novel Posterior Atlantoaxial auto Anti-Rotation Reduction Rod (PAAR)\u0026rdquo;, performed by Xiangyang Ma, Junlin Chen, Xiaobao Zou, Mandi Cai et al, had been examined by Ethical Review Committee of General Hospital of Southern Theatre Command of PLA, People\u0026rsquo;s Republic of China. All investigations were conducted in conformity with ethical principles of research. The informed consent for participation in the study was obtained. Details that might disclose the identity of the subjects under study were omitted. This study had been performed in accordance with the ethical standards in the 1964 Declaration of Helsinki.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003cp\u003e In accordance with ethical standards, consent for publication was obtained from all patients whose data, images, or videos are included in this manuscript. For patients under the age of 18, consent was obtained from their parent or legal guardian. The identities of the patients have been anonymized to ensure privacy and confidentiality.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003ch2\u003eCompeting interests\u003c/h2\u003e\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThis work was supported by fund of the Guangzhou Municipal Science and Technology Project (No.2024A03J0635) and the National Natural Science Foundation of China (No.82272582).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eXiangyang Ma conceptualized and designed the study, supervised the surgical procedures, and performed the surgical procedures was responsible for data interpretation and analysis. Junlin Chen contributed to the collection, and prepared figures analysis of clinical data. Xiaobao Zou prepared tables and drafting of the manuscript. Mandi Cai, Haozhi Yang, Rencai Ma, Zexing Chen contributed to the statistical analysis. All authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e\u003cp\u003eNot applicable.\u003c/p\u003e\u003ch2\u003eAvailability of data and materials\u003c/h2\u003e\u003cp\u003eThe datasets used and analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eYin QS, Wang JH. Current Trends in Management of Atlantoaxial Dislocation. Orthop Surg. 2015;7:189\u0026ndash;99.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eElliott RE, Tanweer O, Boah A, et al. Outcome comparison of atlantoaxial fusion with transarticular screws and screw-rod constructs: meta-analysis and review of literature. J Spin Disord Tech. 2014;27:11\u0026ndash;28.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGuan J, Chen Z, Wu H, et al. Effectiveness of posterior reduction and fixation in atlantoaxial dislocation: a retrospective cohort study of 135 patients with a treatment algorithm proposal. European spine journal: official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical. Spine Res Soc. 2019;28:1053\u0026ndash;63.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eStulik J, Vyskocil T, Sebesta P, et al. Atlantoaxial fixation using the polyaxial screw-rod system. European spine journal: official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical. Spine Res Soc. 2007;16:479\u0026ndash;84.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGuo SL, Zhou DB, Yu XG, et al. Posterior C1-C2 screw and rod instrument for reduction and fixation of basilar invagination with atlantoaxial dislocation. European spine journal: official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine. Res Soc. 2014;23:1666\u0026ndash;72.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHuang DG, Hao DJ, He BR, et al. Posterior atlantoaxial fixation: a review of all techniques. spine journal: official J North Am Spine Soc. 2015;15:2271\u0026ndash;81.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJeanneret B, Magerl F. Primary posterior fusion C1/2 in odontoid fractures: indications, technique, and results of transarticular screw fixation. J Spinal Disord. 1992;5:464\u0026ndash;75.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSuchomel P, Stul\u0026iacute;k J, Kl\u0026eacute;zl Z, et al. Transarticular fixation of C1-C2: a multicenter retrospective study. Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca. 2004;71:6\u0026ndash;12.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGoel A, Laheri V. Plate and screw fixation for atlanto-axial subluxation. Acta Neurochir. 1994;129:47\u0026ndash;53.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGoel A, Achawal S. The surgical treatment of Chiari malformation association with atlantoaxial dislocation. Br J Neurosurg. 1995;9:67\u0026ndash;72.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHarms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine. 2001;26:2467\u0026ndash;71.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMa XY, Yin QS, Wu ZH, et al. Anatomic considerations for the pedicle screw placement in the first cervical vertebra. Spine. 2005;30:1519\u0026ndash;23.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMa XY, Yin QS, Wu ZH et al. Biomechanical evaluation of four different posterior atlantoaxial screw-rod fixation techniques. Chin J Spine Spinal Cord 2008:464\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSinha AK, Goyal S. Myoarchitectonic advancement of the C2 spinous process for C1-C2 posterior fusion: A novel technique. J neurosciences rural Pract. 2015;6:267\u0026ndash;71.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eEshra MA. C2 pars/pedicle screws in management of craniocervical and upper cervical instability. Asian spine J. 2014;8:156\u0026ndash;60.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDavidson CT, Bergin PF, Varney ET, et al. Planning C2 pedicle screw placement with multiplanar reformatted cervical spine computed tomography. J craniovertebral junction spine. 2019;10:46\u0026ndash;50.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWright NM. Posterior C2 fixation using bilateral, crossing C2 laminar screws: case series and technical note. J Spin Disord Tech. 2004;17:158\u0026ndash;62.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMa XY, Yin QS, Wu ZH, et al. The clinical combination of multi C1-C2 screw-rods fixation techniques in atlantoaxial instabilit. Chin J Clin Basic Orthop Res. 2010;2:12\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Atlantoaxial dislocation, Posterior atlantoaxial reduction, Auto anti-rotation","lastPublishedDoi":"10.21203/rs.3.rs-6848247/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6848247/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground: \u003c/strong\u003eAtlantoaxial dislocation (AAD) is a common upper cervical spine disorder caused by various factors, including trauma, congenital anomalies, and inflammation, which can lead to spinal cord compression and neurological dysfunction. The posterior atlantoaxial screw-rod (PASR) system, though widely used for reduction and fixation, has limitations such as insufficient reduction force and potential spinal cord injury due to rod rotation. This study aimed to evaluate a novel posterior atlantoaxial reduction (PAAR) system with enhanced reduction capabilities and an auto anti-rotation feature.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods:\u003c/strong\u003e This was a retrospective study involving 11 patients who underwent posterior atlantoaxial surgery using the PAAR system. The patients' demographic data, dislocation types, surgical time, and blood loss were recorded. Pre- and post-operative measurements of the atlantodental interval (ADI), rotational angle (RA), neurological function, and occipital cervical pain were assessed. Statistical analysis was performed using paired t-test and Wilcoxon ranks test to evaluate significant differences between preoperative and postoperative outcomes.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults:\u003c/strong\u003e The PAAR system demonstrated excellent reduction capabilities in all patients, with satisfactory outcomes for anterior, posterior, and rotational dislocations. The average surgical time was 110.5 minutes, and the average blood loss was 75 ml. Significant improvements were observed in the Japanese Orthopaedic Association (JOA) scores, Visual Analog Scale (VAS) scores for occipital cervical pain, ADI, and RA (P \u0026lt; 0.05). Additionally, MRI and CT scans showed complete decompression and stable fixation without complications.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions:\u003c/strong\u003e The novel PAAR system provides effective reduction and fixation for various types of atlantoaxial dislocations. Its auto anti-rotation function and versatile design overcome the limitations of traditional PASR systems, offering a safe and efficient treatment option for patients with atlantoaxial dislocation. This approach may help improve clinical outcomes and reduce surgical complications.\u003c/p\u003e","manuscriptTitle":"Development and Preliminary Clinical Application of a Novel Posterior Atlantoaxial auto Anti-Rotation Reduction Rod (PAAR)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-18 13:21:31","doi":"10.21203/rs.3.rs-6848247/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"57a1162e-2259-4bcc-b2f6-22c2241e0160","owner":[],"postedDate":"July 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-07-18T13:21:33+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-18 13:21:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6848247","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6848247","identity":"rs-6848247","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}