Unexpected Neurological Deterioration Following Occipitocervical Fusion Surgery

Unexpected Neurological Deterioration Following Occipitocervical Fusion Surgery | 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 Case Report Unexpected Neurological Deterioration Following Occipitocervical Fusion Surgery Takane Nakagawa, Hiroshi Takahashi, Kousei Miura, Hisanori Gamada, and 7 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5340263/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 27 Jan, 2025 Read the published version in Cureus → Version 1 posted You are reading this latest preprint version Abstract Background Occipitocervical posterior decompression and fusion (O-C fusion) surgery is occasionally required for treating high cervical myelopathy due to atlantoaxial subluxation. The advance of the instrumentation systems has led to favorable clinical outcomes following O-C fusion surgery. However, the rate of perioperative complications in O-C fusion surgery is relatively high, including instrumentation failure, respiratory complications, and dysphagia. Here we report a rare case involving an unexpected deterioration of myelopathy following O-C fusion surgery. Case presentation: A 49-year-old male was transported to our hospital by ambulance with left-sided upper and lower limb paralysis. At the initial visit, a neurological examination revealed left upper limb weakness (MMT grade 2). X-ray and CT revealed severe atlantoaxial subluxation due to Os Odontoideum, while MRI revealed significant spinal cord compression at the C2 level. On the diagnosis of acute exacerbation of high cervical myelopathy, an O-C2 posterior decompression and fusion surgery including C1 laminectomy was performed. Postoperatively, the patient exhibited a deterioration in right-sided upper limb paralysis (MMT grade 2), despite proper implant placement confirmed by CT. During two weeks postoperatively, there was no improvement in the right-sided upper limb paralysis, and bilateral deep sensory impairment worsened. Follow-up X-rays revealed a progressive decrease in the O-C2 angle and dynamic X-ray imaging demonstrated a recurrence of instability at the O-C2 level. On the diagnosis of the instrumentation failure, a revision surgery was performed 3 weeks after the primary surgery. Intraoperative findings revealed instability at the C2 screw head and loosening of the set screw on the C2 screw head. To achieve a more secure fixation, we extended the fusion to C4 with a triple rod connection. Following the revision surgery, his myelopathy and paralysis gradually improved. At the final follow-up 6 months after surgery, X-rays showed that O-C2 was firmly stabilized. Conclusions In O-C fusion surgery, screw head fixation close to the O-C rod bending site may result in unexpected instrumentation failure. occipitocervial fusion surgery Os Odontoideum instrumentation failure Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Background Occipitocervical posterior decompression and fusion (O-C fusion) surgery is occasionally required to treat high cervical myelopathy associated with atlantoaxial subluxation. Recent advancements in instrumentation techniques have contributed to improved clinical outcomes[ 1 , 2 ]. Nevertheless, the rate of perioperative complications in this procedure is relatively high, including instrumentation failure, respiratory complications, and dysphagia[ 3 – 7 ]. Here we report a rare case involving an unexpected deterioration of myelopathy following O-C fusion surgery. Case Presentation A 49-year-old Japanese man was transported to our hospital by ambulance after experiencing a loss of consciousness and weakness in his left upper and lower limbs while working. At the initial examination, manual muscle testing (MMT) revealed grade 2 muscle weakness in the distal muscles of the left upper limb, while the lower limbs exhibited no detectable muscle weakness. Superficial sensation remained intact, and deep tendon reflexes were hyperactive in all four extremities. The Japanese Orthopaedic Association (JOA) score for cervical myelopathy was 6 points out of 17. X-ray revealed significant instability, with an O-C2 angle measuring − 11.3° at flexion and 33.8° at extension (Fig. 1 A). Computed Tomography (CT) revealed the presence of Os Odontoideum and atlantoaxial subluxation. Magnetic Resonance Imaging (MRI) demonstrated anterior spinal cord compression and intramedullary T2 high-signal-change at the C2 level (Fig. 1 B). On the diagnosis of acute exacerbation of high cervical myelopathy due to atlantoaxial subluxation associated with Os Odontoideum, O-C fusion surgery was performed (Fig. 2 A). The surgery was involved in the removal of the C1 posterior arch, insertion of bilateral C2 pedicle screws, placement of an occipital plate, manual reduction of the C1/2 subluxation, fixation with 3.5mm diameter rods, and iliac bone grafting. Postoperatively, the patient was managed with intubation in the High Care Unit based on the anesthesiologist’s decision, and was extubated the following day. Neurological evaluation conducted the day after surgery revealed progression of paralysis in bilateral upper limbs (MMT: left upper limb grade 3, right upper limb grade 2) and deep sensory disturbances in both lower extremities. The JOA score for cervical myelopathy was deteriorated to 3.5 points out of 17. Postoperative CT revealed no issues with screw positioning. Despite additional support with a Philadelphia neck collar immobilization, there was no improvement in paralysis. At one week after the surgery, muscle weakness in the right lower limb and bilateral deep sensory disturbances worsened. Postoperative MRI revealed persistent anterior spinal cord compression at the C2 level despite intraoperative reduction of C1/2 (Fig. 2 B). Upon serial examination of postoperative X-rays, a gradual loss of correction was observed in the O-C2 angle over time. The intermediate lateral view demonstrated an O-C2 angle of 15.7° immediately post-surgery, which decreased to 8.3° at one week, and further reduced to 2.2° at two weeks postoperatively (Fig. 3 A, B). Furthermore, dynamic X-ray imaging at three weeks postoperatively demonstrated an O-C2 angle of -1.3° at flexion and 8.2° at extension. Notably these images revealed evident instability of the C2 pedicle screw heads during flexion-extension, suggesting fixation failure (Fig. 3 C, D). Given these findings, a revision surgery was performed three weeks following the initial surgery. Intraoperative findings revealed that the C2 screw heads were unstable due to their attachment at the rod bending points, and the set screws were loosened (Fig. 4 A). All implants were removed and replaced with a 4.0mm rod system, additional lateral mass screws were placed in C3 and C4, and the O-C2 angle was adjusted and secured with additional rods for reinforcement (Fig. 4 B). After the revision surgery, his paralysis of lower extremities gradually improved (MMT: right upper limb 3, left upper limb 4 at two weeks). Furthermore, his deep sensory disturbances also improved, allowing the patient to start gait training. Postoperative X-ray demonstrated adequate reduction with an O-C2 angle of 25 degrees (Fig. 4 C). MRI revealed an expansion of the posterior subarachnoid space, indicating successful posterior decompression of the spinal cord (Fig. 4 D). At the final follow-up one year after surgery, the JOA score for cervical myelopathy improved to 10 points out of 17. The O-C2 angle was maintained without loss of correction, indicating posterior fusion (Fig. 5 ). Discussion While reports of instrumentation failure in O-C fusion surgery, such as rod fracture and screw loosening or breakage, are occasionally observed in the literature[ 4 ], to our knowledge, there have been no reports of instrumentation failure due to loosening of the set screws at the screw heads, as encountered in the present case. During the initial surgery, the set screws were tightened to the appropriate torque, and sufficient fixation was achieved intraoperatively. Nevertheless, in the present case, set screw loosening occurred in the early postoperative phase. We hypothesized that this phenomenon was caused by the attachment of the C2 set screws at the rod bending sites. In O-C fusion surgery, it is reported that an inappropriately small O-C2 angle can lead to dysphagia and respiratory complications[ 3 ]. However, attempting to increase the O-C2 angle inevitably brings the C2 screw heads closer to the rod bending sites. In addition, steep rod bending is often required to increase the O-C2 angle. Consequently, the set screws may not be able to adequately secure the rod at the screw head, leading to insufficient fixation. Therefore, in cases requiring a large O-C2 angle, it is important to be aware of the potential for the C2 screw heads to be positioned close to the rod bending sites, as observed in the present case (Fig. 6 ). During the revision surgery for the present case, we extended the fixation to C4 and reinforced the instrumentation with a triple rod system to achieve more reliable and robust fixation. In O-C fusion surgery, there are some reports discussing methods to reinforce the instrumentation to prevent early instrumentation failure[ 8 ]. In retrospect, for cases with severe instability like the present case, it might have been better to increase the number of fixation anchors during the initial surgery[ 9 ]. Conclusion In O-C fusion surgery, particularly in cases requiring a large O-C2 angle, it is crucial to be aware that set screw fixation at the rod bending sites can lead to unexpected early instrumentation failure. Careful consideration of rod application is essential to prevent this phenomenon. Abbreviations MMT Manual Muscle Testing JOA Japanese Orthopaedic Association CT Computed Tomography MRI Magnetic Resonance Imaging Declarations Ethical approval and consent to participate Written informed consent was obtained from all the participants. This study was approved by the Institutional Review Board of our institution (R06-110, Institutional Review Board of the University of Tsukuba Hospital). Availability of data and materials The datasets used during the current study are available from the corresponding author on reasonable request. Consent for publication Not applicable. Competing interests The authors declare that they have no competing interests. Funding This research did not receive any specific grant funding agencies in the public, commercial, or not-for-profit sectors. Author’s contributions Conceptualization: TN, HT, MK Data curation: TN, HT, KM, HN, TF Formal analysis: KM, HN Funding acquisition: HT, MK Investigation: TN, KM, HG, SO, KS, TS, YO Methodology: HT, HN, TF Project administration: HT, KM, HN, TF Resources: HG, SO, KS, TS, YO Software: HG, SO, KS, TS, YO Supervision: HT, HN, TF, MK Validation: KM, HG, SO Visualization: TN, KM Writing – Original Draft: TN Writing – review and editing: All the authors reviewed and edited the manuscript. Acknowledgments Portions of this work were presented at the 14th Annual Meeting of the Cervical Spine Research Society Asia Pacific Section, Shangri-La, Singapore, March 22-24, 2024. References Joaquim AF, Osorio JA, Riew KD. Occipitocervical Fixation: General Considerations and Surgical Technique. Global Spine J. 2020;10(5):647-656. doi: 10.1177/2192568219877878 Winegar CD, Lawrence JP, Friel BC, Fernandez C, Hong J, Maltenfort M, Anderson PA, Vaccaro AR. A systematic review of occipital cervical fusion: techniques and outcomes. J Neurosurg Spine. 2010;13(1):5-16. doi: 10.3171/2010.3.Spine08143 Miyata M, Neo M, Fujibayashi S, Ito H, Takemoto M, Nakamura T. O-C2 angle as a predictor of dyspnea and/or dysphagia after occipitocervical fusion. Spine (Phila Pa 1976). 2009;34(2):184-188. doi: 10.1097/BRS.0b013e31818ff64e Yang DS, Patel SA, DiSilvestro KJ, Li NY, Daniels AH. Postoperative complication rates and hazards-model survival analysis of revision surgery following occipitocervical and atlanto-axial fusion. N Am Spine Soc J. 2020;3:100017. doi: 10.1016/j.xnsj.2020.100017 Zileli M, Akıntürk N. Complications of occipitocervical fixation: retrospective review of 128 patients with 5-year mean follow-up. Eur Spine J. 2022;31(2):311-326. doi: 10.1007/s00586-021-07037-2 Liu G, Li Q, Sheng F, Xu N, Li M, Wang Y, Ma W. Outcomes of occipitocervical fixation using a spinous process screw in C2 as a third anchor point for occipitocervical fixation: a case presentation. BMC Musculoskelet Disord. 2020;21(1):307. doi: 10.1186/s12891-020-03258-6 Chen H, Lian P, Tu Q, Wang J, Ma X, Ai F, Yi H, Xia H, Zhu C. Incidences, causes and risk factors of unplanned reoperation within 30 days of craniovertebral junction surgery: a single-center experience. Eur Spine J. 2023;32(6):2157-2163. doi: 10.1007/s00586-023-07729-x Collins AP, Mumtaz M, Tripathi S, Varier SK, Turner AW, Clark AJ, Goel VK, Theologis AA. Multirod posterior occipitocervical instrumentation constructs: a biomechanical analysis and initial case series of 10 patients with complex craniocervical pathology. Spine J. 2024;in press. doi: 10.1016/j.spinee.2024.09.022 Eto F, Takahashi H, Funayama T, Koda M, Yamazaki M. A Novel Technique for Occipitocervical Fusion with Triple Rod Connection to Prevent Implant Failure. Cureus. 2022;14(5):e24821. doi: 10.7759/cureus.24821 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 27 Jan, 2025 Read the published version in Cureus → 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. 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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-5340263","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":371717196,"identity":"8a905399-ab18-4181-80f9-7ea56a8f6bbe","order_by":0,"name":"Takane 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Tsukuba","correspondingAuthor":false,"prefix":"","firstName":"Masao","middleName":"","lastName":"Koda","suffix":""}],"badges":[],"createdAt":"2024-10-27 08:08:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5340263/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5340263/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.7759/cureus.78129","type":"published","date":"2025-01-28T00:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":69353838,"identity":"aaf88ce5-bf00-4adc-b212-204355a79e45","added_by":"auto","created_at":"2024-11-19 13:31:09","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":103802,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eInitial Cervical Imaging.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(A) At flexion (O-C2 angle: -11.3°).\u003c/p\u003e\n\u003cp\u003e(B) At extension (O-C2 angle: 33.8°).\u003c/p\u003e\n\u003cp\u003e(C) CT shows Os odontoideum(arrow head),\u003c/p\u003e\n\u003cp\u003e(D) MRI(T2WI) shows spinal cord compression and T2 high-signal-change at C2 level (arrowhead).\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5340263/v1/36e231b035ed5f8083cc42b6.jpg"},{"id":69353843,"identity":"c3af0881-a17f-4508-b8b9-8f3905038b60","added_by":"auto","created_at":"2024-11-19 13:31:09","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":76185,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Postoperative Xray.O-C2 angle was15.7°.\u003c/p\u003e\n\u003cp\u003e(B) After Initial Surgery, MRI(T2WI) shows remaining and exacerbation of cord compression (arrowhead).\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5340263/v1/91d634173731e8bf04118d8b.jpg"},{"id":69355238,"identity":"184ede98-9dda-4557-aaf0-257326e544cd","added_by":"auto","created_at":"2024-11-19 13:39:09","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":111671,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Postoperative 1 week at neutral position (O-C2 angle: 8.3°).\u003c/p\u003e\n\u003cp\u003e(B) Postoperative 2 weeks at neutral position (O-C2 angle: 2.2°). O-C2 angle was decreased gradually.\u003c/p\u003e\n\u003cp\u003e(C) Postoperative 3 weeks at flexsion(O-C2 angle:-1.3°).\u003c/p\u003e\n\u003cp\u003e(D) Postoperative 3 weeks at extension (O-C2 angle :-8.2°). Functional Radiograph shows instability at O-C2 level.\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5340263/v1/7cfd40480cf69a350470dbce.jpg"},{"id":69353842,"identity":"d8f3bc35-dfbb-4424-b356-a6e0cb35d836","added_by":"auto","created_at":"2024-11-19 13:31:09","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":170822,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Intraoperative findings at revision surgery revealed instability at the C2 screw head and loosening of the set screw on the C2 screw head (arrowhead).\u003c/p\u003e\n\u003cp\u003e(B) Revision Surgery, extending fusion to C4 and adding the triple rod.\u003c/p\u003e\n\u003cp\u003e(C) O-C2 angle was improved to 25 °.\u003c/p\u003e\n\u003cp\u003e(D) After revision surgery, MRI(T2WI) shows improving cord compression (arrowhead).\u003c/p\u003e","description":"","filename":"Figure4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5340263/v1/29876f8bd336083efa338346.jpg"},{"id":69353841,"identity":"18976e50-ca37-4880-90d2-067a2aae7a5e","added_by":"auto","created_at":"2024-11-19 13:31:09","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":60318,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray lateral image one year after surgery. The O-C2 angle was maintained without loss of correction. In addition, the posterior bony fusion was observed (arrow head).\u003c/p\u003e","description":"","filename":"Figure5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5340263/v1/41ffe41718377c16216661ce.jpg"},{"id":69353839,"identity":"805b0e1e-3c5d-4c56-9797-c950800baf57","added_by":"auto","created_at":"2024-11-19 13:31:09","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":89595,"visible":true,"origin":"","legend":"\u003cp\u003e(A) The intraoperative findings revealed that the set screw was loosening.\u003c/p\u003e\n\u003cp\u003e(B) After the set screw was removed. The C2 screw head was positioned close to the rod bending site.\u003c/p\u003e","description":"","filename":"Figure6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5340263/v1/94bc82127e001d78f7fa452e.jpg"},{"id":81061287,"identity":"02f979fd-f8c2-4318-8699-ebd3894efd68","added_by":"auto","created_at":"2025-04-21 19:09:10","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1055342,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5340263/v1/1f254482-09b6-4be3-9c00-f9970fad6286.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Unexpected Neurological Deterioration Following Occipitocervical Fusion Surgery","fulltext":[{"header":"Background","content":"\u003cp\u003eOccipitocervical posterior decompression and fusion (O-C fusion) surgery is occasionally required to treat high cervical myelopathy associated with atlantoaxial subluxation. Recent advancements in instrumentation techniques have contributed to improved clinical outcomes[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Nevertheless, the rate of perioperative complications in this procedure is relatively high, including instrumentation failure, respiratory complications, and dysphagia[\u003cspan additionalcitationids=\"CR4 CR5 CR6\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Here we report a rare case involving an unexpected deterioration of myelopathy following O-C fusion surgery.\u003c/p\u003e"},{"header":"Case Presentation","content":"\u003cp\u003eA 49-year-old Japanese man was transported to our hospital by ambulance after experiencing a loss of consciousness and weakness in his left upper and lower limbs while working. At the initial examination, manual muscle testing (MMT) revealed grade 2 muscle weakness in the distal muscles of the left upper limb, while the lower limbs exhibited no detectable muscle weakness. Superficial sensation remained intact, and deep tendon reflexes were hyperactive in all four extremities. The Japanese Orthopaedic Association (JOA) score for cervical myelopathy was 6 points out of 17. X-ray revealed significant instability, with an O-C2 angle measuring \u0026minus;\u0026thinsp;11.3\u0026deg; at flexion and 33.8\u0026deg; at extension (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). Computed Tomography (CT) revealed the presence of Os Odontoideum and atlantoaxial subluxation. Magnetic Resonance Imaging (MRI) demonstrated anterior spinal cord compression and intramedullary T2 high-signal-change at the C2 level (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOn the diagnosis of acute exacerbation of high cervical myelopathy due to atlantoaxial subluxation associated with Os Odontoideum, O-C fusion surgery was performed (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). The surgery was involved in the removal of the C1 posterior arch, insertion of bilateral C2 pedicle screws, placement of an occipital plate, manual reduction of the C1/2 subluxation, fixation with 3.5mm diameter rods, and iliac bone grafting.\u003c/p\u003e\u003cp\u003ePostoperatively, the patient was managed with intubation in the High Care Unit based on the anesthesiologist\u0026rsquo;s decision, and was extubated the following day. Neurological evaluation conducted the day after surgery revealed progression of paralysis in bilateral upper limbs (MMT: left upper limb grade 3, right upper limb grade 2) and deep sensory disturbances in both lower extremities. The JOA score for cervical myelopathy was deteriorated to 3.5 points out of 17. Postoperative CT revealed no issues with screw positioning. Despite additional support with a Philadelphia neck collar immobilization, there was no improvement in paralysis. At one week after the surgery, muscle weakness in the right lower limb and bilateral deep sensory disturbances worsened. Postoperative MRI revealed persistent anterior spinal cord compression at the C2 level despite intraoperative reduction of C1/2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). Upon serial examination of postoperative X-rays, a gradual loss of correction was observed in the O-C2 angle over time. The intermediate lateral view demonstrated an O-C2 angle of 15.7\u0026deg; immediately post-surgery, which decreased to 8.3\u0026deg; at one week, and further reduced to 2.2\u0026deg; at two weeks postoperatively (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA, B). Furthermore, dynamic X-ray imaging at three weeks postoperatively demonstrated an O-C2 angle of -1.3\u0026deg; at flexion and 8.2\u0026deg; at extension. Notably these images revealed evident instability of the C2 pedicle screw heads during flexion-extension, suggesting fixation failure (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC, D). Given these findings, a revision surgery was performed three weeks following the initial surgery. Intraoperative findings revealed that the C2 screw heads were unstable due to their attachment at the rod bending points, and the set screws were loosened (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). All implants were removed and replaced with a 4.0mm rod system, additional lateral mass screws were placed in C3 and C4, and the O-C2 angle was adjusted and secured with additional rods for reinforcement (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003eAfter the revision surgery, his paralysis of lower extremities gradually improved (MMT: right upper limb 3, left upper limb 4 at two weeks). Furthermore, his deep sensory disturbances also improved, allowing the patient to start gait training. Postoperative X-ray demonstrated adequate reduction with an O-C2 angle of 25 degrees (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC). MRI revealed an expansion of the posterior subarachnoid space, indicating successful posterior decompression of the spinal cord (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD). At the final follow-up one year after surgery, the JOA score for cervical myelopathy improved to 10 points out of 17. The O-C2 angle was maintained without loss of correction, indicating posterior fusion (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e "},{"header":"Discussion","content":"\u003cp\u003eWhile reports of instrumentation failure in O-C fusion surgery, such as rod fracture and screw loosening or breakage, are occasionally observed in the literature[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], to our knowledge, there have been no reports of instrumentation failure due to loosening of the set screws at the screw heads, as encountered in the present case. During the initial surgery, the set screws were tightened to the appropriate torque, and sufficient fixation was achieved intraoperatively. Nevertheless, in the present case, set screw loosening occurred in the early postoperative phase. We hypothesized that this phenomenon was caused by the attachment of the C2 set screws at the rod bending sites. In O-C fusion surgery, it is reported that an inappropriately small O-C2 angle can lead to dysphagia and respiratory complications[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. However, attempting to increase the O-C2 angle inevitably brings the C2 screw heads closer to the rod bending sites. In addition, steep rod bending is often required to increase the O-C2 angle. Consequently, the set screws may not be able to adequately secure the rod at the screw head, leading to insufficient fixation. Therefore, in cases requiring a large O-C2 angle, it is important to be aware of the potential for the C2 screw heads to be positioned close to the rod bending sites, as observed in the present case (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDuring the revision surgery for the present case, we extended the fixation to C4 and reinforced the instrumentation with a triple rod system to achieve more reliable and robust fixation. In O-C fusion surgery, there are some reports discussing methods to reinforce the instrumentation to prevent early instrumentation failure[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. In retrospect, for cases with severe instability like the present case, it might have been better to increase the number of fixation anchors during the initial surgery[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e"},{"header":"Conclusion","content":" \u003cp\u003eIn O-C fusion surgery, particularly in cases requiring a large O-C2 angle, it is crucial to be aware that set screw fixation at the rod bending sites can lead to unexpected early instrumentation failure. Careful consideration of rod application is essential to prevent this phenomenon.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMMT\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eManual Muscle Testing\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eJOA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eJapanese Orthopaedic Association\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCT\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eComputed Tomography\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMRI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMagnetic Resonance Imaging\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWritten informed consent was obtained from all the participants. This study was approved by the Institutional Review Board of our institution (R06-110, Institutional Review Board of the University of Tsukuba Hospital).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research did not receive any specific grant funding agencies in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor\u0026rsquo;s contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eConceptualization: TN, HT, MK\u003c/p\u003e\n\u003cp\u003eData curation: TN, HT, KM, HN, TF\u003c/p\u003e\n\u003cp\u003eFormal analysis: KM, HN\u003c/p\u003e\n\u003cp\u003eFunding acquisition: HT, MK\u003c/p\u003e\n\u003cp\u003eInvestigation: TN, KM, HG, SO, KS, TS, YO\u003c/p\u003e\n\u003cp\u003eMethodology: HT, HN, TF\u003c/p\u003e\n\u003cp\u003eProject administration: HT, KM, HN, TF\u003c/p\u003e\n\u003cp\u003eResources: HG, SO, KS, TS, YO\u003c/p\u003e\n\u003cp\u003eSoftware: HG, SO, KS, TS, YO\u003c/p\u003e\n\u003cp\u003eSupervision: HT, HN, TF, MK\u003c/p\u003e\n\u003cp\u003eValidation: KM, HG, SO\u003c/p\u003e\n\u003cp\u003eVisualization: TN, KM\u003c/p\u003e\n\u003cp\u003eWriting \u0026ndash; Original Draft: TN\u003c/p\u003e\n\u003cp\u003eWriting \u0026ndash; review and editing: All the authors reviewed and edited the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePortions of this work were presented at the 14th Annual Meeting of the Cervical Spine Research Society Asia Pacific Section, Shangri-La, Singapore, March 22-24, 2024.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eJoaquim AF, Osorio JA, Riew KD. Occipitocervical Fixation: General Considerations and Surgical Technique. Global Spine J. 2020;10(5):647-656. doi: 10.1177/2192568219877878\u003c/li\u003e\n\u003cli\u003eWinegar CD, Lawrence JP, Friel BC, Fernandez C, Hong J, Maltenfort M, Anderson PA, Vaccaro AR. A systematic review of occipital cervical fusion: techniques and outcomes. J Neurosurg Spine. 2010;13(1):5-16. doi: 10.3171/2010.3.Spine08143\u003c/li\u003e\n\u003cli\u003eMiyata M, Neo M, Fujibayashi S, Ito H, Takemoto M, Nakamura T. O-C2 angle as a predictor of dyspnea and/or dysphagia after occipitocervical fusion. Spine (Phila Pa 1976). 2009;34(2):184-188. doi: 10.1097/BRS.0b013e31818ff64e\u003c/li\u003e\n\u003cli\u003eYang DS, Patel SA, DiSilvestro KJ, Li NY, Daniels AH. Postoperative complication rates and hazards-model survival analysis of revision surgery following occipitocervical and atlanto-axial fusion. N Am Spine Soc J. 2020;3:100017. doi: 10.1016/j.xnsj.2020.100017\u003c/li\u003e\n\u003cli\u003eZileli M, Akınt\u0026uuml;rk N. Complications of occipitocervical fixation: retrospective review of 128 patients with 5-year mean follow-up. Eur Spine J. 2022;31(2):311-326. doi: 10.1007/s00586-021-07037-2\u003c/li\u003e\n\u003cli\u003eLiu G, Li Q, Sheng F, Xu N, Li M, Wang Y, Ma W. Outcomes of occipitocervical fixation using a spinous process screw in C2 as a third anchor point for occipitocervical fixation: a case presentation. BMC Musculoskelet Disord. 2020;21(1):307. doi: 10.1186/s12891-020-03258-6\u003c/li\u003e\n\u003cli\u003eChen H, Lian P, Tu Q, Wang J, Ma X, Ai F, Yi H, Xia H, Zhu C. Incidences, causes and risk factors of unplanned reoperation within 30 days of craniovertebral junction surgery: a single-center experience. Eur Spine J. 2023;32(6):2157-2163. doi: 10.1007/s00586-023-07729-x\u003c/li\u003e\n\u003cli\u003eCollins AP, Mumtaz M, Tripathi S, Varier SK, Turner AW, Clark AJ, Goel VK, Theologis AA. Multirod posterior occipitocervical instrumentation constructs: a biomechanical analysis and initial case series of 10 patients with complex craniocervical pathology. Spine J. 2024;in press. doi: 10.1016/j.spinee.2024.09.022\u003c/li\u003e\n\u003cli\u003eEto F, Takahashi H, Funayama T, Koda M, Yamazaki M. A Novel Technique for Occipitocervical Fusion with Triple Rod Connection to Prevent Implant Failure. Cureus. 2022;14(5):e24821. doi: 10.7759/cureus.24821\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"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":"occipitocervial fusion surgery, Os Odontoideum, instrumentation failure","lastPublishedDoi":"10.21203/rs.3.rs-5340263/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5340263/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eOccipitocervical posterior decompression and fusion (O-C fusion) surgery is occasionally required for treating high cervical myelopathy due to atlantoaxial subluxation. The advance of the instrumentation systems has led to favorable clinical outcomes following O-C fusion surgery. However, the rate of perioperative complications in O-C fusion surgery is relatively high, including instrumentation failure, respiratory complications, and dysphagia. Here we report a rare case involving an unexpected deterioration of myelopathy following O-C fusion surgery.\u003c/p\u003e\u003ch2\u003eCase presentation:\u003c/h2\u003e \u003cp\u003eA 49-year-old male was transported to our hospital by ambulance with left-sided upper and lower limb paralysis. At the initial visit, a neurological examination revealed left upper limb weakness (MMT grade 2). X-ray and CT revealed severe atlantoaxial subluxation due to Os Odontoideum, while MRI revealed significant spinal cord compression at the C2 level. On the diagnosis of acute exacerbation of high cervical myelopathy, an O-C2 posterior decompression and fusion surgery including C1 laminectomy was performed. Postoperatively, the patient exhibited a deterioration in right-sided upper limb paralysis (MMT grade 2), despite proper implant placement confirmed by CT. During two weeks postoperatively, there was no improvement in the right-sided upper limb paralysis, and bilateral deep sensory impairment worsened. Follow-up X-rays revealed a progressive decrease in the O-C2 angle and dynamic X-ray imaging demonstrated a recurrence of instability at the O-C2 level. On the diagnosis of the instrumentation failure, a revision surgery was performed 3 weeks after the primary surgery. Intraoperative findings revealed instability at the C2 screw head and loosening of the set screw on the C2 screw head. To achieve a more secure fixation, we extended the fusion to C4 with a triple rod connection. Following the revision surgery, his myelopathy and paralysis gradually improved. At the final follow-up 6 months after surgery, X-rays showed that O-C2 was firmly stabilized.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eIn O-C fusion surgery, screw head fixation close to the O-C rod bending site may result in unexpected instrumentation failure.\u003c/p\u003e","manuscriptTitle":"Unexpected Neurological Deterioration Following Occipitocervical Fusion Surgery","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-19 13:31:04","doi":"10.21203/rs.3.rs-5340263/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":"577c59bc-53e8-4019-a1af-f663f3a8d9f2","owner":[],"postedDate":"November 19th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-04-21T19:09:01+00:00","versionOfRecord":{"articleIdentity":"rs-5340263","link":"https://doi.org/10.7759/cureus.78129","journal":{"identity":"cureus","isVorOnly":true,"title":"Cureus"},"publishedOn":"2025-01-28 00:00:00","publishedOnDateReadable":"January 28th, 2025"},"versionCreatedAt":"2024-11-19 13:31:04","video":"","vorDoi":"10.7759/cureus.78129","vorDoiUrl":"https://doi.org/10.7759/cureus.78129","workflowStages":[]},"version":"v1","identity":"rs-5340263","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5340263","identity":"rs-5340263","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}