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Weakness of the muscles of the nape of the neck and back of the spine and its related instability is the nodal point of pathogenesis of a number of clinical and pathological events at the craniovertebral junction and the spine. Whilst acute instability results in sudden and relatively severe symptoms, chronic or long-standing instability is associated with a range of musculoskeletal and structural spinal alterations. Telescoping of the spinal segments results in "vertical" spinal instability in the subaxial spine and central or axial atlantoaxial instability (CAAD) at the craniovertebral junction. Instability in such cases might not be observed on dynamic radiological imaging. Chiari formation, basilar invagination, syringomyelia, and Klippel-Feil alteration are some of the secondary alterations as a result of chronic atlantoaxial instability. Radiculopathy/myelopathy related to spinal degeneration or ossification of posterior longitudinal ligament appears to have their origin from vertical spinal instability. All the secondary alterations in the craniovertebral junction and subaxial spine that are traditionally considered pathological and to have compressive and deforming role are essentially protective in nature, are indicative of instability, and are potentially reversible following atlantoaxial stabilization. Stabilization of unstable spinal segments is the basis of surgical treatment., (© 2023. The Author(s), under exclusive license to Springer Nature Switzerland AG.)

Background: A number of complications following surgery aimed at atlantoaxial fixation have been reported. However, there is no report in the literature describing visual loss following vertebral artery injury., Objective: Vision loss as a complication of vertebral artery injury during surgery for atlantoaxial fixation is reported., Material and Methods: This is a report of two patients who were operated for atlantoaxial instability by the Goel technique of atlantoaxial fixation. During surgery, there was an injury to the vertebral artery and the artery had to be sacrificed., Results: Both patients suffered severe visual loss following surgery. One patient had a partial visual recovery that started within few days of surgery while the other patient remained completely blind., Conclusions: Although rare, visual loss can be a complication of vertebral artery sacrifice during surgery for atlantoaxial stabilization., Competing Interests: None

This is a report of two patients who were diagnosed to have NF-1. The patients had severe dystrophic soft tissue and bone changes leading to craniovertebral junction and subaxial cervical spinal instability and deformity. Both the patients underwent atlantoaxial and subaxial cervical spinal stabilization. No bone, soft tissue or tumor resection was done for decompression. Both patients had gratifying clinical recovery. Follow-up in both the patients is more than 12 months., Competing Interests: None

Objective: The potential significance of relationship of atlantoaxial instability with retro-odontoid pseudotumor, pannus, and/or cyst (RPC) is analyzed., Methods: We searched the database of patients with craniovertebral junction-related instability treated by atlantoaxial fixation from January 2000 to March 2020. We identified 63 patients in whom there was an RPC in the region posterior to the odontoid process or posterior to the posterior aspect of the C2 body., Results: The RPC was solid in 10 patients, predominantly cystic in 39 patients, and had both solid and cystic components in 14 patients. The vertical dimension of the RPC varied from 4.5 to 10.5 mm (average, 7.9 mm) and the transverse dimension ranged from 2 to 5.2 mm (average, 3.4 mm). In 51 patients, the RPC was in the midline and in 9 patients, it was eccentric in location. In 38 patients, there was erosion of the C2 body adjoining the RPC. Analysis of investigations showed that in 100% of patients, the dome of the RPC was in line with the most susceptible point of potential bone compression of neural structures. The RPC was eccentric in location in 9 patients presenting with torticollis. RPC indicated the presence of atlantoaxial instability even when there were no other positive and validated radiologic indicators. After atlantoaxial stabilization, the RPC spontaneously regressed or disappeared. Direct resection of the RPC was neither performed nor was necessary in any case., Conclusions: RPCs are secondary consequences of atlantoaxial instability and need not be primarily addressed by surgical resection. Their location suggests that they might have a neural protective function., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Background: The rationale of only fixation without any kind of bone, ligament, disc, or osteophyte decompression as a treatment for single- or multiple-level cervical spinal degeneration was analyzed. The concept was based on the understanding that muscle weakness-related spinal instability is the cause of spinal degeneration, and spinal stabilization is the treatment., Materials and Methods: During the period June 2012 to June 2019, 215 patients with single- or multiple-level cervical spinal degeneration who presented with symptoms of radiculopathy and/or myelopathy were treated. Age range of patients was 35-76 years. The series included 194 men and 21 women. Patients with acute symptoms and disc herniation, prolapse, or extrusion were excluded from the analysis. Only spinal stabilization by deploying facet screw fixation techniques was done in all cases. No decompression by resection of any bone, soft tissue, disc, or osteophyte was done. The minimum follow-up was 6 months., Results: Postoperative clinical outcome was measured using Japanese Orthopaedic Association score, Goel clinical grade, and visual analog scale score. In addition, 2 specialist neurosurgeons were recruited to assess clinical outcome. Clinical assessments and videos were used to document the outcome. There were no significant complications. Varying degree of clinical recovery was seen in all patients. None of the patients in the series underwent reoperation for persistence or recurrence of symptoms., Conclusions: Instability of spinal segments forms the basis of spinal degeneration. Stabilization forms the basis of surgical treatment. The role of decompression needs to be re-evaluated., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Background: Ossification of the posterior longitudinal ligament (OPLL) is a hyperostotic condition resulting in a progressive narrowing of the spinal canal and subsequent neurologic deficits. Although systemic and local factors in combination with genetic abnormality have been considered in its etiopathogenesis, OPLL remains a poorly understood pathology. Surgical management of OPLL and the choice of the most appropriate treatment are still controversial issues. Here the authors report a series of OPLL-affected patients treated by "only-fixation" technique., Methods: Between June 2012 and June 2019, 52 patients having OPLL were treated by a surgical strategy involving only spinal fixation without any form of bone or soft tissue decompression. Facetal fixation for both the atlantoaxial and subaxial spine formed the basis of the surgical treatment. Clinical parameters, analysis of video recordings before and after surgery, and patient self-assessment were included in the analysis of outcome., Results: During the mean follow-up period there was an immediate postoperative and progressive recovery in symptoms in 51 patients. Of 14 patients who were wheelchair bound before surgery, 12 walked independently on follow-up assessment of 6 months. All patients had successful arthrodesis in the surgically treated segments. There were no infective- or implant-related complications., Conclusions: Decision making in the surgical management of cervical OPLL is still controversial. The concept of spinal instability has been shown to be a nodal point in the pathogenesis of OPLL, and "only-spinal fixation" can be considered a rationale for an appropriate surgical treatment., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Aim: To discuss the rare association of atlantoaxial instability in patients with the Dyggve-Melchior-Clausen syndrome, a rare autosomal recessive disease characterized by progressive spondyloepimetaphyseal dysplasia and mild to severe mental retardation., Material and Methods: We report an uncommon association of two siblings with Dyggve-Melchior-Clausen syndrome, odontoid hypoplasia and atlantoaxial instability. Both the patients were treated with Goel?s atlantoaxial fixation procedure., Results: The patients had a remarkable neurological recovery following the stabilization procedure., Conclusion: Atlantoaxial instability is a potentially life-threatening condition in patients with this syndrome and should be treated early with atlantoaxial stabilization. Recognition and treatment of atlantoaxial instability in patients with Dyggve-Melchior- Clausen syndrome can give gratifying results.

Objective: To analyze the probable causes of failed craniovertebral junction stabilization procedures, and to evaluate the advantages of the Goel technique in revision surgery and the positive factors that lead to reduction of the instability and achieve ultimate arthrodesis., Methods: During the period from January 2010 to June 2018, we treated 30 cases where previous attempt at craniovertebral stabilization with various fixation techniques had failed and the patients presented with progressively worsening neurologic deficits. All patients were re-operated by lateral mass fixation techniques described by the senior author. The technique involved opening of the atlantoaxial joint, denuding the articular cartilage, introduction of bone graft within the articular cavity, and plate and screw fixation. No bone decompression was done., Results: Fixation of multiple subaxial spinal segments (n = 9), inclusion of occipital bone in the fixation construct (n = 21), and dependence on metal stabilization rather than bone fusion (n = 19) appear to be important causes of implant failure. All patients improved in clinical symptoms after revision surgery. Postoperative images of all patients demonstrated significant reduction of the atlantoaxial dislocation and craniovertebral junction realignment. During the average follow-up period of 32 months, all reoperated patients continued to show clinical recovery. No further surgery was necessary., Conclusions: Although relatively difficult, when indicated, reoperation and direct stabilization of the atlantoaxial joint can result in significant and enduring clinical recovery., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Background: The outcome of neurophysiologic motor evoked potential (MEP) monitoring during surgery for Chiari formation by atlantoaxial fixation and without any bone or dural foramen magnum decompression is analyzed., Methods: During the period August 2017 to October 2018, 20 patients having Chiari formation with or without syringomyelia were surgically treated by atlantoaxial fixation. Apart from other forms of monitoring, MEP monitoring formed the basis of study. MEP monitoring was done during various phases of surgery that included monitoring immediately after screw tightening for atlantoaxial fixation., Results: It was observed that there was positive improvement in MEP in 100% of the patients when measured in the surgical stage immediately after the procedure of screw tightening for atlantoaxial fixation. The improvement in MEP correlated with parallel improvement in neurologic function., Conclusions: Improvement in MEP adds credence to the hypothesis that atlantoaxial instability forms the nodal point of pathogenesis of Chiari formation., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Aim: In this paper we evaluate the role of atlantoaxial instability in the pathogenesis of Chiari formation type I and the role of atlantoaxial stabilization for treatment of this condition in cases with no obvious bone malformation in the region of the craniovertebral junction., Materials, Methods and Results: During the period from January 2010 to July 2016, we identified 57 cases of Chiari formation where there was no bone malformation or evidence of craniovertebral junction instability that could be diagnosed on the basis of an abnormal increase in the atlantodental interval on dynamic imaging. Forty-eight of these patients had syringomyelia. The average duration of follow-up was 42 months. There were 30 males and 27 females in the series. The ages of the patients ranged from 4 to 57 years. The Japanese Orthopaedic Association (JOA), visual analogue scale (VAS) and Goel clinical grading systems were used to assess the patients' clinical status. Atlantoaxial instability was diagnosed on the basis of vertical mobility of the odontoid process on dynamic radiographs, facetal malalignment on imaging or direct bone handling during the surgical procedure. Surgical treatment was achieved using atlantoaxial fixation. Foramen magnum decompression or syrinx manipulation was not done. All patients had immediate postoperative and sustained clinical symptomatic recovery. A reduction in the size of the syrinx was observed in ten patients and regression of tonsillar herniation was observed in 12 of 23 cases in which postoperative magnetic resonance imaging (MRI) was possible., Conclusion: Atlantoaxial instability is the prime factor in the genesis of Chiari formation even when there is no bone abnormality in the craniovertebral junction.

Objective: The role of atlantoaxial instability in the pathogenesis of Chiari 1 formation (Chiari formation) in pediatric age-group patients is evaluated., Material and Methods: During the period of January 2010 to June 2017, 33 pediatric patients having Chiari formation were treated with atlantoaxial fixation. Twenty-four patients had basilar invagination, and 9 patients had no bone abnormality at the craniovertebral junction. Sixteen patients had syringomyelia, and 9 patients had both basilar invagination and syringomyelia. Considering the type of facet alignment and atlantoaxial instability, the patients were divided into 3 groups. Type 1 dislocation (13 patients) was anterior atlantoaxial instability wherein the facet of the atlas was dislocated anterior to the facet of the axis. Type 2 dislocation (5 patients) was posterior atlantoaxial instability wherein the facet of the atlas was dislocated posterior to the facet of the axis. Type 3 dislocation (15 patients) was the absence of demonstrable facet malalignment. Type 2 and 3 atlantoaxial facet instability were labeled as central atlantoaxial dislocation. In 14 patients, dynamic images showed mobile and at least partially reducible vertical atlantoaxial dislocation., Results: All patients were treated with atlantoaxial plate and screw fixation using techniques described in 1994 and 2004. Foramen magnum decompression or syrinx manipulation was not performed in any patient. Occipital bone and subaxial spinal elements were not included in the fixation construct. All patients had gratifying and sustained clinical improvement., Conclusions: The outcome further confirms the cause-effect relationship of Chiari formation and atlantoaxial instability., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Objective: To evaluate the musculoskeletal and soft tissue neural alterations in cases with group A basilar invagination., Methods: Between January 2007 and August 2016, 510 patients with group A basilar invagination were surgically treated. The radiologic images of these patients were reviewed retrospectively. The patients were divided into 4 groups: group A1, comprising 60 patients with syringomyelia; group A2, comprising 354 patients with "external syrinx," marked by excessive cerebrospinal fluid (CSF) in the extramedullary space; group A3, comprising 51 patients with both syringomyelia and external syrinx; and group A4, comprising 45 patients with no abnormality of CSF cavitation in the spinal canal., Results: A number of musculoskeletal and neural parameters, including the extent of basilar invagination, degree of angulation of the odontoid process, and facet malalignment, were evaluated in each of the 4 groups. The degree of basilar invagination was 6-27.4 mm (average, 15.85 mm) in group A1, 4.3-24.5 mm (average, 12.56 mm) in group A2, 5.6-17.6 mm (average 10.8 mm) in group A3, and 5.2-17.3 mm (average, 11.74 mm) in group A4. The angle of inclination of the odontoid process was 61.1-90.7 degrees (average, 71.4 degrees) in group A1, 30.5-79.8 degrees (average, 60.05 degrees) in group A2, 68.5-78.3 degrees (average, 73.4 degrees) in group A3, and 62.2-87.4 degrees (average, 71.2 degrees) in group A4., Conclusions: The nature of bone malformations directly influences the presence or absence of external syrinx and syringomyelia., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background: We present 2 cases involving a previously unreported clinical situation in which basilar invagination, atlantoaxial instability, and C2-3 instability were associated with a bifid posterior arch of the axis bone., Case Descriptions: Two young males presented with limb weakness, spasticity, and paresthesias. Both patients had altered voice quality, with reduced and thin volume, and difficulty sleeping supine. Radiologic imaging showed an absence of the posterior elements of the C2 vertebrae. The C3 spinous process mimicked the C2 spinous process in shape and size. C1-2 and C2-3 posterior fixations were performed., Conclusions: C1-2 and C2-3 fixation resulted in firm fixation of the region and a remarkable clinical recovery. The most significant features were an immediate postoperative improvement in voice quality and the ability to sleep comfortably in the supine position., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Objective: We discuss the role of instability of multiple spinal segments including the atlantoaxial joint in the pathogenesis of cervical kyphotic deformity., Material and Methods: Two male patients (5 and 17 years old) had severe cervical kyphosis and presented with symptoms related to myelopathy. The patients underwent multisegmental spinal distraction and fixation that included atlantoaxial joint. No bone decompression was done., Results: At a follow-up of >30 months, both patients had significant neurologic recovery. Investigations at follow-up showed successful arthrodesis of treated spinal segments. Although incomplete, there was recovery in kyphosis., Conclusions: Multisegmental spinal distraction and fixation can lead to reduction in kyphosis and relief from symptoms related to myelopathy. Role of spinal instability in general and atlantoaxial joint instability in particular in pathogenesis of cervical kyphosis need to be assessed on the basis of studies with a larger number of patients., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Backgrounds: The role of subaxial and atlantoaxial instability in the pathogenesis of "degeneration"-related cervical kyphosis is evaluated., Material and Methods: During the period 2013-2016, the authors treated 21 patients having cervical kyphosis that was related to degenerative spinal disease. The patients presented with symptoms related to cervical myelopathy. Kyphosis was diagnosed on the basis of described radiologic parameters. The patients were divided into 3 groups. Group A (10 patients) had manifest radiologic evidence of atlantoaxial dislocation, type 1 facetal instability, abnormal increase in atlantodental interval, and evidence of cord compression by the odontoid process. Group B (5 patients) had axial or central atlantoaxial facetal instability (type 2 or 3 atlantoaxial facetal instability) and subaxial spinal instability. Group C (6 patients) had subaxial spinal instability. The patients were treated by only stabilization. Group A patients underwent atlantoaxial fixation, group B patients underwent atlantoaxial and subaxial fixation, and group C patients underwent only subaxial spinal fixation. The operation was aimed at arthrodesis of the spinal segments. No bone or soft tissue decompression was done., Results: During the minimum follow-up period of 6 months, all patients improved in their neurologic symptoms and demonstrated evidence of spinal arthrodesis. There were no major surgical complications., Conclusions: Spinal instability plays a major role in the generation of cervical spinal kyphosis. Atlantoaxial instability may form the primary and nodal site of development of the process of spinal degeneration in general and kyphosis in particular., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background: We discuss the rationale of surgical treatment of group B basilar invagination by atlantoaxial facet joint stabilization and segmental arthrodesis., Methods: From January 2010 to April 2016, 63 patients with group B basilar invagination were surgically treated. All patients had varying degree of myelopathy-related functional disability. Fifty-two patients had both Chiari malformation and syringomyelia. All patients were treated by atlantoaxial plate and screw fixation with the techniques described by us in 1994 and 2004. Foramen magnum decompression or syrinx manipulation was not carried out in any patient. Occipital bone and subaxial spinal elements were not included in the fixation construct., Results: Three patients died in the immediate postoperative phase. In the remaining patients, there was clinical improvement and no patient's neurologic function worsened after surgery. In 12 of 38 patients in whom postoperative magnetic resonance imaging was possible, at a follow-up of at least 3 months, there was reduction in the size of the syrinx., Conclusions: The pathogenesis of basilar invagination in group B is related to atlantoaxial instability. The clinical outcome suggests that the surgical treatment in these cases should be directed toward atlantoaxial stabilization and aimed at segmental arthrodesis. Inclusion of the occipital bone in the fixation construct is not necessary. Foramen magnum decompression and procedures involving manipulation of Chiari malformation and syringomyelia are not necessary., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Objective: To analyze the role of multisegmental spinal instability in the pathogenesis of Hirayama disease., Material and Methods: From June 2014 to January 2016, the authors managed 5 patients with Hirayama disease. The patients were diagnosed on the basis of classical described radiologic and clinical guidelines. All 5 patients were treated with multilevel cervical fixation that included fixation of the atlantoaxial joint in 4 patients by the adoption of the facetal fixation methods. No dural or bone decompression was performed. The follow-up ranged from 7 to 26 months (average 17.6 months)., Results: The most remarkable feature was an immediate postoperative and progressive improvement in the symptoms of weakness, wasting, and deformity of hands in all patients. The other remarkable feature was an immediate postoperative reduction in extradural mass in all patients and its complete disappearance in 2 patients., Conclusions: From the observations, it appears that atlantoaxial and subaxial spinal instability plays a major role in the pathogenesis of Hirayama disease., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Background: We evaluated the radiologic features of 75 patients with group B basilar invagination who exhibited no evidence of atlantoaxial instability based on the conventional parameter of an abnormal increase in the atlantodental interval. We specifically studied the variability and possible significance of the presence of cerebrospinal fluid (CSF) within and outside the confines of neural tissues., Materials and Methods: During the period January 2008-May 2015, we encountered 75 cases with group B basilar invagination. These patients were divided into 4 groups depending on cervical spinal imaging that showed the presence of syringomyelia (group B1), increased CSF volume in the extramedullary space or external syrinx (group B2), the presence of both syringomyelia and external syrinx (group B3), and no abnormality of CSF cavitation in the spinal canal (group B4)., Results: Our cohort comprised 39 group B1 cases, 10 group B2 cases, 20 group B3 cases, and 6 group B4 cases. The neck size and posterior fossa height were simultaneously reduced, by 15.89% and 15%, respectively, but the length of the neural structures remained within the normal range. Excessive amounts of CSF were present within or outside the confines of neural structures, including the spinal cord, brainstem, and cerebellum., Conclusions: In cases of basilar invagination, various musculoskeletal and neural alterations seem to have a common functional role in protecting the craniocervical cord and delaying or stalling neurologic dysfunction., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Object: The authors retrospectively analyzed a series of 108 patients in whom was diagnosed atlantoaxial instability due to degenerative osteoarthritis of the atlantoaxial joints. The management issues in such cases are discussed., Methods: One hundred eight patients with osteoarthritis of the atlantoaxial joints and resultant craniovertebral instability-diagnosed on the basis of presenting clinical features, radiological imaging, and direct observation of the joint status during surgery-were retrospectively analyzed. Between 1990 and 2008, these patients were treated with a C1-2 lateral mass plate and screw method of atlantoaxial fixation and joint distraction using bone graft with or without the assistance of metal spacers., Results: Patient ages ranged from 48 to 84 years (average 63 years). There was a history of mild to moderate head and/or neck trauma 2 months to 11 years prior to diagnosis in 40% of the cases. All patients had symptoms of neck pain, and 82% of the patients had progressive myelopathy. A reduction in the height of the atlantoaxial lateral mass complex (100%), mobile atlantoaxial dislocation (100%), basilar invagination (68%), and periodontoid degenerative tissue mass (90%) were the more frequently encountered radiological features. Two patients died in the immediate postoperative period. At an average follow-up of 64 months, all surviving patients remarkably improved to varying degrees in their neurological condition., Conclusions: Atlantoaxial joint arthritis frequently leads to craniovertebral instability and cord compression. Treatment by joint distraction and lateral mass fixation can be an optimum form of treatment.