The occipitoatlantal capsular ligaments are the primary stabilizers of the occipitoatlantal joint in the craniocervical junction: a finite element analysis

Atlas Subluxation Complex, National Upper Cervical Chiropractic Association Intervention, and Dizziness Improvement: A Narrative Review of Historical Perspectives, Literature Synthesis, and a Path for Future Care

Dizziness is a non-specific and common condition in which the afflicted individual experiences abnormal sensations such as lightheadedness, imbalance, or a false sense of spinning (vertigo). The experience of "dizziness" can result from a wide spectrum of abnormal physiological states, including exhaustion, hypotension, and hypoglycemia, but could also indicate a serious underlying health issue. Since it has many potential generating causes, accurate identification of the underlying etiology of dizziness can present a challenge to clinicians, often resulting in ineffective treatments. We present a hypothesis that atlas subluxation complex (ASC) may comprise an etiological agent of dizziness that can be successfully addressed with National Upper Cervical Chiropractic Association (NUCCA) chiropractic care. In this review, we discuss the pathophysiology of the ASC, introduce the NUCCA chiropractic procedure, and complete a literature review and synthesis. Conceptual evidence, case reports, and theory provide foundational evidence that the ASC may be a contributory factor of dizziness generation and that NUCCA chiropractic corrective care of the ASC may produce favorable dizziness outcomes. However, high-quality studies are lacking. The foundation evidence provides indication that further research via observational studies and randomized controlled trials (RCTs) is warranted.

Traumatic posterior atlantoaxial dislocation without an associated fracture: a PRISMA-compliant case-based systematic review and meta-analysis

Traumatic posterior atlantoaxial dislocation (TPAD) without an associated fracture is a rare and challenging spinal injury. This PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses)-compliant case-based systematic review and meta-analysis aimed to comprehensively explore TPAD, covering clinical presentation, diagnosis, treatment, and clinical and radiological outcomes. Following the presentation of a case of TPAD without an associated fracture, we conducted a systematic search of electronic databases, including Scopus, PubMed, and Web of Science, from inception through October 2023, without language restrictions. Cases involving dislocations due to congenital anomalies or inflammatory processes were excluded. The search yielded 31 eligible cases of TPAD without an associated fracture. The majority (81%) of the cases were males, with traffic accidents being the leading cause (87%). Notably, 52% of the cases presented without any neurological deficits. Regarding treatment approaches, 23% of the cases were managed through closed reduction alone, 32% required fusion following closed reduction, and 45% underwent open reduction and fusion. A time delay exceeding 7.5 days was associated with a significantly higher risk of closed reduction failure (odds ratio, 56.463; p =0.011). This review identified key management strategies for TRAD without fracture, informed by the available evidence. Optimal management entails prompt closed reduction under C-arm while monitoring neurological status once hemodynamic stability is achieved. Surgical fusion is indicated for cases with magnetic resonance imaging-confirmed transverse ligament rupture or residual instability. If closed reduction fails, open reduction and fusion should be carried out. Posterior C1-C2 screws fixation is the preferred fusion technique, providing high levels of safety and biomechanical stability.

The ligamentous cervical instability etiology of human disease from the forward head-facedown lifestyle: emphasis on obstruction of fluid flow into and out of the brain

Ligamentous cervical instability, especially ligamentous upper cervical instability, can be the missing structural cause and/or co-morbidity for many chronic disabling brain and systemic body symptoms and diagnoses. Due to the forward head-facedown lifestyle from excessive computer and cell phone usage, the posterior ligament complex of the cervical spine undergoes a slow stretch termed "creep" which can, over time, lead to cervical instability and a breakdown of the cervical curve. As this degenerative process continues, the cervical curve straightens and ultimately becomes kyphotic, a process called cervical dysstructure; simultaneously, the atlas (C1) moves forward, both of which can lead to encroachment of the structures in the carotid sheath, especially the internal jugular veins and vagus nerves. This obstruction of fluid flow can account for many brain diseases, and compression and stretch of the vagus nerve for body diseases, including dysautonomia. This article describes the consequences of impaired fluid flow into and out of the brain, especially venous flow through the internal jugular veins, leading to intracranial hypertension (formerly called pseudotumor cerebri). Cervical structural, internal jugular vein, and optic nerve sheath measurements are presented from a retrospective chart review of 227 consecutive patients with no obvious cause for 1 of 8 specific brain or mental health symptoms-anxiety, brain fog, concentration difficulty, depression/hopelessness, headaches, obsessive thoughts, panic attacks, and rumination on traumatic events. A case example is given to demonstrate how cervical structural treatments can open up internal jugular veins and improve a patient's chronic symptoms.

Pediatric Cervical Spine Trauma: A Narrative Review

STUDY DESIGN

Narrative review.

OBJECTIVE

To provide an updated overview of pediatric cervical spine trauma.

SUMMARY OF BACKGROUND DATA

Pediatric cervical spine trauma can cause debilitating morbidity and mortality and neurological impairment. The unique anatomic features of the developing cervical spine can predispose children to injuries.

METHODS

We reviewed the pediatric cervical spine trauma literature in PubMed and EMBASE.

RESULTS

Pediatric cervical spine injury occurs in 1%-2% of pediatric trauma. The most frequent cause is motor vehicle collisions, with sports-related injuries being more common in older children. Larger head-to-body ratios and tissue elasticity can predispose young children to a greater risk of injury higher in the craniocervical junction and cervical spine. Standardized protocols and classification systems, such as the Pediatric Cervical Spine Clearance Working Group protocol and the AO Spine Injury and Subaxial Cervical Spine Injury Classifications, are valuable in triage as well as for assessing the need for operative versus nonoperative management. In general, operative approaches and principles are similar to those in adults, with modern instrumentation and fusion techniques achieving high rates of successful arthrodesis.

CONCLUSIONS

Effective management and treatment of pediatric cervical spine injuries depends on early and accurate diagnosis, a thorough understanding of pediatric spinal anatomy, and a versatile surgical armamentarium.

Functional Anatomy and Biomechanics of the Craniovertebral Junction

The craniovertebral junction (CVJ) involves the atlas, axis, and occiput along with the atlanto-occipital and atlantoaxial joints. The anatomy and neural and vascular anatomy of the junction render the CVJ unique. Specialists treating disorders that affect the CVJ must appreciate its intricate anatomy and should be well versed in its biomechanics. This first article in a three-article series provides an overview of the functional anatomy and biomechanics of the CVJ.

Craniocervical Instability in Ehlers-Danlos Syndrome-A Systematic Review of Diagnostic and Surgical Treatment Criteria

STUDY DESIGN

Systematic review.

OBJECTIVE

Ehlers-Danlos Syndrome (EDS) comprises a spectrum of connective tissue disorders, which may be associated with cranio-cervical instability (CCI). There is a lack of consensus on diagnostic imaging parameters, indications, and outcomes of surgical treatment.

METHODS

This systematic review analyses the literature on diagnostic methods and/or criteria for CCI, screening the databases Ovid Medline, Embase, Cochrane Library, and PubMed. Articles were included based on the PRISMA guidelines and assessed using the Newcastle-Ottawa Quality Assessment Scale (NOS) and according to their evidence level.

RESULTS

Sixteen articles, including 78 surgical patients, met the inclusion criteria. The main diagnostic measures for CCI were dynamic x-rays and CT imaging. Ten different radiographic parameters were reported, of which 4 were the most frequently applied for surgical decision-making: the clivo-axial angle (CXA), the Harris measurement, the Grabb-Mapstone-Oakes measurement, and the angular displacement of C1 to C2. The evidence level ranged between III and V and the article quality between 4 and 8 out of 9 stars on the NOS Scale.

CONCLUSIONS

There is a lack of high quality, prospective evidence regarding the evaluation of suspected CCI in patients with EDS. Based on our systematic review, we recommend that the CXA, Harris measurement, Grabb-Mapstone-Oakes measurement, and the angular displacement of C1 to C2 be used to evaluate suspected CCI in EDS patients. Surgical fixation of suspected CCI should only be performed in cases with clear radiographic presence of instability and concordant symptoms/signs. Consensus-based guidelines and care pathways are required.

Pathoanatomy, biomechanics, and treatment of upper cervical ligamentous instability: A literature review

BACKGROUND

Cervical spine instability broadly refers to compromise of the articular congruity. It can be stratified according to spinal level, functional compromise, and mechanism of instability. Conventional wisdom advocates for use of bracing and physical therapy with only a subset of patients proceeding to obtain surgical treatment.

OBJECTIVE

The purpose of this review article is to summarize the current state of knowledge on upper cervical ligamentous instability.

METHODS

The literature search was performed in Mendeley. Search fields were varied until redundant. All articles were screened by title and abstract and a preliminary decision to include an article was made. The full-text screening was performed on the selected articles. Any question regarding the inclusion of an article was discussed by 3 authors until an agreement was reached.

RESULTS

Many articles report on the etiological factors including ligamentous laxity, traumatic injury, syndrome instability, iatrogenic instability, congenital, and inflammatory causes. A few recent studies elucidate new findings regarding pathoanatomy through the use of finite element analysis. A few articles demonstrate the diagnosis and show that radiographs alone have a low diagnostic rate and that functional MRI may be able to better quantify instability. Conservative treatment has been described, but there are no outcome studies in the literature. Surgical treatment has been described in many different populations with good radiologic and clinical outcomes. Recently the use of preoperative 3D CT reconstruction has been described with radiographic and immediate postoperative patient-reported outcomes.

CONCLUSION

The presentation of upper cervical spinal instability can be asymptomatic, symptoms of isolated instability, symptoms of nerve irritation, vertebrobasilar insufficiency, or severe neurologic compromise. 3D fine element analysis models and motion-capture systems have the potential to increase our understanding of the pathoanatomic cascade in both traumatic and non-traumatic cases of upper cervical spinal instability. A few modalities on the horizon could increase diagnostic potential. More efforts are needed regarding the use of fine element analysis in understanding the pathoanatomic cascade, the long-term outcomes of children over a spectrum of syndromic causes, and the potential of preoperative virtual simulation to improve surgical outcomes.

FEBio finite element model of a pediatric cervical spine

OBJECTIVE

The underlying biomechanical differences between the pediatric and adult cervical spine are incompletely understood. Computational spine modeling can address that knowledge gap. Using a computational method known as finite element modeling, the authors describe the creation and evaluation of a complete pediatric cervical spine model.

METHODS

Using a thin-slice CT scan of the cervical spine from a 5-year-old boy, a 3D model was created for finite element analysis. The material properties and boundary and loading conditions were created and model analysis performed using open-source software. Because the precise material properties of the pediatric cervical spine are not known, a published parametric approach of scaling adult properties by 50%, 25%, and 10% was used. Each scaled finite element model (FEM) underwent two types of simulations for pediatric cadaver testing (axial tension and cardinal ranges of motion [ROMs]) to assess axial stiffness, ROM, and facet joint force (FJF). The authors evaluated the axial stiffness and flexion-extension ROM predicted by the model using previously published experimental measurements obtained from pediatric cadaveric tissues.

RESULTS

In the axial tension simulation, the model with 50% adult ligamentous and annulus material properties predicted an axial stiffness of 49 N/mm, which corresponded with previously published data from similarly aged cadavers (46.1 ± 9.6 N/mm). In the flexion-extension simulation, the same 50% model predicted an ROM that was within the range of the similarly aged cohort of cadavers. The subaxial FJFs predicted by the model in extension, lateral bending, and axial rotation were in the range of 1-4 N and, as expected, tended to increase as the ligament and disc material properties decreased.

CONCLUSIONS

A pediatric cervical spine FEM was created that accurately predicts axial tension and flexion-extension ROM when ligamentous and annulus material properties are reduced to 50% of published adult properties. This model shows promise for use in surgical simulation procedures and as a normal comparison for disease-specific FEMs.

Unilateral atlanto-occipital injury: A case series and detailed radiographic description

Context

Atlanto-occipital dissociation is a highly lethal ligamentous injury at the craniocervical junction (CCJ). Previous studies have described rare cases of milder forms of atlanto-occipital injury (AOI) which might be managed nonoperatively, but there is a paucity of literature on this subject.

Aims:

We retrospectively reviewed our institutional experience to characterize the injury patterns, treatments, and clinical courses of patients with unilateral AOI.

Methods:

We included patients with radiographic evidence of unilateral occipitocervical joint capsular disruption, distraction, or edema ± injury of the apical ligament, tectorial membrane, anterior atlanto-occipital membrane, posterior atlanto-occipital membrane, alar ligaments, or cruciate ligament. The long-term outcomes were gathered from medical records, and six patients were available for Neck Disability Index via phone call at the time of the study.

Results:

Eight patients were included in the study. The mean age was 45.1 years ± 26.5. Causes of trauma included motor vehicle collision for five patients (5/8, 62.5%), falls for two (2/8, 25), and assault for one (1/8, 12.5%). All patients had a widened condyle-C1 interval >2 mm. Three patients underwent occipitocervical fusion, one patient underwent atlantoaxial fusion, and another received subaxial fusions for other injuries. Three patients underwent no surgical intervention. All patients were seen at least once as an outpatient following hospital discharge. There were no delayed neurologic injuries or deaths.

Conclusions:

We propose that ligamentous injury at the CCJ functions more as a spectrum rather than dichotomous diagnosis, of which a subset can likely be safely managed nonoperatively.

EuroQol-5 dimensions health-related quality of life questionnaire in craniovertebral instability treated with posterior fixation with or without occipital plating: A comparative study with matched datasets

Objective:

Methods:

Results:

Conclusions:

Ligament deformation patterns of the craniocervical junction during head axial rotation tracked by biplane fluoroscopes

BACKGROUND

Frequently, treatment decisions for craniocervical injuries and instability are based on imaging findings, but in vivo ligament kinematics were poorly understood. This study was to determine in vivo deformation patterns of primary ligaments in the craniocervical junction (i.e., C0-2), including the cruciform ligament, alar ligaments, and accessory ligaments, during dynamic head axial rotation.

METHODS

The skulls and cervical spines of eight asymptomatic female subjects were dynamically imaged using a biplane fluoroscopic imaging system, when they performed left and right head axial rotations. Using a 3D-to-2D registration technique, the in vivo positions and orientations of cervical segments were determined. An optimization algorithm was implemented to determine ligament wrapping paths, and the resulting ligament deformations were represented by percent elongations. Using paired t-tests, ligament deformations in the end-range position were compared to those in the neutral position.

FINDINGS

No significant differences were observed in segmental motions during left and right head rotations (p > 0.05). In general, slight deformations occurred in each component of the cruciform ligament. For the alar ligaments, the ipsilateral ligament was lengthened from -0.7 ± 13.8% to 16.6 ± 15.7% (p < 0.001*). For the accessory ligaments, the contralateral ligament was lengthened from -2.9 ± 7.5% to 10.1 ± 6.2% (p < 0.001*).

INTERPRETATION

This study reveals that there are distinct deformation patterns in craniocervical junction ligaments during dynamic axial head rotation. These ligament deformation data can enhance our understanding of the synergic function of craniocervical junction ligaments, and guide the treatment of craniocervical instability.

Finite element modeling to compare craniocervical motion in two age-matched pediatric patients without or with Down syndrome: implications for the role of bony geometry in craniocervical junction instability

OBJECTIVE

Instability of the craniocervical junction (CCJ) is a well-known finding in patients with Down syndrome (DS); however, the relative contributions of bony morphology versus ligamentous laxity responsible for abnormal CCJ motion are unknown. Using finite element modeling, the authors of this study attempted to quantify those relative differences.

METHODS

Two CCJ finite element models were created for age-matched pediatric patients, a patient with DS and a control without DS. Soft tissues and ligamentous structures were added based on bony landmarks from the CT scans. Ligament stiffness values were assigned using published adult ligament stiffness properties. Range of motion (ROM) testing determined that model behavior most closely matched pediatric cadaveric data when ligament stiffness values were scaled down to 25% of those found in adults. These values, along with those assigned to the other soft-tissue materials, were identical for each model to ensure that the only variable between the two was the bone morphology. The finite element models were then subjected to three types of simulations to assess ROM, anterior-posterior (AP) translation displacement, and axial tension.

RESULTS

The DS model exhibited more laxity than the normal model at all levels for all of the cardinal ROMs and AP translation. For the CCJ, the flexion-extension, lateral bending, axial rotation, and AP translation values predicted by the DS model were 40.7%, 52.1%, 26.1%, and 39.8% higher, respectively, than those for the normal model. When simulating axial tension, the soft-tissue structural stiffness values predicted by the DS and normal models were nearly identical.

CONCLUSIONS

The increased laxity exhibited by the DS model in the cardinal ROMs and AP translation, along with the nearly identical soft-tissue structural stiffness values exhibited in axial tension, calls into question the previously held notion that ligamentous laxity is the sole explanation for craniocervical instability in DS.

Febio finite element models of the human cervical spine

Finite element (FE) analysis has proven to be useful when studying the biomechanics of the cervical spine. Although many FE studies of the cervical spine have been published, they typically develop their models using commercial software, making the sharing of models between researchers difficult. They also often model only one part of the cervical spine. The goal of this study was to develop and evaluate three FE models of the adult cervical spine using open-source software and to freely provide these models to the scientific community. The models were created from computed tomography scans of 26-, 59-, and 64-year old female subjects. These models were evaluated against previously published experimental and FE data. Despite the fact that all three models were assigned identical material properties and boundary conditions, there was notable variation in their biomechanical behavior. It was therefore apparent that these differences were the result of morphological differences between the models.

Successful non-operative management for atlanto-occipital dislocation resulting in spinal cord contusion in a patient with atlanto-occipital assimilation and severe Chiari I malformation

Background:

Atlanto-occipital dislocation (AOD) is a rare, highly morbid, and highly lethal injury that results from high-energy trauma and almost universally requires operative management for satisfactory outcomes. It can be difficult to identify the severity of injury at the time of presentation, and when diagnosis is delayed outcomes worsen significantly. Anatomic anomalies of the craniovertebral junction may further complicate its detection. When such anomalies are present either singly or in combination, they are known to cause space constraints which may increase the likelihood of spinal cord injury. Given that such anomalies and AOD are rare, few examples of patients with both are reported in the literature. Furthermore, it is not clear in what way patient management may be impacted in this context.

Case Description:

We will present a unique case of an 18-year-old patient with traumatic AOD and an intact neurologic examination who was found to have atlanto-occipital assimilation (AOA), platybasia, basilar invagination, and severe Chiari I malformation, who was treated effectively with non-operative management.

Conclusion:

Our case demonstrates the successful application of a non-operative treatment strategy in a carefully selected patient with AOD in the context of AOA.

The atlantoaxial capsular ligaments and transverse ligament are the primary stabilizers of the atlantoaxial joint in the craniocervical junction: a finite element analysis

OBJECTIVE

Prior studies have provided conflicting evidence regarding the contribution of key ligamentous structures to atlantoaxial (AA) joint stability. Many of these studies employed cadaveric techniques that are hampered by the inherent difficulties of testing isolated-injury scenarios. Analysis with validated finite element (FE) models can overcome some of these limitations. In a previous study, the authors completed an FE analysis of 5 subject-specific craniocervical junction (CCJ) models to investigate the biomechanics of the occipitoatlantal joint and identify the ligamentous structures essential for its stability. Here, the authors use these same CCJ FE models to investigate the biomechanics of the AA joint and to identify the ligamentous structures essential for its stability.

METHODS

Five validated CCJ FE models were used to simulate isolated- and combined ligamentous–injury scenarios of the transverse ligament (TL), tectorial membrane (TM), alar ligament (AL), occipitoatlantal capsular ligament, and AA capsular ligament (AACL). All models were tested with rotational moments (flexion-extension, axial rotation, and lateral bending) and anterior translational loads (C2 constrained with anterior load applied to the occiput) to simulate physiological loading and to assess changes in the atlantodental interval (ADI), a key radiographic indicator of instability.

RESULTS

Isolated AACL injury significantly increased range of motion (ROM) under rotational moment at the AA joint for flexion, lateral bending, and axial rotation, which increased by means of 28.0% ± 10.2%, 43.2% ± 15.4%, and 159.1% ± 35.1%, respectively (p ≤ 0.05 for all). TL removal simulated under translational loads resulted in a significant increase in displacement at the AA joint by 89.3% ± 36.6% (p < 0.001), increasing the ADI from 2.7 mm to 4.5 mm. An AACL injury combined with an injury to any other ligament resulted in significant increases in ROM at the AA joint, except when combined with injuries to both the TM and the ALs. Similarly, injury to the TL combined with injury to any other CCJ ligament resulted in a significant increase in displacement at the AA joint (significantly increasing ADI) under translational loads.

CONCLUSIONS

Using FE modeling techniques, the authors showed a significant reliance of isolated- and combined ligamentous–injury scenarios on the AACLs and TL to restrain motion at the AA joint. Isolated injuries to other structures alone, including the AL and TM, did not result in significant increases in either AA joint ROM or anterior displacement.