C2-fractures: part II. A morphometrical analysis of computerized atlantoaxial motion, anatomical alignment and related clinical outcomes

Monoaxial Screws Versus Polyaxial Screws Osteosynthesis for Unstable Atlas Fractures: A Retrospective, Comparative Study With a Minimum Follow-Up of 3 years

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

The study aimed to compare the radiological parameters, clinical outcomes, and long-term effects of the posterior osteosynthesis with polyaxial screw-rod system and the monoaxial screw-rod system in the treatment of unstable atlas fractures.

METHODS

We retrospectively analyzed the clinical data of 33 patients with posterior ORIF for unstable atlas fractures in our hospital from August 2013 to June 2020, with a minimum of 3 years of follow-up. Polyaxial screws (group A) were used in 12 patients and monoaxial screws (group B) in 21 patients. Perioperative data, radiological parameters, and clinical outcomes were collected and compared between the 2 surgical approaches.

RESULTS

The operative time, blood loss, time of screw-rod system placement, and hospital stay were significantly lower in group A than in group B. At the last follow-up, the visual analog scale (VAS) score and anterior arch reduction rate of the atlas in group A were lower than those in group B, while the lateral mass displacement (LMD) in group A was higher than that in group B. There was no significant difference between Group A and Group B in terms of the anterior atlantodental interval (AADI), posterior arch reduction rate of the atlas, range of motion (ROM), and neck disability index (NDI).

CONCLUSIONS

Monoaxial screws can achieve better reduction results for unstable atlas fractures, especially for the anterior arch of atlas. However, the surgical operation of monoaxial screws is more complicated than that of polyaxial screws and has more complications. Appropriate implants should be selected for the treatment of unstable atlas fractures based on the type of atlas fracture, the experience of surgeons, and the demands of patients.

Direct osteosynthesis in the treatment of atlas burst fractures: a systematic review

PURPOSE

The treatment of unstable atlas fractures remains a controversial topic. The study aims at assessing the prognosis and efficacy of osteosynthesis for unstable atlas fractures through a review of the current literature and additionally aims to compare outcomes between the transoral and posterior approaches.

METHODS

A systematic review of databases including PubMed, EMBASE, Cochrane, Web of Science, CNKI, and Wanfang was conducted. Titles and abstracts were screened by two reviewers to identify studies meeting pre-defined inclusion criteria for comprehensive analysis.

RESULTS

The systematic review included 28 articles, 19 employing the posterior approach and 9 utilizing the transoral approach. It covered osteosynthesis in 297 patients with unstable atlas fractures, comprising 169 treated via the posterior approach and 128 via the transoral approach. Analysis revealed high healing rates and clinical improvement in both approaches, evidenced by improvements in the visual analog scale, range of motion, atlantodens interval, and lateral displacement distance post-surgery.

CONCLUSION

Osteosynthesis offers effective treatment for unstable atlas fractures. Both transoral and posterior approaches can achieve good clinical outcomes for fracture, and biomechanical studies have confirmed that osteosynthesis can maintain the stability of the occipitocervical region, preserve the motor function of the atlantoaxial and occipito-atlantoaxial joints, and greatly improve the quality of life of patients. However, variations exist in the indications and surgical risks associated with each method, necessitating their selection based on a thorough clinical evaluation of the patient's condition.

Design of a novel lateral mass screw-plate system for the treatment of unstable atlas fractures: a finite element analysis

BACKGROUND

Osteosynthesis of unstable atlas fractures preserves joint motion and therefore has a distinct advantage over a range of treatment procedures. To prevent the potential disadvantages associated with osteosynthesis, a new atlas lateral mass screw-plate (LMSP) system has been designed. However, the biomechanical role of using the LMSP system in atlas internal fixation is not known. The aim of this study was to compare the biomechanical stability of a new LMSP with traditional posterior screw and rod (PSR) fixation techniques on the occipitocervical junction (C0-C2) through finite element analysis.

METHODS

A nonlinear C0-C2 finite element model of the intact upper cervical spine was developed and validated. The unstable model using the PSR system was then compared with the model using the LMSP system for fixation. A vertical load of 40 N was applied to the C0 to simulate head weight, while a torque of 1.5 Nm was applied to the C0 to simulate flexion, extension, lateral bending, and axial rotation.

RESULTS

The range of motion of both systems was close to the intact model. Compared with the LMSP system model, the PSR system model increased flexion, extension, lateral bending, and axial rotation by 4.9%, 3.0%, 5.0%, and 29.5% in the C0-C1 segments, and 4.9%, 2.7%, 2.4%, and 22.6% in the C1-C2, respectively. In flexion, extension, and lateral bending motion, the LMSP system model exhibited similar stress to the PSR system model, while in axial rotation, the PSR system model exhibited higher stress.

CONCLUSIONS

The findings of our study indicate that the two tested system models provide comparable stability. However, better stability was achieved during axial rotation with the LMSP system, and in this system, the maximum von Mises stress was less than that of the PSR one. As the atlantoaxial joint functions primarily as a rotational joint, the use of the LMSP system may provide a more stable environment for the joint that has become unstable due to fracture.

Dynamics of atlantoaxial rotation related to age and sex: a cross-sectional study of 308 subjects

BACKGROUND CONTEXT

Physiological ranges and dynamic changes of atlantoaxial rotation (ROTC1/2), total cervical spine rotation (ROTCs) and the percentage of ROTC1/2 from ROTCs (ROTCperc) for different age groups have not yet been investigated in a sufficiently sized cohort. Furthermore, it is not clear whether demographic variables such a sex, smoking status or diabetes affect ROTC1/2, ROTCs and ROTCperc.

PURPOSE

Obtain physiological ranges of ROTC1/2, ROTCs and ROTCperc for different age groups and determine their age-based dynamics. Investigate whether ROTC1/2, ROTCs and ROTCperc are affected by sex, smoking status or diabetes.

DESIGN

Observational cross-sectional study.

PATIENT SAMPLE

Patients undergoing elective CT examinations of the head and neck region between August 2020 and January 2022.

OUTCOME MEASURES

Ranges of motion of ROTC1/2, ROTCs and ROTCperc in degrees.

METHODS

A total of 308 subjects underwent dynamic rotational CT examinations of the upper cervical spine. Patients were divided into three age categories A1 (27-49 years), A2 (50-69 years) and A3 (≥70 years). Category A3 was further divided into B1 (70-79 years) and B2 (≥80 years). Values of ROTC1/2, ROTCs and ROTCperc were compared between all age groups, males and females, smokers and nonsmokers, diabetics a nondiabetics. Dynamics of ROTC1/2, ROTCs related to age and sex were visualized using scatterplot and trendline models.

RESULTS

ROTC1/2 significantly decreased from group A1 (64.4°) to B2 (46.7°) as did ROTCs from A1 (131.2°) to B2 (97.6°). No significant differences of ROTperc were found between groups A1-B2 with values oscillating between 49% and 51%. Smoking and diabetes did not significantly affect ROTC1/2, ROTCs and ROTCperc, females had significantly higher ROTCs than males. Males and females demonstrated a different dynamic of ROTC1/2 and ROTCs demonstrated by out scatterplot and trendline models.

CONCLUSIONS

Both ROTC1/2 and ROTCs significantly decrease with age, whereas ROTCperc remains stable. Females demonstrated higher ROTCs and their decrease of ROTC1/2 and ROTCs occurred in higher age groups compared to males. The functional repercussions atlantoaxial fusion are variable based on patient age and sex and should be taken into account prior to surgery.

The association between unilateral high-riding vertebral artery and atlantoaxial joint morphology: a multi-slice spiral computed tomography study of 396 patients and a finite element analysis

BACKGROUND CONTEXT

A high-riding vertebral artery (HRVA) can deviate too medially, too posteriorly, or too superiorly to allow the safe insertion of screws. However, it is unknown whether the presence of a HRVA is associated with morphological changes of the atlantoaxial joint.

PURPOSE

To investigate the association between HRVA and atlantoaxial joint morphology in patients with and without HRVA.

STUDY DESIGN

A retrospective case-control study and finite element (FE) analysis.

PATIENT SAMPLE

A total of 396 patients with cervical spondylosis underwent multi-slice spiral computed tomography (MSCT) of cervical spine at our institutions from 2020 to 2022.

OUTCOME MEASURES

A series of atlantoaxial joint morphological parameters, including C2 lateral mass settlement (C2 LMS), C1-2 sagittal joint inclination (C1-2 SI), C1-2 coronal joint inclination (C1-2 CI), atlanto-dental interval (ADI), lateral atlanto-dental interval (LADI), and C1-2 relative rotation angle (C1-2 RRA) were measured, and lateral atlantoaxial joints osteoarthritis (LAJs-OA) was recorded. The stress distribution on the C2 facet surface under different torques of flexion-extension, lateral bending, and axial rotation was analyzed by FE models. A 2-Nm moment was applied to all models to determine the range of motion (ROM).

METHODS

A total of 132 consecutive cervical spondylosis patients with unilateral HRVA were enrolled in the HRVA group, and 264 patients without HRVA matched for age and sex were enrolled in the normal (NL) group. Atlantoaxial joint morphological parameters were compared between two sides of C2 lateral mass within HRVA or NL group, and between HRVA and NL groups. A 48-year-old woman with cervical spondylosis without HRVA was selected for cervical MSCT. A three-dimensional (3D) FE intact model of the normal upper cervical spine (C0-C2) was created. We established the HRVA model by simulating atlantoaxial morphological changes of unilateral HRVA with FE method.

RESULTS

The C2 LMS was significantly smaller on the HRVA side than that on the non-HRVA side in the HRVA group, but C1-2 SI, C1-2 CI, and LADI on HRVA side were significantly larger than those on non-HRVA side. There was no significant difference between left and right sides in the NL group. The difference in C2 LMS (d-C2 LMS) between HRVA side and non-HRVA side in the HRVA group was larger than that in the NL group (P < 0.05). Meanwhile, the differences in C1-2 SI (d-C1/2 SI), C1-2 CI (d-C1/2 CI), and LADI (d-LADI) in the HRVA group were significantly larger than those in the NL group. The C1-2 RRA in the HRVA group was significantly larger than that in the NL group. Pearson correlations showed that d-C1/2 SI, d-C1/2 CI, and d-LADI were positively associated with d-C2 LMS (r=0.428, 0.649, 0.498, respectively, p<.05 for all). The incidence of LAJs-OA in the HRVA group (27.3%) was significantly larger than that in the NL group (11.7%). Compared with the normal model, the ROM of C1-2 segment declined in all postures of the HRVA FE model. We found a larger distribution of stress on the C2 lateral mass surface of the HRVA side under different moment conditions.

CONCLUSIONS

We suggest that HRVA affects the integrity of the C2 lateral mass. This change in patients with unilateral HRVA is associated with the nonuniform settlement of the lateral mass and an increase in the lateral mass inclination, which may further affect the degeneration of the atlantoaxial joint because of the stress concentration on the C2 lateral mass surface.

Assessment of atlantoaxial rotation: how accurate is clinical measurement? a comparative study of cervical range of motion using MRI and standard orthopedic techniques

PURPOSE

Measurement of neck rotation is currently reliant on radiologic imaging. Given the radiation exposure for CT imaging and the additional inconvenience for the patients, an alternative assessment is needed. Goniometers are comfortably to use and easy to access, also for private consulting. The aim of this study was the assessment of whether a handheld goniometer can be used for accurately measuring the rotation of C1-C2.

METHODS

Clinical measurement of rotation was taken in flexed position of the neck. As comparison functional MRI was used. The measured rotation of C1-C2 was compared to identify the accuracy of the goniometer, in comparison to functional MRI scan.

RESULTS

Analysis of accuracy using a goniometer and dynamic MRI to assess C1-2 axial rotation showed significant differences for absolute values, but not regarding the percentage of rotation compared to total neck rotation.

CONCLUSION

The goniometer is exact to impartially determine the percentage contribution of C1-2 rotation to total neck rotation.

Factors associated with the increased risk of atlantoaxial osteoarthritis: a retrospective study

Purpose Atlantodens osteoarthritis and atlantoaxial osteoarthritis cause neck pain and suboccipital headaches. Currently, knowledge on the risk factors for atlantoaxial osteoarthritis is lacking. This study aimed to investigate the factors related to the increased risk of atlantoaxial osteoarthritis. Methods We analyzed computed tomography (CT) images of the upper cervical spine of 1266 adult trauma patients for whom upper cervical spine CT was performed at our hospital between 2014 and 2019. The degree of atlantoaxial osteoarthritis was quantified as none-to-mild (not having osteoarthritis) or moderate-to-severe (having osteoarthritis). Risk factors associated with atlantoaxial osteoarthritis were identified using univariate and multivariable logistic regression analyses. Results The study group included 69.4% men, and the overall average age of the study population was 54.9 ± 20.4 years. The following factors were independently and significantly associated with atlantoaxial osteoarthritis in the multivariable logistic regression analysis: age in the sixth decade or older (odds ratio [OR], 20.5; 95% confidence interval [CI], 6.2‒67.2, p < 0.001), having calcific synovitis (OR, 4.9; 95% CI, 2.4‒9.9, p < 0.001), women sex (OR, 3.3; 95% CI, 1.9‒5.7, p = 0.002), and not having atlantodens osteoarthritis (OR, 2.1; 95% CI, 1.2‒3.8, p = 0.014). Conclusion In the multivariable logistic regression analysis, age in the sixth decade or older, calcification of the transverse ligament, being women, and not having atlantodens osteoarthritis were found to be significantly associated with atlantoaxial osteoarthritis. Delayed diagnosis and treatment can be avoided by focusing on these risk factors.

Bicortical Short C2 Pars Screw Fixation for High-Riding Vertebral Artery Provided Sufficient Biomechanical Stability: A Finite Element Study

STUDY DESIGN

Finite element analysis.

OBJECTIVE

To determine and compare the biomechanical stability of the bicortical short C2 pars screw fixation for high-riding vertebral artery (HRVA) with the C2 pedicle screw and C2 translaminar screw fixation in finite element models.

SUMMARY OF BACKGROUND DATA

Fixation of C2 is technically demanding in the case of HRVA. However, there is no consensus on the alternative technique for the C2 screw fixation for HRVA in the literature.

METHODS

A finite element model of the upper cervical spine (C0-C2) with HRVA had been developed. C1 pedicle screw was applied at C1 by using notching technique. Bicortical short C2 pars screws, C2 pedicle screws, and C2 translaminar screws were used in each model. Then a vertical load of 50 N and a 1.5 Nm torque were applied to the C0 to simulate flexion, extension, lateral bending, and axial rotation respectively.

RESULTS

Compared with C2 pedicle screw fixation, the bicortical short C2 pars screw fixation increased the range of motion by -1.45%, 2.13%, 62.0%, and 22.0% under flexion, extension, lateral bending, and axial rotation, respectively. However, the C2 translaminar screw fixation increased the range of motion by 43.6%, 17.8%, 423.4%, and 19.9%, respectively. In terms of the peak von Mises stress, compared with C2 pedicle screw fixation, bicortical short C2 pars screw decreased 46.1%, 41.6%, 71.3%, and -12.5% under flexion, extension, lateral bending, and axial rotation, respectively; C2 translaminar screw decreased -2.66%, -4.87%, 73.0%, and -10.1%, respectively.

CONCLUSION

For a patient with HRVA, bicortical short C2 pars screw fixation provides sufficient stability and exhibited a smaller von Mises distribution on the screw-rod construct, indicating it could be an effective C2 internal fixation method for HRVA to promote C1-C2 stability and avoid the vertebral artery injury.Level of Evidence: N/A.

Management of fresh odontoid fractures using posterior C1-2 fixation without fusion: a long-term clinical follow-up study

OBJECTIVE

Posterior C1-2 fixation without fusion makes it possible to restore atlantoaxial motion after removing the implant, and it has been used as an alternative technique for odontoid fractures; however, the long-term efficacy of this technique remains uncertain. The purpose of the present study was to explore the long-term follow-up outcomes of patients with odontoid fractures who underwent posterior C1-2 fixation without fusion.

METHODS

A retrospective study was performed on 62 patients with type II/III fresh odontoid fractures who underwent posterior C1-2 fixation without fusion and were followed up for more than 5 years. The patients were divided into group A (23 patients with implant removal) and group B (39 patients without implant removal) based on whether they underwent a second surgery to remove the implant. The clinical outcomes were recorded and compared between the two groups. In group A, the range of motion (ROM) of C1-2 was calculated, and correlation analysis was performed to explore the factors that influence the ROM of C1-2.

RESULTS

A solid fracture fusion was found in all patients. At the final follow-up, no significant difference was found in visual analog scale score or American Spinal Injury Association Impairment Scale score between the two groups (p > 0.05), but patients in group A had a lower Neck Disability Index score and milder neck stiffness than did patients in group B (p < 0.05). In group A, 87.0% (20/23) of the patients had atlantoodontoid joint osteoarthritis at the final follow-up. In group A, the C1-2 ROM in rotation was 6.1° ± 4.5° at the final follow-up, whereas the C1-2 ROM in flexion-extension was 1.8° ± 1.2°. A negative correlation was found between the C1-2 ROM in rotation and the severity of tissue injury in the atlantoaxial region (r = -0.403, p = 0.024) and the degeneration of the atlantoodontoid joint (r = -0.586, p = 0.001).

CONCLUSIONS

Posterior C1-2 fixation without fusion can be used effectively for the management of fresh odontoid fractures. The removal of the implant can further improve the clinical efficacy, but satisfactory atlantoaxial motion cannot be maintained for a long time after implant removal. A surgeon should reconsider the contribution of posterior C1-2 fixation without fusion and secondary implant removal in preserving atlantoaxial mobility for patients with fresh odontoid fractures.

Development and first application testing of a new protocol for CT-based stability evaluation of the injured upper cervical spine

PURPOSE

For trauma surgeons, the evaluation of the stability of the upper cervical spine may be demanding. The aim of this study was to develop a protocol for decision-making on upper cervical spine stability in trauma patients based on established parameters obtained by CT imaging as well as testing the protocol by having it applied by trauma surgeons.

METHODS

A structured literature search on upper cervical spine stability was performed. The best evaluated instability criteria in CT imaging were determined. Based on these parameters a protocol for stability evaluation of the injured upper cervical spine was developed. A first application testing was performed. In addition to the assessment of instability, the time required for the assessment was analyzed.

RESULTS

A protocol for CT-based stability evaluation of the injured upper cervical spine based on the current literature was developed and displayed in a flow chart. Testing of the protocol found the stability of the cervical spine was correctly assessed in 55 of 56 evaluations (98.2%). In one test run, a stable upper cervical spine was judged to be unstable. Further analysis showed that this case was based on a measurement error. The assessment time of CT-images decreased significantly during repeat application of the protocol (p < 0.0001), from 336 ± 108 s (first case) to 180 ± 30 s (fourth case).

CONCLUSION

The protocol can be applied quickly and safely by non-specialized trauma surgeons. Thus, the protocol can support the decision-making process in CT-based evaluation of the stability of the injured upper cervical spine.

The Relationship between the Occipitocervical Junction and Thoracic Kyphosis in Ankylosing Spondylitis: A Retrospective Cohort Study of 86 Cervical Fractures in Surgically Treated Patients

Study Design

Retrospective analysis of prospectively collected data.

Purpose

To describe the radiological characteristics of the occipitocervical area in patients with ankylosing spondylitis (AS) using the novel measure X-angle and to describe the correlation between the ankylosed occipitoatlantoaxial (OAA) joint and thoracic kyphosis (TK).

Overview of Literature

AS affects the axial skeleton, leading to progressive ankylosis of all vertebral segments. The effect of ankylosis on the upper cervical area of these patients is not well documented.

Methods

All patients with complete ankylosis of the spinal column between C3 and T1, treated for cervical spinal fracture between 2007 and 2014, were eligible for inclusion in this study. The level of cervical fracture was identified. The T1–12 and T5–12 angles were measured using preoperative lateral radiography. The progressive degeneration of the C0-C1-C2 joints was evaluated via the new indicator X-angle, through the measurement of the angle of the C0-C1-C2 articulations in the coronal plane using computed tomography.

Results

We included 86 consecutive patients with AS (67 males) aged 69±12 years. The patients were divided into two groups according to the degenerative change in the C0–C1 joint (62 patients with a mobile joint and 24 patients with an ankylosed joint). There was no significant difference between the two groups in terms of age (p =0.094) and level of fracture (p =0.949). The most commonly affected level was C6. There was no requirement for revision due to non-union in any of the patients. There was a statistically significant difference observed in the T1–12, T5–12, and X-angles (p =0.004, 0.001, and <0.001, respectively). TK was greater in the ankylosed joint group than in the mobile joint group. The X-angle was also greater in the ankylosed joint group because of the vertical destruction of the OAA joint.

Conclusions

Thoracic hyperkyphosis resulted in degenerative changes in the C0-C1-C2 joint in patients with AS. The X-angle is a reliable method for measuring the integrity of the C0-C1-C2 joint in such patients.

Assessment of cervical range of motion in patients after axis fracture

BACKGROUND

Surgical treatment of odontoid fractures with posterior C1/C2 fusion always leads to severe limitations in mobility of the cervical spine and head.

PURPOSE

To assess the mobility of the cervical spine in patients treated with various surgical methods after an axis body fracture.

MATERIAL AND METHODS

A group of 61 subjects receiving surgical treatment in a group of 214 subjects treated for odontoid fractures at one ward of neurosurgery at a regional hospital. Studies also included odontoid peg and Hangman fractures. The range of motion of the head was compared to standards by the International Standard Orthopedic Measurements (ISOM) and to head mobility in a control group of 80 healthy subjects without any pathologies or complaints associated with the cervical spine. Ranges of motion were measured with the CROM goniometre with regard to flexion, extension, right and left lateral flexion and right and left rotation. The functional status was evaluated with Neck Disability Index (NDI) standard questionnaires indicated for patients with cervical spine pain.

RESULTS

Except for flexion and extension, patients after odontoid fractures had a statistically significantly smaller range of motion of the cervical spine in all planes compared to the control group and ISOM standards.

CONCLUSIONS

Odontoid fractures lead to limitations in mobility of the cervical spine even after treatment with methods that in theory should preserve the C1/C2 mobility.

Treatment of Axis Body Fractures: A Systematic Review

STUDY DESIGN

Evidence-based systematic review.

OBJECTIVES

To define the optimal treatment of fractures involving the C2 body, including those with concomitant injuries, based upon a systematic review of the literature.

SUMMARY OF BACKGROUND DATA

Axis body fractures have customarily been treated nonoperatively, but there are some injuries that may require operative intervention. High-quality literature is sparse and there are few class I or class II studies to guide treatment decisions.

MATERIALS AND METHODS

A literature search was conducted using PubMed (MEDLINE), Cochrane Central Register of Controlled Trials, and Scopus (EMBASE, MEDLINE, COMPENDEX). The quality of literature was rated according to a grading tool developed by the Center for Evidence-based Medicine. Operative and nonoperative treatment of axis body fractures were compared using fracture bony union as the primary outcome measure. As risk factors for nonunion were not consistently reported, cases were analyzed individually.

RESULTS

The literature search identified 62 studies, of which 10 were case reports which were excluded from the analysis. A total of 920 patients from 52 studies were included. The overall bony union rate for all axis body fractures was 91%. Although the majority of fractures were treated nonoperatively, there has been an increasing trend toward operative intervention for Benzel type III (transverse) axis body fractures. Nearly 76% of axis body fractures were classified as type III fractures, of which 88% united successfully. Nearly all Benzel type I and type II axis body fractures were successfully treated nonoperatively. The risk factors for nonunion included: a higher degree of subluxation, fracture displacement, comminution, concurrent injuries, delay in treatment, and older age.

CONCLUSIONS

High rates for fracture union are reported in the literature for axis body fractures with nonoperative treatment. High-quality prospective studies are required to develop consensus as to which C2 body fractures require operative fixation.

Patterns of C-2 fracture in the elderly: comparison of etiology, treatment, and mortality among specific fracture types

OBJECTIVE Previous studies have focused on Type II odontoid fractures and have failed to report on the effect of other C-2 fracture types on treatment and outcome. The purpose of this study was to compare patient characteristics, cause of injury, predisposing factors to fracture, treatments, and mortality rates among C-2 fracture types in a cohort of elderly patients 70 years of age and older. METHODS A retrospective cohort study design was used. Patients who sustained a C-2 fracture between 2002 and 2011 and who were admitted to the authors' Level 1 trauma center were identified using the Discharge Abstract Database and the International Statistical Classification of Diseases and Related Health Problems (ICD-10) code S12.1. Fractures were classified as odontoid Type I, II, or III; hangman's; C-2 complex (hangman's appearance on sagittal images, Type III odontoid on coronal cuts); and other (miscellaneous). Age, sex, predisposing factors to falls, cause of injury, treatment, presence of autofusion in the subaxial cervical spine, and mortality rates were compared between fracture patterns. RESULTS One hundred forty-one patients were included; their mean age was 82 years. Fractures included Type II odontoid (57%), complex (19%), Type III odontoid (11%), hangman's (8%), and other (5%). Falls from a standing height accounted for 47% of injuries, and 65% of patients had ≥ 3 risk factors for falls. Subaxial autofusion was more common in odontoid fractures (p = 0.002). Treatment was mainly nonoperative (p < 0.0001). The 1-year mortality rate was 27%. Four patients died of spinal cord injury. CONCLUSIONS Although not as common as Type II odontoid fractures, other C-2 fractures including hangman's, complex, and Type III odontoid fractures accounted for close to half of the injuries in the study cohort. There were few differences between the fracture types with respect to cause of injury, predisposing factors, or mortality rate. However, surgical treatment was more common for Type II odontoid fractures.

Dynamic in vivo 3D atlantoaxial spine kinematics during upright rotation

Diagnosing dysfunctional atlantoaxial motion is challenging given limitations of current diagnostic imaging techniques. Three-dimensional imaging during upright functional motion may be useful in identifying dynamic instability not apparent on static imaging. Abnormal atlantoaxial motion has been linked to numerous pathologies including whiplash, cervicogenic headaches, C2 fractures, and rheumatoid arthritis. However, normal C1/C2 rotational kinematics under dynamic physiologic loading have not been previously reported owing to imaging difficulties. The objective of this study was to determine dynamic three-dimensional in vivo C1/C2 kinematics during upright axial rotation. Twenty young healthy adults performed full head rotation while seated within a biplane X-ray system while radiographs were collected at 30 images per second. Six degree-of-freedom kinematics were determined for C1 and C2 via a validated volumetric model-based tracking process. The maximum global head rotation (to one side) was 73.6±8.3°, whereas maximum C1 rotation relative to C2 was 36.8±6.7°. The relationship between C1/C2 rotation and head rotation was linear through midrange motion (±20° head rotation from neutral) in a nearly 1:1 ratio. Coupled rotation between C1 and C2 included 4.5±3.1° of flexion and 6.4±8.2° of extension, and 9.8±3.8° of contralateral bending. Translational motion of C1 relative to C2 was 7.8±1.5mm ipsilaterally, 2.2±1.2mm inferiorly, and 3.3±1.0mm posteriorly. We believe this is the first study describing 3D dynamic atlantoaxial kinematics under true physiologic conditions in healthy subjects. C1/C2 rotation accounts for approximately half of total head axial rotation. Additionally, C1 undergoes coupled flexion/extension and contralateral bending, in addition to inferior, lateral and posterior translation.

Patient-reported outcome following nonsurgical management of type II odontoid process fractures in adults

Background:

Transverse (type II) odontoid process fracture is among the most commonly encountered cervical spine fractures. Nonsurgical management through external immobilization is occasionally preferred to surgical management but is criticized for its higher rates of failure and lower patient satisfaction. Our aim is to analyze patient-reported outcomes in patients who underwent nonsurgical treatment for type II odontoid fractures.

Methods:

We identified patients >18-year-old who underwent external immobilization as a treatment for isolated type II odontoid fracture between 2007 and 2012. We collected demographic parameters, clinical presentation, mode of injury, imaging studies and modality and duration of treatment (soft collar, halo-vest, or both). Patients were contacted by telephone to participate in a 15-min survey addressing their recovery including their subjective rate of return to preinjury level of functioning.

Results:

Fifteen patients met the inclusion/exclusion criteria and participated in our survey. Patients were followed up for an average of 19 months after injury. Overall mean age was 61 years. Injury followed a mechanical fall or a road traffic accident in 11 and 4 cases, respectively. External immobilization was achieved by halo vest only in nine patients, soft collar only in two patients (13%), and through a sequential combination in the remaining 4 (27%). This was deployed for a mean of 7.8 months. Radiological studies at the last follow-up showed bony healing (27%), fibrous nonunion (60%), and persistent instability (13%). Patients reported gradual recovery of function throughout the 1^st year after injury with levels above 70% of preinjury functioning achieved by 13% of patients at 6 months, 33% at 9 months, and 47% at 12 months. Overall satisfaction with nonsurgical management was 68%.

Conclusion:

In selected patients with type II odontoid fractures, external immobilization represents a good option with acceptable course of recovery.

Outcome Instruments in Spinal Trauma Surgery: A Bibliometric Analysis

Study Design Literature review. Objective To identify outcomes instruments used in spinal trauma surgery over the past decade, their frequency of use, and usage trends. Methods Five top orthopedic journals were reviewed from 2004 to 2013 for clinical studies of surgical intervention in spinal trauma that reported patient-reported outcome instruments use or neurologic function scale use. Publication year, level of evidence (LOE), and outcome instruments were collected for each article and analyzed. Results A total of 58 studies were identified. Among them, 26 named outcome instruments and 7 improvised questionnaires were utilized. The visual analog scale (VAS) for pain was used most frequently (43.1%), followed by the Short Form 36 (34.5%), Frankel grade scale (25.9%), Oswestry Disability Index (20.7%) and American Spinal Injury Association Impairment Scale (15.5%). LOE 4 was most common (37.9%), and eight LOE 1 studies were identified (10.3%). Conclusions The VAS pain scale is the most common outcome instrument used in spinal trauma. The scope of this outcome instrument is limited, and it may not be sufficient for discriminating between more and less effective treatments. A wide variety of functional measures are used, reflecting the need for a disease-specific instrument that accurately measures functional limitation in spinal trauma.

Biomechanical Role of the C1 Lateral Mass Screws in Occipitoatlantoaxial Fixation: A Finite Element Analysis

STUDY DESIGN

Finite element analysis.

OBJECTIVE

To determine and compare the construct stability of occipitoatlantoaxial (C0-C1-C2) fixation provided by occipital plate, rod, and screw fixation with or without C1 lateral mass screw (C1LMS).

SUMMARY OF BACKGROUND DATA

Occipitoatlantoaxial fixation techniques use C2 pedicle screw (C2PS) with and without C1LMS that are then incorporated into occipital plate fixation points using occipital screw. There has, however, been no consensus about the standard occiput to C2 fixation in literature and few reports exist about the effects of additional intervening rigid C1LMS on the biomechanics. The role of biomechanics of the addition of C1LMS in occipitoatlantoaxial fixation for fusion is not known.

METHODS

A nonlinear finite element model (FEM) of the intact upper cervical spine had been developed and validated. Then an FEM of an unstable model treated with occipital plate combined with C2PS and C1LMS fixation (C1LMS + C2PS + plate), was compared to that with C2PS fixation (C2PS + plate). Vertical load of 50 N was applied on the C0, to simulate head weight and 1.5 Nm torque was applied to the C0 to simulate flexion, extension, lateral bending, and axial rotation.

RESULTS

Compared with C2PS + plate, the C1LMS + C2PS + plate reduced the range of motion of C0-C2 segment by 3.0%, 35.4%, 29.2%, and 56.9% in flexion, extension, lateral bending, and axial rotation, respectively, and it also led to lower occipital screw and superior rod stresses in all loading conditions.

CONCLUSION

The addition of supplemental C1LMS to occiput-C2 fixation not only enhances greater stability, especially during axial rotation, but also has the capability of distributing the stress evenly and reduces the risk of construct failure because of occipital screw pullout and rod fracture. Therefore, this method may be important to elderly patients with osteopenia or osteoporosis and it may promote a high occipitoatlantoaxial fusion rate.

LEVEL OF EVIDENCE

N/A.

Unilateral lag-screw technique for an isolated anterior 1/4 atlas fracture

STUDY DESIGN

Fractures of the atlas are classified based on the fracture location and associated ligamentous injury. Among patients with atlas fractures treated using external immobilization, nonunion of the fracture could be seen.

OBJECTIVE

Ideally, treatment strategy for an unstable atlas fracture would involve limited fixation to maintain the fracture fragments in a reduced position without restricting the range of motion (ROM) of the atlantoaxial and atlantooccipital joints.

SUMMARY OF BACKGROUND DATA

Such a result can be established using either transoral limited internal fixation or limited posterior lateral mass fixation. However, due to high infection risk and technical difficulty, posterior approaches are preferred but none of these techniques can fully address anterior 1/4 atlas fractures such as in this case.

MATERIALS AND METHODS

A novel open and direct technique in which a unilateral lag screw was placed to reduce and stabilize a progressively widening isolated right-sided anterior 1/4 single fracture of C1 that was initially treated with a rigid cervical collar is described.

RESULTS

Radiological studies made after the surgery showed no implant failure, good cervical alignment, and good reduction with fusion of C1.

CONCLUSIONS

It is suggested that isolated C1 fractures can be surgically reduced and immobilized using a lateral compression screw to allow union and maintain both C1-0 and C1-2 motions, and in our knowledge this is the first description of the use of a lag screw to achieve reduction of distracted anterior 1/4 fracture fragments of the C1 from a posterior approach. This technique has the potential to become a valuable adjunct to the surgeon's armamentarium, in our opinion, only for fractures with distracted or comminuted fragments whose alignment would not be expected to significantly change with classical lateral mass screw reduction.

Health-related quality-of-life outcomes after thoracic (T1-T10) fractures

BACKGROUND CONTEXT

The thoracic spine exhibits a unique response to trauma as the result of recognized anatomical and biomechanical differences. Despite this response, clinical studies often group thoracic fractures (T1-T10) with more caudal thoracolumbar injuries. Subsequently, there is a paucity of literature on the functional outcomes of this distinct group of injuries.

PURPOSE

To describe and identify predictors of health-related quality-of-life outcomes and re-employment status in patients with thoracic fractures who present to a spine injury tertiary referral center.

STUDY DESIGN

An ambispective cohort study with cross-sectional outcome assessment.

PATIENT SAMPLE

A prospectively collected fully relational spine database was searched to identify all adult (>16 years) patients treated with traumatic thoracic (T1-T10) fractures with and without neurologic deficits, treated between 1995 and 2008.

OUTCOME MEASURES

The Short-Form-36, Oswestry Disability Index, and Prolo Economic Scale outcome instruments were completed at a minimum follow-up of 12 months. Preoperative and minimum 1-year postinjury X-rays were evaluated.

METHOD

Univariate and multivariate regression analysis was used to identify predictors of outcomes from a range of demographic, injury, treatment, and radiographic variables.

RESULTS

One hundred twenty-six patients, age 36±15 years (mean±SD), with 135 fractures were assessed at a mean follow-up of 6 years (range 1-15.5 years). Traffic accidents (45%) and translational injuries (54%) were the most common mechanism and dominant fracture pattern, respectively. Neurologic deficits were frequent-53% had complete (American Spinal Injury Association impairment scale [AIS] A) spinal cord deficits on admission. Operative management was performed in 78%. Patients who sustain thoracic fractures, but escaped significant neurologic injury (AIS D or E on admission) had SF-36 scores that did not differ significantly from population norms at a mean follow-up of 6 years. Eighty-eight percent of this cohort was re-employed. Interestingly, Oswestry Disability Index scores remained inferior to healthy subjects. In contrast, SF-36 scores in those with more profound neurologic deficits at presentation (AIS A, B, or C) remained inferior to normative data. Fifty-seven percent were re-employed, 25% in their previous job type. Using multiple regression analysis, we found that comorbidity status (measured by the Charlson Comorbidity index) was the only independent predictor of SF-36 scores. Neurologic impairment (AIS) and adverse events were independent predictors of the SF-36 physical functioning subscale. Sagittal alignment and number of fused levels were not independent predictors.

CONCLUSIONS

At a mean follow-up of 6 years, patients who presented with thoracic fractures and AIS D or E neurologic status recovered a general health status not significantly inferior to population norms. Compared with other neurologic intact spinal injuries, patients with thoracic injuries have a favorable generic health-related quality-of-life prognosis. Inferior outcomes and re-employment prospects were noted in those with more significant neurologic deficits.

Pooled analysis of non-union, re-operation, infection, and approach related complications after anterior odontoid screw fixation

Background

Anterior odontoid screw fixation (AOSF) has been one of the most popular treatments for odontoid fractures. However, the true efficacy of AOSF remains unclear. In this study, we aimed to provide the pooled rates of non-union, reoperation, infection, and approach related complications after AOSF for odontoid fractures.

Methods

We searched studies that discussed complications after AOSF for type II or type III odontoid fractures. A proportion meta-analysis was done and potential sources of heterogeneity were explored by meta-regression analysis.

Results

Of 972 references initially identified, 63 were eligible for inclusion. 54 studies provided data regarding non-union. The pooled non-union rate was 10% (95% CI: 7%–3%). 48 citations provided re-operation information with a pooled proportion of 5% (95% CI: 3%–7%). Infection was described in 20 studies with an overall rate of 0.2% (95% CI: 0%–1.2%). The main approach related complication is postoperative dysphagia with a pooled rate of 10% (95% CI: 4%–17%). Proportions for the other approach related complications such as postoperative hoarseness (1.2%, 95% CI: 0%–3.7%), esophageal/retropharyngeal injury (0%, 95% CI: 0%–1.1%), wound hematomas (0.2%, 95% CI: 0%–1.8%), and spinal cord injury (0%, 95% CI: 0%–0.2%) were very low. Significant heterogeneities were detected when we combined the rates of non-union, re-operation, and dysphagia. Multivariate meta-regression analysis showed that old age was significantly predictive of non-union. Subgroup comparisons showed significant higher non-union rates in age ≥70 than that in age ≤40 and in age 40 to <50. Meta-regression analysis did not reveal any examined variables influencing the re-operation rate. Meta-regression analysis showed age had a significant effect on the dysphagia rate.

Conclusions/Significances

This study summarized the rates of non-union, reoperation, infection, and approach related complications after AOSF for odontoid factures. Elderly patients were more likely to experience non-union and dysphagia.

Classification and surgical management for the axis fracture complicated with adjacent segment instability

This study was to classify the axis fracture complicated with adjacent segment instability and to explore its significance to surgical management. 42 patients (25 males and 17 females) with axis fractures with an average age of 44.14 years (range, 23 to 65) who received surgery between January 2006 and June 2012 were analyzed retrospectively. Results suggest that all patients underwent surgery safely without spinal cord injury, cerebrospinal fluid leakage or vertebral artery injury. The average follow up was 18 months (12-48 months). There was significant difference (t = 2.339, P = 0.011) in JOA score between pre-operation (13.10 ± 4.51) and post-operation time points (15.24 ± 3.86). 1-2 degree improvement of neurofunction was achieved in all except 1 Frankel B. After operation, all patients were immobilized in a hard collar for 3 months. Fusion was achieved in all cases (mean 4.5 months). X-ray showed no malposition of the screws. No instrument failure was noted during follow up. Thus, axis fracture complicated with adjacent segment instability should be treated individually based on the fracture type and adjacent segment instability. Our classification can be used to guide the surgical management.

Unstable Jefferson fractures: Results of transoral osteosynthesis

BACKGROUND

Majority of C1 fractures can be effectively treated conservatively by immobilization or traction unless there is an injury to the transverse ligament. Conservative treatment usually involves a long period of immobilization in a halo-vest. Surgical intervention generally involves fusion, eliminating the motion of the upper cervical spine. We describe the treatment of unstable Jefferson fractures designed to avoid these problems of both conservative and invasive methods.

MATERIALS AND METHODS

A retrospective review of 12 patients with unstable Jefferson fractures treated with transoral osteosynthesis of C1 between July 2008 and December 2011 was performed. A steel plate and C1 lateral mass screw fixation were used to repair the unstable Jefferson fractures. Our study group included eight males and four females with an average age of 33 years (range 23-62 years).

RESULTS

Patients were followed up for an average of 16 months after surgery. Range of motion of the cervical spine was by and large physiologic: Average flexion 35° (range 28-40°), average extension 42° (range 30-48°). Lateral bending to the right and left averaged 30° and 28° respectively (range 12-36° and 14-32° respectively). The average postoperative rotation of the atlantoaxial joint, evaluated by functional computed tomography scan was 60° (range 35-72°). Total average lateral displacement of the lateral masses was 7.0 mm before surgery (range 5-12 mm), which improved to 3.5 mm after surgery (range 1-6.5 mm). The total average difference of the atlanto-dens interval in flexion and extension after surgery was 1.0 mm (range 1-3 mm).

CONCLUSIONS

Transoral osteosynthesis of the anterior ring using C1 lateral mass screws is a viable option for treating unstable Jefferson fractures, which allows maintenance of rotation at the C1-C2 joint and restoration of congruency of the atlanto-occipital and atlantoaxial joints.

Anterior screw fixation for an odontoid fracture using an Acutrak 4/5 screw: a case report

The direct anterior screw fixation of odontoid fractures by a single cancellous screw, especially for osteoporotic vertebrae, has a potential risk of leading to insufficient stability and implant failures. We experienced good results following surgery using a single Acutrak 4/5 screw to obtain sufficient stability for an odontoid fracture in a patient with osteopenia. The screw is a cannulated self-tapping headless screw and has a tapered profile and full threads with variable pitches, and it can yield sufficient compression force as the screw is inserted. The preoperative severe neck pain of the patient was diminished immediately after the surgery. The patient achieved bone union in a short time and had a good clinical result for at least 3 years. Some biomechanical studies showed that the compression force of Acutrak standard screws was stronger than that of both 4.0-mm cancellous screws inserted with the lag screw technique and Herbert screws, and other studies showed that the compression force of Acutrak 4/5 screws was equivalent to that of 4.5-mm cortical screws. However, there has been no clinical report of surgery using an Acutrak 4/5 screw for odontoid fractures. This is the first clinical report of fixation by an Acutrak 4/5 screw.

Treatment of C2 body fracture with unusual distractive and rotational components resulting in gross instability

Cervical fractures can result in severe neurological compromise and even death. One of the most commonly injured segments is the C2 vertebrae, which most frequently involves the odontoid process. In this report, we present the unusual case of a 28-year-old female who sustained a C2 vertebral body fracture (comminuted transverse fracture through the body and both transverse processes) that had both a significant distractive and rotational component, causing the fracture to be highly unstable. Application of halo bracing was unsuccessful. The patient subsequently required a C1-C4 posterior spinal fusion. Follow-up computer tomography imaging confirmed fusion and the patient did well clinically thereafter.

Unstable atlas fracture treatment by anterior plate C1-ring osteosynthesis using a transoral approach

STUDY DESIGN

A retrospective study was conducted to evaluate anterior plate fixation of unstable atlas fractures using a transoral approach.

OBJECTIVE

To further investigate the safety and efficacy of this surgical technique, as there is currently a paucity of available data. While most atlas fractures can be managed by external immobilization with favorable results, surgery is usually preferable in highly unstable cases. Surgical stabilization is most commonly achieved using a posterior approach with fixation of C1-C2 or C0-C2, but these techniques usually result in loss of joint function and cannot fully stabilize anterior arch fractures of the atlas. Although a transoral approach circumvents these issues, only nine cases were described in the literature to our knowledge.

METHODS

Twenty patients with unstable atlas fractures were treated with this technique during a 6-year period. Screw and plate placement, bone fusion, and integrity of spinal cord and vertebral arteries were assessed via intraoperative and follow-up imaging. Neurologic function, range of motion, strength, pain levels, and signs of infection were assessed clinically upon follow-up.

RESULTS

There were no incidents of screw loosening or breakage, plate displacement, spinal cord injury, or vertebral artery injury. A total of 20 plates were placed and all 40 screws were inserted into the atlas lateral masses. CT scans demonstrated that two screws were placed too close to the vertebral artery canal, but without clinical consequences. Imaging demonstrated that bone fusion was achieved in all cases by 6 months postoperatively, without intervertebral instability. No plate-related complications were observed in any patients during the follow-up period.

CONCLUSIONS

C1 anterior plate fixation using a transoral approach appears to be a safe, reliable, and function-preserving surgical method for the management of unstable atlas fractures. For this type of fracture, a transoral approach with anterior fixation should be considered as an alternative to posterior approaches or conservative treatments.

An evidence-based medicine process to determine outcomes after cervical spine trauma: what surgeons should be telling their patients

STUDY DESIGN

A systematic review of the available medical literature from 1980 to 2010 was conducted and combined with expert opinion from a recent survey of experts regarding cervical spine fractures. Using an objective, hierarchical approach, the best available evidence is presented for health-related quality-of-life outcomes for these injuries.

OBJECTIVE

To provide an evidence-based set of guidelines for cervical spine injuries in order to reduce variability in the information given to patients and their families.

SUMMARY OF BACKGROUND DATA

Patients' expectations regarding quality-of-life outcomes are highly dependent on the information provided by surgeons early in the treatment course. Our previous work has demonstrated that there is substantial variability in what surgeons tell patients regarding outcomes of cervical spine injuries, thus patients' expectations will differ and outcomes vary.

METHODS

Four common cervical spine injuries (C1 burst, Hangman fracture, odontoid fracture, and unilateral facet fracture) treated both surgically and nonsurgically were considered. We assessed the evidence regarding 5 health-related quality-of-life outcomes: time to return to work, activity level, hospital stay, the proportion of patients who are pain free and patients who have regained full range of motion at 1 year after the injury.

RESULTS

Published outcome data were available for most injuries. Using consensus expert opinion and the literature, answers to each question were achieved. Overall, expert opinion was relatively homogeneous across injury types, suggesting that experts do not distinguish between specific injuries when advising patients of expected outcomes such as pain.

CONCLUSION

By overcoming gaps in the literature with consensus expert opinion, our study provides surgeons and others with evidence-based medicine guidelines for patient-centered outcomes after cervical spine injury. This information can be presented to patients to frame expectations of typical outcomes during and after treatment to optimize patient care and quality of life.

Posterior C1-2 fusion with C1 lateral mass and C2 isthmic screws: accuracy of screw position, alignment and patient outcome

BACKGROUND

Transarticular screw fixation is seen as the "gold standard" in instrumented fusion of C1 and C2. However, drawbacks are the necessity of a reduction before instrumentation and a risk of vertebral artery injury. Therefore, C1 lateral mass and C2 isthmic screws are an alternative. The present study assessed the feasibility of C1-2 stabilization with C1 lateral mass and C2 isthmic screws and evaluated quality of life.

METHOD

All data of 35 consecutive patients treated from May 2006 to September 2009 were collected. Patients had C1 lateral mass and C2 isthmic screws.

RESULTS

Twenty patients were operated on for traumatic instabilities, six for neoplastic instabilities, five for infectious instabilities and two each for degenerative and congenital instabilities. Sixty-six of 70 C1 screws had an ideal position, while four were placed suboptimal without the need for revision. Twelve of 68 C2 screws were not ideal but acceptable; one screw needed a surgical revision. There was one non-surgery related case of neurological deterioration after multilevel instrumentation. No vascular injuries occurred. Realignment was correct in all patients. After a median follow-up of 12 months, patients showed a reduction of pain, disability and improvements in EQ-5D items. SF36 data compared with a normative population and a historical cohort showed lower levels of function in all domains.

CONCLUSION

C1-C2 instrumented fusion with lateral mass and isthmic screws is a safe procedure. Sufficient screw position and alignment was possible in all cases. Therefore, at our institution transarticular screws were abandoned in favor of C1 lateral mass and C2 isthmic screws.

Direct repair of displaced anterior arch fracture of the atlas under microendoscopy: experience with seven patients

INTRODUCTION

In general, bony injuries heal well with immobilization when the fractured segments are well apposed in the cases of stable atlas fracture. Osseous nonunion of the displaced anterior arch fracture of the atlas has been reported in the literature. However, there have been no reports published on the treatment of nonunion of the atlas fractures.

OBJECTIVE

The objective of this study is to describe a new technique for direct repair of the displaced anterior arch fracture of the atlas in a minimally invasive manner.

METHODS

Seven patients with the atlas fracture were treated by a minimally invasive approach. Reduction of anterior arch fractures was not performed by skull traction and the displacement of fractures was more than 5 mm. Direct autograft was performed under microendoscope to improve union of the anterior arch fractures. Radiographic and CT evaluation of the atlas fractures were performed at 3, 6 and 12 months postoperatively.

RESULTS

Seven cases of the atlas fractures (one old and six new fractures) underwent the surgical procedure smoothly without major complications. Total average displacement of the anterior arch fracture was 5.7 mm (range 5-8 mm) before surgery. Of the seven patients, bony union of the fracture developed in six. At latest follow-up, two patients had neck pain associated with movement and limited range of rotational motion.

CONCLUSION

Direct repair under microendoscope is a new technique that improves bony union of displaced anterior arch of the atlas fractures.

A biomechanical rationale for C1-ring osteosynthesis as treatment for displaced Jefferson burst fractures with incompetency of the transverse atlantal ligament

Nonsurgical treatment of Jefferson burst fractures (JBF) confers increased rates of C1-2 malunion with potential for cranial settling and neurologic sequels. Hence, fusion C1-2 was recognized as the superior treatment for displaced JBF, but sacrifies C1-2 motion. Ruf et al. introduced the C1-ring osteosynthesis (C1-RO). First results were favorable, but C1-RO was not without criticism due to the lack of clinical and biomechanical data serving evidence that C1-RO is safe in displaced JBF with proven rupture of the transverse atlantal ligament (TAL). Therefore, our objectives were to perform a biomechanical analysis of C1-RO for the treatment of displaced Jefferson burst fractures (JBF) with incompetency of the TAL. Five specimens C0-2 were subjected to loading with posteroanterior force transmission in an electromechanical testing machine (ETM). With the TAL left intact, loads were applied posteriorly via the C1-RO ramping from 10 to 100 N. Atlantoaxial subluxation was measured radiographically in terms of the anterior antlantodental interval (AADI) with an image intensifier placed surrounding the ETM. Load-displacement data were also recorded by the ETM. After testing the TAL-intact state, the atlas was osteotomized yielding for a JBF, the TAL and left lateral joint capsule were cut and the C1-RO was accomplished. The C1-RO was subjected to cyclic loading, ramping from 20 to 100 N to simulate post-surgery in vivo loading. Afterwards incremental loading (10-100 N) was repeated with subsequent increase in loads until failure occurred. Small differences (1-1.5 mm) existed between the radiographic AADI under incremental loading (10-100 N) with the TAL-intact as compared to the TAL-disrupted state. Significant differences existed for the beginning of loading (10 N, P = 0.02). Under physiological loads, the increase in the AADI within the incremental steps (10-100 N) was not significantly different between TAL-disrupted and TAL-intact state. Analysis of failure load (FL) testing showed no significant differences among the radiologically assessed displacement data (AADI) and that of the ETM (P = 0.5). FL was Ø297.5 +/- 108.5 N (range 158.8-449.0 N). The related displacement assessed by the ETM was Ø5.8 +/- 2.8 mm (range 2.3-7.9). All specimens succeeded a FL >150 N, four of them >250 N and three of them >300 N. In the TAL-disrupted state loads up to 100 N were transferred to C1, but the radiographic AADI did not exceed 5 mm in any specimen. In conclusion, reconstruction after displaced JBF with TAL and one capsule disrupted using a C1-RO involves imparting an axial tensile force to lift C0 into proper alignment to the C1-2 complex. Simultaneous compressive forces on the C1-lateral masses and occipital condyles allow for the recreation of the functional C0-2 ligamentous tension band and height. We demonstrated that under physiological loads, the C1-RO restores sufficient stability at C1-2 preventing significant translation. C1-RO might be a valid alternative for the treatment of displaced JBF in comparison to fusion of C1-2.