Minimally invasive anterior transarticular screw fixation and microendoscopic bone graft for atlantoaxial instability

Biomechanical properties of different anterior and posterior techniques for atlantoaxial fixation: a finite element analysis

BACKGROUND

Many techniques for atlantoaxial fixation have been developed. However, the biomechanical differences among various atlantoaxial fixation methods remain unclear. This study aimed to evaluate the biomechanical influence of anterior and posterior atlantoaxial fixation techniques on fixed and nonfixed segments.

METHODS

An occiput-C7 cervical finite element model was used to construct 6 surgical models including a Harms plate, a transoral atlantoaxial reduction plate (TARP), an anterior transarticular screw (ATS), a Magerl screw, a posterior screw-plate, and a screw-rod system. Range of motion (ROM), facet joint force (FJF), disc stress, screw stress, and bone-screw interface stress were calculated.

RESULTS

The C1/2 ROMs were relatively small in the ATS and Magerl screw models under all loading directions except for extension (0.1°-1.0°). The posterior screw-plate system and screw-rod system generated greater stresses on the screws (77.6-1018.1 MPa) and bone-screw interfaces (58.3-499.0 MPa). The Harms plate and TARP models had relatively small ROMs (3.2°-17.6°), disc stress (1.3-7.6 MPa), and FJF (3.3-106.8 N) at the nonfixed segments. Changes in disc stress and FJF of the cervical segments were not consistent with changes in ROM.

CONCLUSIONS

ATS and Magerl screws may provide good atlantoaxial stability. The posterior screw-rod system and screw-plate system may have higher risks of screw loosening and breakage. The Harms plate and TARP model may more effectively relieve nonfixed segment degeneration than other techniques. The C0/1 or C2/3 segment may not be more susceptible to degeneration than other nonfixed segments after C1/2 fixation.

Patient-rated outcome after atlantoaxial (C1-C2) fusion: more than a decade of evaluation of 2-year outcomes in 126 patients

INTRODUCTION

Various surgical techniques have been introduced for atlantoaxial (C1-C2) fusion, the most common being Magerl's (transarticular) or the Harms/Goel screw fixation. Common indications include degenerative osteoarthritis (OA), trauma or rheumatoid arthritis (RA). Only few, small studies have evaluated patient-reported outcomes after C1-C2 fusion. We investigated 2-year outcomes in a large series of consecutive patients undergoing isolated C1-C2 fusion.

METHODS

We analysed prospectively collected data (2005-2016) from our Spine outcomes database, collected within the framework of EUROSPINE's Spine Tango Registry. It included 126 patients (34 (27%) men, 92 (73%) women; mean (SD) age 67 ± 19 y) who had undergone first-time isolated C1-C2 fusion (61% Magerl, 39% Harms(-Goel)) at least 2 years ago for OA (83 (66%)), RA (20 (16%)), fracture (15 (12%)) or other (8 (6%)). Patients completed the multidimensional Core Outcome Measures Index (COMI; 0-10) and various single item outcomes.

RESULTS

Questionnaires were returned by 118/126 (94%) patients, 2 years post-operative. Mean COMI scores showed a significant reduction from baseline: 6.9 ± 2.4 to 2.7 ± 2.5 (p < 0.0001). Overall, 75% patients achieved the MCIC of ≥ 2.2 points reduction in COMI and 88% reported a good global outcome. 91% patients were satisfied/very satisfied with their care. Self-reported complications were declared by 16% patients and further surgery at the same segment, by 2.5%.

CONCLUSION

In this large series with almost complete follow-up, C1-C2 fusion showed extremely good results. Despite the complexity of the intervention, outcomes surpassed those typically reported for simple procedures such as ACDF and lumbar discectomy, suggesting reservations about the procedure should perhaps be reviewed.

[Minimally invasive techniques for traumatic injuries of the cervical spine]

Nowadays, although minimally invasive procedures are the standard for the treatment of thoracolumbar spinal injuries, these techniques are not yet established for the cervical spine. This is due to anatomical and technical reasons and also due to the fact that the classical anterior decompression and fusion procedure already fulfils the criteria of minimally invasiveness and is suitable for the vast majority of injuries. The existing literature consists mainly of case reports and small comparative cohort studies, the results of which are presented. There is a minimally invasive variant for nearly all open procedures, mainly in the upper cervical spine but also in the lower cervical spine. The further development of these promising techniques is still pending.

Design a novel integrated screw for minimally invasive atlantoaxial anterior transarticular screw fixation: a finite element analysis

PURPOSE

To design a new type of screw for minimally invasive atlantoaxial anterior transarticular screw (AATS) fixation with a diameter that is significantly thicker than that of traditional screws, threaded structures at both ends, and a porous metal structure in the middle. The use of a porous metal structure can effectively promote bone fusion and compensate for the disadvantages of traditional AATSs in terms of insufficient fixation strength and difficulty of bone fusion. The biomechanical stability of this screw was verified through finite element analysis. This instrument may provide a new surgical option for the treatment of atlantoaxial disorders.

METHODS

According to the surgical procedure, the new type of AATS was placed in a three-dimensional atlantoaxial model to determine the setting of relevant parameters such as the diameter, length, and thread to porous metal ratio of the structure. According to the results of measurement, the feasibility and safety of the new AATS were verified, and a representative finite element model of the upper cervical vertebrae was chosen to establish, and the validity of the model was verified. Then, finite element-based biomechanical analysis was performed using three models, i.e., atlantoaxial posterior pedicle screw fixation, traditional atlantoaxial AATS fixation, and atlantoaxial AATS fixation with the new type of screw, and the biomechanical effectiveness of the novel AATS was verified.

RESULTS

By measuring the atlantoaxial parameters, the atlantoaxial CT data of the representative 30-year-old normal adult male were selected to create a personalized 3D printing AATS screw. In this case, the design parameters of the new screw were determined as follows: diameter, 6 mm; length of the head thread structure, 10 mm; length of the middle porous metal structure, 8 mm (a middle porous structure containing an annular cylinder ); length of the tail thread structure, 8 mm; and total length, 26 mm. Applying the same load conditions to the atlantoaxial complex along different directions in the established finite element models of the three types of atlantoaxial fusion modes, the immediate stability of the new AATS is similar with Atlantoaxial posterior pedicle screw fixation.They are both superior to traditional atlantoaxial anterior screw fixation.The maximum local stress on the screw head in the atlantoaxial anterior surgery was less than those of traditional atlantoaxial anterior surgery.

CONCLUSIONS

By measuring relevant atlantoaxial data, we found that screws with a larger diameter can be used in AATS surgery, and the new AATS can make full use of the atlantoaxial lateral mass space and increase the stability of fixation. The finite element analysis and verification revealed that the biomechanical stability of the new AATS was superior to the AATS used in traditional atlantoaxial AATS fixation. The porous metal structure of the new AATS may promote fusion between atlantoaxial joints and allow more effective bone fusion in the minimally invasive anterior approach surgery.

The Anterior Transarticular Fixation of C1/C2 in the Elderly With Dens Fractures

Background

Anterior transarticular screw fixation (ATSF) of C1/C2 can be used for the treatment of unstable dens fractures. Here, we evaluated the feasibility of an anterior C1/C2 fixation in elderly patients with unstable dens fractures. Furthermore, we tried to analyze safe entry zones for ATSF surgery.

Methods

A consecutive cohort of 13 patients with unstable dens fractures were treated with ATSF of C1/C2 between January 2015 and October 2016. If necessary, an additional screw was placed into the odontoid process. The placement was radiographically analyzed using the 3D Arcadis Orbic (Siemens, Erlangen, Germany). Additionally, computed tomography scans of the cervical spine from 50 trauma patients were analyzed to evaluate safe entry zones for anterior odontoid screw fixation and for ATSF.

Results

ATSF was performed in 13 cases (7 female, 6 male; mean age 81.80 years). One screw had to be corrected intraoperatively due to initial malplacement. Neurological deficits or an injury of the vertebral artery were not observed. All patients suffered from swallowing difficulties during the postoperative course, without lesions of the esophagus or the trachea. In 4 patients (30.8%), an additional posterior fixation was offered to the patients due to progressive loosening of the screws.The anatomical-radiographic analyzes revealed a significantly shallower angle of trajectory for anterior odontoid screw fixation (24.9° ± 5.85°) than for ATSF (39.1° ± 6.44° (left); 40.5° ± 6.79° (right) P = 0.02).

Conclusions

The ATSF of C1/C2 might be a valuable option in the treatment of instable C1/C2 fractures, especially in the elderly or in patients with short necks and/or high body mass index due to the steeper trajectory compared with odontoid screw placement. Yet available screws seem to be of inferior resistance compared with the biomechanical properties of a dorsal fixation. Further studies should focus on screws with better mechanical properties and probably additional cement augmentation.

Level of Evidence

4.

Radiologic Characteristics of Anterior Transarticular Crossing Screw Placement for Atlantoaxial Joint Instability

OBJECTIVE

The feasibility of anterior transarticular crossing screws (ATCS) was confirmed in cadaveric specimens and it has been used in clinic. However, no study has documented the morphometric characteristics of ATCS. This study seeks to determine the morphometric characteristics of ATCS in C1-C2 fixation.

METHODS

A total of 100 patients without abnormality of C1-2 were enrolled. The range of screw lateral angles (LAs) and the screw lengths of ATCS on coronal images were measured on multiplanar computed tomography images, as well as the screw incline angles (IAs) in the sagittal plane. The ideal trajectory was designed as toward to the posterosuperior points of the opposite C1 lateral mass, which had the longest screw.

RESULTS

The LAs were relatively small in men (31.4°-45.3°) compared with women (32.6°-46.0°). In the sagittal plane, the IAs were ranged from 41.0° to 68.4° in men and from 44.4° to 68.1° in women. The overall screw lengths were longer in men (34.7-44.8 mm) than in women (32.2-39.6 mm). In the ideal path, the LA and IA were 38.4° and 41.0° in men and 39.6° and 44.4° in women, and the screw lengths were 44.8 mm in men and 39.6 mm in women.

CONCLUSIONS

This study provides the range of screw angles and lengths of ATCS, which will help surgeons to perform ATCS safely and accurately.

Insights into the Past and Future of Atlantoaxial Stabilization Techniques

Over the past century, atlantoaxial stabilization techniques have improved considerably. To our knowledge there has been a scarcity of articles published that focus specifically on the history of atlantoaxial stabilization. Examining the history of instrumentation allows us to evaluate the impact of early influences on current modern stabilization techniques. It also provides inspiration to further develop the techniques and prevents repetition of mistakes. This paper reviews the evolution of C1-C2 instrumentation techniques over time and provides insights into the future of these practices.We did an extensive literature search in PubMed, Embase and Google Scholar, using the following search terms: 'medical history', 'atlantoaxial', 'C1/C2', 'stabilization', 'instrumentation', 'fusion', 'arthrodesis', 'grafting', 'neuroimaging', 'biomechanical testing', 'anatomical considerations' and 'future'.Many different entry zones have been tested, as well as different constructs, from initial attempts with use of silk threads to use of hooks and rod-wire techniques, and handling of bone grafts, which eventually led to the development of the advanced screw-rod constructs that are currently in use. Much of this evolution is attributable to advancements in neuroimaging, a wide range of new materials available and an improvement in biomechanical understanding in relation to anatomical structures.

Traumatic upper cervical spinal fractures in teaching hospitals of China over 13 years: A retrospective observational study

To investigate the incidence and pattern of patients managed for traumatic upper cervical spinal fractures (TUCSFs) in teaching hospitals in China over 13 years.We retrospectively reviewed 351 patients with TUCSF admitted to our teaching hospitals. Incidence rates were calculated with respect to age, gender, etiologies of trauma, anatomical distribution, anatomical classification, American spinal injury association impairment scale (ASIA) classification of neurological deficit and associated injuries.There were 260 male and 91 female patients, with a mean age of 44.2 ± 16.3 years. The mean age of the patients significantly increased by year of admission, from 35.2 ± 14.5 years to 47.5 ± 17.2 years (P = 0.005). Motor vehicle accidents (MVAs) (n = 132, 37.6%) and high falls (n = 104, 29.6%) were the 2 most common mechanisms. The number of C2 fractures (n = 300, 85.5%) was significantly higher than that of C1 (n = 99, 28.2%) (P < 0.001). High falls resulted in significantly more Type I C1 fractures than other etiologies (all P < 0.001). MVAs resulted in many more Type II and Type III C1 fractures and Type II and Type III C2 fractures than other etiologies. High falls were the most common injury type (n = 44, 36.4%) resulting in neurological deficits. Patients who presented with Landell classification Type I single C1 fracture (n = 6, 42.9%) had the highest rate of neurological deficits. Eighty-two patients had combined injuries; the most common pattern was cervical + cervical spine (n = 44, 12.5%), followed by cervical + thoracic spine (n = 27, 7.7%). A total of 121 patients (34.5%) suffered neurological deficits. Of all patients with TUCSF without combined injuries, single C2 fractures accounted for the highest rate of neurological deficits (n = 62, 32.0%). Multivariate logistic regression analysis indicated that sex (OR = 1.876, 95% CI: 1.022-3.443, P = 0.042), etiology (MVA pedestrians vs high fall: OR = 0.187, 95% CI: 0.056-0.629, P = 0.007), level (C1 + OFs vs C1: OR = 6.264, 95% CI: 1.152-34.045, P = 0.034), and injury severity scoring (ISS) (OR = 1.186, 95% CI: 1.133-1.242, P < 0.001) were independent risk factors of neurological deficit.The most common causes of TUCSF were MVAs and high falls; single C2 fractures without combined injuries accounted for the most common neurological deficits. Different etiologies resulted in different specific anatomical injuries and neurological deficits. We should make early diagnoses and initiate timely treatment according to different TUCSF patterns.

A Method to Prevent Occipitocervical Joint Violation Using Plain Radiography During Percutaneous Anterior Transarticular Screw Fixation

STUDY DESIGN

A prospective study of anterior transarticular screw (ATS) fixation patients.

OBJECTIVE

To develop a method to determine screw tip position through plain radiography after percutaneous ATS fixation to prevent occipitocervical joint (OCJ) violation.

SUMMARY OF BACKGROUND DATA

No studies using plain radiography to prevent OCJ violation during percutaneous ATS fixation have been performed.

METHODS

In total, 34 subjects (with 68 screws) who had undergone percutaneous ATS fixation were enrolled. To evaluate the screw tip location in relation to the C1 lateral mass (LM), the screw tip positions were graded 1, 2, or 3 on anteroposterior (AP) radiographs, and I, II, or III on lateral radiographs. OCJ violation was analyzed by postoperative computed tomography (CT).

RESULTS

Screws with tips located lower (tip I) in the LM did not result in OCJ violation. Only one tip in the tip 3 position showed OCJ perforation, and this screw was also located in tip III. Screw perforation rates of tip 1-tip II, tip 1-tip III, and tip 2-tip III were the highest (100%), followed by tip 2-tip II (10.5%) and tip3-tip III (10%).

CONCLUSION

This study provides insights into OCJ violation during percutaneous ATS fixation. According to AP radiography, a percutaneous ATS with the screw tip located in the lateral part of the LM resulted in a lower rate of OCJ perforation, whereas screws located in the medial LM resulted in the highest rate of perforation. Percutaneous ATS with the screw tip located in the neutral part of the LM should ensure that the screw tip is below the upper part of the LM, preventing OCJ violation. These findings may help surgeons assess screw positioning both during and after the operation.

LEVEL OF EVIDENCE

3.

A novel computed method to reconstruct the bilateral digital interarticular channel of atlas and its use on the anterior upper cervical screw fixation

Purpose. To investigate a novel computed method to reconstruct the bilateral digital interarticular channel of atlas and its potential use on the anterior upper cervical screw fixation.

Methods. We have used the reverse engineering software (image-processing software and computer-aided design software) to create the approximate and optimal digital interarticular channel of atlas for 60 participants. Angles of channels, diameters of inscribed circles, long and short axes of ellipses were measured and recorded, and gender-specific analysis was also performed.

Results. The channels provided sufficient space for one or two screws, and the parameters of channels are described. While the channels of females were smaller than that of males, no significant difference of angles between males and females were observed.

Conclusion. Our study demonstrates the radiological features of approximate digital interarticular channels, optimal digital interarticular channels of atlas, and provides the reference trajectory of anterior transarticular screws and anterior occiput-to-axis screws. Additionally, we provide a protocol that can help make a pre-operative plan for accurate placement of anterior transarticular screws and anterior occiput-to-axis screws.

Feasibility and trajectory study of anterior transarticular crossing screw placement for atlantoaxial joint instability: a cadaveric study and description of a novel technique

PURPOSE

In unique clinical situations where C1-C2 anterior transarticular screw (ATS) fixation is not available or has failed, an anterior transarticular crossing screw (ATCS) with transcorporal pathway of the screws inside the contralateral promontory of C2 may enhance the stabilization and achieve atlantoaxial arthrodesis. The present study was to describe a novel technique of ATCS fixation for atlantoaxial joint instability and its applied anatomy, and compared it with ATS fixation method.

METHODS

Direct measurements using digital calipers and a goniometer were conducted on 30 pairs of dried human C1 and C2 vertebrae. The ATS and ATCS with screws (Φ 4.0 mm) were performed on 11 fresh cervical spine specimens. The screw lengths in the C1 and C2, and screw entry angles of the ATS and ATCS were measured, respectively. Cadaver specimens were dissected to observe the incidence of violation to the important structures surrounding the ATS and ATCS fixation technique.

RESULTS

There was enough osseous space for ATCS placement. The lateral and incline angle of the ATCS was 36.2° and 28.7°, respectively. Screw purchase in C2 of the ATCS (25.6 mm) was greater than that of the ATS (11.4 mm). The ATCS C1 purchase (14.8 mm) was similar to the ATS C1 purchase (14.9 mm). No violation to the vertebral artery groove, the spinal canal or the atlanto-occipital joint was observed after the ATCS placement.

CONCLUSION

Anterior transarticular crossing screw is a feasible and viable option for atlantoaxial fixation in selected cases. This technique achieved remarkable longer screw purchase and could enhance the atlantoaxial stability.

Anterior transarticular screw fixation as a conventional operation for rigid stabilization

Background:

Anterior transarticular screw (ATS) fixation is a useful surgical option for atlantoaxial (AA) stabilization. This report presents a revised ATS method for AA fusion.

Methods:

A 79-year-old male presented with AA instability attributed both to an old odontoid fracture and severe degeneration of the lateral atlantoaxial joints (LAAJs). ATS fixation was performed through the conventional anterior cervical approach. The longest screw trajectories were planned preoperatively using multiplanar reconstruction computed tomography (CT) scans, with entry points of the screws situated at the midpoint on the inferior border of the axial body. The surgical exposure was limited to opening at the entry points alone. Our retractor of choice was the Cusco speculum; it sufficiently secured space for utilizing the required instruments for screw placement while offering sufficient protection of soft tissues. Cannulated full-threaded bicortical screws stabilized the LAAJs. Screw insertion required a significant amount of coronal angulation up to the superior articular process of the atlas under open-mouth and lateral fluoroscopy image guidance. After ATS fixation, bone grafting was performed between the posterior laminae of the axis and the atlas through a conventional posterior approach.

Results:

Bony fusion between the atlas and the axis was confirmed radiographically. Arthrodesis of the LAAJs occurred despite no bone grafting.

Conclusions:

Rigid fixation of the LAAJs was obtained by our ATS technique, indicating that it is an alternative method for AA fixation when posterior rigid internal fixation is not applicable.

Atlantoaxial anterior transarticular screw fixation: a case series and reappraisal of the technique

BACKGROUND CONTEXT

Atlantoaxial instability is commonly treated with C1-C2 fixation performed via posterior approaches. Although anterior transarticular screw (ATS) fixation, performed with a classic retropharyngeal approach, was described more than 10 years ago, the published literature still lacks a comprehensive analysis of the procedure and a real case series.

PURPOSE

We report a series of patients treated with atlantoaxial ATS, describing the surgical procedure in detail and discussing advantages and disadvantages of the technique.

STUDY DESIGN

The study design includes case series and technical report.

METHODS

We prospectively enrolled 15 patients affected by atlantoaxial instability secondary to trauma, degenerative diseases, or inflammatory diseases. Anterior transarticular screw fixation was performed with anteroposterior open-mouth and lateral intraoperative radiographs. All patients were evaluated radiologically at follow-up to identify bone fusion.

RESULTS

Anterior transarticular screw was performed successfully in 14 patients without complications. The procedure was aborted in a case of vertebral invagination, and one case required revision surgery owing to C2 articular bone fracture. Solid C1-C2 fusion was achieved in all cases (at 10- to 21-week follow-up) except in an elderly patient affected by severe osteoporosis. No complications occurred.

CONCLUSIONS

Although the procedure is still not widely known, ATS allows the effective and safe treatment of C1-C2 instability even in patients with systemic comorbidities. It offers several advantages over posterior approaches.

Radiographic and clinical assessment on the accuracy and complications of C1 anterior lateral mass and C2 anterior pedicle screw placement in the TARP-III procedure: a study of 106 patients

PURPOSE

To investigate the (1) radiographic and clinical accuracy of C1 anterior lateral mass screw (C1ALMS) and C2 anterior pedicle screw (C2APS) placement in the transoral atlantoaxial reduction plate (TARP)-III procedure, (2) screw insertion-associated clinical complications and (3) fusion status between C1 and C2.

METHODS

Radiographic and clinical data were obtained from the electronic medical record system. Studies were carried out to assess the accuracy of C1ALMS and C2APS placement, the screw insertion-associated clinical complications and the fusion status between C1 and C2. Placement of the screws was assessed using the modified All India Institute of Medical Sciences outcome-based classification.

RESULTS

Two-hundred and twelve C1ALMS and 207 C2APS in 106 patients were assessed. The ideal accurate rates were 92.0% (195) and 53.1% (110), and the acceptable accurate rates were 97.6% (207) and 87.0% (180), respectively. One patient died postoperatively due to C2 screw misplacement. There were no symptoms of neurologic and vertebral artery injuries in the rest of the patients. 102 patients (97.1%) achieved solid fusion between C1 and C2. No instrumentation failure due to delayed union or nonunion was observed.

CONCLUSION

C1ALMS placement in TARP-III procedures appears to be safe. The cortical breach rate of C2APS is high though clinically the neurovascular complication rate is similar to that of posterior atlantoaxial procedures. Advanced navigation strategies may help improve the accuracy of C2APS placement and decrease potential complications.

Fluoroscopically guided anterior atlantoaxial transarticular screws: a feasibility and trajectory study using CT-based simulation software

BACKGROUND CONTEXT

Anterior transarticular screw (ATAS) fixation has been suggested as a viable alternative to posterior stabilization. However, we are not aware of previous reports attempting to establish the usefulness of specific fluoroscopic landmark-guided trajectories in the use of ATAS, and we could find no reference to it in a computerized search using MEDLINE.

PURPOSE

To determine the anatomic feasibility of ATAS placement using defined fluoroscopic landmarks to guide screw trajectory.

STUDY DESIGN

Evaluation using three-dimensional screw insertion simulation software and 1.0-mm-interval computed tomographic scans.

PATIENT SAMPLE

Computed tomographic scans of 100 patients including 50 men and 50 women.

OUTCOME MEASURES

Incidence of violation of the vertebral artery groove of C1 and C2, the spinal canal, and the atlanto-occipital joint and screw lengths and lengths of C1 and C2 purchase.

METHODS

Four screw trajectories were determined: promontory screw (PS), single central facet (CF) screw, and medial (MF) and lateral (LF) double facet screws. Placement of a 4.0-mm screw was simulated using defined fluoroscopic landmarks for each trajectory. The previously mentioned outcome measures were evaluated and compared for the four trajectories. This study was not supported by any financial sources, and there is no topic-specific potential conflict of interest with this study.

RESULTS

No violation of the C1 or C2 vertebral artery groove or of the spinal canal was observed for any of the screw types. Screw lengths and the length of C2 purchase were by far the longest for PS (40.4±2.8 and 25.7±2.1 mm, respectively; p<.001 in all post hoc comparisons). The length of C1 purchase was longer for CF (16.4±2.3 mm) and LF (15.8±1.6 mm) than PS (14.7±2.0 mm) and MF (14.6±2.4 mm) (p≤.001, respectively). There was no atlanto-occipital joint violation if the length of C1 purchase was set at 12 mm for CF and LF and at 10 mm for PS and MF.

CONCLUSIONS

Our results suggest that it may be possible to place ATASs without violating the vertebral artery groove, spinal canal, or the atlanto-occipital joint by using the described entry points, trajectories, and fluoroscopic landmarks.