Biomechanical analysis of screw constructs for atlantoaxial fixation in cadavers: a systematic review and meta-analysis

The effect of C2 screw type on perioperative outcomes and long-term stability after C2-T2 posterior cervical decompression and fusion

PURPOSE

To determine if C2 pedicle versus pars screw type predicts change in fusion status, C2 screw loosening, cervical alignment, and patient-reported outcomes measures (PROMs) after C2-T2 posterior cervical decompression and fusion (PDCF).

METHODS

All adult patients who underwent C2-T2 PCDF for myelopathy or myeloradiculopathy between 2013-2020 were retrospectively identified. Patients were dichotomized by C2 screw type into bilateral C2 pedicle and bilateral C2 pars screw groups. Preoperative and short- and long-term postoperative radiographic outcomes and PROMs were collected. Univariate and multivariate analysis compared patient factors, fusion status, radiographic measures, and PROMs across groups.

RESULTS

A total of 159 patients met the inclusion/exclusion criteria (76 bilateral pedicle screws, 83 bilateral pars screws). Patients in the C2 pars relative to C2 pedicle screw group were on average more likely to have bone morphogenic protein (p = 0.001) and four-millimeter diameter rods utilized intraoperatively (p = 0.033). There were no significant differences in total construct and C2-3 fusion rate, C2 screw loosening, or complication and revision rates between C2 screw groups in univariate and regression analysis. Changes in C2 tilt, C2-3 segmental lordosis, C0-2 Cobb angle, proximal junctional kyphosis, atlanto-dens interval, C1 lamina-occiput distance, C2 sagittal vertical axis, C2-7 lordosis, and PROMs at all follow-up intervals did not vary significantly by C2 screw type.

CONCLUSION

There were no significant differences in fusion status, hardware complications, and radiographic and clinical outcomes based on C2 screw type following C2-T2 PCDF. Accordingly, intraoperative usage criteria can be flexible based on patient vertebral artery positioning and surgeon comfort level.

Biomechanical Study of Horizontal Screw-screw Crosslink in C1-2 Pedicle Screw-rod Fixation

STUDY DESIGN

This is a biomechanical study in vitro.

OBJECTIVE

To investigate the biomechanical differences between horizontal rod-rod crosslink (hR-R CL) and the horizontal screw-screw crosslink (hS-S CL) implementation in C1-2 pedicle screw-rod (C1-2 PSR) fixation.

SUMMARY OF BACKGROUND

To improve internal fixation stability, transverse connector (TC) is used in C1-2 PSR to increase torsional stiffness. The connection mode of horizontal connection includes hR-R CL and hS-S CL. hS-S CL adopted in C1-2 PSR was rarely reported and its biomechanics are still unclear.

MATERIALS AND METHODS

Six fresh cadaveric cervical spine specimens were each tested as an Intact model, then modified and tested as an Instability model (unstable odontoid fractures), and then as 3 internal fixation models, including C1-2 PSR, C1-2 pedicle screw-rod+horizontal rod-rod crosslink (C1-2 PSR+ hR-R CL), C1-2 pedicle screw-rod+horizontal screw-screw crosslink (C1-2 PSR+ hS-S CL). The ROM of the C1-2 segments was measured by applying 1.5 nm load in 6 loading conditions, including flexion-extension (FE), left and right lateral bending (LB), and left and right axial rotation (AR).

RESULTS

The C1-2 PSR+hR-R CL and C1-2 PSR+hS-S CL models, respectively, showed 60% and 75% lower ROM than the C1-2 PSR model in LB and AR conditions ( P <0.05). ROM was comparable between the C1-2 PSR+hR-R CL and the C1-2 PSR+hS-S CL models in all loading conditions ( P >0.05).

CONCLUSION

Both types of crosslinks showed superior C1-2 stability under LB and AR conditions than PSR without crosslinks. The C1-2 segment stability was comparable between the 2 types of crosslinks themselves.

C2 Superior Facetal Osteotomy: A Novel Technique in Complex Craniovertebral Junction Surgery for C1 Lateral Mass Screw Placement

Complex craniovertebral junction (CVJ) defects account for a considerable proportion of CVJ diseases. Given the heavily assimilated C1, an unfavorable C1-C2 joint orientation, an overriding C2 superior facet, a low-hanging occiput, and an abnormal vertebral artery course with a high-riding vertebral artery, placement of C1 lateral mass screws might be difficult. To address this, a novel technique for placing C1 lateral mass screws that avoid vertebral artery injury, low-hanging occiput, and overriding C2 superior facet was developed in this study. This approach enables firm fixation of C1-C2 even in difficult situations where the placement of the C1 lateral mass is challenging.

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.

Regional variations in C1-C2 bone density on quantitated computed tomography and clinical implications

Background

Our elderly population is growing and the number of spine fractures in the elderly is also growing. The elderly population in general may be considered as poor surgical candidates experience a high rate of fractures at C1 and C2 compared with the general population. Nonoperative management of upper cervical fractures is not benign as there is a high nonunion rate for both C1 and C2 fractures in the elderly, and orthosis compliance is often suboptimal, or complicated by skin breakdown. The optimal technique for upper cervical stabilization in the elderly may be different than in younger populations as the bone quality is inferior in the elderly. The objective of this basic science study is to determine whether the bone mineral density (BMD) of C1 and C2 vary by region, and if this is a gender difference in this elderly age group.

Methods

Twenty cadaveric spines from 45 to 83 years of age were used to obtain BMD using quantitated computed tomography (QCT). BMD was measured using a QCT. For C1, 8 regions were determined: anterior tubercle, bilateral anterior and medial lateral masses, bilateral posterior arches, and posterior tubercle. For C2, 7 regional BMDs were determined: top of odontoid, base of odontoid-body interface, mid body, bilateral lateral masses, anterior inferior body near the discs space, and the C2 spinous process.

Results

The BMD was greatest at the C1 anterior tubercle (564.4±175.8 mg/cm³) and C1 posterior ring (420.8±110.2 mg/cm³), and least at the anterior and medial lateral masses (262.8±59.5 mg/cm³, 316.9±72.6 mg/cm³). At C2 QCT BMD was greatest at the top of the dens (400.6±107.9 mg/cm³) decreasing down through the odontoid-C2 body junction (267.8±103.5 mg/cm³) and least in the mid C2 body 249.1±68.8 mg/cm³). The posterior arch of C1 and the spinous process of C2 had higher BMD's 420.8±110.2 mg/cm³ and 284.1±93.0 mg/cm³, respectively. A high correlation was observed between the BMD at the interface of the dens-vertebral body with the vertebral body with a Pearson correlation coefficient of 0.86. The BMD of the top of dens was significantly higher (p<.05) than all the regions in C2.

Conclusions

Regional and segmental BMD variations at C1 and C2 have clinical implications for surgical constructs in the elderly population. Given the higher BMDs of the C1 and C2 spinous process and posterior arches, consideration should be given to incorporate these areas using various C1-C2 wiring techniques. In the elderly, lateral masses particularly at C1 with lower BMD may result in potential screw loosening and nonunion in this age group. Old-school wiring techniques have a track record of efficacy and safety with less blood loss, reduced operative time, reduced X-ray exposure, and should be considered in the elderly as a primary stabilization technique or a belt-over suspenders approach based on regional variations in BMD in the elderly.

Posterior Atlantoaxial Screw Placement in a Portuguese Population: A Morphometric Analysis Based on Computed Tomography Scan Measurements

Objective  The present study aims to evaluate the screw length and trajectory angles for posterior atlantoaxial fixation in a Portuguese population, through the study of cervical computed tomography (CT) scans. Methods  Cervical CT scans of 50 adults were measured according to predefined screw trajectories of C1-C2 transarticular (C1C2TA), C1 lateral mass (C1LM), C2 pedicle (C2P), C2 pars and C2 laminar (C2L) screws. For each of these trajectories, screw length and angles were measured and compared between males and females. Results  For the C1C2TA screw trajectory, the mean length, medial, and cranial angles were 34.12 ± 3.19 mm, 6.24° ± 3.06, and 59.25° ± 5.68, respectively, and for the C1LM screw trajectory, they were 27.12 ± 2.15 mm, 15.82° ± 5.07, and 13.53° ± 4.80, respectively. The mean length, medial, and cranial angles for the C2P screw trajectory were 23.44 ± 2.49 mm, 27.40° ± 4.88, and 30.41° ± 7.27, respectively; and for the C2 pars screw trajectory, they were 16.84 ± 2.08 mm, 20.09° ± 6.83, and 47.53° ± 6,97. The mean length, lateral, and cranial angles for the C2L screw trajectory were 29.10 ± 2.48 mm, 49.80° ± 4.71, and 21.56° ± 7.76, respectively. There were no gender differences except for the lengths of the C1C2TA ( p  = 0,020) and C2L ( p  = 0,001) screws, which were greater in males than in females. Conclusion  The present study provides anatomical references for the posterior atlantoaxial fixation in a Portuguese population. These detailed data are essential to aid spine surgeons to achieve safe and effective screw placement.

Comparison of the clinical efficacy of unilateral and bilateral pedicle screw short-segment fixation and fusion in the treatment of atlantoaxial fracture-dislocation

BACKGROUND

Few studies have compared the clinical efficacy of unilateral and bilateral pedicle screw fixation and fusion in treating atlantoaxial fracture-dislocation.

OBJECTIVE

To compare the efficacy of unilateral and bilateral fixation and fusion for atlantoaxial fracture-dislocation and to explore the feasibility of the unilateral surgical procedure.

METHODS

Twenty-eight consecutive patients with atlantoaxial fracture-dislocation were included in the study from June 2013 to May 2018. They were divided into a unilateral fixation group and a bilateral fixation group (14 patients in each group with an average age of 43.6 ± 16.3 years and 51.8 ± 15.4 years, respectively). The unilateral group had a unilateral anatomical variation of the pedicle or vertebral artery, or traumatic pedicle destruction. All patients underwent atlantoaxial unilateral or bilateral pedicle screw fixation and fusion. Intraoperative blood loss and operation time were recorded. The visual analog scale (VAS) and Japanese Orthopedic Association (JOA) scoring systems were used to evaluate pre- and postoperative occipital-neck pain and neurological function. X-ray and computerized tomography (CT) were used to assess atlantoaxial stability, the implants' position, and bone graft fusion.

RESULTS

All patients were followed up for 39-71 months postoperatively. Intraoperatively, no spinal cord or vertebral artery injury was observed. At the last follow-up, occipital-neck pain and neurological function in the two groups were significantly improved (P< 0.05). The X-ray films and CT showed satisfactory atlantoaxial stability, implant position, and osseous fusion in all the patients at 6 months postoperatively.

CONCLUSION

Unilateral and bilateral pedicle screw fixation and fusion can restore atlantoaxial stability and improve occipital-neck pain and neurological function in patients with atlantoaxial fracture-dislocation. The unilateral surgical procedure can be a supplementary option for patients with unilateral abnormal atlantoaxial lesions.

Improving stability of atlantoaxial fusion: a biomechanical study

PURPOSE

The incidence of atlanto-axial injuries is continuously increasing and often requires surgical treatment. Recently, Harati developed a new procedure combining polyaxial transarticular screws with polyaxial atlas massae lateralis screws via a rod system with promising clinical results, yet biomechanical data is lacking. This biomechanical study consequently aims to evaluate the properties of the Harati technique.

METHODS

Two groups, each consisting of 7 cervical vertebral segments (C1/2), were formed and provided with a dens axis type 2 fracture according to Alonzo. One group was treated with the Harms and the other with the Harati technique. The specimen was loaded via a lever arm to simulate extension, flexion, lateral flexion and rotation. For statistical analysis, dislocation (°) was measured and compared.

RESULTS

For extension and flexion, the Harati technique displayed a mean dislocation of 4.12° ± 2.36° and the Harms technique of 8.48° ± 1.49° (p < 0.01). For lateral flexion, the dislocation was 0.57° ± 0.30° for the Harati and 1.19° ± 0.25° for the Harms group (p < 0.01). The mean dislocation for rotation was 1.09° ± 0.48° for the Harati and 2.10° ± 0.31° for the Harms group (p < 0.01). No implant failure occurred.

CONCLUSION

This study found a significant increase in biomechanical stability of the Harati technique when compared to the technique by Harms et al. Consequently, this novel technique can be regarded as a promising alternative for the treatment of atlanto-axial instabilities.

Atlas (C1) lateral mass screw placement using the intersection between lateral mass and inferomedial edge of the posterior arch: a cadaveric study

PURPOSE

To compare the Atlas (C1) lateral mass screw placement between screw trajectories of 0° and 15° medial angulation while using the intersection between lateral mass and inferomedial edge of the posterior arch.

METHODS

Forty-eight Atlas lateral masses were prepared and divided into 2 groups: Group 1; screws inserted at 3 mm lateral to the reference point with screw trajectory of 0° angulation(N = 24) and Group 2; those inserted with screw trajectory of 15° medial angulation(N = 24). We evaluated the atlas anatomy, screw purchase and the presence of any breaches using CT scan.

RESULTS

The radiographic parameters for Groups 1 and 2 were found statistically different (p-value < 0.05): bilateral intraosseous screw lengths (17.92 ± 1.47 mm. vs. 20.71 ± 2.4 mm.), bilateral screw length (29.92 ± 1.72 mm. vs. 33.13 ± 1.78 mm.), left screw medial angulation (x°) (0.67° ± 0.78° vs.14.17° ± 3.51°), right screw medial angulation (y°) (0.83° ± 1.03° vs.14.25° ± 2.53°) and bilateral screw medial angulation (0.75° ± 0.9° vs. 14.21° ± 2.99°). Twenty-two screws (91.67%) using the 0° medial angulation and nineteen screws (79.17%) using the 15° medial angulation had no cortical violations (Grade 0). However, two screws (8.33%) with 0° medial angulation and five screws (20.83%) with 15° medial angulation had breach less than 2 mm (Grade 1). There were no screws with breach between 2 and 4 mm (Grade 2) or greater than 4 mm. (Grade 3).

CONCLUSION

A starting point of 3-mm lateral to the intersection between lateral mass and inferomedial edge of the Atlas posterior arch can be safely and effectively used to insert C1 lateral mass using both 0° and 15° medial angulation.

Referencing for anterior atlantoaxial trans-articular osteosynthesis: a radiological study and proposal of a decisional algorithm

PURPOSE

Anterior trans-articular C1-C2 screw placement can be considered as a surgical alternative in different conditions affecting the atlantoaxial region. While its rigidity is similar to posterior Magerl and Harms techniques, it also provides some surgical advantages. However, the literature lacks papers exhaustively describing indication criteria, surgical steps, and pitfalls.

METHODS

This is a radiological study on 100 healthy subjects. Thin-layer CT scans of the craniovertebral junction were retrieved from the institutional database. The coronal inclination of the C1-C2 joint rim and the depth of the entry point of the screw with respect to the anterior profile of C2 were measured. The antero-posterior and the medio-lateral surgical corridors for the screw placement, and the wideness of the target area on the upper surface of C1 were also measured.

RESULTS

The multivariate analysis showed that the coronal inclination of the C1-C2 articular joint rim strongly influences the surface extension of the C1 target area; the depth of the entry point and the C1-C2 articular rim inclination seem to be independent factors in influencing both the medio-lateral and the antero-posterior surgical corridors wideness. A decisional algorithm on whether to perform an anterior or posterior approach to the atlantoaxial region was also proposed.

CONCLUSIONS

We can conclude that, as much as the C1-C2 articular rim is tending to the horizontal line, and as deeper is the entry point of the screw on the anterior profile of C2, as easier the anterior C1-C2 trans-articular screw placement will result.

Radiological evaluation of atlantoaxial fusion using C2 translaminar screws and C2 pedicle screws: Does the screw halo sign imply fusion failure?

The purpose of this study was to identify the criteria for atlantoaxial (AA) fusion by comparing follow-up lateral radiographs and computed tomography (CT) images. We retrospectively analyzed data from 161 consecutive patients undergoing AA fusion. Patients with a minimum of 1 year of CT follow-up after AA fusion surgery using C2 pedicle screws or translaminar screws (C2TLS) were included. Patients were followed up radiographically at 3, 6, and 12 months after surgery, and dynamic lateral radiographs were also evaluated. A total of 49 patients were analyzed, with a mean CT image follow-up of 41.6 ± 37.6 months. Thirty eight patients had C2 pedicle screw placement, and 11 patients underwent planned C2TLS. AA fusion with bridging bone mass formation was achieved in 45/49 (91.8%) patients. Screw halos were observed in 14/49 (28.6%) patients. Among them, final fusion failure occurred in 2 (14.3%) patients. The last follow-up CT showed no difference in the fusion failure rate according to the presence or absence of a screw halo (no halo, 5.7%; halo, 14.3%; P = .33). The differences in C1-2 segmental angles (SA) in flexion-extension dynamic lateral radiographs were 1.99 ± 1.62° in the fusion group and 4.37 ± 2.13° in the non-fusion group (P = .01). The likelihood of fusion failure increased when the SA gap was greater than 2.62° (P = .05). C2TLS placement had a significantly higher incidence of screw halos. However, the halo sign was not significantly related to final bone fusion. Bone fusion could be predicted when the SA gap of C1-2 was less than 2.62° on the dynamic radiograph.

Posterior atlantoaxial internal fixation using Harms technique assisted by 3D-based navigation robot for treatment of atlantoaxial instability

Background

To evaluate the accuracy of screw placement using the TiRobot surgical robot in the Harms procedure and to assess the clinical outcomes of this technique.

Methods

This retrospective study included 21 patients with atlantoaxial instability treated by posterior atlantoaxial internal fixation (Harms procedure) using the TiRobot surgical robot between March 2016 and June 2021. The precision of screw placement, perioperative parameters and clinical outcomes were recorded. Screw placement was assessed based on intraoperative guiding pin accuracy measurements on intraoperative C-arm cone-beam computed tomography (CT) images using overlay technology and the incidence of screw encroachment identified on CT images.

Results

Among the 21 patients, the mean age was 44.8 years, and the causes of atlantoaxial instability were os odontoideum (n = 11), rheumatoid arthritis (n = 2), unknown pathogenesis (n = 3), and type II odontoid fracture (n = 5). A total of 82 screws were inserted with robotic assistance. From intraoperative guiding pin accuracy measurements, the average translational and angular deviations were 1.52 ± 0.35 mm (range 1.14–2.25 mm) and 2.25° ± 0.45° (range 1.73°–3.20º), respectively. Screw placement was graded as A for 80.5% of screws, B for 15.9%, and C for 3.7%. No complications related to screw misplacement were observed. After the 1-year follow-up, all patients with a neurological deficit experienced neurological improvement based on Nurick Myelopathy Scale scores, and all patients with preoperative neck pain reported improvement based on Visual Analog Scale scores.

Conclusions

Posterior atlantoaxial internal fixation using the Harms technique assisted by a 3D-based navigation robot is safe, accurate, and effective for treating atlantoaxial instability.

C2 Screw fixation techniques in atlantoaxial instability: A technical review

Atlantoaxial instability (AAI) is surgically a complex entity due to its proximity to vital neurovascular structures. C1-C2 fusion has been an established standard in its treatment for a considerable time now. Here, we have outlined the most common techniques for C2 screw fixation in practice at present such as C2 pedicle, C2 pars, C2 translaminar, C2 subfacetal, C2-C3 transfacetal, and C2 inferior facet screw. We have discussed in detail the technical as well as biomechanical aspects of each technique of C2 screw fixation in AAI and explored the intricacies of each technique.

Robot-assisted atlantoaxial fixation: illustrative cases

BACKGROUND

Placing screws in the high cervical spine can be challenging because of the vital anatomical structures located in that region. Precision and accuracy with screw placement is needed. The use of robotics in the cervical spine has been described before; however, here the authors describe the use of a new robotic setup.

OBSERVATIONS

The authors describe 2 cases of robot-assisted placement of C2 pars screws and C1–2 transarticular screws. The operative plans for each patient were as follows: placement of C2 pars screws with C2–4 fusion for hangman’s fracture and placement of C1–2 transarticular screws for degenerative disease. Intraoperative computed tomography (CT) was used to plan and navigate the screws. Postoperative CT showed excellent placement of hardware. Both patients presented for initial postoperative clinic visits with no recurrence of prior symptoms.

LESSONS

Intraoperative robotic assistance with instrumentation of the high cervical spine, particularly C2 pars and C1–2 transarticular screws, may ensure proper screw placement and help avoid injury.

The Comparison Between Transarticular Screw Fixation and Segmental Screw-Rod Fixation for Posterior Fusion of the C1-2 Segment: A Systematic Review and Meta-Analysis

OBJECTIVE

Both transarticular screw fixation (TAS) and segmental screw-rod fixation (SF) have been widely performed for C1-2 fusion; however, just only small clinical studies and a few meta-analyses comparing the 2 surgical techniques for C1-2 posterior fusion have been reported.

METHODS

We searched the Cochrane, Embase, and Medline databases for articles comparing the intraoperative and postoperative outcomes of TAS and SF for C1-2 posterior fusion with April 14, 2022, as the publication cutoff date. The odds ratio (OR) and standardized mean difference were used to analyze differences in outcomes between the 2 abovementioned surgical techniques. A P value < 0.05 was considered statistically significant.

RESULTS

A total of 5101 publications were assessed, and 6 studies were finally included in the study. In terms of the fusion rate, SF produced significantly better outcomes than TAS did (OR = 2.96, P = 0.02). With respect to surgical outcomes, blood loss and operation times were significantly lower in the TAS group than those in the SF group (P = 0.008 and P < 0.00001, respectively). The rate of vertebral artery injury was significantly lower in the SF group than that in the TAS group (OR = 3.95, P = 0.04). However, other complications, such as screw malposition, infection, hardware failure, and nonunion, were not significantly different between the 2 groups.

CONCLUSIONS

SF showed a greater fusion rate and lower risk of vertebral artery injury than TAS did, but TAS showed less blood loss and lower operation times than SF.

The medial window technique as a salvage method to insert C2 pedicle screw in the case of a high-riding vertebral artery or narrow pedicle: a technical note and case series

PURPOSE

To describe the safety and feasibility of C2 medial window screw (C2MWS) as an alternative salvage method for C2 pedicle screws in cases of high-riding vertebral artery (HRVA) or narrow pedicle.

METHODS

The C2MWS technique involves screw insertion by intentionally breaching the medial cortex of the pedicle to avoid vertebral artery injury. Twelve patients who underwent C2 screw insertion via the C2MWS were retrospectively reviewed. C2MWS was indicated in cases of high-riding vertebral artery (HRVA) or narrow pedicle (pedicle width ≤ 4 mm). The width of the canal breach by screw, vertebral artery groove (VAG) breach, solid fusion, neck pain visual analogue scale (VAS) score, and Japanese Orthopedic Association (JOA) score were assessed as outcome measurements.

RESULTS

C2MWS was indicated due to both HRVA and narrow pedicle for 11 screws, narrow pedicle for one screw, and HRVA for two screws. No screw VAG breach or vertebral artery injury was noted postoperatively. The mean width of canal breach was 2.9 ± 1.3 mm. There were no cases demonstrating neurologic deterioration, and 11 patients (91.7%) demonstrated solid fusion at 1-year follow-up. Furthermore, neck pain VAS and JOA scores significantly improved after the surgery.

CONCLUSIONS

The C2MWS technique can provide 3-column fixation while reliably avoiding VA injury. C2MWS could be considered as a salvage alternative method when the insertion of C2 pedicle screw is complicated by HRVA or a narrow pedicle, while there is a need to provide firmer fixation strength than that provided by pars or translaminar screws.

LEVEL OF EVIDENCE: 4

Atlantoaxial instability and cervical noninfectious spondylodiscitis in a patient with Wegener's granulomatosis: A case report

A 61-year-old male patient with Wegener's granulomatosis was admitted due to neck pain and quadriparesis. Clinical evaluation showed severe cervical noninfectious spondylodiscitis, myelopathy, sagittal imbalance, and atlantoaxial instability. A combined anterior and posterior approach was implemented. Postoperative clinical evaluation showed improved neurologic status.

Clinical application of the C2 pars screw technique in the treatment of ossification of the posterior longitudinal ligament

BACKGROUND

Our research was designed to decide whether the application of C2 pars screws is an alternative choice for patients with OPLL involving the C2 segment.

METHODS

A total of 40 patients who underwent cervical laminectomy with fusion (LF) from C2 to C6 for OPLL were reviewed. Among them, C2 pedicle screws were placed in 23 patients, who were the pedicle group, and C2 pars screws were placed in 17 patients, who were the pars group. The screw placement and vertebral artery (VA) anatomy presented by standard CT. General clinical characteristics and health-related outcomes were evaluated and compared preoperatively and during the follow-up period.

RESULTS

The Pars group tended to have a shorter operation duration and less blood loss than the pedicle group (operation time: 115.29 ± 28.75 vs 133.48 ± 26.22, p = 0.044; blood loss: 383.53 ± 116.19 vs 457.83 ± 145.45, p = 0.039). Operation time and blood loss were both independently related to the pars group (operation time: OR = 0.966, p = 0.021; blood loss: OR = 0.993, p = 0.046). The idealization and acceptability of C2 screws in the pars group exceeded those in the pedicle group (100% vs 91.3%). However, no statistically obvious variation in the included complications or health-related outcomes between the pedicle and pars groups was observed.

CONCLUSION

In the treatment of patients with OPLL involving the C2 segment, the application of C2 pars screws is an alternative choice, which is not only safer but also reduces the amount of blood loss, shortens the operation time and obtains a more ideal screw placement.

Fluoroscopy-Assisted C1-C2 Posterior Fixation for Atlantoaxial Instability: A Single-Center Case Series of 78 Patients

Background and Objectives: Posterior C1-C2 fixation, with trans-articular screws (TAS) or screw-rod-construct (SRC), is the main surgical technique for atlantoaxial instability, and can be performed with a fluoroscopy-assisted free-handed technique or 3D navigation. This study aimed to evaluate complications, radiological and functional outcome in patients treated with a fluoroscopy-assisted technique. Materials and Methods: A single-center consecutive cohort study was conducted of all adult patients who underwent posterior C1-C2 fixation, using TAS or CRS, between 2005-2019. Results: Seventy-eight patients were included, with a median follow-up time of 6.8 years. Trauma was the most common injury mechanism (64%), and cervicalgia the predominant preoperative symptom (88%). TAS was used in 33%, and SRC in 67% of cases. Surgery was associated with a significant reduction in cervicalgia (from 88% to 26%, p < 0.001). The most common complications were vertebral artery injury (n = 2, 2.6%), and screw malposition (n = 5, 6.7%, of which 2 were TAS and 3 were SRC). No patients deteriorated in their functional status following surgery. Conclusions: Fluoroscopy-assisted C1-C2 fixation with TAS or SRC is a safe and effective treatment for atlantoaxial instability, with a low complication rate, few surgical revisions, and pain relief in the majority of the cases.

Posterior fusion for fragility type 2 odontoid fractures

OBJECTIVE

The purpose of this study was to evaluate the outcomes of elderly patients with type 2 odontoid fractures treated with an instrumented posterior fusion.

METHODS

Ninety-three consecutive patients older than 65 years of age in whom a type 2 odontoid fracture had been treated with a variety of C1-2 posterior screw fixation techniques were retrospectively reviewed.

RESULTS

The average age was 78 years (range 65-95 years). Thirty-seven patients had an additional fracture, 30 of which involved C1. Three patients had cervical spinal cord dysfunction due to their injury. All patients had comorbidities. The average total hospitalization was 9.6 days (range 2-37 days). There were 3 deaths and 19 major complications, the most common of which was pneumonia. No patient suffered a vertebral artery injury. Imaging studies were obtained in 64 patients at least 12 months postsurgery (mean 19 months). Fusion was assessed by dynamic radiographs in all cases and with a CT scan in 80% of the cases. Four of the 64 patients did not achieve fusion (6.25% overall). All patients in whom fusion failed had undergone C1 lateral mass fixation and C2 pars (1/29, 3.4%) or laminar (3/9, 33.3%) fixation.

CONCLUSIONS

Instrumented posterior cervical fusions may be performed in elderly patients with acceptable morbidity and mortality. The fusion rate is excellent except when bilateral C2 translaminar screws are used for axis fixation.

Reducible Nonunited Type II Odontoid Fracture with Atlantoaxial Instability: Outcomes of Two Different Fixation Techniques

Displaced nonunited type II odontoid fracture can result in atlantoaxial instability, causing delayed cervical myelopathy. Both Magerl's C1-C2 transarticular screw fixation technique and Harms-Goel C1-C2 screw-rod segmental fixation technique are effective techniques to provide stability. This study aimed to demonstrate the results of two surgical fixation techniques for the treatment of reducible nonunited type II odontoid fracture with atlantoaxial instability. Medical records of patients with reducible nonunited type II odontoid fracture hospitalized for spinal fusion between April 2007 and April 2018 were reviewed. For each patient, specific surgical fixation, either Magerl's C1-C2 transarticular screw fixation technique augmented with supplemental wiring or Harms-Goel C1-C2 screw-rod fixation technique, was performed according to our management protocol. We reported the fusion rate, fusion period, and complications for each technique. Of 21 patients, 10 patients were treated with Magerl's C1-C2 transarticular screw fixation technique augmented with supplemental wiring, and 11 were treated with Harms-Goel C1-C2 screw-rod fixation technique. The bony fusion rate was 100% in both groups. The mean time to fusion was 69.7 (95%CI 53.1, 86.3) days in Magerl's C1-C2 transarticular screw fixation technique and 75.2 (95%CI 51.8, 98.6) days in Harms-Goel C1-C2 screw-rod fixation technique. No severe complications were observed in either group. Displaced reducible, nonunited type II odontoid fracture with cervical myelopathy should be treated by surgery. Both fixation techniques promote bony fusion and provide substantial construct stability.

The Intersection Between Lateral Mass and Inferomedial Edge of the C1 Posterior Arch: A Reference Point for C1 Lateral Mass Screw Insertion

Objective

To determine the ideal Atlas (C1) lateral mass screw placement and trajectory using the intersection between the lateral mass and inferomedial edge of the posterior arch as an easily identifiable and reproducible medial reference point. Selection of an ideal entry point and trajectory of C1 lateral mass screw insertion can help to minimize neurovascular injuries. While various techniques for screw insertion have been proposed in the past, they all require extensive dissection of the C1 lateral mass, which can cause profuse bleeding.

Methods

Ninety-three 3-dimensional computed tomography reconstructed images of C1 lateral masses in adult patients were utilized to simulate the placement of C1 lateral mass screws via 4 entry points and 2 trajectory angles referencing off of a medial reference point using Vero’s VISI 17 software. The safety during screw insertion simulation, as well as the screw length, were evaluated.

Results

We found that C1 lateral mass screws could be safely placed bilaterally at 3 mm lateral to the reference point in both 0° and 15° medial screw angulation without violation of the cortex. The 15° medial angulation allowed for longer (18 mm) screws than the 0° angulation.

Conclusion

We recommend starting C1 lateral mass screws 3 mm lateral to the intersection between the lateral mass and inferomedial edge of the posterior arch at a 15° medial angulation.

Surgical nuances and construct patterns influence construct stiffness in C1-2 stabilizations: a biomechanical study of C1-2 gapping and advanced C1-2 fixation

PURPOSE

Stabilization of C1-2 using a Harms-Goel construct with 3.5 mm titanium (Ti) rods has been established as a standard of reference (SOR). A reduction in craniocervical deformities can indicate increased construct stiffness at C1-2. A reduction in C1-2 can result in C1-2 joint gapping. Therefore, the authors sought to study the biomechanical consequences of C1-2 gapping on construct stiffness using different instrumentations, including a novel 6-screw/3-rod (6S3R) construct, to compare the results to the SOR. We hypothesized that different instrument pattern will reveal significant differences in reduction in ROM among constructs tested.

METHODS

The range of motion (ROM) of instrumented C1-2 polyamide models was analyzed in a six-degree-of-freedom spine tester. The models were loaded with pure moments (2.0 Nm) in axial rotation (AR), flexion extension (FE), and lateral bending (LB). Comparisons of C1-2 construct stiffness among the constructs included variations in rod diameter (3.5 mm vs. 4.0 mm), rod material (Ti. vs. CoCr) and a cross-link (CLX). Construct stiffness was tested with C1-2 facets in contact (Contact Group) and in a 2 mm distracted position (Gapping Group). The ROM (°) was recorded and reported as a percentage of ROM (%ROM) normalized to the SOR. A difference > 30% between the SOR and the %ROM among the constructs was defined as significant.

RESULTS

Among all constructs, an increase in construct stiffness up to 50% was achieved with the addition of CLX, particularly with a 6S3R construct. These differences showed the greatest effect for the CLX in AR testing and for the 6S3R construct in FE and AR testing. Among all constructs, C1-2 gapping resulted in a significant loss of construct stiffness. A protective effect was shown for the CLX, particularly using a 6S3R construct in AR and FE testing. The selection of rod diameter (3.5 mm vs. 4.0 mm) and rod material (Ti vs. CoCr) did show a constant trend but did not yield significance.

CONCLUSION

This study is the first to show the loss of construct stiffness at C1-2 with gapping and increased restoration of stability using CLX and 6S3R constructs. In the correction of a craniocervical deformity, nuances in the surgical technique and advanced instrumentation may positively impact construct stability.

A novel 3D-printed locking cage for anterior atlantoaxial fixation and fusion: case report and in vitro biomechanical evaluation

BACKGROUND

Treatment of atlantoaxial dislocation is aimed at reduction and stabilization of the atlantoaxial joint. 3D printing refers to a process where additive manufacturing is achieved under precise computer control. Literature on its utilization in anterior atlantoaxial fixation and fusion is rare. This study is the first report on a 3D-printed locking cage used in the anterior procedure for atlantoaxial dislocation.

METHODS

A middle-aged male in his 40s presented with weakness and numbness of his extremities for 3 years and could only walk slowly with assistance. Imaging studies revealed severe anterior migration of C1, irreducible atlantoaxial dislocation, and severe cervical-medullary compression. A preoperative plan consisting of trans-oral soft tissue release and fixation using tailor-designed 3D-printed cages was devised. Following fluoroscopic confirmation of reduction of the atlantoaxial joints, two customized 3D-printed cages made of titanium alloy were inserted into the bilateral facet joints, which were then locked by six screws into the lateral masses of C1 and C2. The microstructure of the inserted cages was optimized for improved biomechanical stability and enhanced osseo-integration, without the need for bone grafting. In addition, a biomechanical test was performed on seven human cadaveric specimens comparing the novel implant with the conventional C1 lateral mass-C2 pedicle screw construct in three modes of motion (flexion-extension, lateral bending, axial rotation).

RESULTS

Improvement of neurologic function in the patient was evident immediately after surgery. He was able to walk independently 1 month post-operatively. At the 12-month follow-up, coronal reconstruction of CT demonstrated properly-positioned 3D-printed cages, evidence of osseo-integration at the bone-implant interface, and no subsidence or displacement of the implant. Eighteen months out of surgery, the mJOA score improved to 15, and lateral X-ray confirmed reduction of atlanto-axial dislocation. Additionally, the new construct provided strong fixation comparable to that conferred by conventional constructs as there was no significant difference observed between the two groups in all three directions of motion.

CONCLUSIONS

The novel implant represents a new option in the treatment of irreducible atlantoaxial dislocation. It can provide strong anterior support for solid fixation and fusion with a low profile and a microstructure that obviates the need for bone grafting.

Usefulness of ipsilateral translaminar C2 screws insertion for cervical fixation in children with a low laminar profile: a technical note

PURPOSE

The fusion of the upper cervical spine in children is demanding due to its reduced size, its anatomical complexity, or a severe pathology of the cranio-cervical junction. In some pediatric patients with today's more popular C1-C2 or, occipito-C2 techniques, it is impossible, or very risky to perform a short upper cervical fixation.

METHODS

We present the utility and good results of ipsilateral laminar C2 screws insertion technique in two pediatric cases with low C2 laminar profile. Case 1: a 5-year-old child with a C1-C2 unstable subluxation, and a condylar assimilation of C1, where we performed an occipito-C2 fixation using an occipital plate and this modified translaminar C2 screw technique. Case 2: a 8-year-old Down syndrome boy who suffered an unstable subluxation of C1-C2 upon whom we performed a C1-C2 screw fixation using the same technique.

RESULTS

Both cases have been followed up over a period of 7 and 2 years respectively, with good clinical results.

CONCLUSIONS

We describe the technique and the feasibility of the ipsilateral insertion of translaminar C2 screws in children with low laminar profiles, as a good alternative to other techniques when the anatomy of the C2 does not permit its use or make them very risky.

A biomechanical comparison of crossed and parallel rod configurations in atlantoaxial internal fixation

BACKGROUND

Posterior atlantoaxial fixation with screw rod forms an approximate "II" shape or "H" increasing transverse link for better stability. In order to improve stability and in consideration of difficult placement of transverse connecting rod, possibility of inadequate bone graft, some scholars have preliminarily researched biomechanics of a novel crossed rod as an approximate "X" configuration of screw rod.

PURPOSE

The aim of this study was to evaluate and compare the biomechanics of the crossed and parallel rod configurations in the screw rod system for posterior atlantoaxial fixation on a cadaveric model.

METHODS

Six fresh cervical specimens were used to complete the range of motion (ROM) testing by applying pure moments of ± 2.0 nm. Following intact state and under destabilization testing, screws were implanted. The specimens were then tested in the following sequence: Group BLS + PR (C2 bilateral laminar screws + parallel rod), Group BLS + CR (C2 bilateral laminar screws + crossed rod), LPRLS + PR (C2 left pedicle screw and right laminar screw + parallel rod), LPRLS + CR (C2 left pedicle screw and right laminar screw + crossed rod), BPS + PR (C2 bilateral pedicle screws + parallel rod) and BPS + CR (C2 bilateral pedicle screws + crossed rod). The ROM of the C1-2 segments was measured in flexion-extension, lateral bending and axial rotation. Six surgical constructs were compared between the groups and with intact condition, respectively.

RESULTS

The six fixed modes significantly increased stability compared with both the intact and destabilization group in flexion-extension, lateral bending and axial rotation (p < .05). In extension, BPS + CR and BLS + CR showed greater stability than BLS + PR (p < .05). During flexion, the six fixation methods showed no statistical significance (p > .05). In left lateral bending, stability of the other five screw rod fixation techniques significantly increased when compared with BLS + PR (p < .05). In the right lateral bending direction, the stability of BLS + PR was worse than that of BPS + CR and BPS + PR (p < .05). In the left axial rotation, stability of BLS + CR, LPRLS + CR and BPS + CR was greater than that of BLS + PR, LPRLS + PR and BPS + PR (p < .05). In the right axial rotation, the stability of BPS + CR and BLS + CR was greater than that of BLS + PR (p < .05).

CONCLUSION

The six investigated fixation methods provide sufficient biomechanical stability. The crossed rod configuration can further enhance the axial rotation stability of the screw rod system, which consists of C1 bilateral pedicle and C2 pedicle, or C2 lamina screws. The crossed rod can also improve the stability of the screw rod system made up of C1 bilateral pedicle and C2 lamina screws in lateral bending and extension. The crossed rod configuration is reliable and provides superior stability for clinical application.

The C2 Cortical Screw, an Alternative Fixation Technique for the C2 Segment During High Cervical Spine Surgery: Technical Note

BACKGROUND

For posterior fixation of C2 vertebra (the axis), several fixation techniques such as pedicle screw, laminar screw, and pars screw have been reported. A pedicle screw (PS) is considered the strongest among the techniques, but certain situations make PS fixation impossible or difficult. These include patients with a narrow C2 pedicle or high-riding vertebral artery. We introduced an alternative screw technique for C2 that addressed the aforementioned problems with safely placing it, which we termed a cortical screw (CS) for C2.

METHODS

Among a total of 28 cases using C2 CS for high cervical spine surgery, 2 cases using C2 CS were described. One patient was a 76-year old woman with a gait disturbance and myelopathic symptoms and diagnosed with C1-C2 myelopathy and translational instability. The other case was 54-year old man with posterior neck pain after traffic accident and diagnosed with C1-C2 fracture-dislocation. We used the C2 CS as an alternative technique for high cervical spine surgery in these patients and describe the ideal entry point and trajectory.

RESULTS

A postoperative computed tomography scan confirmed proper positioning of the C1 posterior arch screw and C2 CS, with satisfactory reduction of the C2 dens and adequate restoration of the C1-C2 spinal canal. The patient experienced no screw-related postoperative complications, and postoperative 1-year computed tomography images showed that solid union and good alignment of C1-2 segment was achieved.

CONCLUSIONS

C2 CS can be suitable alternative for C2 screw fixation technique in posterior high cervical spine fusion surgery.

The Role of Transverse Connectors in C1-C2 fixation for Atlantoaxial Instability: Is It Necessary? A Biomechanical Study

OBJECTIVE

To investigate the biomechanical effect of C1 lateral mass-C2 pedicle screw-rod (C1LM-C2PS) fixation with and without transverse connectors (TC) in an atlantoaxial instability (AAI) model.

METHODS

Ten freshly frozen cadaveric specimens were tested using an industrial robot under the following conditions: intact model, AAI model, C1-C2 model, C1-C2 with one TC model, and C1-C2 with two TCs model. Three types of motion, flexion-extension (FE), lateral bending (LB), and axial rotation (AR), were applied (1.5 Nm) to the specimens. The range of motion (ROM) and neutral zone (NZ) between C1 and C2 in all directions were measured.

RESULTS

Compared with those of the intact and AAI models, the C1-C2 ROM and NZ of all instrumented groups were decreased significantly in each direction of loading motion (P < 0.05). The mean FE ROM in the no TC, 1 TC, and 2 TC groups was 2.12° ± 0.41°, 2.29° ± 0.42°, and 2.04° ± 0.69°, respectively (P = 0.840, 0.981, 0.628, respectively); the mean LB ROM in the 3 intervention groups was 1.26° ± 0.67°, 1.02° ± 0.51° and 1.03° ± 0.57°, respectively (P = 0.489, 0.501, 1.000, respectively). During AR, the ROM and NZ of the no TC group (3.19° ± 0.89° and 1.51° ± 0.42°) were significantly reduced by more than 60% compared with those in the 1 (0.98° ± 0.28° and 0.40° ± 0.11°) and 2 TC groups (1.17° ± 1.69° and 0.42° ± 0.61°) (P < 0.001). Two TCs were equivalent for all loading motions to 1 TC (P > 0.05).

CONCLUSIONS

Adding TCs to C1LM-C2PS can effectively decrease the axial rotation ROM and enhance the stability of C1-C2 segment. Therefore, it is necessary to use TC-strengthened C1 lateral mass -C2 pedicle screw-rod fixation in patients with instability of C1-C2.

Three-point atlantoaxial fixation with C1-C2 transarticular screws and C1 lateral mass screws

BACKGROUND

Based on established posterior atlantoaxial fixation techniques, we present a novel technique that uses a polyaxial screw rod system and utilizes a combination of C1 lateral mass and C1-C2 transarticular screws.

METHODS

We conducted a retrospective review of six men and four women (mean age: 57, range: 20-86). Indication for atlantoaxial fixation was type II odontoid fractures or pseudarthrosis after odontoid fracture (n = 7), rheumatoid arthritis (n = 2) and os odontoideum (n = 1).

RESULTS

The mean follow-up time was 48 months (range: 24-72). There were no intraoperative complications such as vertebral artery, nerve root or spinal cord injury. Post-operative imaging showed no screw malposition. During follow-up, no patient had screw loosening, screw fracture or bone absorption around the screws. Clinically, patient neck pain improved in all cases.

CONCLUSIONS

C1 lateral mass and C1-C2 transarticular polyaxial screw rod fixation is a novel and potentially effective surgical technique for achieving immediate rigid immobilization of the C1-C2 motion segment. However, further biomechanical studies should be performed to prove our clinical results.

[Application of transarticular C1/2 screws connected with C1 lateral mass screws in a rod-screw system]

Fractures of the second cervical vertebra with involvement of the odontoid process can mostly be treated conservatively by immobilization. In the case of high-grade unstable fractures and pseudarthrosis dorsal C1/2 spondylodesis should be considered.Based on established atlantoaxial osteosynthesis techniques for dorsal C1/2 spondylodesis, a polyaxial screw-rod system with C1/2 transarticular screws connected with C1 lateral mass screws was carried out in a 56-year-old male patient with dislocated odontoid fracture.No intraoperative or postoperative complications occurred. During a follow-up of 36 months there was no screw loosening or dislocation.The presented alternative technique of dorsal C1/2 spondylodesis is a safe and effective method for stabilizing the atlantoaxial movement segment in cases of posttraumatic instability.

Effects of transverse connector on reduction and fixation of atlantoaxial dislocation and basilar invagination using posterior C1-C2 screw-rod technique

BACKGROUND CONTEXT

The mechanical strength provided by internal fixation is crucial for maintaining reduction and facilitating bony fusion. Though satisfactory results with the C1-C2 technique have been acquired in most clinical reports, the related problems of fusion delay and pseudarthrosis still exist. To increase the chance of bony fusion, a transverse connector (TC) is frequently used to augment torsional stiffness of thoracolumbar screw/rod constructs. Nevertheless, the clinical implication of TC in the management of atlantoaxial dislocation (AAD) and basilar invagination (BI) remains largely unknown.

PURPOSE

To evaluate the effects of TC application on C1-C2 screw-rod constructs based on consecutive adult patients with AAD and BI in a single institution over a 10-year period.

STUDY DESIGN

A retrospective study.

PATIENT SAMPLE

Patients with AAD and BI, who were treated with posterior C1-C2 screw-rod technique with or without TC usage from June 2007 to June 2017 at a single institution.

OUTCOME MEASURES

The radiological measurements included the anterior atlantodental interval (AADI), posterior atlantodental interval (PADI), height of odontoid process above Chamberlain line, and cervicomedullary angle (CMA). Patients' neurologic status was evaluated with the Japanese Orthopaedic Association (JOA) score. Fusion status was evaluated at different follow-up periods.

METHODS

We compared the difference of clinical, radiological, and surgical outcomes between the TC and NTC groups postoperatively.

RESULTS

In total, there were 149 consecutive patients in the TC group and 168 patients in the NTC group. On average, 1.2 TCs per patient were used in the TC group. No significant differences were identified for operative time and blood loss between groups. There was also no statistical difference in the radiological measurements of AADI, PADI, Chamberlain line, and CMA between the TC and NTC groups preoperatively and postoperatively. A significantly higher JOA score was obtained in the TC group than that in the NTC group postoperatively. The fusion rates were higher in the TC group than those in the NCT group at the early stage postoperatively (3 and 6 months; p<.01).

CONCLUSIONS

Use of TCs seems to improve bony fusion and neurologic outcomes in the treatment of AAD and BI with C1-C2 screw-rod technique.

Importance of the Occipitoaxial Angle and Posterior Occipitocervical Angle in Occipitocervical Fusion

OBJECTIVE

To observe the effects of occipitoaxial angle (O-C2 angle, OC2A) and posterior occipitocervical angle (POCA) selection on postoperative clinical efficacy and lower cervical curvature in patients with acute acquired atlantoaxial dislocation after occipitocervical fusion (OCF).

METHODS

A total of 150 healthy subjects without cervical disease (healthy group) were randomly selected based on gender and age. Three spine surgeons measured the OC2A and POCA of the healthy group and averaged the values. A total of 30 patients with an average age of 51.0 years (range, 18-70 years; 16 male and 14 female) with trauma or rheumatoid arthritis (disease group) who underwent occipitocervical fusion (OCF) for atlantoaxial dislocation between January 2012 and June 2016 were reviewed. OC2A, POCA, and cervical spinal angle (CSA) were measured postoperative/soon after surgery and ambulation, and at the final follow-up visit. The preoperative and final follow-up visual analog scale (VAS), Japanese orthopedics association score (JOA), neck disability index (NDI), and dCSA (change of CSA from postoperative/soon after surgery and ambulation to final follow-up) were recorded.

RESULTS

The values of OC2A and POCA in 150 healthy subjects were 14.5° ± 3.7° and 108.2° ± 8.1°, respectively, and the 95% confidence interval (CI) were 7.2°-21.8° and 92.3°-124.0°, respectively. There was a negative correlation between OC2A and POCA (r = -0.386, P < 0.001). There were 18 patients (group one) of ideal OC2A and POCA (both within 95% CI of the healthy group) postoperative/soon after surgery and ambulation with a mean follow-up time of 26.3 ± 20.9 months in disease group. The remaining patients (group two) with a mean follow-up time of 31.3 ± 21.3 months. There was no statistically significant difference in the baseline data as well as pre-operative outcomes, including VAS score, JOA score, and NDI between the two groups. Likewise, the post-operative outcomes in final follow-up, including VAS and JOA score, had no distinct difference in the two groups. However, NDI (11.0 ± 2.9) in group two at the final follow-up was significantly higher than that in group one (7.0 ± 2.3) (P < 0.001). And group two showed statistically greater dCSA (5.9 ± 7.5°) than group one (-2.3° ± 6.2°) (P = 0.003).

CONCLUSIONS

The negative correlation between OC2A and POCA plays an important role in maintaining the biodynamic balance of the occipital-cervical region. OC2A and POCA should be controlled of a normal population in patients with acute acquired atlantoaxial dislocation during OCF, which can further improve the clinical efficacy and prevent loss of lower cervical curvature after surgery.

Recommendations for Diagnosis and Treatment of Odontoid Fractures in Geriatric Patients

BACKGROUND

Odontoid fractures in geriatric patients represent an entity of increasing incidence with a high rate of morbidity and mortality. The optimal diagnostic and therapeutic management is being controversially discussed in the literature.

METHODS

In a consensus process and based on the current literature, the members of the working groups "Osteoporotic Fractures" and "Upper Cervical Spine" of the German Society for Orthopaedics and Trauma Surgery (DGOU) defined recommendations for the diagnostics and treatment of odontoid fractures in geriatric patients.

RESULTS

For the diagnosis of odontoid fractures in symptomatic patients, computed tomography represents the gold standard, along with conventional radiographs. Magnetic resonance and dynamic imaging can be used as ancillary imaging modalities. With regard to fracture classification, the systems described by Anderson/D'Alonzo and by Eysel/Roosen have proved to be of value. A treatment algorithm was developed based on these classifications. Anderson/D'Alonzo type 1, type 3, and non-displaced type 2 fractures usually can be treated non-operatively. However, a close clinical and radiological follow-up is essential. In Anderson/D'Alonzo type 2 fractures, operative treatment is associated with better fracture healing. Displaced type 2 and type 3 fractures should be stabilized operatively. Type 2 fractures with suitable fracture patterns (Eysel/Roosen 2A/B) can be stabilized anteriorly. Posterior C I/II-stabilization procedures are well established and suitable for all fracture patterns.

A novel screw view model of 3D navigation for upper cervical pedicle screw placement: A case report

RATIONALE

The purpose of this study is to introduce the technique of screw view model of navigation (SVMN) for upper cervical pedicle screw (UCPS) insertion. With the assistance of SVMN technology, the difficulty of screw placement manipulation can be diminished and the accuracy of placement can be improved.

PATIENT CONCERNS

A 49-year-old man presented with numbness of extremities and limited activity for 2 years.

DIAGNOSES

He was diagnosed with old fracture of C1 vertebra and atlantoaxial subluxation.

INTERVENTIONS

We used SVMN to assist UCPS insertion and lateral mass screw insertion in this patient.

OUTCOMES

A total of 2 pedicle screws and 2 lateral mass screws were inserted, all screws were defined as excellent position according to postoperative computer tomography (CT). The neurological function was intact postoperatively. The operation time was 293 minutes, the total fluoroscopic time was 4.1 minutes and the bleeding volume was 302 ml. There were no complications during the 48 months follow-up period.

CONCLUSIONS

The application of SVMN in UCPS insertion could achieve satisfactory effect of internal fixation for upper cervical spine and avoid neurovascular damage. The utilization of SVMN for UCPS insertion is a safe and efficacious method. Besides, it also increased the patients' hospital cost, and the surgeon must be quite familiar with the functional state of computer navigation.

Planning C2 pedicle screw placement with multiplanar reformatted cervical spine computed tomography

Object:

Careful preoperative planning with thin-slice computed tomography (CT) scan is useful for hardware placement at C2. Prior studies have shown considerable variability in the proportion of C2 vertebrae considered safe for pedicle screw placement, depending on the imaging technique used. Our work sought to more carefully define that proportion using a refined imaging technique on a large number of submillimeter CT scans.

Materials and Methods:

We reviewed 150 submillimeter cervical spine studies randomly selected from CT scans performed at a Level 1 trauma center. OsiriX™ image analysis software was used to propagate a 5-mm cylinder through the plane of the pedicle on paracoronal reformatted CT scans. Hounsfield unit attenuation was used to determine whether the cylinder violated the pedicle. Binomial data were generated to determine the proportion of pedicles that would allow safe screw placement.

Results:

We analyzed 300 pedicles in 150 patients. Using a standard C2 pedicle starting point, 32% of pedicles were breached by the 5-mm diameter cylinder. When screw trajectory was adjusted by moving the cylinder to fit the pedicle isthmus, establishing an optimized starting point, only 14% of pedicles were breached. Average pedicle length was 27.3 mm for screws that would have crossed the isthmus versus 13.2 mm for screws that would have stopped short due to potential breach.

Conclusions:

Findings of the current work suggest that preoperative imaging analysis or navigation can be useful adjuncts when anatomical variants are present.

Finding the "Sweet Spot" for C2 Root Transection in C1 Lateral Mass Exposure

BACKGROUND

Atlantoaxial fusion often requires C2 nerve transection for complete C1 lateral mass exposure. Nerve transection is made ideally at the preganglionic segment proximal to the dorsal root ganglion to minimize the risk of postoperative dysesthesias. If the nerve is transected too proximally, cerebrospinal fluid leak may be encountered by violation of the dura and arachnoid where the sensory and motor nerve rootlets exit the subarachnoid space. In this study we aimed to quantify the length of the C2 nerve preganglionic segment using cadaveric specimens and develop a method for reliable intraoperative localization for sectioning during C1-2 arthrodesis.

METHODS

Using microsurgical techniques, 16 C2 nerves from 8 frozen and injected cadaveric cervical spine specimens were dissected. Two key measurements were taken to establish a reliable method of preganglionic segment identification. The "sweet spot" for nerve transection was based on the approximate location of the midpoint of the preganglionic segment.

RESULTS

The final determination of the ideal spot for C2 nerve transection using these calculations was 3 mm lateral to the medial border of the lateral mass.

CONCLUSIONS

This anatomic study found remarkable consistency in the preganglionic segment length. The medial border of the lateral mass appeared to be a consistently reliable landmark for identification of the preganglionic segment of the C2 nerve root. By using relationships between known anatomic structures intraoperatively, safety of atlantoaxial fixation can be optimized to maximize complication avoidance and satisfactory patient outcomes.

Biomechanical Comparison of C1 Lateral Mass-C2 Short Pedicle Screw-C3 Lateral Mass Screw-Rod Construct Versus Goel-Harms Fixation for Atlantoaxial Instability

STUDY DESIGN

A biomechanical in vitro study using human cadaveric spines.

OBJECTIVE

The aim of this study was to compare atlantoaxial stability and stiffness of a C1 lateral mass - C2 short pedicle - C3 lateral mass screw-rod construct versus C1 lateral mass - C2 pedicle screw-rod construct.

SUMMARY OF BACKGROUND DATA

The C1 lateral mass - C2 pedicle screw-rod construct provides excellent atlantoaxial fixation, but C2 pedicle screw placement is associated with risk of vertebral artery injury. The use of shorter C2 pedicle screws may mitigate the risk of vascular injury but may result in reduced C1-C2 stabilization. Extending C1 lateral mass - C2 short pedicle screw-rod construct with C3 lateral mass screws may mitigate the risk of vascular injury without compromising C1-C2 fixation.

METHODS

Seven cervical spines were tested with internal control experimental design in the following sequence: intact state, and following creation of type II odontoid fracture, the specimen was instrumented with C1 lateral mass - C2 pedicle screw fixation (C2PED), C1 lateral mass - C2 short pedicle screw fixation (C2SPED), and C1 lateral mass - C2 short pedicle - C3 lateral mass screw fixation (C2SPED-C3LM). For each condition, the angular stiffness and range of motion (ROM) with 1.5-Nm load in flexion/extension (FE), lateral bending (LB), and right/left axial rotation (RAR/LAR) were quantified.

RESULTS

Instrumented conditions demonstrated significantly lower C1-C2 angular ROM and greater stiffness than the intact state. Compared with C2PED, C2SPED-C3LM demonstrated significantly lower C1-C2 ROM during FE and LB, significantly greater C1-C2 stiffness in flexion and right/left LB, similar C1-C2 ROM and stiffness in RAR/LAR, and similar stiffness in extension. C2SPED-C3LM demonstrated significantly greater atlantoaxial stabilization in the sagittal and coronal planes than C2PED construct.

CONCLUSION

Compared with C2PED, C2SPED-C3LM may be a suitable alternative surgical strategy for atlantoaxial instability that provides superior atlantoaxial fixation.

LEVEL OF EVIDENCE

N/A.

Traumatic Atlantoaxial and Fracture-Related Dislocation

Traumatic atlantoaxial dislocation due to ligamentous and combined osseous injuries rarely occurs in adults. There are only few cases published in the literature. In this level 4 study, a cohort of nine consecutive patients suffering from traumatic atlantoaxial dislocation has been analyzed regarding morphology of injury, trauma mechanism, and outcome since 2007. Three types of those injuries have been found regarding direction of dislocation indicating the underlying ligamentous injuries as well as the accompanying grade of instability. Firstly, there was rotatory dislocation, if the alar ligaments were injured. Secondly, there occurred horizontal dislocation, when transverse atlantal ligament was damaged additionally. Thirdly, excessive ligamentous injury led to distraction of the atlantoaxial complex resulting in dissociation of the atlas against the axis. Additionally fractures of the atlas as well as of the odontoid process (type II or III according to Anderson/D'Alonzo) were diagnosed frequently. Atlantoaxial dislocation injuries, especially distraction injuries, offer a high risk for accompanied neurovascular disorders deserving reduction followed by surgical fixation. Only rotatory injuries leading to ligamentous damage solitarily can safely be successfully treated conservatively. Understanding of the injuries' morphology is essential, in order to set the correct diagnosis and to implicate the most advantageous treatment regime.

Preclinical evaluation of a novel anterior non-fusion fixation device for atlantoaxial instability: an in vivo comparison study in a canine model

PURPOSE

The Anterior Atlantoaxial Non-Fusion Fixation System (AANFS) was a novel motion preservation device for atlantoaxial instability to replace traditional fusion techniques. The purpose of this in vivo study was to evaluate the clinical features and biomechanical properties of this new device in a canine model by comparing it with a conventional method.

METHODS

Eighteen adult male canines were randomly divided into group 1, which received the AANFS replacement, group 2 which received the Harms rigid fixation procedures, and group 3, which served as the control group. Routine follow-up evaluations were performed postoperatively. Specimens were harvested 12 weeks after the operation. Biomechanical tests were conducted to obtain the range of motion (ROM) and neutral zone (NZ) at C1-C2 segment in different groups.

RESULTS

The canines successfully tolerated the entire experimental procedure. No significant differences were found in surgery time, blood loss and recovery time between the AANFS group and the Harms rigid fixation group. Radiological examinations revealed that the position of the implant was good. Biomechanical results showed that, compared with the intact group, the mean ROM and NZ in flexion, extension, lateral bending and rotation were significantly reduced after rigid fixation. However, after the AANFS implantation, ROM and NZ in all directions were similar to those of the intact state.

CONCLUSIONS

This study for the first time provides an animal model for studying non-fusion strategies of upper cervical spine. The AANFS was able to maintain movement function of the atlantoaxial joint and may be an alternative to traditional fusion techniques. These slides can be retrieved under Electronic Supplementary Material.

Surgical Treatment of Stenosis of Spinal Canal and Dural Sac at the Craniovertebral Junction

The paper presents the results of surgical treatment of 12 patients with stenosing processes of the vertebral canal at the craniovertebral transition due to chronic, unstable type 2 injuries of the C odontoid process (classification of fractures of odontoid process proposed in 1974 by Anderson and D’Alonzo). Patient examination included clinical-neurologic examination, review spondylograms of the cervical spine in 2 projections, MSCT, MRI. All patients were admitted to the clinic with external fixators (cervical support collar or Philadelphia collar). In the preoperative period, all patients were divided into 2 groups according to indications and contraindications for the application of the HALO-device. The first group consisted of 7 people, with cervical spine still fixed with the cervical support collar or Philadelphia collar, and the second group consisted of 5 patients with CII fracture fixed and corrected in the preoperative period by the HALO-device. All patients underwent surgical intervention – posterior approach decompression of the spinal canal and dural sack in the craniovertebral passage by CI laminectomy, partial resection of the posterior margin of the occipital aperture followed by the implementation of atlanto-axial occipitospondylodesis (a clamp with shape-memory effect for posterior occipitospondylodesis, OOO “MITS SPF”, Novokuznetsk, Russia). A comparative analysis of the results of surgical treatment of posttraumatic stenoses of the vertebral canal with and without the use of the HALO-traction device was performed. The results was better in the second group, which makes it possible to consider the second variant of surgical treatment more pathogenetically justified. Thus, HALO-traction restors anatomo-topographic relationships in the craniovertebral zone creating hard external fixation, helping to avoid intraoperative complications.

Spinal instrumentation in infants, children, and adolescents: a review

OBJECTIVEThe evolution of pediatric spinal instrumentation has progressed in the last 70 years since the popularization of the Harrington rod showing the feasibility of placing spinal instrumentation into the pediatric spine. Although lacking in pediatric-specific spinal instrumentation, when possible, adult instrumentation techniques and tools have been adapted for the pediatric spine. A new generation of pediatric neurosurgeons with interest in complex spine disorder has pushed the field forward, while keeping the special nuances of the growing immature spine in mind. The authors sought to review their own experience with various types of spinal instrumentation in the pediatric spine and document the state of the art for pediatric spine surgery.METHODSThe authors retrospectively reviewed patients in their practice who underwent complex spine surgery. Patient demographics, operative data, and perioperative complications were recorded. At the same time, the authors surveyed the literature for spinal instrumentation techniques that have been utilized in the pediatric spine. The authors chronicle the past and present of pediatric spinal instrumentation, and speculate about its future.RESULTSThe medical records of the first 361 patients who underwent 384 procedures involving spinal instrumentation from July 1, 2007, to May 31, 2018, were analyzed. The mean age at surgery was 12 years and 6 months (range 3 months to 21 years and 4 months). The types of spinal instrumentation utilized included occipital screws (94 cases); C1 lateral mass screws (115 cases); C2 pars/translaminar screws (143 cases); subaxial cervical lateral mass screws (95 cases); thoracic and lumbar spine traditional-trajectory and cortical-trajectory pedicle screws (234 cases); thoracic and lumbar sublaminar, subtransverse, and subcostal polyester bands (65 cases); S1 pedicle screws (103 cases); and S2 alar-iliac/iliac screws (56 cases). Complications related to spinal instrumentation included hardware-related skin breakdown (1.8%), infection (1.8%), proximal junctional kyphosis (1.0%), pseudarthroses (1.0%), screw malpositioning (0.5%), CSF leak (0.5%), hardware failure (0.5%), graft migration (0.3%), nerve root injury (0.3%), and vertebral artery injury (0.3%).CONCLUSIONSPediatric neurosurgeons with an interest in complex spine disorders in children should develop a comprehensive armamentarium of safe techniques for placing rigid and nonrigid spinal instrumentation even in the smallest of children, with low complication rates. The authors' review provides some benchmarks and outcomes for comparison, and furnishes a historical perspective of the past and future of pediatric spine surgery.

Differences in fixation strength among constructs of atlantoaxial fixation

OBJECTIVETo avoid jeopardizing an aberrant vertebral artery, there are three common options in placing a C2 screw, including pedicle, pars, and translaminar screws. Although biomechanical studies have demonstrated similar strength among these C2 screws in vitro, there are limited clinical data to address their differences in vivo. When different screws were placed in each side, few reports have compared the outcomes. The present study aimed to evaluate these multiple combinations of C2 screws.METHODSConsecutive adult patients who underwent posterior atlantoaxial (AA) fixation were retrospectively reviewed. Every patient uniformly had bilateral C1 lateral mass screws in conjunction with 2 C2 screws (1 C2 screw on each side chosen among the three options: pedicle, pars, or translaminar screws, based on individualized anatomical consideration). These patients were then grouped according to the different combinations of C2 screws for comparison of the outcomes.RESULTSA total of 63 patients were analyzed, with a mean follow-up of 34.3 months. There were five kinds of construct combinations of the C2 screws: 2 pedicle screws (the Ped-Ped group, n = 24), 2 translaminar screws (the La-La group, n = 7), 2 pars screws (the Pars-Pars group, n = 6), 1 pedicle and 1 pars screw (the Ped-Pars group, n = 7), and 1 pedicle and 1 translaminar screw (the Ped-La group, n = 19). The rate of successful fixation in each of the groups was 100%, 57.1%, 100%, 100%, and 78.9% (Ped-Ped, La-La, Par-Par, Ped-Par, and Ped-La, respectively). The patients who had no translaminar screw had a higher rate of success than those who had 1 or 2 translaminar screws (100% vs 73.1%, p = 0.0009). Among the 5 kinds of construct combinations, 2 C2 pedicle screws (the Ped-Ped group) had higher rates of success than 1 C2 pedicle and 1 C2 translaminar screw (the Ped-La group, p = 0.018). Overall, the rate of successful fixation was 87.3% (55/63). There were 7 patients (4 in the Ped-La group and 3 in the La-La group) who lost fixation/reduction, and they all had at least 1 translaminar screw.CONCLUSIONSIn AA fixation, C2 pedicle or pars screws or a combination of both provided very high success rates. Involvement of 1 or 2 C2 translaminar screws in the construct significantly lowered success rates. Therefore, a C2 pars screw is recommended over a translaminar screw.

Biomechanical comparison of cemented versus non-cemented anterior screw fixation in type II odontoid fractures in the elderly: a cadaveric study

BACKGROUND CONTEXT

Odontoid process fractures are the most common injuries of the cervical spine in the elderly. Anterior screw stabilization of type II odontoid process fractures improves survival and function in these patients but may be complicated by failure of fixation.

PURPOSE

The present study aimed to determine whether cement augmentation of a standard anterior screw provides biomechanically superior fixation of type II odontoid fractures in comparison with a non-cemented standard screw.

STUDY DESIGN

Twenty human cadaveric C2 vertebrae from elderly donors (mean age 83 years) were obtained.

METHODS

Anderson and D'Alonzo type IIa odontoid fracture was created by transverse osteotomy, and fluoroscopy-guided anterior screw fixation was performed. The specimens were divided into two matched groups. The cemented group (n=10) had radiopaque high viscosity polymethylmethacrylate cement injected via Jamshidi needle into the base of the odontoid process. The other group was not augmented. A V-shaped punch was used for loading the odontoid in an anteroposterior direction until failure. The failure state was defined as screw cutout or 5% force decrease. Mean failure load and bending stiffness were calculated.

RESULTS

The mean failure load for the cemented group was 352±12 N compared with 168±23 N for the non-cemented group (p<.001). The mean initial stiffness of the non-cemented group was 153±19 N/mm compared with 195±29 N/mm for the cemented group (p<.001) CONCLUSIONS: Cement augmentation of an anterior standard screw fixation of type II odontoid process fractures in elderly patients significantly increased load to failure under anteroposterior load in comparison with non-augmented fixation. This may be a valuable technique to reduce failure of fixation.

Reoperation for Symptomatic Nonunions in Atlantoaxial (C1-C2) Fusions with and without Bone Morphogenetic Protein: A Cohort of 108 Patients with >2 Years Follow-Up

OBJECTIVE

To determine if there is a difference in reoperation rates for symptomatic nonunions in atlantoaxial (C1-C2) fusions with or without bone morphogenetic protein (BMP) using data from a national spine registry and to analyze the different types of bone grafts used in the non-BMP group.

METHODS

Data from the Kaiser Permanente spine registry were used to identify patients with C1-C2 fusions with >2 years follow-up. Patient characteristics, diagnosis, operative times, length of stay, and reoperations were extracted from the registry. The data set was divided into patients with and without BMP. Further analysis was made of the different types of non-BMP grafts as well as the instrumentation used.

RESULTS

In our cohort, we found 58 patients (53.7%) with BMP and 50 patients (46.3%) without with an average follow-up time of 5 years (interquartile range, 2.04-8.49). The BMP versus non-BMP groups differed in admitting diagnosis, operative times, length of stay, and follow-up times. There were no reoperations for symptomatic nonunions in both groups. The non-BMP group included iliac crest graft (with or without allograft [+/-] allograft); lamina (+/- allograft); and allograft alone.

CONCLUSIONS

Using one of the largest retrospective studies on C1-C2 fusions with and without BMP, we found no difference in reoperation rates for symptomatic nonunions. For the non-BMP group, we found that lamina (+/- allograft) or allograft alone may also be just as effective as iliac crest graft (+/- allograft) in having no reoperations for symptomatic nonunions.

Posterior C2 Fixation Using Trans-C2 Inferior Articular Process Screws: A Case Series and Technical Note

OBJECTIVE

Upper cervical fixation with C2 pedicle screw insertion may predispose patients to vertebral artery injury, in particular, patients with craniovertebral junction anomalies. The aim of this study was to describe an alternative technique with trans-C2 inferior articular process screw (C2IAPS) insertion for rigid C2 fixation, which can be used to anchor the C2 vertebra for upper cervical fixation.

METHODS

Records of 19 patients who underwent posterior atlantoaxial fixation using C2IAPS combined with C1 lateral mass screw were retrospectively reviewed. Efficacy was assessed by postoperative imaging and Japanese Orthopaedic Association scores.

RESULTS

There were 22 C2IAPSs successfully implanted (3 on both sides and 16 on 1 side). With the exception of 2 screws that had intruded into the outlet of the intervertebral foramen, all screws were safely implanted. Average Japanese Orthopaedic Association scores improved from 11.8 ± 1.9 preoperatively to 15.3 ± 1.3 postoperatively. Bony fusion rate was 100%.

CONCLUSIONS

For patients who are not eligible for C2 pedicle screw fixation, C2IAPS fixation can be considered as an alternative technique for upper cervical fixation of C2.

Biomechanical Comparison of Four Different Atlantoaxial Posterior Fixation Constructs in Adults: A Finite Element Study

STUDY DESIGN

Finite element analysis.

OBJECTIVE

To compare the biomechanical stability imparted to the C1 and C2 vertebrae by the transarticular (TA), C1 lateral mass (LM)-C2 pedicle (PS), C1LM-C2 pars, and C1LM-C2 translaminar (TL) screw fixation techniques.

SUMMARY OF BACKGROUND DATA

Cadaveric biomechanical studies of several atlantoaxial posterior fixation techniques have been performed, showing significant heterogeneity in biomechanical properties among the studies.

METHODS

From computed tomography images, a nonlinear intact three-dimensional C1-2 finite element model was developed and validated. Four finite element models were reconstructed from different C1-2 fixation techniques. The range of motion (ROM) and maximum von Misses stresses for the four screw techniques were compared under flexion, extension, lateral bending, and axial rotation.

RESULTS

C1LM-C2PS showed the greatest decrease in ROM with flexion/extension and lateral bending. C1-2TA and C1LM-C2 pars showed less ROM reduction than the other techniques, in flexion/extension. C1LM-C2TL showed the least decrease in ROM during axial rotation. For C1-2TA, the maximum stress was in the C1-2 joint region. In the C1LM-C2PS, the C1 rod head, C2 pars screw, and C2TL screw were stressed at the C2 rod head. The maximal von Mises stress on the C1-2TA at the C1-2 joint site was the highest at flexion/extension, whereas the C1LM-C2PS had the lowest stress on the screw at flexion/extension and lateral bending. The C1LM-C2TL showed the highest stress in axial rotation and lateral bending.

CONCLUSION

In this study, C1LM-C2PS fixation was the most stable technique. If surgeons have to use other fixation methods besides the C2 pedicle screw, they need to be aware that additional fixation or postoperative immobilization may be required to achieve ROM restriction. Careful observation at the maximum stress site on the screw including screw loosening, screw-bone interface disruption or screw fracture will be necessary during follow-up imaging examinations (x-ray and computed tomography scan) after atlantoaxial fixation.

LEVEL OF EVIDENCE

N/A.

Minimally Invasive Microscope-Assisted Stand-Alone Transarticular Screw Fixation without Gallie Supplementation in the Management of Mobile Atlantoaxial Instability

Study Design

Retrospective study.

Purpose

To evaluate the clinico-radiological efficacy of stand-alone minimally invasive transarticular screw (MIS-TAS) fixation without supplemental Gallie fixation in the management of mobile C1–C2 instability.

Overview of Literature

Data evaluating the efficacy and feasibility of MIS-TAS in the literature is scanty.

Methods

Patients with mobile atlantoaxial instability and >2 years follow-up were included and managed by stand-alone TAS fixation using the Magerl technique and morselized allograft without additional fixation. Patient demographics and intra-operative parameters were noted. Clinical parameters (Visual Analog Scale [VAS] and Oswestry Disability Index [ODI]), neurology (modified Japanese Orthopaedic Association [mJOA]), and radiological factors (anterior atlanto-dens interval and space available for cord) were evaluated pre and postoperatively. Computed tomography (CT) was performed in patients who did not show interspinous fusion on X-ray at 1 year, to verify intra-articular fusion. Statistical analysis was performed using IBM SPSS ver. 20.0 (IBM Corp., Armonk, NY, USA); the Student t-test and analysis of variance were used to assess statistical significance (p <0.05).

Results

A total of 82 consecutive cases (three males, one female; mean age, 36.26±5.78 years) were evaluated. In total, 163 TASs were placed. Significant improvement was noticed in clinical (mean preoperative VAS=7.2±2.19, postoperative VAS=3.3±1.12; mean preoperative ODI=78.3±4.83, postoperative ODI=34.05±3.26) and neurological features (mean preoperative mJOA=14.73±2.68, postoperative mJOA=17.5±2.21). Radiological evidence of fusion was noted in 97.5% cases at final follow-up. Seventeen patients were found to have no interspinous fusions upon X-rays, but CT revealed facet fusion in all patients except in two. Inadvertent vertebral artery injury was noted in three cases.

Conclusions

Stand-alone TAS fixation with morselized allograft provides excellent radiological and clinical outcomes. The addition of a supplementary tension band and structural graft are not essential. This provides the opportunity to avoid the complications associated with graft harvesting and wiring.

Safety and accuracy of freehand versus navigated C2 pars or pedicle screw placement

BACKGROUND CONTEXT

C2 pedicle and pars screws require accurate placement to avoid injury to nearby neurovascular structures. Freehand, fluoroscopically guided, and computed tomography (CT)-based navigation techniques have been described in the medical literature.

PURPOSE

The present study aims to compare the safety and accuracy of the freehand technique versus stereotactic navigation for the placement of C2 pedicle and pars screws.

STUDY DESIGN/SETTING

This study was a retrospective review of consecutive patients treated with posterior fixation constructs.

PATIENT SAMPLE

A total of 220 consecutive patients were treated with posterior fixation constructs containing C2 pars or pedicle screws placed at our institution.

OUTCOME MEASURES

Computed tomography imaging was used to assess the accuracy of screw placement. Intraoperative complications and incidence of stroke or mortality within 30 days of the operation were analyzed.

METHODS

A retrospective review was conducted of consecutive patients treated with posterior fixation constructs containing C2 pars or pedicle screws placed by spine surgeons between January 1, 2010, and August 31, 2016. Clinical and radiographic data were collected and analyzed. Screw accuracy was graded independently by two reviewers according to the following criteria: grade A (no breach), grades B-E (breach with transverse foramen obstruction of 1%-25%, 26%-50%, 51%-75%, or 76%-100%, respectively), and grade M (medial breach). Screws were divided into acceptable (grades A and B) and unacceptable (grades C-E and M).

RESULTS

A total of 426 C2 pars or pedicle screws (312 freehand, 114 navigated) were placed in 220 patients (160 freehand, 60 navigated). Complications were similar between the groups: three vertebral artery injuries (two [1%] freehand, one [2%] navigated; p>.99), five deaths (four [3%] freehand, one [2%] navigated; p>.99), and one (2%) stroke in the navigated group (p=.61). Computed tomography imaging was available for accuracy grading of 182 screws (131 freehand, 51 navigated). No breaches (grade A) occurred in 113 of the freehand screws (86%) and in 34 of the navigated screws (67%) (p=.006). More screws had acceptable placement in the freehand group (123 of 131, 94%) than in the navigated group (42 of 51, 82%) (p=.02).

CONCLUSIONS

In patients with postoperative CT imaging (43%), the freehand technique was found to be more accurate than CT-based navigation for C2 pedicle or pars screw placement. Complication rates did not differ between the two techniques in this study.