Subaxial Sagittal Alignment After Atlantoaxial Fixation Techniques

Three-dimensional kinematic analysis of the cervical spine following posterior atlantoaxial fusion under physiological loading: An in vivo study

BACKGROUND

This study aimed to analyze the three-dimensional cervical motion characteristics in patients who underwent posterior atlantoaxial fusion surgeries using cone beam computed tomography and 3D3D registration technology.

METHODS

The study selected 20 patients who underwent posterior atlantoaxial fusion surgery and 20 healthy people as the control group. All subjects underwent cone beam computed tomography scans of the occipital and cervical spine in 7 different functional positions, then 3D3D registration of Occipital-C7 was performed at each functional position to calculate the motion characteristics of each segment. The ranges of motion of the entire cervical spine and each segment were obtained in each functional position.

FINDINGS

In the experimental group, ranges of motion of C1-C7 in flexion-extension and left-right twisting were significantly lower compared to controls (41.9° ± 13.8° vs. 56.6° ± 11.6°, 29.3° ± 9.6° vs. 91.2° ± 13.7°, respectively, P < 0.05). In the occipital-atlas segment, range of motion in flexion-extension was significantly smaller in the experimental group than controls (10.7° ± 3.2° vs. 19.4° ± 4.2°, P < 0.001), but it was larger in twisting (5.3° ± 4.2° vs. 2.1° ± 1.8°, P < 0.05). The twisting range of motion of C2-C3 was 4.7° ± 2.0° in the experimental group and 3.1° ± 1.6° in the control group (P < 0.05). Additionally, the alteration in ranges of motion during flexion-extension was primarily characterized by less extension.

INTERPRETATION

The posterior atlantoaxial fusion surgery induced biomechanical changes in the cervical spine. Following the procedure, the movement of C1-C7 during flexion-extension and twisting was significantly lower, with varying degrees of impact on adjacent and lower cervical segments. Moreover, the surgery had a greater effect on cervical extension than flexion.

Radiological Features in Type II Odontoid Fractures in Older Adults After High- and Low-Energy Trauma

STUDY DESIGN

Retrospective study.

OBJECTIVES

Although type II odontoid fractures mainly occur due to high-energy trauma (HET), the number of odontoid type II fractures after low-energy trauma (LET) in the elderly is on the rise. However, there is a paucity of conclusive evidence on the relationship between trauma mechanism and cervical spine alignment in the elderly population. Consequently, we examined cervical alignment and osteoporotic and osteoarthritic patterns in elderly individuals (aged ≥65 years) with type II odontoid fractures.

METHODS

We retrospectively assessed cervical spine alignment in 76 elderly individuals who experienced type II odontoid fractures after HET (n = 36) and LET (n = 40) between 2005 and 2020. Osteoporotic and osteoarthritic changes on computed tomography and cervical alignment parameters on sagittal plane radiographs were examined.

RESULTS

Moderate and severe osteoporosis of the dens-body junction and osteoarthritis of the atlanto-odontoid joint were more prevalent in the LET than the HET group (P<.005). The anterior atlantodental interval (ADI) was significantly smaller in the LET group than in the HET group (.7 [.7] millimeter vs 1.2 [.8] mm; P=.003). An ADI equal 0 mm indicative for anterior fusion of C1/C2 was present in 37.5% of patients of the LET group. The C0-C2 angle, C1-C2 lordosis, and C2-C7 sagittal vertical axis were significantly different (HET vs LET: 33.2 [7.2]° vs 41.6 [11.4]°, P=.005; 28.1 [7.0]° vs 34.0 [8.0]°, P=.002; and 16.1 [11.1] millimeter vs 27.1 [12.4] mm, P=.008; respectively).

CONCLUSION

Significantly higher rates of osteoporotic and degenerative changes were observed after LET. Furthermore, previous cervical malalignment represents a risk factor for type II odontoid fractures after LET.

An In Vitro Biomechanical Study of the Ectopic Functional Reconstruction of the Transverse Ligament of Atlas

OBJECTIVE

To evaluate the stability and function of the C1-C2 joint after ectopic functional reconstruction (EFR) of the C1 transverse ligament.

METHODS

Eight human cadaveric cervical spines (C0-C4) were subjected to in vitro biomechanical test with moment control. Spine specimens were tested under the following conditions: 1) left intact; 2) destabilized by severing the transverse ligament of atlas; 3) after EFR of the transverse ligament. Range of motion was measured in flexion, extension, lateral bending, and axial rotation.

RESULTS

Destabilization significantly increased range of motion in all directions compared with the intact status (P < 0.001). However, after EFR of the transverse ligament, range of motion in all directions was restored to the intact state. Meanwhile, coupling motions were reproduced in the axial rotation.

CONCLUSIONS

EFR of the transverse ligament virtually recovers all the physiological functions of the native transverse ligament and might be a promising alternative for the treatment of anterior atlantoaxial dislocation. Further studies are warranted before clinical application of EFR of the transverse ligament.

Efficacy and Safety of Goel-Harms Technique in Upper Cervical Spine Surgery: A Systematic Review and Meta-Analysis

OBJECTIVE

The main purpose of this systematic review and meta-analysis was to estimate the incidence of implant-associated complications and fusion rates for the Goel-Harms technique (GHT) and to show potential factors affecting the complications and nonunion development.

METHODS

A systematic search of the PubMed database according to PRISMA guidance was performed. The main inclusion criteria comprised description of fusion rate and/or implant-associated complications rate.

RESULTS

This systematic review included 86 articles focused on the results of surgery in 4208 patients. The rate of screw-related complications was as follows: 1) vertebral artery (VA) injury, 2.8%; 2) screw malposition in the direction of the VA, 5.8%; and 3) C2 nerve root irritation, 6.1%. The nonunion rate was 4.2%. Transpedicular screw insertion to the C1 and C2 vertebrae were the safest regarding VA injury and correlated with lower blood loss. For C1-C2 fusion, there was no statistical difference for the different bone graft localization. C2 nerve root irritation rate did not depend on screw insertion technique. The use of a freehand technique did not correlate with a high rate of screw-related complications.

CONCLUSIONS

The Goel-Harms technique is a promising method of C1-C2 fusion, with a relatively low nonunion and VA injury rate. It can be performed safely without C-arm or navigation system assistance. Transpedicular screw insertion trajectories to the C1 and C2 vertebrae were safest regarding VA injury and blood loss volume. Further comparative studies of various C1-C2 stabilization methods with a high level of significance should be carried out to identify the optimal approach.

The Impact of Upper Cervical Spine Alignment on Patient-reported Outcome Measures in Anterior Cervical Decompression and Fusion

STUDY DESIGN

This was a retrospective cohort study.

OBJECTIVE

To determine the extent to which the upper cervical spine compensates for malalignment in the subaxial cervical spine, and how changes in upper cervical spine sagittal alignment affect patient-reported outcomes.

SUMMARY OF BACKGROUND DATA

Previous research has investigated the relationship between clinical outcomes and radiographic parameters in the subaxial cervical spine following anterior cervical discectomy and fusion (ACDF). However, limited research exists regarding the upper cervical spine (occiput to C2), which accounts for up to 40% of neck movement and has been hypothesized to compensate for subaxial dysfunction.

MATERIALS AND METHODS

Patients undergoing ACDF for cervical radiculopathy and/or myelopathy at a single center with minimum 1-year follow-up were included. Radiographic parameters including cervical sagittal vertical axis, C0 angle, C1 inclination angle, C2 slope, Occiput-C1 angle (Oc-C1 degrees), Oc-C2 degrees, Oc-C7 degrees, C1-C2 degrees, C1-C7 degrees, and C2-C7 degrees cervical lordosis (CL) were recorded preoperatively and postoperatively. Delta (Δ) values were calculated by subtracting preoperative values from postoperative values. Correlation analysis as well as multiple linear regression analysis was used to determine relationships between radiographic and clinical outcomes. Alpha was set at 0.05.

RESULTS

A total of 264 patients were included (mean follow-up 20 mo). C2 slope significantly decreased for patients after surgery (Δ=-0.8, P =0.02), as did parameters of regional cervical lordosis (Oc-C7 degrees, C1-C7 degrees, and C2-C7 degrees; P <0.001, <0.001, and 0.01, respectively). Weak to moderate associations were observed between postoperative CL and C1 inclination ( r =-0.24, P <0.001), Oc-C1 degrees ( r =0.59, P <0.001), and C1-C2 degrees ( r =-0.23, P <0.001). Increased preoperative C1-C2 degrees and Oc-C2 degrees inversely correlated with preoperative SF-12 Mental Composite Score (MCS-12) scores ( r =-0.16, P =0.01 and r =-0.13, P =0.04). Cervical sagittal vertical axis was found to have weak but significant associations with Short Form-12 (SF-12) Physical Composite Score (PCS-12) ( r =-0.13, P =0.03) and MCS-12 ( r =0.12, P =0.05).

CONCLUSION

No clinically significant relationship between upper cervical and subaxial cervical alignment was detected for patients undergoing ACDF for neurological symptoms. Upper cervical spine alignment was not found to be a significant predictor of patient-reported outcomes after ACDF.

LEVEL OF EVIDENCE

Level III.

Subaxial lordosis loss and influence factors after posterior atlantoaxial fusion

Summary of background data

Cervical sagittal balance is an important evaluation index of cervical physiological function and surgical efficacy. Subaxial kyphosis after atlantoaxial fusion is negatively associated with worse clinical outcomes and higher incidence of lower cervical disk degeneration.

Objectives

This study aimed to confirm the factors that influence subaxial lordosis loss after posterior atlantoaxial fusion.

Methods

We performed a retrospective review of all patients following posterior C1–C2 fusion for atlantoaxial dislocation between January 2015 and December 2017. All charts, records, and imaging studies were reviewed for each case, and preoperative, immediate postoperative, and final follow-up plain films were evaluated. Comparing final follow-up and preoperative C2–C7 angle, patients were divided into two groups for further comparison: subaxial lordosis loss group and subaxial lordosis increase group.

Results

A total of 18 patients were included in the review, with an average radiographic follow-up of 8.4 ± 3.7 months (range 6–17 months). Subaxial lordosis loss was observed in 5 cases (27.8%) at the final follow-up, whereas 13 cases had an increase in subaxial lordosis. The cervical sagittal parameters of preoperative and final follow-up between two groups were compared, the preoperative C2–C7 angle of the subaxial lordosis loss group was bigger than the subaxial lordosis increase group (27.6° ± 10.5° vs 10.5° ± 10.5°, P < 0.05), but there was no statistical difference in other parameters. Univariate chi-square analysis showed that reduction in subaxial lordosis after posterior atlantoaxial fusion was associated with preoperative C2–C7 angle ≥ 20° (χ² = 4.923, P = 0.026). However, Logistic regression analysis showed that the preoperative C2–C7 angle ≥ 20° was not an independent risk factor (OR = 0.147, P = 0.225).

Conclusion

Our study demonstrates that subaxial lordosis loss may occur after posterior atlantoaxial fusion, and preoperative C2–C7 angle ≥ 20° was a risk factor of postoperative loss of subaxial lordosis.

Dynamic cervical flexion/extension atlantodental interval and functional outcome of the Harms technique for posterior C1/2 fixation: A retrospective analysis of 16 atlantoaxial subluxation cases in a tertiary medical center

BACKGROUND

The aim of this study was to assess the relationship between the atlantodental interval (ADI) on dynamic flexion/extension cervical radiographs and functional outcomes of posterior spinal fixation by the Harms technique for atlantoaxial subluxation (AAS). Dynamic flexion/extension on cervical radiographs is a standard assessment for evaluation of C1/2 instability in AAS patients. Most studies focused on postoperative ADI and functional outcome, including pain and fusion rate; only few studies compared dynamic ADI change pre- to post-operatively.

MATERIAL AND METHODS

Retrospectively, we reviewed the medical records of 16 patients who underwent posterior spinal fixation in our center from 2018 to 2019. We used dynamic cervical flexion/extension radiographs to assess the pre- to postoperative change at 12 months in ADI of flexion (ADI_f), ADI of extension (ADI_e), ADI between flexion/extension (ADI_Δ), C1/2 fusion rate and functional outcomes measured by the modified Japanese Orthopaedic Association scale (mJOA scale). Postoperative CT at 3∼12 months assessed screw positioning on the Gertzbein and Robbins classification.

RESULTS

In the 16 patients included in this study, ADI_f, ADI_e and ADI_Δ were significantly reduced, from respectively 8.0mm, 5.0mm and 3.0mm preoperatively to 4.6mm, 3.8mm and 0.8mm at 12 months' follow-up. The fusion rate was 81% and the mJOA score recovery rate was 34.9±14.7%. Although the screw malposition rate was higher than in other studies in C1(10%) and C2(20%), there were no new neurologic deficits or worsening of symptoms at follow-up.

CONCLUSIONS

The ADI_Δ showed significant reduction, showing that the Harms technique of posterior spinal fixation can effective in maintaining the stability of the atlantoaxial joint and improving functional outcome.

Radiological changes in sagittal parameters after C1-C2 arthrodesis and their clinical correlation: Is there a difference between traumatic and non-traumatic causes?

Background: Compensatory changes in cervical sagittal alignment after C1-C2 arthrodesis have been reported in a few studies. No studies have explored the differences in these compensatory changes between traumatic and non-traumatic pathologies. Conflicting reports exist on the correlation between cervical sagittal parameters and neck pain or function.Methodology: Medical records of 81 consecutive patients [Jan 2010 - Dec 2018] who underwent Harms arthrodesis were retrospectively reviewed. 53 patients were included in the final analysis. Radiological parameters [C0-C1, C1-C2, C2-C7 angles and T1 slope] and clinical parameters [VAS (Visual analogue scale) and NDI (Neck disability index)] were compared between the two groups, Group A (traumatic) and Group B (non-traumatic).Results: The 53 patients [Group A (n = 24,) and Group B (n = 29)] had a mean age of 49.98 ± 21.82 years (42 males, 11 females). Mean follow up duration was 48.9 months. Δ C1-C2 angle is significantly correlated with ΔC2-C7 angle (Group A, p = 0.004; Group B, p = 0.015) but not with ΔC0-C1 angle (Group A, p = 0.315; Group B, p = 0.938). Though significant improvement in the clinical parameters (VAS/NDI) has been noted in both groups, Group A showed a greater improvement in VAS scores [Group A, (p < 0.001); Group B, (p < 0.023)].Conclusions: The sub-axial sagittal profile was strongly correlated with the ΔC1-C2 angle in both groups. Group B showed greater changes in sagittal parameters after Harms fixation and Group A showed greater improvement in long-term functional outcomes. The final functional outcomes were not related to the initial or final radiological sagittal profile in both groups.

Kinematic MRI Analysis of Reducible Atlantoaxial Dislocation for Decompression

Background

Many doctors ignored the possibility that there is still a spinal cord compression (SCC) need for decompression after atlantoaxial reduction. Reduction can be achieved on kinematic magnetic resonance imaging (MRI); thus, we want to analyze the role of kinematic MRI in reducible atlantoaxial dislocation and make a preoperative decision whether to perform decompression.

Methods

36 patients with atlantoaxial reduction on preoperative kinematic MRI in extension postures were enrolled retrospectively. Grouping was based on the condition of SCC after atlantoaxial reduction preoperatively. Group A: patients with SCC after atlantoaxial reduction on dynamic cervical MRI were treated with C1 laminectomy for decompression and atlantoaxial fixation. Group B: patients with no significant SCC, according to dynamic MRI, underwent only atlantoaxial fixation. Clinical outcomes were evaluated using JOA score for spinal cord function. Radiological outcomes were assessed by measuring spinal cord diameter on MRI.

Results

The mean follow-up time was 17.1 months. Postoperative JOA score and percentage of SCC in both groups were significantly better than its preoperative score. There were no significant statistical differences in the JOA score at 12 months after surgery and the JOA improvement rate between two groups. All patients in the two groups had a lower percentage of SCC on preoperative extension MRI, compared with neutral MRI. No significant statistical differences in the spinal decompression improvement rate were observed between the two groups.

Conclusions

Decompression should be performed in patients who still have significant SCC on preoperative kinematic MRI. Kinematic MRI could be used to assess SCC and decide whether to perform decompression preoperatively.

Relationship between the atlantodental interval and T1 slope after atlantoaxial fusion in patients with rheumatoid arthritis

BACKGROUND

Atlantoaxial fusion has been widely used for the treatment of atlantoaxial instability (AAI). However, atlantoaxial fusion sacrifices the motion of atlantoaxial articulation, and postoperative loss of cervical lordosis and aggravation of cervical kyphosis are observed. We investigated various factors under the hypothesis that the atlantodental interval (ADI) and T1 slope may be associated with sagittal alignment after atlantoaxial fusion in patients with rheumatoid arthritis (RA).

METHODS

We retrospectively investigated 64 patients with RA who underwent atlantoaxial fusion due to AAI. Radiological factors, including the ADI, T1 slope, Oc-C2 angle, cervical sagittal vertical axis, and C2-C7 angle, were measured before and after surgery.

RESULTS

The various factors associated with atlantoaxial fusion before and after surgery were compared according to the upper and lower preoperative ADIs. There was a significant difference in the T1 slope 1 year after surgery (p = 0.044) among the patients with lower preoperative ADI values. The multivariate logistic regression analysis showed that the preoperative ADI (> 7.92 mm) defined in the receiver-operating characteristic curve analysis was an independent predictive factor for the increase in the T1 slope 1 year after atlantoaxial fusion (odds ratio, 4.59; 95% confidence interval, 1.34-15.73; p = 0.015).

CONCLUSION

We found an association between the preoperative ADI and difference in the T1 slope after atlantoaxial fusion in the patients with RA. A preoperative ADI (> 7.92 mm) was an independent predictor for the increase in the T1 slope after atlantoaxial fusion. Therefore, performing surgical treatment when the ADI is low would lead to better cervical sagittal alignment.

The Effect of Straight or Lordotic Rods on Cervical Subaxial Alignment While Fusing C1-C2

BACKGROUND

The C1 lateral mass and C2 pedicle screw with rod fixation system has been used commonly in recent years. Despite the numerous reports on this technique in the literature, there are no studies regarding the effect of the angle of the rod used. We investigated the effect of rod angle on subaxial lordosis, cervical sagittal balance, and pain scores.

METHODS

Clinical records and radiologic images of 58 patients who underwent procedures between 2011 and 2016 at our clinic were assessed retrospectively. We recorded clinical findings, visual analog scale (VAS) scores, angles of cervical and segmental lordosis, and the distance between the C2 sagittal vertical axis (SVA) and the C7 posterior-superior corner.

RESULTS

A total of 36 male and 22 female patients were enrolled. A negative correlation was found between the C1-C2 lordosis angle and the C2-C7 lordosis angle irrespective of surgical technique. In patients who were operated on using 30°-angled rods, there was a postoperative increase in C1-C2 lordosis degree and an improvement in C2 cervical SVA values. Postoperative month 6 VAS scores were significantly better in the patients who were operated on with angled rods compared with those who received straight rods.

CONCLUSIONS

We believe this is because of the positive effect of the angled rod on sagittal balance. Nevertheless, prospective case-control studies should be conducted with larger groups of subjects. Furthermore, every patient should be evaluated considering the whole spinal sagittal balance.

Risk factor analysis of postoperative kyphotic change in subaxial cervical alignment after upper cervical fixation

OBJECTIVE

Little is known about the risk factors for postoperative subaxial cervical kyphosis following craniovertebral junction (CVJ) fixation. The object of this study was to evaluate postoperative changes in cervical alignment and to identify the risk factors for postoperative kyphotic change in the subaxial cervical spine after CVJ fixation.

METHODS

One hundred fifteen patients were retrospectively analyzed for postoperative subaxial kyphosis after CVJ fixation. Relations between subaxial kyphosis and radiological risk factors, including segmental angles and ranges of motion (ROMs) at C0-1, C1-2, and C2-7, and clinical factors, such as age, sex, etiology, occipital fixation, extensor muscle resection at C2, additional C1-2 posterior wiring, and subaxial laminoplasty, were investigated. Univariate and multivariate logistic regression analyses were conducted to identify the risk factors for postoperative kyphotic changes in the subaxial cervical spine.

RESULTS

The C2-7 angle change was more than -10° in 30 (26.1%) of the 115 patients. Risk factor analysis showed CVJ fixation combined with subaxial laminoplasty (OR 9.336, 95% CI 1.484-58.734, p = 0.017) and a small ROM at the C0-1 segment (OR 0.836, 95% CI 0.757-0.923, p < 0.01) were related to postoperative subaxial kyphotic change. On the other hand, age, sex, resection of the C2 extensor muscle, rheumatoid arthritis, additional C1-2 posterior wiring, and postoperative segmental angles were not risk factors for postoperative subaxial kyphosis.

CONCLUSIONS

Subaxial alignment change is not uncommon after CVJ fixation. Muscle detachment at the C2 spinous process was not a risk factor of kyphotic change. The study findings suggest that a small ROM at the C0-1 segment with or without occipital fixation and combined subaxial laminoplasty are risk factors for subaxial kyphotic change.

Influence of Atlantoaxial Fusion on Sagittal Alignment of the Occipitocervical and Subaxial spines in Os Odontoideum with Atlantoaxial Instability

Study Design

Retrospective case analysis.

Purpose

We hypothesized that larger the C1–C2 fusion angle, greater the severity of the sagittal malalignment of C0–C1 and C2–C7.

Overview of Literature

In our experience, instances of sagittal malalignment occur at C0–C1 and C2–C7 following atlantoaxial fusion in patients with Os odontoideum (OO).

Methods

We assessed 21 patients who achieved solid atlantoaxial fusion for reducible atlantoaxial instability secondary to OO. The mean patient age at the time of the operation was 42.8 years, and the mean follow-up duration was 4.9 years. Radiographic parameters were preoperatively measured and at the final follow-up. The patients were divided into two groups (A and B) depending on the C1–C2 fusion angle. In group A (n=11), the C1–C2 fusion angle was ≥22°, whereas in group B, it was <22°. The differences in the radiographic parameters of the two groups were evaluated.

Results

At the final follow-up, the C1–C2 angle was increased. However, this increase was not statistically significant (18° vs. 22°, p=0.924). The C0–C1 angle (10° vs. 5°, p<0.05) and C2–C7 angle (22° vs. 13°, p<0.05) significantly decreased. The final C1–C2 angle was negatively correlated with the final C0–C1 and C2–C7 angles. The final C0–C1 angle (4° vs. 6°, p<0.05) and C2–C7 angle (8° vs. 20°, p<0.05) were smaller in group A than in group B. After atlantoaxial fusion, the C0–C1 range of motion (ROM; 17° vs. 9°, p<0.05) and the C2–C7 ROM (39° vs. 31°, p<0.05) were significantly decreased.

Conclusions

We found a negative association between the sagittal alignment of C0–C1 and C2–C7 after atlantoaxial fusion and the C1–C2 fusion angle along with decreased ROM. Therefore, overcorrection of C1–C2 kyphosis should be avoided to maintain good physiologic cervical sagittal alignment.

Potential intraoperative factors of screw-related complications following posterior transarticular C1-C2 fixation: a systematic review and meta-analysis

PURPOSE

This study aimed to evaluate the impact of several factors, including patients' intraoperative position, intraoperative visualization technique, fixation method, and type of screws and their parameters, on the frequency of intraoperative screw-associated complications in posterior transarticular C1-C2 fixation.

METHODS

A systematic review of the PubMed database between January 1986 and March 2018 was performed. The key inclusion criteria comprised detailed descriptions of the surgical technique and post-operative screw-associated complications.

RESULTS

The initial search resulted in 1041 abstracts, and a total of 54 abstracts were included in the present study. The overall number of operated patients was 2306. In this group, 4439 screws were inserted. The rate of screw-associated complications during the different time periods was estimated upon meta-analysis. Statistical analysis of the screw malposition rate, vertebral artery injury rate, screw breakage rate based on patients' intraoperative position, intraoperative visualization technique, fixation method, and type of implants and their parameters was also performed.

CONCLUSIONS

The factors that help reduce the rate of screw-associated complications include the intraoperative application of biplanar fluoroscopy or neuronavigation system, the use of 4 mm or thicker lag screws, and screw insertion through contraincisions using cannulated ported instruments. On the other hand, the potential risk factors of screw-associated complications include inadequate intraoperative head fixation using skeletal traction, uniplanar fluoroscopy-guided screw insertion, screw insertion using the posterior midline approach, and the use of 3.5 mm or thinner full-threaded screws. These slides can be retrieved under Electronic Supplementary Material.

Incidence and risk factors for adjacent segment degeneration following occipitoaxial fusion for atlantoaxial instability in non-rheumatoid arthritis

PURPOSE

To investigate the incidence and risk factors for adjacent segment degeneration (ASD) following occipitoaxial fusion (OAF) for atlantoaxial instability (AAI) in non-rheumatoid arthritis (RA).

METHODS

The study group comprised 41 patients without RA who underwent OAF due to AAI. Fifteen patients with postoperative ASD after OAF were classified as the ASD group, and the other 26 patients without postoperative ASD were included in the non-ASD group. There were 12 men and 3 women with a mean age of 43.52 years in the ASD group, and 19 men and 7 women with a mean age of 45.31 years in the non-ASD group. The mean follow-up period was 6.1 and 5.9 years in the ASD group and non-ASD group, respectively. Clinical outcomes and plain radiographs were retrospectively reviewed and compared between the two groups.

RESULTS

The difference between pre- and postoperative O-C2 angles in the non-ASD group was significantly greater than that in the ASD group. The C2-7 angles changed significantly between the pre- and postoperative periods. It was suggested that the small O-C2 angle and large C2-7 angle observed in the early postoperative period were risk factors for the development of ASD. We also demonstrated a high incidence of subaxial subluxation (SAS) and swan neck deformity in the ASD group (27 versus 3.8% and 20 versus 0%, respectively).

CONCLUSION

Under-correction of the O-C2 angle is likely to cause malalignment of the cervical spine, resulting in the development of postoperative ASD, SAS, and swan neck deformity.

Comparison of Cervical Alignment and Clinical Outcomes in Patients with Os Odontoideum versus Non-Os Odontoideum after Atlantoaxial Fixation

OBJECTIVE

The purpose of this study was to compare the effect of atlantoaxial fixation on cervical alignment and clinical outcomes in patients with os odontoideum (OO) versus non-os odontoideum (non-OO).

METHODS

A total of 119 patients who underwent atlantoaxial fixation for instability were identified between January 1998 and January 2014. Inclusion criteria included age more than 21 years and diagnosis of OO and non-OO. There were 22 OO patients, and 20 non-OO patients. Measuring the Oc-C1 Cobb angle, C1-2 Cobb angle, C2-7 Cobb angle, and C2-7 sagittal vertical axis (SVA) was assessed. Clinical outcome was assessment of suboccipital pain was determined using a visual analogue scale (VAS), and Japanese Orthopedic Association (JOA) scores were obtained in all patients pre- and postoperatively.

RESULTS

The preoperative C1-2 angle in the OO group (26.02°±10.53°) was significantly higher than the non-OO group (p=0.04). After C1-2 fixation, the OO group had significantly higher kyphotic change in the C1-2 angle (ΔC1-2) (3.2°±7.3° [OO] vs. -1.46°±7.21° [non-OO]) (p=0.04), and higher decrease in postoperative C2-7 SVA (ΔC2-7 SVA) (5.64±11.56 mm [OO] vs. -0.51± 6.57 mm [non-OO]) (p=0.04). Both groups showed improvements in the health related quality of life (HRQOL) after surgery based on the VAS and JOA score (p<0.001).

CONCLUSION

After fixation, kyphotic angular change in atlantoaxial joint and decrease C2-7 SVA were marked in the OO group. Both the OO and non-OO groups improved in neurological function and outcome after surgery.

Long-Term Influence of C1-C2 Pedicle Screw Fixation on Occipitoatlantal Angle and Subaxial Cervical Spine in the Pediatric Population

OBJECTIVE

The goal of this study was to evaluate the impact of C1-C2 pedicle screw fixation on the occipitoatlantal angle and subaxial cervical spine for a pediatric population, and the clinical efficacy and adjacent-segment degeneration after C1-C2 pedicle screw fixation with a minimum of 2 years of follow-up.

METHODS

Twenty-two pediatric patients with atlantoaxial dislocation who were enrolled in this study underwent atlantoaxial pedicle screw fixation. The correlation between C0-C1, C2-C7, and C1-C2 pre- and postoperative sagittal angles was assessed using plain radiographs, and adjacent-segment degeneration (ASD) and JOA scores (Japanese Orthopaedic Association scores) were evaluated after atlantoaxial pedicle screw fixation.

RESULTS

The C1-C2 angle increased from 16.1 ± 13.37 to 28.1 ± 5.1° (p < 0.01). The pre- and postoperative C1-C2 angles were negatively correlated with the pre- and postoperative C0-C1 and C2-C7 angles, respectively. In accordance with the optimal atlantoaxial fusion angle (25-30°) obtained from the literature, postoperative JOA scores were greater in the groups with angles of more than 30° and less than 25°, although the difference in ASD was not statistically significant. Postoperative JOA scores were not relevant to the postoperative C1-C2 angle; however, there was a positive correlation between JOA improvement rate and the change of the C1-C2 angle postoperatively.

CONCLUSION

Atlantoaxial pedicle screw fixation can be used easily to reduce atlantoaxial dislocation in the pediatric population; however, outside the range of the optimal atlantoaxial fusion angle it can change the occipitoatlantal angle and subaxial alignment, which induces ASD and influences the clinical efficacy. It is necessary to achieve an optimal atlantoaxial angle when using atlantoaxial pedicle screw fixation.

Surgical overreduction and hyperlordotic fusion of C1-C2 joint are associated with cervical sagittal malalignment

INTRODUCTION

Previous studies have shown that hyperlordotic C1-C2 fusion was related to postoperative subaxial kyphosis. However, most of the patients in these studies were complicated with rheumatoid arthritis (RA). Moreover, no studies have specifically evaluated the relationship between C1-C2 fusion angle and cervical sagittal vertical axis (cSVA), T1 slope or cranial tilt (CRT) after posterior C1-C2 fusion. This study aimed to investigate the cervical sagittal alignment in non-RA patients following posterior C1-C2 fusion and the correlation between C1-C2 fusion angle and postoperative cervical sagittal alignment.

MATERIALS AND METHODS

From August 2004 to December 2015, twenty-eight consecutive patients with an average age of 39.2 years (range 6-70 years) who underwent posterior C1-C2 fusion from a single institution were enrolled. The mean follow-up period was 30.7 months (range 12-77 months). Angles of Oc-C1, C1-C2, C2-C3 and C2-C7, cSVA, T1 slope and CRT were measured in lateral cervical radiographs in neutral position before surgery and at the final follow-up.

RESULTS

C1-C2 angle significantly increased from 13.6° ± 12.4° to 22.0° ± 8.1° at the final follow-up (P < 0.001). A significant decrease was found both in Oc-C1 and C2-C7 angles from pre-operation to the final follow-up (P < 0.001 and P = 0.011, respectively). Moreover, cSVA and CRT dramatically increased from pre-operation to the final follow-up (P < 0.001). C1-C2 fusion angle was significantly associated with Oc-C1, C2-C7 angle, cSVA and CRT at the final follow-up. A significant correlation was also observed between postoperative change of C1-C2 angle and that of Oc-C1, C2-C7 angle, cSVA and CRT.

CONCLUSIONS

Apart from decreased subaxial lordosis, posterior C1-C2 fusion in hyperextension may also lead to kyphotic change of atlanto-occipital alignment and increased tilting forward of the cervical spine. Therefore, intraoperative overreduction of C1-C2 angle and hyperlordotic C1-C2 fusion should be avoided to maintain the physiologic cervical sagittal alignment.

Neurological outcomes following iatrogenic vascular injury during posterior atlanto-axial instrumentation

BACKGROUND

Iatrogenic vascular injury is a feared complication of posterior atlanto-axial instrumentation. A better understanding of clinical outcome and management options following this injury will allow surgeons to better care for these patients. The object of the study was to systematically review the neurologic outcomes after iatrogenic vascular injury during atlanto-axial posterior instrumentation.

METHODS

We performed a systematic review of the Medline database following PRISMA guidelines. In our analysis, we included any retrospective cohort studies, prospective cohort studies, case reports, cases series, or systematic reviews with patients who had undergone posterior atlanto-axial fusion via screw rod constructs (SRC) or transarticular screws (TAS) that reported a patient with an injury to an arterial vessel directly attributable to the surgical procedure.

RESULTS

Sixty cases of vascular injury were reported in 2078 (2.9%) patients over 27 publications. The average age for this patient population was 55.7+/-17.9. Vascular injury following posterior C1/2 instrumentation resulted in ipsilateral stroke in 10.0% (n=6/60) and non-persistent neurologic deficit in 6.7% (n=4/60) of cases with the deficit being permanent (not including death) in 1.7% (n=1/60) of cases. Four patients (6.7%) died. Arteriovenous fistula or pseudoaneurysm occurred in 8.3% (n=5/60) and 3.3% (n=2/60) of cases, respectively. Eight patients (13.3%) underwent endovascular repair of the injury with no permanent deficit.

CONCLUSION

Neurological morbidity after iatrogenic vascular injury during posterior C1/2 fixation is higher than previously reported in literature. Some patients may benefit from endovascular treatment. Surgeons should be aware of normal and anomalous vertebral artery anatomy to avoid this potentially catastrophic complication.