To evaluate which radiologic parameters affect clinical outcomes in patients underwent posterior C1–2 fusion for atlantoaxial dislocation.
From January 2014 to December 2017, among 98 patients underwent C1–2 posterior fusion, patients with previous cervical surgery or extending to subaxial spine or basilar invagination were excluded. Finally, 38 patients were included. O–C2, C1–2, C1–C7, C2–C7 cobb angle (CA), T1 slope, C1–7, C2–7 sagittal vertical axis (SVA), and posterior atlantodental interval (PADI) were measured at preoperative and postoperative 1 year. The difference between postoperative and preoperative values for each parameter was designated as Δvalue. Postoperative subaxial kyphosis (PSK) was defined to decrease ≥ 10° at subaxial spine. Visual analogue scale (VAS), Japanese Orthopedic Association (JOA) score, Neck Disability Index (NDI) were used to evaluate clinical outcomes.
Mean age was 54.4 ± 15.9. Male to female was 14 to 24. Of radiologic parameters, C1–7 SVA and PADI were significantly changed from 26.4 ± 12.9 mm, 17.1 ± 3.3 mm to 22.6 ± 13.0 mm, 21.6 ± 3.4 mm. ΔC1–2 CA was correlated with ΔC1–7 CA and ΔC2–7 SVA. ΔPADI correlates with ΔO–C2 CA. VAS correlates with ΔC1–7 CA (p = 0.03). JOA score also correlates with ΔC2–7 SVA (p = 0.02). NDI was associated with ΔPADI (p < 0.01). The incidence of PSK was 23.7%, and not significant with clinical outcomes.
ΔC1–2 CA was correlated with ΔC1C7 CA, ΔC2–7 SVA. ΔC1–7 CA, ΔC2–7 SVA, and ΔPADI were the key radiologic parameters to influence clinical outcomes. Postoperative C1–2 angle should be carefully determined as a factor affecting clinical outcomes and cervical sagittal alignment.
Atlantoaxial dislocation (AAD) can cause severe neurologic deficit which make patients disabled or neck pain results from kyphosis at upper cervical spine [
As these surgical techniques have been popularized, some surgeons gradually interested in postoperative changes in cervical sagittal balance [
Previous studies focused on evaluating the relationship between postoperative C1–2 angle and subaxial sagittal alignment, but there were a few studies stated that the association between postoperative radiologic parameters related with sagittal balance and clinical outcomes [
A retrospective analysis of medical records and radiologic data was performed on patients that had undergone posterior atlantoaxial fusion for AAD at a single center from January 2014 to June 2017. This study was approved by the Institutional Review Board of Catholic Medical Center (OC21RISI0008). Ninety-eight patients treated by posterior C1–2 fusion during this period. Patients had previous cervical surgery history or concomitant with basilar invagination were excluded. In addition, patients needed additional fusion extension to occipital or subaxial spine were also excluded. Finally, 38 patients were included in the study.
The patient was placed in prone position with Mayfield head fixator under general anesthesia. The surgeon reduced C1–2 dislocation as much as possible by adjusting patient’s head by flexion or extension while pulling out the Mayfield head fixator. C1–2 reduction was confirmed under the C-arm fluoroscopy. When we cannot achieve acceptable reduction by adjusting patients’ position, we usually released C1–2 facet joint in order to reduce dislocation additionally by removing the capsule surrounded it during surgery. C2 roots were preserved by protecting root retractor during the releasing of C1–2 facet. All procedures were performed under intraoperative monitoring (IOM). Vascular anomalies were evaluated preoperatively to avoid neurovascular injury. Atlantoaxial fixation was accomplished using a variety of surgical constructs combined with C1 lateral mass to C2 pedicle screw, C2 pars screw, or to C2 laminar screw fixation. We controlled C1–2 angle by compressing or distracting the interspace between 2 polyaxial screws along the rods. Autograft bone harvested from the posterior superior iliac spine was inserted to the interlaminar space of C1–2 to enhance the fusion. Modified brook’s Wiring technique between C1 and C2 lamina was performed to fix the autograft bone and obtain additional biomechanical strength [
Two neurosurgeons (JTH and JHP) measured all radiologic parameters on cervical standard lateral radiographs using INFINIT PACS (INFINIT Healthcare, Seoul, Korea) using an electrical caliper on 2 occasions. The 4 sets of radiologic parameters measured were then averaged for statistical analysis. Lateral radiographs were obtained in the neutral head position. A standard distance of 1.8 m was maintained between the tube and patients. The following parameters were measured on radiograph before surgery and at 1 year after surgery.
• C2 cobb angle (CA): The angle between the line connecting McGregor line and the inferior endplate of C2 (
• C1–2 cobb angle (CA): The angle between the line connecting the middle point of the anterior and posterior arch of C1 and the inferior endplate of C2 (
• C1–7 cobb angle (CA): The angle between the line connecting the middle point of the anterior and posterior arch of C1 and the inferior endplate of C7 (
• C2–7 cobb angle (CA): The angle between the inferior endplate of C2 and C7 (
• T1 slope: The angle between horizontal line and the T1 superior endplate. (
• C1–7 sagittal vertical axis (SVA): The distance between the plumb line from the anterior margin of C1 and posterior superior corner of C7 (
• C2–7 sagittal vertical axis (SVA): The distance between the plumb line from the center of C2 and the posterior superior corner of C7 (
• Posterior atlantodental interval (PADI): The distance between the line connecting the middle point of the anterior and posterior arch of C1 and the dens of C2 (
The difference between preoperative and postoperative values for each parameter was designated as the Δvalue.
PSK was defined as the postoperative change of ≥ 10° at C2–7 CA.
Clinical outcomes were assessed using visual analogue scale (VAS) for neck pain, Neck Disability Index (NDI) [
The Student t-test, the paired t-test, and Mann-Whitney Utest were used to analyze continuous and ordinal variables, as appropriate. Correlation test and a linear logistic regression model were used to evaluate the natures of correlations between the radiologic parameters and clinical outcome. p-values of < 0.05 (2-tailed) were considered statistically significant, and IBM SPSS Statistics ver. 20.0 (IBM Co., Armonk, NY, USA) was used for the statistical analysis. The intra-inter reliabilities of radiologic parameters were calculated. Intraclass correlation coefficient values were rated as follows: 0 to 0.2 slight agreement, 0.21 to 0.4 fair agreement, 0.41 to 0.6 moderate agreement, 0.61 to 0.8 substantial agreement, and 0.81 to 1.0 excellent agreement.
Clinical information is summarized in
Radiologic parameters obtained at preoperative and postoperative are summarized in
Correlations between radiologic parameters are presented in
VAS, NDI, and JOA score improved significantly at postoperative. Mean VAS decreased from 5.1±2.9 to 1.7±1.6 (p<0.01). Mean JOA scores increase from 13.2±2.7 to 15.3±2.6 (p=0.02). Mean NDI decreased form 22.2 ±11.0 to 6.7 ±5.8 (p < 0.01). However, 3 patients deteriorated neck pain at postoperative. One patient suffered severe neck pain at VAS 9. The patient showed that reciprocal kyphotic change from 34° to 1.5° in subaxial spine after surgery. The other presented neck pain at VAS 4. The patient represented slight change of ΔC2–7 CA from 32.5° to 34.4°, but we failed to make lordotic C1–2 angle (from 4.5° to 4.8°) intraoperatively. Another complained neck pain VAS 5. The patient also showed that reciprocal kyphotic change from 10.9° to 2.2° in subaxial spine even though we made kyphotic C1–2 angle from 22.2° to 13.1°. This patient complained neck pain and developed subaxial kyphosis although we tried to underreduce C1–2 angle.
VAS, NDI, JOA score were associated with several radiologic parameters. Δ VAS correlated with ΔC1–7 CA, ΔT1S negatively (r= -0.357, p= 0.03, r= -0.341, p= 0.04). ΔNDI correlated with ΔPADI negatively (r= -0.499, p= 0.01). ΔJOA score correlated with ΔC2–7 SVA positively (r= 0.354, p= 0.03). In linear logistic regression, ΔC1–7 CA represented negatively linear correlation with ΔVAS, ΔPADI also showed negatively linear correlation with ΔNDI, ΔC2–7 SVA represented positively linear correlation with ΔJOA score, respectively (
The incidence of PSK was 23.7%, it was not significantly associated with VAS (p = 0.26), NDI (p = 0.32), JOA score (p = 0.97).
Atlantoaxial fusion is frequently associated with sagittal realignment in subaxial spine, and many authors stated the negative correlation between ΔC1–2 CA and ΔC2–7 CA after surgery [
The correlation of each radiologic parameter was summarized in
ΔC1–2 CA was associated with ΔO–C2, ΔC1–7 CA, and ΔC2–7 SVA. Moreover, ΔC1–7 CA was negatively correlated with ΔVAS (
ΔC1–7 CA was associated with ΔC1–2 CA, ΔC2–7 CA, ΔT1 slope. This correlation is taken for granted that C1–7 CA was the parameter including C1–2 and C2–7 CA. ΔT1 slope was changed according to ΔC1–7 CA.
ΔC2–7 CA also correlated with ΔO–C2 CA, ΔC1–7 CA, ΔT1 slope, ΔC1–7 SVA, and ΔC2–7 SVA. It was the most subjective radiologic parameter that was correlated with various others and also associated with VAS and JOA score such like ΔC1–2 CA. Nevertheless, surgeons can adjust ΔC1–2 CA as determining intraoperative C1–2 CA under C-arm fluoroscopy, but ΔC2–7 CA cannot be controlled intraoperatively and be predicted during follow-up. Therefore, surgeons should carefully observe the change of C2–7 CA in the patient after posterior C1–2 fusion.
ΔT1 slope was relative with ΔC1–7 CA, ΔC2–7 CA. This change in T1 slope explains that ΔT1 slope was complementary to the change of cervical spine.
ΔC2–7 SVA was correlated with ΔC1–2 CA, ΔC2–7 CA, ΔC1–7 SVA, JOA score. ΔC2–7 SVA was affected simply not only ΔC2–7 CA, but also ΔC1–2 CA. ΔC1–7 SVA was correlated with ΔC2–7 SVA each other. However, ΔC1–7 SVA showed the difference to ΔC2–7 SVA in that there was not correlated with ΔC1–2 CA. This different point interestingly affected that ΔC1–7 SVA was not significant with JOA score.
ΔPADI correlates with ΔO–C2 CA, and it was a factor associated with ΔNDI. ΔPADI increased significantly after surgery, it pointed out that most patients obtained enough reduction of AAD intraoperatively. This point explained why the reduction of AAD is important in the improvement of quality of life. Several Authors emphasized the importance of enough reduction of AAD, but this was still controversial. Jun et al. [
The PSK that occurred 23.7% of patients was not correlated with clinical outcomes. There are some studies that PSK was one of causes for postoperative neck pain [
Several studies reported the PSK between the changes in subaxial alignment and intraoperative C1–2 angle [
The weaknesses of this study are its retrospective design and small sample size. In addition, patients had various pathologies, which included RA, congenital anomalies, and osteoarthritis. This study included 2 irreducible AAD patients. We performed the releasing of C1–2 facet in these patients, but we could not obtain sufficient reduction of AAD, which may have made a different sagittal realignment comparing to other patients. Moreover, C1–2 constructs for posterior fusion was not monotonous, it composed of hybrid structures such like C2 pedicle, lamina, and pars screws. Although we compressed or distracted the rod under C-arm fluoroscopy to control appropriate C1–2 CA, some patients obtained postoperative C1–2 CA showed a large deviation around 20°. Patient numbers 6 and 36 obtained kyphotic C1–2 angle of 4.8° and 9.4°. Patient numbers 12 and 38 obtained lordotic C1–2 angle of 34.3° and 36°. It is difficult for us to adjust intraoperative C1–2 CA closely as looking images in C-arm fluoroscopy. Finally, the long-term radiographic and clinical outcomes more than one year were not evaluated in the present study.
ΔC1–7 CA, ΔC2–7 SVA, and ΔPADI were the key radiologic parameters to influence clinical outcomes. Postoperative C1–2 angle relative to ΔC1–7 CA and ΔC2–7 SVA should be carefully determined as improving individual’s pain and neurologic improvement. Indirect decompression obtained by reduction of AAD is also important to increase ΔPADI and then decrease NDI.
The authors have nothing to disclose.
This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Conceptualization: JTH; Data curation: JP, JTH; Formal analysis: JP, JTH; Methodology: JP, JTH; Project administration: JTH; Visualization: JP, JTH; Writing - original draft: JP; Writing-review & editing: JTK, ISK, JTH
Radiologic and surgical figures of the patient treated by C1 lateral mass–C2 pars and lamina screw construct wiring interlamina with autograft bone. Preoperative lateral (A) and postoperative lateral (B) and anteroposterior (C) radiographs. (D) Midsagittal image of computed tomography after surgery. (E) Intraoperative figure represents wiring interlamina (black arrow) with an autograft bone (white arrow).
Radiologic parameters on a cervical lateral plain radiograph in patient with atlantoaxial dislocation. (A) O–C2, C1–2, C1–7, C2–7, T1 slope are measured between the lines on cervical lateral plain radiograph. (B) C1–7 (blue line), C2–C7 sagittal vertical axis (SVA; green line), and posterior atlantodental interval (PADI; red line) are measured on cervical lateral plain radiograph. CA, cobb angle.
Linear logistic regression plots between radiologic parameters and clinical outcomes. A linear correlation with ΔC1–7 CA (A), ΔVAS a linear correlation with ΔPADI (B) and ΔNDI a linear correlation with ΔC2–C7 SVA and ΔJOA score (C). CA, cobb angle; VAS, visual analogue scale; PADI, posterior atlantodental interval; NDI, Neck Disability Index; SVA, sagittal vertical axis; JOA, Japanese Orthopedic Association. Asterisk (*) means multiple.
Clinical information of the 38 patients with atlantoaxial dislocation
Characteristic | Value |
---|---|
Sex | |
Male | 14 (36.8) |
Female | 24 (63.2) |
Age (yr) | 54.4 ± 15.9 |
Body mass index (kg/m2) | 23.3 ± 3.6 |
Height (m) | 1.6 ± 0.1 |
Weight (kg) | 59.6 ± 10.8 |
Pathology (%) | |
Spondylosis | 7 (18.4) |
Rheumatoid arthritis | 20 (52.6) |
Congenital anomaly | 11 (29) |
C1–2 constructs (%) | |
Lateral mass-pedicle screws | 14 (36.8) |
Lateral mass-hybrid screws | 4 (10.5) |
Lateral mass-pars screws | 20 (52.6) |
Reducibility | |
Irreducible AAD | 2 (5.3) |
Reducible AAD | 36 (94.7) |
Decompression | |
Direct | 2 (5.3) |
Indirect | 36 (94.7) |
Values are presented as number (%) or mean±standard deviation.
Hybrid screws, C2 pedicle–pars or translaminar screws; AAD, atlantoaxial dislocation.
Comparison of preoperative and postoperative radiologic parameters
Radiologic measurement | Preoperative | Postoperative | p-value |
---|---|---|---|
O–C2 CA (˚) | 11.3 ± 8.6 | 12.8 ± 6.9 | 0.175 |
C1–2 CA (˚) | 18 ± 11.2 | 19.5 ± 6.2 | 0.402 |
C1–7 CA (˚) | 35 ± 11.1 | 33.4 ± 10.6 | 0.471 |
C2–7 CA (˚) | 16.9 ± 10.3 | 14.0 ± 10.2 | 0.087 |
T1 slope (˚) | 19.9 ± 8.7 | 19.2 ± 7.2 | 0.523 |
C1–7 SVA (mm) | 26.4 ± 12.9 | 22.6 ± 13 | 0.032 |
C2–7 SVA (mm) | 11.8 ± 12.1 | 14.4 ± 10.6 | 0.141 |
PADI (mm) | 17.1 ± 3.3 | 21.6 ± 3.4 | < 0.001 |
CA, cobb angle; SVA, sagittal vertical axis; PADI, posterior atlantoaxial interval.
p<0.05, statistical significance.
Reciprocal relationship of the difference between preoperative and postoperative radiologic measurements
Radiologic measurements | ΔO–C2 CA | ΔC1–2 CA | ΔC1–7 CA | ΔC2–7 CA | ΔT1 slope | ΔC1–7 SVA | ΔC2–7 SVA | ΔPADI |
---|---|---|---|---|---|---|---|---|
ΔO–C2 CA | 1.000 | 0.561 |
0.128 | -0.403 |
-0.102 | 0.065 | 0.225 | 0.561 |
ΔC1–2 CA | 0.561 |
1.000 | 0.624 |
-0.225 | 0.058 | 0.241 | 0.384 |
0.001 |
ΔC1–7 CA | 0.128 | 0.624 |
1.000 | 0.621 |
0.357 |
-0.239 | -0.141 | -0.203 |
ΔC2–7 CA | -0.403 |
-0.225 | 0.621 |
1.000 | 0.387 |
-0.540 |
-0.561 |
-0.253 |
ΔT1 slope | -0.102 | 0.058 | 0.357 |
0.387 |
1.000 | 0.171 | 0.197 | -0.069 |
ΔC1–7 SVA | 0.065 | 0.241 | -0.239 | -0.540 |
0.171 | 1.000 | 0.953 |
0.054 |
ΔC2–7 SVA | 0.225 | 0.384 |
-0.141 | -0.561 |
0.197 | 0.953 |
1.000 | 0.099 |
ΔPADI | 0.561 |
0.001 | -0.203 | -0.253 | -0.069 | 0.054 | 0.099 | 1.000 |
CA, cobb angle; SVA, sagittal vertical axis; PADI, posterior atlantodental interval.
p<0.05, statistical significance.