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Illustrations of the MCD, OCA, and OCD on one lateral radiograph. The MCD is the shortest distance (BD) from the midpoint (point B) of the two apices of the mandible angles (points A and C) to the curve of the anterior border from C2 to C3 (a). The OCA is the intersection of McRae’s line and a line drawn parallel to the superior endplate of C3 (b). The OCD was the shortest distance from the superior aspect of the C2 spinous process to the occipital protuberance (c).
Source publication
Background
Intraoperative assessment of neutral occipitocervical balance during a fusion procedure is challenging. We designed this study to introduce a more comprehensive method of evaluating the occipitocervical neutral position using lateral radiographs.Methods
One hundred neutral lateral cervical spine radiographs interpreted as normal were stu...
Citations
... In contrast, the measurement of OC2A calls for localizing anatomical structures, which are hard to visualize fluoroscopically during operation. Identifying the inferior endplate of the C2 vertebra can also be difficult in cases with deformation resulting from vertebral body fusion, bone spurs, and bone destruction (7,14). ...
... Riel et al. hallmarked angle formed by the connecting line between the posterior margin of the facet joints in C3 and C4, and the flat area of the occipital protuberance was counted as a reliable measure to define optimal fusion position (15). Tan et al. described that mandible cervical distance, placed between the midpoint of the two mandibular angles and the anterior border of the C2 body, could be significantly affected by slight head rotation (14). Yoon et al. labeled the angle forming the line connecting the posterior border of the C4 vertebral body and McGregor's line and reported it as a superior method in inter-observer and intra-observer reliability (16). ...
Background: Occipitocervical fusion (OCF) is a rare and often challenging surgical procedure. Several methods have been introduced to obtain the best measures for occipitocervical alignment. The mandible-C2 angle was first introduced in 2020. In this study, we aimed to evaluate the out-of-sample validity of these measures. Methods: We retrospectively studied 274 lateral cervical radiographs of patients aged 1 to 87 years with no cervical pathology evident on X-ray. A board-certified radiologist and a second-year radiology resident performed the measurements on five specific angles as suggested by Bellabarba. The five angles measured consisted of: 1) anterior C2 body/anterior mandible angle (AB/AM), 2) anterior C2 body/posterior mandible angle (AB/PM), 3) posterior C2 body/anterior mandible angle (PB/AM), 4) posterior C2 body/posterior mandible angle (PB/PM), and 5) occipito-C2 angle (OC2A). Results: Inter-rater correlation data were calculated for single and average measures. The inter-rater agreement for individual angle measures of O-C2A, AB/AM, AB/PM, PB/AM, and PB/PM were 0.49, 0.11, 0.25, 0.33, and 0.49, respectively. The intraclass correlation coefficient (ICC) for average measures of O-C2A, AB/AM, AB/PM, PB/AM, and PB/PM were 0.66, 0.20, 0.40, 0.50, and 0.66, respectively. Conclusion: Our study did not find statistically significant evidence to confirm that these angles were dependable indicators of occipitocervical alignment, except for the PB/PM angle, which showed a validity comparable to our reference angle
... Researchers reported several methods for measuring the O-C2 angle using the mandible. 12,15) Bellabarba et al. reported that the mandible-C2 angle can provide reliable information on occipitocervical alignment comparable to the O-C2 angle. 12) However, intraoperative measurement of the specific angle seems to be challenging, as stated above. ...
... Tan et al. advocated the mandibular critical distance (MCD) as a sensitive parameter for occipitocervical alignment. 15) They defined the normal value of MCD as 9 to 13 mm as a reference for the neutral position on the lateral radiographs; however, they did not investigate the changes in MCD between the flexed and extended positions. Thus, we devised a novel parameter for the Gonion-C2 distance that can be easily measured intraoperatively and demonstrates a good relationship with the O-C2 angle in accordance with postural changes. ...
The Occipito (O) -C2 angle reflects the correct craniocervical spine alignment; however, the poor image quality of standard intraoperative fluoroscopy at times lead to inaccurate measurements. Herein, we preliminarily investigated the relationship between the O-C2 angle and the Gonion-C2 distance, which is based on the positioning of the mandible and the cervical spine. We enrolled patients who underwent cervical spine radiography in neutral, flexion, and extension positions from January 2020 to October 2020. The difference by posture changes for each parameter was defined as the Δ value, and the Spearman's rank correlation coefficient was determined. Furthermore, we determined the cutoff value of the ΔGonion-C2 distance to predict a decrease of > 10° in the ΔO-C2 angle, which is reported to be related to dysphagia and dyspnea. Seventy-four patients were included. Spearman's rank correlations for the neutral, flexion, and extension positions were 0.630 (P < 0.001), 0.471 (P < 0.001), and 0.625 (P < 0.001), respectively, while the cutoff values of the ΔGonion-C2 distance for predicting > 10° in the ΔO-C2 angle were 9.3 mm for the neutral flexion change (sensitivity: 0.435, specificity: 0.882) and 8.3 mm for the extension-neutral change (sensitivity: 0.712, specificity: 0.909). The O-C2 angle and Gonion-C2 distances correlated; however, this correlation was weaker in the flexed position. Nevertheless, the ΔGonion-C2 distance can be used as a warning sign for postoperative complications after posterior occipital bone fusion surgery, because a decrease of > 10° in the ΔO-C2 angle can be predicted with high specificity.
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... On the one hand, it is due to the difference of measurement methods. On the other hand, it is more important that variation of C2 spinous process has great influence on the individual difference of measurement results [13]. We found that our novel OC4D measurement has unique advantages compared with those of the OCD in previously reported studies [4,5,13]. ...
... On the other hand, it is more important that variation of C2 spinous process has great influence on the individual difference of measurement results [13]. We found that our novel OC4D measurement has unique advantages compared with those of the OCD in previously reported studies [4,5,13]. First, we found that the OC4D was a more accurate parameter compared to OCD in our present study. ...
... Additionally, in terms of the OCD, previous studies have demonstrated significant inter-individual morphologic variation in the C2 spinous process (including gender differences). Jiang et al. found that variations in the C2 spinous process may affect the OCD value, and that there was a significant difference in OCD values between male and female subjects [13]. Additionally, the inter-and intra-observer reliabilities of OCDs had ICC values of only 0.651 and 0.754 in a previous study [5]. ...
Background:
The aim of the present study was to describe and measure the occipital-cervical distance by a novel method utilizing the occiput-C4 distance (OC4D) in normal subjects, as a proposed tool to guide restoration of vertical dislocations of the occipitocervical region in patients with basilar invaginations and for performing standardized testing of occipitocervical constructs.
Methods:
We analyzed neutral, flexion, and extension lateral cervical spine radiographs of 150 asymptomatic subjects (73 males and 77 females) that were judged to be normal. The mean age of the included asymptomatic subjects was 48.0 ± 8.4 years old (range 20-69 years old; 48.4 ± 10.2 years old for males and 47.6 ± 6.4 years old for females). The OC4D was defined as the shortest distance from the center of the C4 vertebral body to the McGregor's line. Occipitocervical distances (OCDs) were measured and analyzed its correlation with OC4Ds. Two spine surgeons each performed three measurements of the OC4D and OCD from each asymptomatic subject, from which our reported average values were derived. The height, weight, and body mass index (BMI) of each subject were recorded and analyzed for their correlations with the OC4D and OCD.
Results:
The OC4Ds from neutral, flexion, and extension lateral cervical spine radiographs were 69.0 ± 6.9, 68.9 ± 6.8, and 68.1 ± 6.9 mm, respectively. There was no significant difference in the OC4D values among neutral, flexion, and extension lateral cervical spine radiographs (P > 0.05). The neutral, flexion, and extension OCDs were 23.0 ± 4.8, 27.6 ± 6.0, and 13.8 ± 4.7 mm, respectively. In particular, the neutral OCD was significantly different from those in flexion and extension lateral cervical spine radiographs (P < 0.001). There was no significant correlation between OC4D and OCD in neutral, flexion, and extension (P > 0.05 for all). There were positive correlations between OC4D and height, as well as OC4D and weight, in neutral, flexion, and extension lateral cervical spine radiographs (P < 0.001 for all). Furthermore, the intra-class correlation coefficients for inter- and intra-observer reliabilities of OC4Ds in neutral, flexion, and extension lateral cervical spine radiographs were significantly higher than those for OCDs (P < 0.001).
Conclusions:
The OC4D represents a novel measurement for estimating the occipital-cervical distance that is not affected by changes in neutral, flexion, and extension positions. Hence, the OC4D may serve as a valuable parameter and intra-operative tool to guide vertical restoration during occipitocervical fusion (OCF) for patients with altered occiput-cervical anatomy.
... In order to avoid postoperative complications, the occiput should be fused in appropriate functional position. There are several radiographic parameters including occipitocervical angle (OCA) [4], occipitocervical distance (OCD) [4], occiput-C2 angle (O-C2 angle) [2,5] posterior occipitocervical angle [6], and mandible cervical distance [7], used for the measurement of occipitocervical relationship. These parameters were frequently used to evaluate the functional position of the occiput in relation to the cervical spine and for prediction of postoperative dyspnea and dysphagia. ...
... The OCD is the shortest distance between occipital protuberance and the uppermost part of the spinous process of the axis. The axis spinous process has frequent morphological variation with known morphological difference between genders [1,4,7]. The O-C2 is represented by a line drawn parallel to the inferior endplate of the axis and the McGregor's line. ...
... The OCD was the least correlated with the other parameters and had statistically significant differences between genders. Our data confirmed previously published literature that the OCD varied among genders and was dependent on morphological variety of the spinous process of the axis [1,7]. ...
Purpose
To evaluate which cervical level is the most appropriate level to measure occipitocervical inclination (OCI).
Methods
Sixty-two patients with multi-positional MRI: 24 males and 38 females, who had cervical lordosis and had a disk degeneration grade of 3 or less were included. We measured patient’s OCI at C3, C4, and C5, occipitocervical angle (OCA), occipitocervical distance (OCD), C2–7 angle, and cervical sagittal vertical axis (cSVA) in neutral, flexion, and extension position. The correlation between OCI and OCA, OCD, C2–7 angle, and cSVA on each cervical level in all three positions was tested using Pearson’s correlation coefficient test. The difference between OCIs at each cervical level was tested by Wilcoxon signed-rank test. p value of less than 0.05 was set as a statistically significant level.
Results
C5 OCI showed statistically significant correlation with OCA, OCD, C2–7 angle, and cSVA in all three positions (p < 0.05, r = 0.214–0.525). C3 OCI in flexion (p = 0.393, r = 0.081) and C4 OCI in neutral and flexion (neutral p = 0.275, r 0.104; flexion p = 0.987, r = 0.002) did not show significant correlation with C2–7 angle. There was a statistically significant difference between C3, C4, and C5 OCIs in neutral and extension position (p < 0.05). At the same time, OCI showed statistically strong correlation between adjacent cervical levels (p < 0.001, r = 0.627–0.822).
Conclusion
C5 cervical level is the most appropriate level for OCI measurement. OCI should be measured at the same cervical level at all time. C4 OCI can reliably substitute C5 OCI in case C5 which is invisible on radiographic image.
Graphical abstract
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... Non-functional positions may lead to compensatory curvature in subaxial segments [6], subaxial subluxation [7], or airway obstruction [8,9]. Parameters such as the occipitocervical angle (OCA), occipitocervical distance (OCD), mandible cervical distance (MCD) [10], and the narrowest oropharyngeal airway space (nPAS) [11] can be used to define the ''neutral" position on LCR. However, it is relatively difficult to verify these measurements intraoperatively to reliably achieve the planned ''neutral" occipitocervical position even with the aid of fluoroscopy [4,7,10]. ...
... Parameters such as the occipitocervical angle (OCA), occipitocervical distance (OCD), mandible cervical distance (MCD) [10], and the narrowest oropharyngeal airway space (nPAS) [11] can be used to define the ''neutral" position on LCR. However, it is relatively difficult to verify these measurements intraoperatively to reliably achieve the planned ''neutral" occipitocervical position even with the aid of fluoroscopy [4,7,10]. ...
This report describes a novel method for occipitocervical fixation using a patient-specific, 3D-printed implant and tools. A 79-year-old female presented with progressive neck pain due to a pathologic fracture of C1. DICOM data was used to 3D-print 1:1 scale biomodels of the occipitocervical spine for pre-operative planning, patient education, and intraoperative reference. The surgeon collaborated with engineers to design and 3D-print a titanium patient-specific implant (PSI) and a stereotactic drill guide for occipitocervical screw fixation. The surgical plan specified the occipitocervical "neutral" position, screw sizes, entry points, and trajectories. The PSI was pre-contoured to match the posterior occipitocervical bony spine and reproduce the planned occipitocervical "neutral" position. Stereotactic portholes for screw fixation were integrated into the PSI. The planned "neutral" position was achieved by intraoperatively matching the occipitocervical alignment to the PSI. Screw placement under fluoroscopy was simplified using the stereotactic drill guide. There were no intraoperative or postoperative complications. At 6-month follow up, our patient reported resolution of symptoms and demonstrated satisfactory occipitocervical alignment without evidence of implant dysfunction. Our experience demonstrates that preoperative planning can be combined with biomodelling and 3D-printing to develop patient-specific tools and implants that are viable for occipitocervical fixation surgery.
... [4] Despite standardized trauma evaluation protocols, clinical and radiographic diagnosis of AOD remains challenging. [6] In recent decades, computed tomography (CT) has supplanted the use of cervical radiographs in the setting of acute cervical trauma. [7] Past work has demonstrated 99% identification of relevant anatomic landmarks with CT in comparison to only 39%-84% with lateral radiographs. ...
Objective
The objective of this study is to evaluate the the reliability of magnetic resonance imaging (MRI) in diagnosing alar ligament disruption in patients with potential atlanto-occipital dissociation (AOD).
Materials and Methods
Three-blinded readers performed retrospective review on 6 patients with intra-operative confirmed atlanto-occipital dissocation in addition to a comparison cohort of patients with other cervical injuries that did not involve the atlanto-occipital articulation. Ligament integrity was graded from 1 to 3 as described by Krakenes et al. The right and left ligaments were assessed separately. Inter-observer agreement by patient, by group (AOD vs. non-AOD), and intra-observer agreement was calculated using weighted Cohen's kappa.
Results
Interobserver agreement of alar ligament grade for individual patients ranged from slight to fair (κ = 0.05–0.30). Interobserver agreement of alar ligament grade for each group (AOD vs. non-AOD) ranged from fair to substantial (κ = 0.37–0.66). No statistically significant difference in categorical analysis of groups (AOD vs. non-AOD) and grade (0–1 vs. 2–3) was observed. Intraobserver agreement of individual patient's alar ligament grade ranged from moderate to substantial (κ = 0.50–0.62).
Conclusion
The use of MRI to detect upper cervical ligament injuries in AOD is imperfect. Our results show inconsistent and unsatisfactory interobserver and intraobserver reliability in evaluation of alar ligament injuries. While MRI has immense potential for detection of ligamentous injury at the craniovertebral junction, standardized algorithms for its use and interpretation need to be developed.
... When performing rigid internal fixation of the occiput to the cervical spine, the ability to determine that the occiput is in neutral position in relation to the cervical spine is very important. If the head is fixed in a non-functional position, abnormal curvature which will develop into pathology may occur in the subaxial cervical spine and global alignment [3][4][5][6][7]. While some studies have described radiographic parameters for an occipitocervical neutral position, there have been no reports on which parameter is superior; moreover, each of the parameters has definite pros and cons. ...
... Relatively similar (Fig. 5). In OCD, significant interindividual morphologic variation of the C2 spinous process and gender differences have been found (Fig. 6) [3]. This study also found significant gender differences in OCD (P \ 0.001) ( Table 2). ...
... The O-C2 angle, created by McGregor's line and the inferior surface of the axis, has been used frequently and was reported to be a good predictor of postoperative dyspnea and dysphagia [9,10]. However, the O-C2 angle is too sharp to differentiate grossly, and it is not comfortable to obtain accurate measurements during surgery [3]. Moreover, it can be difficult to measure O-C2 angle when the anatomy of C2 has been altered by trauma (Fig. 7). ...
Purpose:
To describe occipitocervical inclination (OCI), a new parameter that could compensate for defects in existing radiographic parameters, and to define occipitocervical neutral position.
Methods:
Neutral, flexion, and extension lateral cervical spine radiographs of 200 patients (100 male and 100 female patients) judged to be normal were analyzed. The mean age was 45.19 years (range 11-74; 42.84 for male and 47.53 for female patients). For OCI, the angle formed by the line connecting the posterior border of the C4 vertebral body and McGregor's line was measured. Occipitocervical angle (OCA) and occipitocervical distance (OCD) were measured and compared with OCI.
Results:
OCI on standard, neutral lateral cervical radiographs was 102.51° ± 8.87°. There was no significant gender difference in neutral OCI 102.81° ± 7.93° for male and 102.21° ± 9.74° for female patients (P = 0.631). The mean neutral OCA was 38.69° ± 9.23°, and the mean neutral OCD was 22.98 ± 5.10 mm. Pearson's correlation coefficient for the value of the cervical lordosis angle and that of neutral OCI was r = 0.274 (P < 0.001). Intraclass correlation coefficient values for inter- and intraobserver reliability for OCI were significantly higher than those for OCA (P < 0.001) and tended to be higher than those for OCD (P = 0.087).
Conclusions:
OCI is a very useful parameter for the determination of neutral position during occipitocervical fusion for patients with altered C0-C2 anatomy.
Dysphagia is a less reported but serious adverse outcome post occipitocervical fusion. Any patient suffering from dysphagia and or nasal regurgitation post fusion in flexion should be offered early revision. The right position for occipitocervical fusion is neutral alignment.
Objective
To assess the application and the effectiveness of a strategy of combining posterior occipitocervical angle (POCA) with occipital-C 2 (O-C 2) angle for adjustment of occipitocervical fixation angle in posterior instrumented occipitocervical fusion.
Methods
The clinical data of 22 patients undergoing posterior instrumented occipitocervical fusions between March 2013 and January 2016 were retrospectively analysed, and all patients were performed by using a strategy combining with POCA and O-C 2 angle for adjustment of occipitocervical fixation angle. All patients suffered from occipitocervical instability, including 7 males and 15 females with an average age of 44.4 years (range, 20-63 years). The patients were diagnosed as skull base depression with atlantoaxial dislocation in 20 cases and rheumatoid arthritis in 2 cases. The preoperative Japanese Orthopaedic Association (JOA) score was 13.2±2.0, and the visual analogue scale (VAS) score was 6.3±0.9. The POCA was first used to guide the pre-bending of the nail-rod system during the operation, so that POCA of 12 patients with abnormal preoperative POCA could be restored to the normal range; then intraoperative fluoroscopy was used to confirm whether the O-C 2 angle was within the normal range (4 cases were abnormal and 2 cases needed intraoperative adjustment); finally, POCA and O-C 2 angles were within normal range after adjustment. The postoperative complications were recorded, and the JOA and VAS scores were used to evaluate the recovery of spinal nerve function and the degree of pain relief after operation. The radiological data were collected to evaluate the bone graft fusion, the changes of postoperative POCA, O-C 2 angle, and lower cervical curvature (Cobb angle).
Results
All 22 patients were followed up 12-48 months, with an average of 24 months. No serious complications and reoperation occurred. At last follow-up, the VAS score and JOA score were 2.9±0.8 and 15.4±0.9 respectively, which were significantly improved when compared with preoperative ones ( t=15.870, P=0.000; t=6.587, P=0.000). Imaging examination showed that 22 patients had occipitocervical osseous fusion, good position of internal fixator without loosening or fracture, and good occipitocervical stability. The POCA and O-C 2 angles were within the normal range at 3 days after operation and at last follow-up, and there were significant differences when compared with preoperative ones ( P<0.05); but no significant difference was found in POCA and O-C 2 angles between at 3 days after operation and at last follow-up ( P>0.05). There was no significant difference in Cobb angle of lower cervical spine between before and after operation ( P>0.05).
Conclusion
The strategy of combination POCA and O-C 2 angle for adjustment of occipitocervical fixation angle during operation can ensure a better effectiveness.
Study Design
A method for measuring occipitocervical angle.
Objective
To develop a new method of measurement for assessing the occipitocervical angle using intraoperative fluoroscopic imaging, and to examine its reliability.
Summary of Background Data
To avoid postoperative complications following occipitocervical fusion, it is vital to obtain a suitable fusion angle between the occipital bone and the upper cervical spine.
Materials and Methods
The subjects were 30 cases with occipito-atlanto-axial lesions and 30 healthy volunteers. Lateral plain radiographs of the cervical spine in neutral position were used to draw the McGregor line, the line between the external occipital protuberance and the most caudal point on the midline occipital curve (Oc line), the tangential line of the inferior endplate of the C2 vertebra (C2 line), and the posterior longitudinal line of the C2 vertebra (Ax line). The angles formed by these 4 lines and the horizontal line were measured. The O-C2 angle and the Oc-Ax angle, the new indicator, were measured by 3 doctors and reliability was evaluated.
Results
In the disease group, mean intraobserver variances of the McGregor, Oc, C2, Ax, O-C2, and Oc-Ax angles were 0.7, 1.3, 1.5, 1.2, 1.6, and 1.9 degrees. Mean intraobserver intraclass correlation coefficients were 0.997, 0.994, 0.994, 0.997, 0.989, and 0.988, showing high intraobserver reliability for all angles. Mean interobserver intraclass correlation coefficients were 0.998, 0.996, 0.994, 0.997, 0.988, and 0.990, showing high interobserver reliability for all angles. The same reliability was obtained in the healthy group.
Conclusions
The Oc-Ax angle is as reliable an indicator as the conventional O-C2 angle, and could be used as a new intraoperative indicator for occipitocervical fusion. It may be particularly useful in cases where it is difficult to identify the McGregor line and/or the inferior endplate of the C2 vertebra.
Level of Evidence
Level 3—diagnostic study.
