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• W2323798823 abstract "We thank Dr Ye-heng Yin and colleagues for the interesting letter. We appreciate and acknowledge their work,1 even though it was not cited in our article. This omission was purely unintentional. We apologize for the same and acknowledge our shortcoming here. However, we wish to state that our study has provided new and different conclusions. We would like to provide the following rebuttal. QUANTITATIVE MEASURE OF JOINT ANGULATIONS We do agree that, in their work, Yin et al1 have quoted various types of inclinations that may occur between the C2 and occipito-C2 joints. Broadly, type I through III included increasing severity of angulation sloping down in a dorsoventral manner, and type IV was joint angulation in a ventrodorsal manner. In our series, we have not found any type IV. In the series described by Yin et al,1 all patients with type IV had basilar invagination (BI) only without atlantoaxial dislocation (AAD). It is possible that we may have not noticed this group because all the patients studied in our series had both AAD and BI. The mean atlantodental interval for AAD in our series was 5.5 ± 3.2 mm (control, 1.0 ± 0.3 mm), and the mean BI (as distance measured from the tip of the dens to the Chamberlain line) was 8.3 ± 4.2 mm (control, 2.5 ± 3.4 mm). We wish to point out that Yin et al have not mentioned any values for quantitative assessment of the degree of severity of joint abnormalities. Our study was the first of its kind to mention quantitative values for normal subjects and patients, as we have claimed. We have clearly demonstrated abnormal values (with a mean and standard deviation) in patients with BI and AAD, which were clearly different from normative values and correlated with increasing severity of BI and AAD (thus increasing severity of clinical features). Interestingly, this fact was also demonstrated by Yin et al (although not in a quantitative manner) when they have found that patients with type III had the worst symptoms. This reiterates our hypothesis that increasing sagittal inclination (SI) predisposes to AAD and BI by displacing the dens upward and posteriorly (Figure 1) and that higher values of SI correlate with more severe BI and AAD. The various values obtained in our study include the following: SI: normal, 87.15 ± 5.65°; in patients with BI and AAD, 127.1 ± 22.05° (P < .01 for both BI and AAD); craniocervical tilt: normal, 60.2 ± 9.2°; in patients with BI and AAD, 84.0 ± 15.1° (P < .01 for both BI and AAD); and coronal joint inclination (CI): normal, 110.3 ± 4.23°; in patients with BI and AAD, 121.15 ± 14.6° (mean P = 0.2 between right and left joints, only for BI and not AAD).FIGURE 1: Computed tomographic sagittal reconstruction showing severe basilar invagination (BI) with atlantoaxial dislocation (AAD; A). The parasagittal section shows the joint (B) with severe sagittal inclination (>150°), which has likely produced both BI and AAD. In our study, we have quantitatively defined the normative and abnormal values for various joint indexes, which correlate with the severity of BI and AAD.THE VALUE OF QUANTITATIVE MEASUREMENT OF JOINT ANGULATIONS Providing a quantitative measurement of the joint angulations has significant advantages for the neurosurgeon. It gives the surgeon the ability to assess the quantitative degree of severity of the joint pathology. The presence of very high values of craniocervical tilt, SI, and CI may require a transoral surgery followed by posterior instrumented fusion rather than a single posterior reducing procedure. In a recent analysis (unpublished, being prepared for publication), we have divided the SI into mild (<130°), moderate (130-150°), and severe (>150°). Distraction, compression, extension, and reduction2,3 surgery can easily be performed in patients with mild SI. Patients with moderate SI may require joint modification. This is a technique (Figure 2) in which the joint surfaces are made parallel to each other using a diamond drill to correct their SIs and to allow optimal placement of a spacer. The presence of severe SI may be a contraindication for the posterior-only approach and will require a transoral followed by a posterior approach.FIGURE 2: A 58-year-old man presented progressive myelopathy with basilar invagination (A-C) with an occipitalized C1 arch and a C2-3 prolapsed disk. As can be seen, the left occipito-C2 joint (D) had a moderate sagittal inclination (130-150°). The patient underwent a joint modification procedure in which a diamond drill was used to make the joint surfaces parallel (dotted lines, D). After this, a distraction, compression, extension, and reduction procedure was performed, including C2 and C3 in the fusion with a C3 laminectomy (E). F, the modified joint with a spacer in situ.VALIDITY OF THE METHOD OF MEASUREMENT OF VARIOUS INDEXES One of the main criticisms has been the validity of our method of measurement. Coronal Inclination Yin et al have stated “they measured coronal joint inclination between 2 lines of the long axis of the odontoid process and C1-C2 facet in the coronal plane.” This is not true at all. As shown in Figure 3, for measuring CI, first, 2 horizontal lines are drawn joining the uncinate processes of C3 and C4 (Figure 3A and 3C) in coronal images of the computed tomographic scan. The midpoints of both of these lines are marked. A vertical line (D) is drawn joining both the midpoints (Figure 3C). Next, a line is drawn along the superior surface of the C2 facet joint (Figure 3C and 3D). This is extended so that it meets the vertical line. The angle subtended by these 2 lines is defined as the CI of the joint. We did not use the dens or C2 as a referential parameter for drawing the vertical line because we have found the dens to be small or deviated to one side in many cases. Thus, the reference lines created for measuring the CI are the C2 and C3 vertebral bodies, which are fairly constant in their structure, and not dens, as wrongly pointed out by Yin et al. In fact, in Figure 3D, it can be seen that the referential line is actually to one side of the dens.FIGURE 3: The method used to measure coronal joint inclination, which is actually the angle between the long axis of the odontoid process and the C1-C2 joints in the coronal plane. In the midcoronal section where the C2-C1 joint is seen well, the midpoints of 2 lines joining the uncinate processes of C2 and C3, respectively, are first marked (E1 and E2, A and C). A line joining these 2 points (line D, A and C) is now drawn extending upward. Another line (line F) is now drawn parallel to the upper border of the C2 joint, which now joins line D (B and D). The angle subtended between the line D and F is called the coronal joint inclination. The normal value of coronal inclination in our series was 110.3 ± 4.23° and in patients with basilar invagination and AAD was 121.15 ± 14.6° (mean P = 0.2 between the right and left joints). From Chandra PS, Goyal N, Chauhan A, et al. The Severity of Basilar Invagination and Atlanto-Axial Dislocation Correlates With Sagittal Joint Inclination, Coronal Joint Inclination and Cranio-cervical Tilt: A Description of New Indices for the Cranio Vertebral Junction. Neurosurgery. 2014;10(4):621-630. Reprinted with permission from Wolters Kluwer.Sagittal Inclination For measuring SI, we have used a straight line along the posterior border of the dens as the referential line (Figure 4). We have used this for 3 reasons. First, in all our patients, we have seen that although the dens may be tilted in a lateral manner, it never tilts posteriorly with respect to the body of the C2; ie, a straight line is always maintained between the posterior border of the dens and C2 body. Second, although the Frankfurt plane (as in the study by Yin et al) may be a reliable referential plane, it is accurate only when the C1 is fused with the occiput. In contrast to this, in our technique, it does matter whether the C1 is fused with C2 or not (Figure 5). Third, it is not easy to measure the Frankfurt plane in routine computed tomographic images, whereas our technique may be applied easily for all routine computed tomographic images with sagittal reconstructions (Figure 5C).FIGURE 4: The method of calculating the sagittal joint inclination. This is actually the angle between the long axis of the odontoid process and the surface of the C1-C2 joint. However, because the odontoid process is in the midline and the C1-C2 joint is at the level of parasagittal section, the figure shows the method to measure this angle. Step 1 (A and C): In the midsagittal section, a line is drawn along the posterior border of the odontoid process (line A). Next, a line is drawn parallel to the border of the image (line B), which now subtends an angle (ang, A). The value of ang is 78.9° in C. Step 2 (B and D): This step is performed in the parasagittal section where the joints are seen. In this step, a line is first drawn parallel to the border of the image (line B1, C and D). Now the same value of angle is constructed as in ang (ang1, B) with another line A1 that now passes along a point on the posterior border of the C2 joint surface. Step 3: This step is also performed in the parasagittal section (B and D). In this step, a line is drawn passing parallel to the C2 facet joint (line C, C and D). The angle now subtended between lines A1 and C is called the sagittal joint inclination (SI). In this case, the SI is about 90.6°. In our series, the value of SI in normal individuals was 87.15 ± 5.65°; in patients with basilar invagination (BI) and atlantoaxial dislocation (AAD), it was 127.1 ± 22.05° (P < .01 for both BI and AAD). Note that the horizontal line B drawn in the midsagittal section (A and C) should be parallel to the border of the film. It may be drawn at any distance from the lower border of the image on the film. Because the entire computed tomography is performed on the patient at the same time point, this line will have the same referential value in midsagittal and parasagittal sections. Hence, this line is useful for measuring the angle between the long axis of odontoid process and the C1-C2 joint, which is the SI. From Chandra PS, Goyal N, Chauhan A, et al. The Severity of Basilar Invagination and Atlanto-Axial Dislocation Correlates With Sagittal Joint Inclination, Coronal Joint Inclination and Cranio-cervical Tilt: A Description of New Indices for the Cranio Vertebral Junction. Neurosurgery. 2014;10(4):621-630. Reprinted with permission from Wolters Kluwer.FIGURE 5: A and B. the Yin et al method of measuring joint inclination with reference to the Frankfurt plane. Although this measurement may be reliable in patients in whom the C1 is fused with the occiput (O; A), it becomes unreliable when the C1 is not fused with the occiput (B). In contrast, our method uses the posterior border of the C2 and dens (C), which is not influenced by whether C1 is occipitalized or not. In addition, special sequences are required to measure the Frankfurt plane, unlike our method, which can be performed easily in all routine computed tomographic images.ROLE OF TRANSORAL SURGERY IN BI AND AAD We also agree with Yin et al about the role of transoral surgery for BI and AAD, and we have mentioned this in our studies.2-4 Goel and Sharma4,5 have demonstrated a single-axis motion for correction of BI. Our technique (distraction, compression, extension, and reduction surgery) provides a 2-axis motion to reduce both BI and AAD effectively. However, there will still be some complex cases, as also mentioned above, that will require a transoral excision of odontoid process followed by posterior instrumented fixation. Finally, we would like to congratulate Yin et al on their extensive work. Their study and ours have provided useful insights into the involvement of joint orientation and morphology in craniovertebral junction anomalies. This is now shifting attention to the joints in patients with craniovertebral junction anomalies. However, we wish to reiterate that ours was the first study to provide quantitative joint measurement parameters to define their abnormalities and that higher values of our parameters correlated with the degree of severity of BI and AAD. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article." @default.
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• W2323798823 modified "2023-10-16" @default.
• W2323798823 title "In Reply" @default.
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