The Morphological Measurement And Clinical Significances Of Cervical Facet Tropism

1. BackgroundCervical spondylosis and cervical Intervertebral disk herniation is a common degenerative cervical disease. Cervical disc arthroplasty (CDA) is one of the methods of surgical treatment, but loosening and slipping of the prosthesis is the most serious complications of cervical disc arthroplasty, cervical vertebral instability is one of the reasons that lead to this complication, is also one of the major contraindications of cervical intervertebral disc replacement.The vertebral rotation is most common manifestation of the vertebral instability, but up to date, there is no effective quantitative diagnostic method. The vertebral instability is often caused by spinal degeneration, facet joints and intervertebral disc are considered to be closely related to the two structures of vertebral stability, which of them can destroy the stability of the vertebral body and even endanger the entire spine, but there is not a unanimous opinion about which is the main cause of the vertebral degeneration. However, there are more controversial about relationship between cervical facet tropism and facet joint degeneration, intervertebral disc degeneration. In addition, CT (Computed Tomography) and MRI (Magnetic Resonance Imaging) is a common diagnostic method to be used in the spine surgery, but in recent years, application of CT in the diagnosis of spinal disorders is relatively reduced, There are two possible reasons: One is the understanding problem, many spine surgeons believe that cervical MRI in the diagnosis of degenerative spinal disorders can replace CT completely. Another is in order to save medical costs to patients, only underwent MRI scan. Therefore, many surgeons just routinely obtained cervical vertebra anteroposterior and lateral radiograph and MRI rather than another cervical CT scan before cervical spinaloperations. Although there are many studies on differences of imaging manifestation in the severity of the facet joints degeneration (osteoarthritis) between CT and MRI, and most researchers believe that the reliability of CT in diagnosis of the severity of the facet joints degeneration is higher than MRI, but comparison of in the diagnosis of facet tropism between CT and MRI is rarely reported at home and abroad. Therefore, this study retrospectively selected over60patients with degenerative cervical spondylolisthesis, which is the most severe manifestations of vertebral instability, and treated in the Nanfang Hospital of Southern Medical University hospital need for surgery from January2005to December2011, as our study object.Meanwhile, to avoid the natural limitations of retrospective study and test our hypothesis, using five fresh cervical specimens and homemade vertebral rotation angles measuring instrument to investigate the relationship between the vertebral rotation and facet tropism on CT and MRI scans. If our hypothesis is established, the next step will be able to establish the threshold whichis vertebral instability caused by facet tropism, thus for spine surgeons provide reliable selection criteria and selection methods to choose surgical method in patients with cervical disc herniation surgery and cervical spondylosis and selection of patients with cervical intervertebral disc replacement, and provide another diagnostic method for patients with cervical vertebral artery disease,cervical spondylotic radiculopathy and sympathetic type of cervical spondylosis, in addition, this study also can provide digital evidence to determine the indications and contraindications for traditional "Overbanding" and so on treatment of cervical diseases with manipulative therapy. This is a study from the image to the entity and from the entity return to the image, and it’s a research mode is image and entity learning from each other and basic and clinical intermingling with each other.2. Objective(1).To investigate the correlation between facet tropism and degree of cervical spondylolisthesis, the severity of facet joint degeneration in degenerative cervical spondylolisthesis,and the clinical significance and the relationship between sagittal facet asymmetry angles and vertebral axial rotation angles.(2).To determine the reliability of MRI in the assessment of facet tropism in degenerative cervical spondylolisthesis.3. MethodsPart Ⅰ:From January2005to December2011, from366patients selected64patients with only one level cervical degenerative spondylolisthesis who need for surgical treatment in affiliated Nanfang Hospital of Southern Medical University and underwent anteroposterior and lateral radiographs, flexion-extension (FE) radiographs, left and right oblique X-ray, MRI and CT scan. To evaluate the sagittal facet angles of spondylolisthesis level and superior level and inferior level on axial CT with bone window, and in the evaluation of the severity of disc degeneration on midsagittal and axial MRI T2-weighted images from the picture archiving and communication system (PACS). According to the method described by Noren et al. whereby a facet line was drawn between the anteromedial and posterolateral points of each facet. A midsagittal line through the disc was considered the sagittal line. The angle formed by the left (and right) facet line and the sagittal line was measured and recorded in degrees (Figure1-2.). Calculating the differences between the left and right angles and using the criterion described by Boden et al., the measured values were divided into four grades:Ⅰ (None)≤6.00°, Ⅱ (Mild)6.01°-10.00°, Ⅲ (Moderate)10.01°-16.00°, IV (Sev-ere)>16°. The values of two angles (left and right) were the absolute differences and were used to define the facet tropism of the facet joints. According to the criterion described by Pathria et al. the severity of facet joints osteoarthritis (FJO) were divided into four grades:I (Normal) Normal facet joint space (2-4mm width); II (Mild) Narrowing of the facet joint space (<2mm) and/or small osteophytes and/or mild hypertrophy of the articular process; III (Moderate) Narrowing of the facet joint space and/or moderate osteophytes and/or moderate hypertrophy of the articular process and/or mild subarticular bone erosions; IV (Severe) Narrowing of the facet joint space and/or large osteophytes and/or severe hypertrophy of the articular process and and/or severe subarticular bone erosions and/or subchondral cysts.According to the modified Pearce criterion (Figure3.), the severity of intervertebral disc (IVD) degeneration were divided into four grades on midsagittal MRI T2-weighted images: Grade Ⅰ:The structure of the disc is homogeneous, with a bright hyperintense white signal intensity and a normal disc height. Or the structure of the disc is inhomogeneous, with a hyperintense white signal. The distinction between nucleus and anulus is clear, and the disc height is normal, with or without horizontal gray bands. Grade Ⅱ:The structure of the disc is inhomogeneous, with an intermediate gray signal intensity. The distinction between nucleus and anulus is unclear, and the disc height is normal or slightly decreased.Grade Ⅲ:The structure of the disc is inhomogeneous, with an hypointense dark gray signal intensity. The distinction between nucleus and anulus is lost, and the disc height is normal or moderately decreased. Grade IV:The structure of the disc is inhomogeneous, with a hypointense black signal intensity. The distinction between nucleus and anulus is lost, and the disc space is collapsed. Grading is performed on T2-weighted midsagittal (repetition time5000msec/echo time130msec) fast spin-echo images. The results were statistically relativity analyzed.Part Ⅱ:From January2005to December2011, random select60patients with cervical degenerative spondylolisthesis who need for surgical treatment in affiliated Nanfang Hospital of Southern Medical University and underwent anteroposterior and lateral radiograph, left and right oblique X-ray, MRI and CT scan. Using the4-point scale described by et al.,3reviewers blindly and independently graded the severity of facet tropism of76cervical facet joints on axial T2-weighted turbo spin echo images and separately on the corresponding axial CT scans. All results were subjected to the kappa coefficient statistic for strength of agreement.Part Ⅲ:From January2005to December2011, select60patientswith only C4/5level cervical degenerative spondylolisthesis as the experimental group, who need for surgical treatment in affiliated Nanfang Hospital of Southern Medical University and underwent anteroposterior and lateral radiograph, flexion-extension (FE) radiographs, left and right oblique X-ray, MRI scan. For the control group,60age-and sex-matched patients without evident spinal disease were selected from a group of826(457of males and369of females) patients that presented for physical examination from January2000to January2012. The facet angles of C3/4-C5/6from axial MRI of the two groups and the slippage degree (categorized into moderate and severe spondylolisthesis grades) at C4/5from neutral lateral radiographs of the experimental group were measured and calculated. Relativity analysis of the obtained parameters was performed.Part Ⅳ:Five fresh cadaveric full cervical (C1-C7) were offered by the department of anatomy of basic medical sciences of Southern Medical University, all specimens were removal the atlas, carefully removed the muscle tissue in the vertebral body and retained intactly anterior longitudinal ligament, posterior longitudinal ligament, articular facet joint, joint capsule, intervertebral discs, transverse process and spinous process structure. After five specimens thawed, using a MRI scans the intervertebral disc from C2/3to C6/7and using a CT scans the facet joints from C2/3to C6/7in a neutral position and kept a lordotic curve of cervical spine. Then the scan resultswere imported into PACS to evaluate the severity of intervertebral disc degeneration on axial and sagittal T2-weighted images and the severity of facet joint degeneration on axial CT, the left and right sagittal facet angles were also measured and calculatedon axial CT, facet joints with the absolute differences than6°were observed and analyzed. Five fresh cervical specimens were put inside the homemade vertebral rotation measuring instrument sequentially, the upper end of the fixture firmly clamped C4vertebral body and the lower end of the fixture firmly grip C5vertebral body, aligned vertebral transverse processes of C4/5as0°position, using CT scan facet joint in0°position and in the clockwise and counterclockwise direction6°,12°position, measured sagittal facet angles from PACS. After statistical analysis, we will get the sagittal facet angles of C4/5corresponding to the vertebral rotation angles.4. ResultsPart Ⅰ:There were no significant differences in the severity of facet tropism, the severity of facet joint osteoarthritis and the severity of intervertebral disc degeneration between the spondylolisthesis levels and adjacent levels (x2=2.672, P=0.263, x2=0.722, P=0.697; x2=1.114, P=0.573, P>0.05),but there were significant differences in the abnormal facet tropism (grade Ⅱ-Ⅳ) between the spondylolisthesis levels and adjacent levels (x2=6.763, P=0.034; P<0.05; spondylolisthesis levels vs. superior adjacent levels:z=-2.343, P=0.019, P<0.05; spondylolisthesis levels vs. inferior adjacent levels:z=-2.059, P=0.039, P<0.05).However, There were no significant differences in the abnormal facet tropism (grade II-IV) between adjacent levels (z=-0.472, P=0.637, P>0.05). Likewise, results of comparisons between moderate and severe cervical spondylolisthesis showed no significant difference in the severity of facet tropism, the severity of facet joint osteoarthritis and the severity of intervertebral disc degeneration (z=-.481, P=0.088; z=-1.791, P=0.073; z=-0.122, P=0.903, respectively; P>0.05), but the abnormal facet joint osteoarthritis (grade Ⅱ-Ⅳ) in moderate cervical spondylolisthesis was significantly higher than that in severe cervical spondylolisthesis (z=-2.336, P=0.019. P<0.05). In addition, there was no significant correlation between the severity of facet tropism, facet joint osteoarthritis and the severity of intervertebral disc degeneration in the spondylolisthesis levels and adjacent levels(facet tropism vs. FJO, spondylolisthesis levels:r=0.207, P=0.136, superior adjacent levels:r=0.070, P=0.519; inferior adjacent levels:r=0.052, P=0.633; facet tropism vs. IVD degeneration, spondylolisthesis levels:r=-.046, P=0.677, superior adjacent levels:r=0.054, P=0.627, inferior adjacent levels:r=0.007, P=0.947; FJO vs. IVD degeneration, spondylolisthesis levels:r=-0.037, P=0.746, superior adjacent levels:r=-0.056, P=0.614, inferior adjacent levels:r=-0.002, P=0.990. P>0.05)Part Ⅱ:The weighted kappa coefficients for agreement between MRI and CT grading were0.76(P<0.001) for the severity of facet tropism, MRI grading of facet tropism was identical to the CT grading in62of76joints (82%), with substantial intermethod concordance. There was perfect agreement in grade Ⅰ (18of76joints) and poor agreement in grade Ⅱ and Ⅲ (14of76joints, respectively). The inter-rater reliability of three reviewer in MRI and CT were0.61-0.74and0.65-0.8(range k), respectively. CT performed better, with substantial to very good inter-rater reliabilitythan MRI, which had substantial inter-rater reliability. Intra-rater reliability was higher than inter-rater reliability for both CT and MRI. intra-rater agreement was substantial for MRI (k=0.83for the first reader, k=0.81for the second reader, and k=0.79for the third reader) and substantial to very good for CT (k=0.86for the first reader, k=0.84for the second reader, and k=0.83for the third reader).Part Ⅲ:There were32males and28females in the experimental group and control group, respectively.There were significant differences of facet tropism among the C3/4-C5/6levels (F=17.941, P<0.001) and facet tropism at C4/5was significantly greater than C3/4and C5/6in the experimental group (C4/5vs. C3/4, P=0.001; C4/5vs. C5/6, P<0.001), but there was no significant difference between C3/4and C5/6(P=0.191); There were no significant differences among the respective levels in the control group (F=0.011, P=0.989).The facet tropism was significantly different at the C3/4levels versus the C4/5levels, but no significant difference was found at the C5/6level when comparing the two groups (C3/4, P=0.014; C4/5, P<0.001; C5/6, P=0.250).Comparison of the abnormal facet angles (grade Ⅱ-Ⅳ), there were also significant differences in the experimental group (F=9.785, P<0.001; C4/5vs. C3/4, P=0.006; C4-/5vs. C5/6, P<0.001; C3/4vs. C5/6, P=0.371), but there was no significant difference in the control group (F=2.829, P=0.065).Facet tropism at C4/5in moderate spondylolisthesis patients was significantly greater than in severe spondylolisthesis patients(t=-2.963, P=0.005), but there is no significant difference in the severity of facet tropism between them(r=-0.178, P=0.175) and the severity of facet tropism did not vary with the spondylolisthesis degree in the experimental group (r=-0.178, P=0.175). Thus this also confirmed that there was no correlation between the severity of facet tropism and the severity of cervical spondylolisthesis.Part Ⅳ:In a neutral position, the cervical specimens without facet tropism (The facet angle differences were≤6°) at the C4/5level, when the vertebral body was turned to6°along clockwise or counterclockwise directions, the facet angle differences were less than6°, but there were slight differences when the vertebral body turn to12°:The facet angle differences at the C4/5level of the No.3and4cervical specimens were still≤6°. However, the facet angle differences at the C4/5level of the No.1cervical specimens were14.82±1.11°when the vertebral body was turned to12°along clockwise direction. In a neutral position, two cervical specimens with facet tropism (The facet angle differenceswere>6°) at the C4/5level, when the vertebral body was turned to6°,12°along clockwise direction, the facet angle differences at the C4/5level were more than before (the facet angle differences at the C4-5level of the No.2cervical specimens were increased from8.82°1.14°to9.41±1.03°,9.02±2.96°, respectively, and the facet angle differences of the No.5cervical specimens were increased from6.49±1.83°to16.33±0.42°,19.95±1.02°, respectively), but when the vertebral body was turned to6°,12°long counterclockwise direction, the facet angle were slight differences than the vertebral body in a neutral position (The facet angle differences of the No.2cervical specimens were decreased from8.82±1.14°to1.01±1.57°, continue to turn the vertebral body to12°, the facet angle differences were increasedto20.62°4.24°. The facet angle differences of the No.5cervical specimens were decreased from6.49±1.83°to2.93±1.78°, continue to turn the vertebral body to12°, the facet angle differences were increased to5.42±1.44°).In addition, we found that the five specimens were followed this principle:when the vertebral body was turned along clockwise direction, the right facet angles were bigger than the left and when turned along counterclockwise directionto6°, on the contrary. However, if the vertebral was turned beyond the normalmotion range of facet joints, the left and/or right facet angle was decreased obviously. 5. Conclusion:(1).There was no significant correlation between the severity of cervical spondylolisthesis and the severity of facet tropism, facet joints osteoarthritis and intervertebral disc degeneration;there were also no significant correlation among the severity of facet tropism, facet joints osteoarthritis and intervertebral disc degenerati-on in degenerative cervical spondylolisthesis.The relationship of facet tropism, facet joints osteoarthritis, intervertebral disc and degenerative cervical spondylolisthesis are needed more longitudinal studies to resolve.(2).When using MRI and CT to assess facet tropism, they all performed excellent, with substantial to very good agreement for both intermethod agreement and inter-rater reliability or intra-rater reliability. This indicates that MRI can reliably determine the presence or degree of facet tropism. Therefore, for comprehensive assessment of facet tropism, an MR scan should not be performed in addition to a CT.(3). The current study found that facet tropism is universally present at the C3/4-C5/6levels and the most serious facet tropism exists in spondylolisthesis-affected level in degenerativecervical spondylolisthesis, the interplaybetween degenerative facet joints and degenerative intervertebral disc contributes to sagittal orientation aggravation of the facet jointsresulting in the severity of facet tropism increased, which may be one of the triggers for degenerativecervical spondyloli-sthesis.(4).In five cervical specimens, within the normal motion range of C4/5segment, the facet angle differences of facet joints without facet tropism (The facet angle differences were≤6°) in a neutral position, were less than6°when the vertebral body was turned along clockwise or counterclockwise directions to6°and12°and they will not to be change; the facet angle differences of facet joints with facet tropism (The facet angle differences were>6°) in a neutral position were increased if the vertebral body was turned along the bigger facet angles direction to6°and12°, and the facet angle differences were decreased when the vertebral body was turned along the smaller facet angles direction to6°and were increased when the vertebral body was continue to turn the vertebral body to12°. Within the normal motion range of C4/5segment, the facet joints whether with or withoutfacet tropism in a neutral position, left and right sagittal facet angles were changed when the vertebral body was turned along clockwise or counterclockwise directions to6°:right facet angles were bigger than the left when the vertebral body was turned along clockwise directions and left facet angles were bigger than the right when the vertebral body was turned along counterclockwise directions, but if the vertebral was turned beyond the normal motion range of facet joints, the left and/or right facet angles was decreased obviously than the previous.6. Clinical SignificancesThis study proved that there is no direct correlation between the facet tropism and the severity of intervertebral disc degeneration, facet joint degeneration. Asymmetric sagittal angle may be congenital facet tropism and degenerative facet tropism, and degenerative facet tropismmay be due tocervical vertebral rotation. We consider that in assessment of patients with cervical disc arthroplasty preoperative should be considered facet tropism, especially with moderate or severe facet tropism. In addition, using "Overbanding" and so on treatment of cervical diseases with manipulative therapy, patients with moderate or severe facet tropism should be careful, so as to avoid aggravate disease or result in accident.