Why the patients with Hirayama disease have abnormal cervical sagittal alignment? A radiological measurement analysis of posterior cervical extensors

Purpose To explore the relationship between the strength of posterior cervical extensors (PCEs) and cervical sagittal alignment in Hirayama disease (HD) patients. Methods We analyzed the (magnetic resonance imaging) MRI T2WI and X-rays of 60 HD patients who visited Huashan Hospital from June 2017 to February 2020. Symptoms of these patients include adolescent onset, manifestation of unilateral upper limb muscle weakness and muscle atrophy of the forearm and hand. MRI images were used to measure (the cross-sectional area) CSA of cervical PCEs. The ratio of muscle CSA to vertebral body areas at the same level is defined as R-CSA. Cervical sagittal alignment includes the C2–7 Cobb angle, T1 slope and C2–7 sagittal vertical axis (SVA). The geometric center of the C3–6 vertebral body was determined using the line connecting the C2 inferior endplate and the C7 upper endplate. When located behind the line, it is defined as a “local kyphotic deformity.” The number of vertebral bodies involved in kyphotic deformity was determined by measuring the local kyphosis angle (LKA). Spearman correlation analysis (α = 0.05) was used to determine the relationship between R-CSA and sagittal parameters. ROC curves were used to analyze the sensitivity and specificity of relevant variables. Results Spearman correlation test revealed that R-CSA negatively correlated with T1S (S = 0.34, r = 0.34, p = 0.01) and LKA (S = 0.44, r = 0.5, p = 0.01), but did not correlate with the C2-C7 Cobb angle (S = 0.20, p = 0.12) or C2-C7 SVA (S = − 0.17, p = 0.46). (p < 0.05). ROC curve analysis showed that the areas under the curve (AUCs) of the T1 slope and LKA was 0.6696 and 0.7646, respectively. T1 slope, cutoff value: 17.2°; sensitivity: 0.5806; specificity: 0.7241; p < 0.05. LKA: cutoff value: − 14°; sensitivity: 1; specificity: 0.5333; p < 0.05. Conclusions In patients with Hirayama disease, the strength of posterior cervical extensors and cervical sagittal alignment are closely related. The local kyphosis angle can be used as a reference for the strength of posterior cervical extensors. These results indicate the weakness of PCEs, which may predispose the cervical spine of HD patients to a less stable situation. Therefore, patients with Hirayama disease should strengthen the exercise of the PCEs.

Differences in Demographic and Radiographic Characteristics between Patients with Visible and Invisible T1 Slopes on Lateral Cervical Radiographic Images

Introduction: The T1 slope is important for cervical surgical planning, and it may be invisible on radiographic images. The prevalence of T1 invisible cases and the differences in demographic and radiographic characteristics between patients whose T1 slopes are visible or invisible remains unexplored. Methods: This pilot study aimed to evaluate the differences in these characteristics between outpatients whose T1 slopes were visible or invisible on radiographic images. Patients (n = 60) who underwent cervical radiography, whose T1 slope was confirmed clearly, were divided into the visible (V) group and invisible (I) group. The following radiographic parameters were measured: (1) C2-7 sagittal vertical axis (SVA), (2) C2-7 angle in neutral, flexion, and extension positions. Results: Based on the T1 slope visibility, 46.7% of patients were included in group I. The I group had significantly larger C2-7 SVA than the V group for males (p < 0.05). The C2-7 SVA tended to be larger in the I group, without significant difference for females (p = 0.362). Discussion: The mean C2-7 angle in neutral and flexion positions was not significantly different between the V and I groups for either sex. The mean C2-7 angle in the extension position was greater in the V group. The T1 slope was invisible in males with high C2-7 SVA.

Postoperative alterations of sagittal cervical alignment and risk factors for cervical kyphosis in 124 Lenke 1 adolescent idiopathic scoliosis patients

Background This study aims to analyze postoperative changes of cervical sagittal curvature and to identify independent risk factors for cervical kyphosis in Lenke type 1 adolescent idiopathic scoliosis (AIS) patients. Methods A total of 124 AIS patients who received all-pedicle-screw instrumentation were enrolled. All patients were followed up for at least 2 years. The following parameters were measured preoperatively, immediately after the operation, and at the last follow-up: pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), lumbar lordosis (LL), thoracic kyphosis (TK), global thoracic kyphosis (GTK), proximal thoracic kyphosis (PrTK), T1-slope, cervical lordosis (CL), McGregor slope (McGS), sagittal vertical axis (SVA), C2–7 SVA (cSVA), and main thoracic angle (MTA). Statistical analysis was performed to evaluate postoperative alterations of and correlations between the parameters and to identify risk factors for cervical kyphosis. Statistical significance was set at P < 0.05. Results After the operation, PrTK and T1-slope significantly increased (3.01 ± 11.46, 3.8 ± 10.76, respectively), cervical lordosis improved with an insignificant increase (− 2.11 ± 13.47, P = 0.154), and MTA, SS, and LL decreased significantly (− 33.68 ± 15.35, − 2.98 ± 8.41, 2.82 ± 9.92, respectively). Intergroup comparison and logistic regression revealed that preoperative CK > 2.35° and immediate postoperative GTK < 27.15° were independent risk factors for final cervical kyphosis, and △T1-slope < 4.8° for a kyphotic trend. Conclusions Postoperative restoration of thoracic kyphosis, especially proximal thoracic kyphosis, and T1-slope play a central role in cervical sagittal compensation. Preoperative CK, postoperative small GTK, and insufficient △T1-slope are all independent risk factors for cervical decompensation.

What is the most accurate substitute for an invisible T1 slope in cervical radiographs? A comparative study of a novel method with previously reported substitutes

OBJECTIVE The ability to utilize the T1 slope is often limited by poor visibility on cervical radiographs. The C7 slope has been proposed as a reliable substitute but may have similar limitations of visibility. Herein, the authors propose a novel method that takes advantage of the superior visibility on CT to accurately substitute for the radiographic T1 slope and compare the accuracy of this method with previously reported substitutes. METHODS Lateral neutral standing cervical radiographs and cervical CT scans were examined. When the T1 slope was clearly visible on radiographs, the C3–7 slopes and T1 slope were measured. In CT method 1, a direct method, the T1 slope was measured from the upper endplate of T1 to the bottom edge of the CT image, assuming the edge was parallel to the horizontal plane. In CT method 2, an overlaying method, the T1 slope was calculated by superimposing the C7 slope angle measured on a radiograph onto the CT scan and measuring the angle formed by the upper endplate of T1 and the superimposed horizontal line of the C7 slope. A Pearson correlation with linear regression modeling was performed for potential substitutes for the actual T1 slope. RESULTS Among 160 patients with available noninstrumented lateral neutral cervical radiographs, the T1 slope was visible in only 54 patients (33.8%). A total of 52 patients met the inclusion criteria for final analysis. The Pearson correlation coefficients between the T1 slope and the C3–7 slopes, CT method 1, and CT method 2 were 0.243 (p = 0.083), 0.292 (p = 0.035), 0.609 (p < 0.001), 0.806 (p < 0.001), 0.898 (p < 0.001), 0.426 (p = 0.002), and 0.942 (p < 0.001), respectively. Linear regression modeling showed R2 = 0.807 for the correlation between C7 slope and T1 slope and R2 = 0.888 for the correlation between T1 slope with the CT method 2 and actual T1 slope. CONCLUSIONS The C7 slope can be a reliable predictor of the T1 slope and is more accurate than more rostral cervical slopes. However, this study disclosed that the novel CT method 2, an overlaying method, was the most reliable estimate of true T1 slope with a greater positive correlation than C7 slope. When CT studies are available in patients with an invisible T1 slope on cervical radiographs, CT method 2 should be used as a substitute for the T1 slope.

Biomechanical aspects of the initial stability of instrumental fixation in the treatment of subaxial cervical dislocations: an experimental study

Objective. To study the influence of thoracic inlet angle (TIA) and the fracture of the articular process on the initial strength of the fixation of the spinal segment during its anterior and circular instrumental surgical stabilization in an experiment on a model of the lower cervical spinal segment.Material and Methods. The material of the study was assembled models of C6–C7 spinal segments made using addictive technologies by 3D printing. After preliminary instrumentation, spinal segments were installed on the stand testing machine using specially manufactured equipment. A metered axial load simulating the native one was applied along the axis of the parameters SVA COG–C7 and C2–C7 SVA, which values were close to the value of 20 mm, at a rate of 1 mm/min until the shear strain was reached. The system’s resistance to displacement was measured, and the resulting load was evaluated. Four study groups were formed depending on the modeling of the T1 slope parameter, the integrity of the facets, and the type of instrumentation. Three tests were conducted in each group. The graphical curves were analyzed, and the values of the parameters of the neutral and elastic zones, the yield point, time to yield point, and the value of the applied load for the implementation of shear displacement were recorded. The data were subjected to comparative analysis.Results. In Group 1, anterior shear displacement of the C6 vertebra could not be induced in all series. In groups 2, 3, and 4 a shear displacement of ≥4 mm was noted in all series. In Group 3 where a fracture of the articular process was additionally modeled, the average value of the yield point was 423.5 ± 46.8 N. Elastic zone, the time to the onset of the yield point, the time at the end point or at a shear of C6 ≥4 mm did not differ significantly. In Group 4, a translational displacement of ≥4 mm was observed, though the average yield point was 1536.0 ± 40.0 N.Conclusion. The direction of the load applied to the fixed spinal segment, as well as the presence of damage to the articular processes, play a crucial role in maintaining resistance to shear deformation of the spinal segment during its instrumental stabilization. At high values of TIA (T1 slope) and the presence of fractures of the articular processes, the isolated anterior stabilization is less effective, circular fixation of 360° under these conditions gives a high initial stability to the spinal segment.

Increased Neck Tilt/T1 slope ratio may play an important role in patients with cervical kyphosis

Background In previous studies, we demonstrated that the T1 slope (T1s) is associated with clinical outcomes, but the results were not specific for individuals. A recent study suggested that an increased pelvic tilt (PT)/sacral slope (SS) ratio may play an important role in the degeneration of lumbar scoliosis and pathogenesis of lumbar spondylolisthesis. Therefore, we aimed to explore the role of neck tilt (NT)/T1s in patients with cervical kyphosis. Methods In total, the data of 36 kyphosis patients who underwent anterior cervical hybrid decompression and fusion (ACHDF) for multilevel (3 levels) cervical spondylotic myelopathy were retrospectively analyzed. The radiographic measurements included the T1s, NT, C2–7 Cobb angle, and C2–7 sagittal vertical axis (SVA). The visual analog scale (VAS) and neck disability index (NDI) scores were used to determine the clinical prognosis. Pearson’s correlation coefficient was calculated to assess the relationships among preoperative imaging examination parameters. Results The mean C2–7 Cobb angle was − 5.93 ± 3.00° before surgery, 9.67 ± 6.61° after surgery, and 7.91 ± 8.73° at the follow-up. The preoperative NT/T1s ratio was positively correlated with the ΔC2–7 Cobb angle (r = 0.358, p < 0.05) and negatively correlated with the preoperative C2–7 Cobb angle (r = -0.515, p < 0.01) and preoperative C2–7 SVA (r = -0.461, p < 0.01). The linear regression model indicated a positive correlation between the preoperative NT/T1s ratio and the ΔC2–7 Cobb angle (R2 = 0.122). Conclusions The preoperative NT/T1s ratio may be positively correlated with changes in postoperative cervical spine curvature (Cobb angle). The NT/T1s ratio may be worthy of increased attention among sagittal parameters.

Association of findings on preoperative extension lateral cervical radiography with osteotomy type, approach, and postoperative cervical alignment after cervical deformity surgery

OBJECTIVE The authors’ objective was to determine whether preoperative lateral extension cervical spine radiography can be used to predict osteotomy type and postoperative alignment parameters after cervical spine deformity surgery. METHODS A total of 106 patients with cervical spine deformity were reviewed. Radiographic parameters on preoperative cervical neutral and extension lateral radiography were compared with 3-month postoperative radiographic alignment parameters. The parameters included T1 slope, C2 slope, C2–7 cervical lordosis, cervical sagittal vertical axis, and T1 slope minus cervical lordosis. Associations of radiographic parameters with osteotomy type and surgical approach were also assessed. RESULTS On extension lateral radiography, patients who underwent lower grade osteotomy had significantly lower T1 slope, T1 slope minus cervical lordosis, cervical sagittal vertical axis, and C2 slope. Patients who achieved more normal parameters on extension lateral radiography were more likely to undergo surgery via an anterior approach. Although baseline parameters were significantly different between neutral lateral and extension lateral radiographs, 3-month postoperative lateral and preoperative extension lateral radiographs were statistically similar for T1 slope minus cervical lordosis and C2 slope. CONCLUSIONS Radiographic parameters on preoperative extension lateral radiography were significantly associated with surgical approach and osteotomy grade and were similar to those on 3-month postoperative lateral radiography. These results demonstrated that extension lateral radiography is useful for preoperative planning and predicting postoperative alignment.