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Study Design: Retrospective study.Objective: To determine the correlations and age-related changes of cervical sagittal parameters in adults without obvious cervical spinal disease.Summary Of Background Data: Cervical sagittal parameters play essential roles in the pathogenesis and therapy of cervical spinal diseases. However, few studies have investigated the correlations and age-related changes of cervical sagittal parameters.Methods: The enrolled participants were divided into three age groups and their cervical sagittal parameters were collected. Correlations and age-related changes of these parameters were analyzed.Results: Significant differences in the C2-C7 angle, center of gravity of the head-C7 sagittal vertical axis (CGH-C7 SVA), C2-C7 SVA, neck tilt (NT), and thoracic inlet angle (TIA) were found among the three age groups. Pearson correlation analysis showed positive correlations between the C0-C2 angle and CGH-C7 SVA, C0-C2 angle and C2-C7 SVA, C2-C7 angle and T1 slope, C2-C7 angle and TIA, CGH-C7 SVA and C2-C7 SVA, C2-C7 SVA and T1 slope, T1 slope and TIA, and NT and TIA as well as negative correlations between the C0-C2 angle and C2-C7 angle, C2-C7 angle and CGH-C7 SVA, and C2-C7 angle and C2-C7 SVA. Paired t tests showed significant changes in the C2-C7 angle in groups I and II, and in the CGH-C7 SVA and C2-C7 SVA in all age groups with increasing age.Conclusion: The results indicate that cross correlations exist between different cervical sagittal parameters in adults without symptoms of cervical spinal disease, and the lower cervical curvature and SVA change obviously with increasing age.Level Of Evidence: 3. [ABSTRACT FROM AUTHOR]

T1 slope has emerged as an important radiographic parameter in the evaluation and surgical management of adult cervical spinal deformity. Given the high rates of nonvisualization of T1 slope on upright cervical radiographs, however, this study examined the evaluation of C7 slope as a potential surrogate marker. This is a retrospective review in adult patients with and without cervical deformity to examine the correlation of C7 and T1 slopes on routine upright cervical radiographs. In secondary analysis, correlations of C7 and T1 slopes were made amongst various demographic variables, different surgical groups, and various measures of cervical alignment. Cervical deformity was defined as sagittal vertical axis >40 mm, coronal Cobb angle >10°, and sagittal Cobb >10° in kyphosis. C7 slope was visualized in 93% of patients as opposed to T1 slope in 68% of patients, leading to a final study population of 129 patients. Mean values of C7 and T1 slopes were 26.5° and 28.1°, respectively. Significant correlation was found in patients with and without cervical deformity (r = 0.9, P < 0.01). This correlation remained significant amongst demographics, surgical groups, and measures of cervical alignment. Results demonstrated that C7 and T1 were in direct correlation in a variety of different cohorts regardless of deformity status or prior fusion. This study indicates that C7 slope may be reliably used a surrogate marker especially when visualization of T1 slope is not possible. [ABSTRACT FROM AUTHOR]

Study Design: Retrospective study.Objective: The preoperative parameters for predicting the loss of lordosis after cervical laminoplasty were investigated in the present study.Summary Of Background Data: Cervical laminoplasty is an effective surgical method to decompress the cervical spinal cord. Maintaining cervical lordosis after laminoplasty is an important factor to ensure the successful surgical treatment. To know the preoperative parameters for predicting loss of lordosis after cervical laminoplasty is important for better outcome after laminoplasty.Methods: In this retrospective study, 106 patients who underwent cervical laminoplasty from 2011 to 2015 were reviewed. The preoperative parameters; T1 slope (TS), Cobb lordotic angle (CLA) and sagittal vertical axis (SVA) at C2-C7, relative cross-sectional area (RCSA), and fatty degeneration of deep extensor muscles (DEMs) were measured. Visual analogue scale (VAS) and modified Japanese Orthopedic Association (mJOA) scores were used for clinical assessment. Correlation analysis was performed between the postoperative CLA change and preoperative parameters. The patients were divided into the decreased- or maintained-lordosis groups based on the difference between postoperative and preoperative CLA. All preoperative parameters were compared between groups.Results: Based on correlation analysis, preoperative TS (P = 0.001), TS-CLA (P = 0.046), RCSA at C7-T1 (P < 0.001), and fatty degeneration of DEMs (P < 0.001) were correlated with loss of lordosis. Among the 106 patients, 68 showed decreased-lordosis and 38 maintained-lordosis. Preoperative TS (P = 0.003), SVA (P = 0.014), TS-CLA (P = 0.015), and RCSA at C7-T1 (P = 0.005) were significantly different between groups. In both correlation and comparative analyses, higher TS and TS-CLA and less RCSA at C7-T1 were associated with loss of lordosis. Neck pain VAS (P < 0.001) and mJOA scores (P < 0.001) were significantly improved in the maintained-lordosis group.Conclusion: Maintaining cervical lordosis is important for clinical outcomes after laminoplasty. Preoperative higher TS, TS-CLA, and less RCSA at C7-T1 were considered as predictors for loss of lordosis. These characteristics should be considered when choosing the surgical method to help maintain cervical lordosis.Level Of Evidence: 3. [ABSTRACT FROM AUTHOR]

Purpose: Cervical spine surgery may affect sagittal alignment parameters and induce accelerated degeneration of the cervical spine. Cervical sagittal alignment parameters of surgical patients will be correlated with radiological adjacent segment degeneration (ASD) and with clinical outcome parameters.Methods: Patients were analysed from two randomized, double-blinded trials comparing anterior cervical discectomy with arthroplasty (ACDA), with intervertebral cage (ACDF) and without intervertebral cage (ACD). C2-C7 lordosis, T1 slope, C2-C7 sagittal vertical axis (SVA) and the occipito-cervical angle (OCI) were determined as cervical sagittal alignment parameters. Radiological ASD was scored by the combination of decrease in disc height and anterior osteophyte formation. Neck disability index (NDI), SF-36 PCS and MCS were evaluated as clinical outcomes.Results: The cervical sagittal alignment parameters were comparable between the three treatment groups, both at baseline and at 2-year follow-up. Irrespective of surgical method, C2-C7 lordosis was found to increase from 11° to 13°, but the other parameters remained stable during follow-up. Only the OCI was demonstrated to be associated with the presence and positive progression of radiological ASD, both at baseline and at 2-year follow-up. NDI, SF-36 PCS and MCS were demonstrated not to be correlated with cervical sagittal alignment. Likewise, a correlation with the value or change of the OCI was absent.Conclusion: OCI, an important factor to maintain horizontal gaze, was demonstrated to be associated with radiological ASD, suggesting that the occipito-cervical angle influences accelerated cervical degeneration. Since OCI did not change after surgery, degeneration of the cervical spine may be predicted by the value of OCI.Neck Trial: Dutch Trial Register Number NTR1289.Procon Trial: Trial Register Number ISRCTN41681847. These slides can be retrieved under Electronic Supplementary Material. [ABSTRACT FROM AUTHOR]

Background Context: Whiplash-associated disorder is a common cause of chronic neck pain. Several radiological cervical angular variables are suggested to have constitutional characteristics, that is, them being minimally influenced by body positioning. However, the association between these variables and pain conditions remains poorly understood. To our knowledge, no previous studies have investigated the association between constitutional angular variables and the outcome after whiplash trauma.Purpose: Our objectives were (1) to study the inter-rater agreement of sagittal radiologic variables between 2 raters and (2) to investigate any association between these variables and self-perceived nonrecovery after whiplash injury.Study Design: Prospective cohort study.Patient Sample: Forty-six patients aged 16 to 70 years, attending an emergency department after a motor vehicle accident resulting in neck pain were recruited.Outcome Measures: Self-perceived nonrecovery (yes/no) was the primary outcome measure. The secondary outcome measure was pain level on a numeric rating scale.Methods: The participants underwent computed tomography scans in a supine position. Sagittal alignment variables (T1 slope, neck tilt, thoracic inlet angle [TIA], and C2-C7 angle) on the computed tomography scans were measured by 2 independent raters. Inter-rater agreement was tested with a paired sample t test and Bland-Altman plots for each variable. The patients were followed up after 6 months.Results: No systematic differences for the assessed variables were found between the 2 raters. The overall nonrecovery rate was 28%. For the group with low neck tilt, the nonrecovery rate was 50% (95% CI: 36%-78%) and for the group with high neck tilt, 8% (95% CI: 3%-25%). The nonrecovery rate for the group low TIA was 50% (95% CI 29%-72%) and for those with high TIA 14% (95% CI 4%-26%). The associations remained significant after adjustments for possible confounders. The inter-rater analysis shows satisfactory agreement without proportional bias.Conclusions: This study indicates the existence of an association between the constitutional sagittal alignment of the cervical spine and the outcome after whiplash injuries. [ABSTRACT FROM AUTHOR]

Background: Laminoplasty is a method of posterior cervical decompression which indirectly decompresses the spinal column. Unfortunately, many patients undergoing laminoplasty develops postoperative loss of cervical lordosis (LCL) or kyphotic alignment of cervical spine even though they have sufficient preoperative lordosis which results in poor surgical outcome. Objective: We would like to highlight the relationship between various radiological parameters of cervical alignment and postoperative LCL in patients undergoing laminoplasty. Methods: We performed extensive literature search using PubMed, Google Scholar, and Web of Science for relevant articles that report factors affecting cervical alignment following laminoplasty. Results: On reviewing the literature, patients with high T1 slope have more lordotic alignment of cervical spine preoperatively. They also have more chances of LCL following laminoplasty. C2–C7 sagittal vertical axis (SVA) has no role in predicting LCL following laminoplasty though patients with low T1 slope (≤20°) and high C2–C7 SVA (>22 mm) had correction of kyphotic deformity following laminoplasty. C2–C7 lordosis, Neck Tilt, cervical range of motion, and thoracic kyphosis has no predictive value for LCL. Lower value of T1 slope (T1S-CL) and CL/T1S has more incidence of developing LCL following laminoplasty. The role of C2–C3 disc angle has not yet been evaluated in patients undergoing laminoplasty. Dynamic extension reserve determines the contraction reserve of SPMLC and lower dynamic extension reserve is associated with higher chances of LCL following laminoplasty. Conclusions: Cervical lordotic alignment is important in maintaining cervical sagittal balance which ultimately is responsible for global spinal sagittal balance and horizontal gaze. Among various radiological parameters, T1 Slope has been reported to be the most important factor affecting cervical alignment following laminoplasty. [ABSTRACT FROM AUTHOR]

Background: T1s, C2-7 lordosis, and C2-7 sagittal vertical axis (SVA) are the three most important sagittal parameters in the cervical spine. This study was conducted to investigate the relationships between classical sagittal alignment parameters and a new parameter, K-line tilt, and to study the impact of K-line tilt. Material and methods: A total of 72 patients who underwent adjacent two-level anterior cervical discectomy and fusion (ACDF) were retrospectively analyzed. Radiographic measurements included T1 slope (T1s), C2-7 lordosis, segment angle (SA), C2-7 SVA, and K-line tilt. The Neck Disability Index (NDI) scores were used to evaluate the clinical prognosis. Pearson correlation coefficients were calculated between radiographic measures. Linear regression analysis was used to analyze the relationship between follow-up K-line tilt and NDI. Results: ΔNDI was positively correlated with ΔT1s (r = 0.620, p < 0.05), ΔC2-7 SVA (r = 0.645, p < 0.05), and ΔK-line tilt (r = 0.702, p < 0.01); ΔK-line tilt was positively correlated with ΔT1s (r = 0.650, p < 0.05), ΔSA (r = 0.269, p < 0.05), and ΔC2-7 SVA (r = 0.293, p < 0.05); ΔT1s was positively correlated with ΔC2-7 lordosis (r = 0.428, p < 0.05), ΔSA (r = 0.631, p < 0.01), and ΔC2-7 SVA (r = 0.235, p < 0.05); ΔC2-7 lordosis was positively correlated with ΔSA (r = 0.666, p < 0.05) and negatively correlated with ΔC2-7 SVA (r = − 0.467, p < 0.01). The preoperative and postoperative K-line tilt values were statistically significant (p < 0.01), increasing from (7.50 ± 6.48)° to (9.95 ± 5.09)°. Preoperative NDI was positively correlated with preoperative C2-7 SVA (r = 0.639, p = 0.011) and K-line tilt (r = 0.516, p = 0.026); follow-up NDI was positively correlated with follow-up T1s (r = 0.664, p = 0.038), C2-7 SVA (r = 0.756, p = 0.004), and K-line tilt (r = 0.832, p = 0.006). The linear regression model showed that when the follow-up K-lint tilt was > 23.75°, NDI scores were > 25 (R2 = 0.737, p = 0.000). Conclusion: This study showed that the K-line tilt was strongly correlated with the C2-C7 SVA, indicating that the K-line tilt can be used as another cervical parameter to evaluate cervical alignment in adjacent two-level ACDF. K-line tilt is an important parameter similar to the classical parameter C2–C7 SVA. In particular, a K-line tilt greater than 23.75 corresponded to a worse clinical prognosis, which was defined as an NDI score greater than 25. [ABSTRACT FROM AUTHOR]

Laminoplasty causes destruction of the posterior musculoligamentous complex, which may result in cervical kyphosis, or more commonly loss of cervical lordosis (LOCL). In this study, we evaluated the role of various preoperative radiologic parameters in predicting not only the LOCL/kyphosis but also the functional outcomes in the form of change in Oswestry Disability Index (ODI) score following laminoplasty. Patients were evaluated both clinically and radiologically with dynamic cervical spine radiograph, noncontrast-enhanced computed tomography, and magnetic resonance imaging of the cervical spine preoperatively as well as at 1 year follow-up. One hundred twenty-one patients who underwent laminoplasty for cervical spondylotic myelopathy/ossified posterior longitudinal ligament from 2011 to 2018 at our center were included in final analysis. In multivariate analysis, preoperative Cobb angle (P = 0.001), T1 slope (TIS; P = 0.001), and dynamic extension reserve (P < 0.001) were found to have an independent effect on LOCL. The receiver operating characteristic curve using the regression model significantly predicted LOCL >10° with an area under the curve of 88.3% (P < 0.001). Similarly, preoperative T1S (P = 0.036) and SVA (P < 0.001) were found to be independent predictors of significant improvement in ODI after laminoplasty. The receiver operating characteristic curve using the regression model significantly predicted change in ODI with an area under the curve of 83.7% (P < 0.001). Based on these findings, classification and scoring systems with good accuracy have been proposed for prediction of LOCL and improvement in ODI. We have found that the chances of significant LOCL is determined by an interplay of preoperative Cobb angle, T1S, and dynamic extension reserve. [ABSTRACT FROM AUTHOR]

Study Design: This study is a post hoc analysis of a multicenter prospective randomized controlled trial which compared artificial disc replacement and anterior cervical discectomy and fusion. Purpose: Useful radiographic parameters for assessing cervical alignment include the Cobb angles, T1 slope (T1S), occipitocervical inclination (OCI), K-line tilt (KLT), and cervical sagittal vertical axis (cSVA). This study aimed to determine measurement accuracy and reliability for these parameters. Overview of Literature: Various authors have assessed repeatability by comparing different methods of measurement, but knowledge of measurement error and minimal detectable change is scarce. Methods: We evaluated 758 lateral cervical radiographs. One medical student and one spine surgeon (i.e., measured ×2 within 4 weeks) independently measured the parameters obtaining 5,850 values. Standard error of measurement (SEm) and minimum detectable change (MDC) were calculated for each parameter. The accuracy and reliability of the Cobb angle measurements were calculated for the different types of angles: cervical lordosis, prosthesis angle, segmental angle with two bone surfaces (SABB), and segmental angle with one bone and one metal surface. Reliability was determined with intraclass correlation coefficient (ICC). Results: SEm was 1.8° and MDC was 5.0° for the Cobb angle, with an intraobserver/interobserver ICC of 0.958/0.886. All the different subtypes of Cobb angles had an ICC higher than 0.950, except SABB (intraobserver/interobserver ICC of 0.922/0.716). The most accurate and reliable measurement was for KLT. Conclusions: This study provides normative data on SEm and MDC for Cobb angles, T1S, KLT, OCI, and cSVA in cervical lateral radiographs. Reliability was excellent for all parameters except SABB (e.g., good). [ABSTRACT FROM AUTHOR]

Abstract Background The cervical sagittal parameters of the normal population and the impact of disc degeneration on cervical sagittal alignment have not been clearly defined yet. This study is applied to investigate the characteristics and relationships of cervical sagittal parameters in normal adults and patients with cervical disc degeneration. Methods We reviewed 50 normal control subjects (normal group, NG) and 50 patients with cervical disc degeneration (degeneration group, DG), who had both cervical MRI and radiographs obtained together, between January 2010 and September 2015. Data including C2–7 lordosis (CL), T1 slope (T1S), thoracic inlet angle (TIA), neck tilt (NT), C2–7 sagittal vertical axis (C2–7 SVA), cervical tilting, and cranial tilting on cervical radiographs were collected and analyzed. Results T1S in the NG was significantly greater than in the DG (P

Jia Li,1,2* Shuhui Qin,1,2* Yongqian Li,1,2 Yong Shen1,2 1Department of Orthopaedic Surgery, The Third Hospital of Hebei Medical University, Shijiazhuang, Peoples Republic of China; 2The Key Laboratory of Orthopedic Biomechanics of Hebei Province, The Third Hospital of Hebei Medical University, Shijiazhuang, People’s Republic of China *These authors contributed equally to this work Background: The purpose of the research was to evaluate cervical sagittal parameters on magnetic resonance imaging (MRI) in patients with Modic changes and its impact on axial neck pain. Methods: This study consisted of 266 consecutive asymptomatic or symptomatic patients with Modic changes, whose average age was 50.9±12.6 years from January 2015 to December 2016. Cervical sagittal parameters included sagittal alignment of the cervical spine (SACS), T1 slope, thoracic inlet angle (TIA), and neck tilt (NT). The Modic changes group was compared with an asymptomatic control group of 338 age- and gender-matched adults. Results: In the Modic changes group, T1 slope was significantly higher (25.8º±6.3º) compared with that in the control group (22.5º±6.8º) (P=0.000). However, there was no significant difference of the NT, TIA, and SACS between the two groups. Patients in the Modic changes group were more likely to have experienced historical axial neck pain compared with the control group (P=0.000). With regard to the disc degeneration, it indicated that the disc in the Modic changes group had more severe disc degeneration (P=0.032). Conclusion: T1 slope in the Modic changes group was significantly higher compared to that of the control group. The findings suggested that a higher T1 slope with broken compensation of cervical sagittal mechanism may be associated with the development of Modic changes in the cervical spine. Keywords: Modic changes, T1 slope, axial neck pain, cervical spine

Peng Yang,1 Yongqian Li,2,3 Jia Li,2,3,* Yong Shen2,3,* 1Department of Neurosurgery, Affiliated Hospital of North China University of Science and Technology, Tangshan, 2Department of Orthopedic Surgery, 3Key Laboratory of Orthopedic Biomechanics of Hebei Province, the Third Hospital of Hebei Medical University, Shijiazhuang, People’s Republic of China *These authors contributed equally to this work Background: This retrospective study investigated an association between preoperative T1 slope and surgical and adjacent segment degeneration (SASD) after Bryan cervical disc arthroplasty (BCDA) in patients with cervical degenerative disc disease.Methods: Based on preoperative standing lateral radiographs, 90 patients were classified according to T1 slope that was higher or lower than the 50th percentile (high T1 or low T1, 28 and 62 patients, respectively). Patients were also classified as SASD or non-SASD (38 and 52 patients, respectively) determined by radiographs at final follow-up. Visual analog scale (VAS) and Neck Disability Index (NDI) scores for neck and arm pain were noted, and changes in the sagittal alignment of the cervical spine (SACS), functional spinal unit (FSU) angle, and FSU range of motion (ROM) were also noted. Univariate and multivariate logistic regression analyses were performed to determine the risk factors for SASD.Results: The overall rate of SASD was 42.2% (38/90). The SACS, FSU angle, FSU ROM, and SASD rates of the high T1 and low T1 slope groups were significantly different at the last follow-up. The NDI and VAS scores of the high T1 slope group were significantly greater than those of the low T1 slope. The multivariate logistic regression analysis showed that high T1 slope and endplate coverage discrepancy (ie, residual space behind the prosthesis) were significant risk factors for SASD after BCDA.Conclusion: High T1 slope and endplate coverage discrepancy were associated with SASD after BCDA. Patients with a high preoperative T1 slope have a smaller FSU angle and more neck pain after BCDA. Keywords: Bryan cervical disc arthroplasty, surgical and adjacent segment degeneration, T1 slope, endplate coverage discrepancy, risk factor, clinical outcomes

To assess whether preoperative T1 slope and cervical lordosis mismatching affect the surgical outcomes of patients with cervical spondylotic myelopathy (CSM) after laminoplasty. A total of 85 patients with CSM who underwent unilateral open-door laminoplasty between January 2013 and May 2017 were retrospectively reviewed. Based on preoperative T1 slope and C2–C7 lordosis matching, the patients were divided into 2 groups: the match group and the mismatch group. The T1 slope minus C2–C7 lordosis (T1S-CL) <20° was defined as matching. Radiographic parameters included T1 slope, C2–C7 lordosis, C2–C7 sagittal vertical axis (SVA), and T1S-CL. Clinical outcomes were based on the Neck Disability Index (NDI) and Japanese Orthopedic Association (JOA) scores. The preoperative T1S-CL had significant correlation with T1 slope (r = 0.283), C2–C7 lordosis (r = -0.611), and C2–C7 SVA (r = 0.331). At the final follow-up, patients in the mismatch group had a higher incidence of postoperative cervical kyphosis (P = 0.007) and C2–C7 SVA >40 mm (P = 0.043). The mismatch group also had greater △C2–C7 lordosis (P = 0.028), △C2–C7 SVA (P = 0.042), and △T1S-CL (P = 0.044). Comparison of clinical outcomes revealed that patients in the match group had better NDI and JOA recovery (P < 0.05). T1S-CL is a clinically relevant parameter for surgical decision making because patients with T1S-CL mismatching are more likely to have postoperative kyphotic alignment changes and cervical sagittal imbalance. Laminoplasty might not be a suitable option for patients with T1S-CL mismatching. [ABSTRACT FROM AUTHOR]

Study Design: Cross-sectional cohort.Objective: To determine normative radiographic sagittal cervical alignment in asymptomatic volunteers based on Roussouly thoracolumbar sagittal alignment subtypes.Summary Of Background Data: Comprehension of differences in cervicothoracic alignment with respect to variations in thoracolumbar alignment is limited.Methods: Asymptomatic adults were recruited and the following parameters measured: PI, PT, SS, LL, orbital tilt, orbital slope, occipital slope and incidence, occiput-C2 lordosis, C2-7 lordosis, occiput-C7 lordosis, CBVA, T1 slope, cervicothoracic alignment, T2-5 kyphosis, and C2-C7 sagittal vertebral alignment (SVA). Each was classified into one of Roussouly's four thoracolumbar subtypes and cervical alignment parameters were compared between groups.Results: Eighty-seven individuals [male-23; female-64; average age 49 ± 16 yr (22-77 yr)] were included for analysis. The four groups were not different by age, sex, and body mass index (BMI). Lumbopelvic parameters (PI, SS, PT, LL) were different between Roussouly types. Average values for all patients included: CBVA (-1 ± 9°), occiput-C2 lordosis (28 ± 9°), occiput-C7 lordosis (39 ± 14°), C2-7 lordosis (11 ± 14°), C2-7 SVA (21 ± 9 mm), T1 slope (25 ± 9°), C6-T4 angle (5 ± 8°), T2-5 angle (16 ± 7°), thoracic kyphosis (47 ± 13°). No sagittal radiographic alignment measurements of the cervical spine and cervicothoracic junction were different between groups, except for the global cervical lordosis (occiput-C7 Cobb), which was found to be lowest for Roussouly type 2 (35 ± 14°) and highest for type 4 (48 ± 14°) (P = 0.01). Mean C2-C7 sagittal Cobb, T2-T5 sagittal Cobb, and T1 slope were not different between groups.Conclusions: In asymptomatic volunteers, normative sagittal alignment parameters of the cervical spine, cervicothoracic junction, and thoracic spine based on variations in thoracolumbar sagittal alignment, as proposed by Roussouly, are established. These data may guide surgical correction of cervicothoracic deformities to ensure appropriate restoration of normal cervicothoracic parameters to maintain good horizontal gaze and overall sagittal plane alignment.Level Of Evidence: 3. [ABSTRACT FROM AUTHOR]

Study Design: Retrospective study of postoperative outcomes of adult spinal deformity (ASD) surgery.Objective: To clarify the differences in postoperative outcomes depending on the presence or absence of thoracic compensatory changes among patients with a T1 slope (TS) more than 40°.Summary Of Background Data: Loss correction after ASD surgery is more likely to occur when preoperative TS is more than 40°. When preoperative TS is more than 40°, some cases involve compensatory changes in the thoracic spine and decreased thoracic kyphosis (TK); others involve increased TK without compensatory changes.Methods: Seventy-nine patients with TS more than 40° who underwent ASD surgery were enrolled and separated into compensated and noncompensated groups (group C: TK <40°; group NC: TK ≥40°). Radiographic parameters obtained by whole-spine standing x-ray, the Oswestry Disability Index (ODI), and Scoliosis Research Society-22 (SRS-22) questionnaire were assessed.Results: There were 41 patients in group C and 38 patients in group NC. Preoperative significant differences in TS did not disappear after surgery (preoperative TS: group C and group NC = 46° and 55°, P < 0.001; just after surgery: group C and group NC = 27° and 40°, P < 0.001; 2 years later: group C and group NC = 34° and 47°, P < 0.001). There were no significant differences in ODI and all domains of the SRS-22 before surgery. However, 2 years after the surgery, ODI (38%), pain (3.5), self-image (3.0), and total (3.2) values of the SRS-22 for group NC were significantly worse than those (28%, 4.0, 3.4, and 3.5, respectively) for group C (P < 0.05).Conclusion: Changes in the thoracic spine (TS and TK >40°) result in poor postoperative outcomes. Extending the upper instrumented vertebra (UIV) to the upper thoracic spine must be considered. Even when TS is more than 40°, TK less than 40°, and upper instrumented vertebra set to the lower thoracic level result in good postoperative outcomes.Level Of Evidence: 3. [ABSTRACT FROM AUTHOR]

Study Design: Retrospective study.Objective: To investigate whether loss of cervical lordosis (LCL) after laminoplasty can be predicted from specific preoperative dynamic radiograph measurements.Summary Of Background Data: Recent studies have focused on the correlation between LCL after laminoplasty and T1 slope. These studies explain this correlation through the injury of the posterior neck muscular-ligament complex (PMLC); however, this muscle injury model could not explain the less kyphotic change in high T1s patients, as reported in some studies as controversy. We have focused on the PMLC constriction reservoir which was represented by extension function (EF).Methods: We retrospectively analyzed 50 consecutive patients who underwent open-door laminoplasty (>1-year follow-up). EF is defined as extension C2-7 Cobb angle (CA) minus neutral C2-7 CA (Ext CA - CA). LCL is defined as follow-up CA minus preoperative CA (CA [FU] - CA [PRE]), and significant kyphotic change was defined as LCL smaller than -10°.Results: The distribution of LCL was -3.70 ± 7.98 and the significant kyphotic change occurred in 20% of the patients (10/50). EF, C2-7 sagittal vertical axis (PRE), and C2 slope (PRE) were found to be risk factors for LCL by multiple linear regression analysis. The receiver operating characteristic curve analysis revealed that EF could predict the significant kyphotic change well than previously known risk factors. The cutoff value of EF was 14°. No significant kyphotic change occurred at EF greater than or equal to 14°. Upon limiting the number of patients with preoperative straight curvature (n = 28), there is also no significant kyphotic change occurred in any patient whose EF was greater than or equal to 14°.Conclusion: In our study sample, we found that there is no relation between T1 slope and LCL. We have identified a new factor, EF, that could predict LCL after laminoplasty. No significant kyphotic changes after laminoplasty occurred particularly when the EF was greater than or equal to 14°.Level Of Evidence: 3. [ABSTRACT FROM AUTHOR]

Study DesignRetrospective evaluation.PurposeTo analyze the effect of T1 slope on degree of degeneration in patients with cervical disc degeneration.Overview of LiteratureThe T1 slope is well known parameter that may be very useful in evaluating sagittal balance. There are no reports on the analysis of the relationship between T1 slope and cervical disc degeneration. We hypothesized that T1 slope has an effect on the degree of cervical degeneration.MethodsSixty patients who had cervical spine magnetic resonance imaging (MRI) in our orthopedic clinic were enrolled. Patients were divided into two groups according to T1 slope. Radiologic parameters obtained from radiography and cervical spine MRI were compared between low T1 slope group (≤25) and high T1 slope group (>25).ResultsAmong low T1 slope group, average degeneration grade of each cervical segment was 2.65 in C2-3, 2.50 in C3-4, 2.62 in C4-5, 3.23 in C5-6, and 2.81 in C6-7. And that of high T1 group was 2.35 in C2-3, 2.32 in C3-4, 2.59 in C4-5, 2.79 in C5-6, and 2.32 in C6-7. Grade of degeneration of low T1 group was significantly higher, as compared with high T1 group in C5-6 (p=0.028) and C6-7 (p=0.009). Percentage of high grade degeneration of more than grand III was 65.4% in low T1 group and 32.4% in high T1 group (p=0.018). Risk of high grade degeneration of C6-7 was significantly higher in low T1 group (odds ratio, 5.63; 95% confidence interval, 1.665-19.057; p=0.005).ConclusionsPatients with low T1 slope had higher grade of degeneration regardless of age and gender. Low T1 slope is a potential risk factor of cervical spondylosis especially in the C6-7 cervical segment.

Objective To investigate the relationships between sagittal alignment parameters and Neck Disability Index (NDI) scores after adjacent 2-level anterior cervical diskectomy and fusion (ACDF) and to study the impact of the T1 slope (T1s) minus C2-7 lordosis (T1s-CL). Methods In total, 76 patients after adjacent 2-level ACDF were retrospectively analyzed. Radiographic measurements included T1s, C2-7 lordosis, T1s-CL, segment angle (SA), and C2-7 sagittal vertical axis (SVA). NDI scores were used to evaluate clinical prognosis. Pearson correlation coefficient was calculated between radiographic measures. Linear regression analysis was used to analyze the relationships between follow-up cervical sagittal parameters and NDI. Results ΔT1s was positively correlated with ΔC2-7 lordosis (r = 0.466, P < 0.001), ΔT1s-CL (r = 0.337, P = 0.003), ΔC2-7 SVA (r = 0.238, P < 0.05), and ΔSA (r = 0.654, P < 0.001). ΔC2-7 lordosis was positively correlated with ΔSA (r = 0.692, P < 0.001) and negatively correlated with ΔT1s-CL (r = −0.676, P < 0.001) and ΔC2-7 SVA (r = −0.418, P < 0.001). ΔT1s-CL was positively correlated with ΔC2-7 SVA (r = 0.644, P < 0.001). The pre- and postoperative SAs were significantly different (P < 0.05), increasing from 3.71° ± 8.92° to 9.63 ± 4.20°. Preoperative NDI was positively correlated with preoperative C2-7 SVA (r = 0.325, P = 0.004) and T1s-CL (r = 0.498, P < 0.001). Follow-up NDI was positively correlated with follow-up T1s (r = 0.359, P = 0.001), C2-7 SVA (r = 0.613, P < 0.001), and T1s-CL (r = 0.696, P < 0.001) and negatively correlated with C2-7 lordosis (r = −0.491, P < 0.001). The linear regression model showed that when preoperative T1s-CL was greater than 21.43°, the NDI score was greater than 25 (R 2 = 0.248, P < 0.001), and when follow-up T1s-CL was greater than 28.07°, the NDI score was greater than 25 (R 2 = 0.484, P < 0.001). Conclusions Changes in cervical sagittal parameters after 2-level ACDF were associated with quality of life. A greater T1S-CL mismatch was related to a greater degree of cervical malalignment. T1s-CL may be a more important predictor of cervical malalignment than C2-7 SVA. Specifically, a mismatch greater than 28.07 corresponded to positive cervical sagittal malalignment, defined as an NDI score greater than 25. [ABSTRACT FROM AUTHOR]

Background: Ossification of the nuchal ligament (ONL) caused by chronic injury to the nuchal ligament (NL) is very common in instability-related cervical disorders.Purpose: To determine possible correlations between ONL, sagittal alignment, and segmental stability of the cervical spine.Material and Methods: Seventy-three patients with cervical spondylotic myelopathy (CSM) and ONL (ONL group) and 118 patients with CSM only (control group) were recruited. Radiographic data included the characteristics of ONL, sagittal alignment and segmental stability, and ossification of the posterior longitudinal ligament (OPLL). We performed comparisons in terms of radiographic parameters between the ONL and control groups. The correlations between ONL size, cervical sagittal alignment, and segmental stability were analyzed. Multivariate logistic regression was used to identify the independent risk factors of the development of ONL.Results: C2-C7 sagittal vertical axis (SVA), T1 slope (T1S), T1S minus cervical lordosis (T1S-CL) on the lateral plain, angular displacement (AD), and horizontal displacement (HD) on the dynamic radiograph increased significantly in the ONL group compared with the control group. The size of ONL significantly correlated with C2-C7 SVA, T1S, AD, and HD. The incidence of ONL was higher in patients with OPLL and segmental instability. Cervical instability, sagittal malalignment, and OPLL were independent predictors of the development of ONL through multivariate analysis.Conclusion: Patients with ONL are more likely to have abnormal sagittal alignment and instability of the cervical spine. Thus, increased awareness and appreciation of this often-overlooked radiographic finding is warranted during diagnosis and treatment of instability-related cervical pathologies and injuries. [ABSTRACT FROM AUTHOR]

Objective: To investigate the relationship between the K-line tilt and classical cervical parameters such as the C2-C7 sagittal vertical axis (SVA), cervical lordosis, and the T1 slope in cervical sagittal alignment. We assessed whether the K-line tilt can be used as an excellent cervical parameter.Methods: We reviewed 50 patients aged 60-89 years who visited the spine center outpatient clinic from May 2017 to September 2017 through cervical spine lateral radiography and checked the cervical spine parameters. All targeted patients were randomized without any prejudice. Radiographic measurements included the K-line tilt, C2-C7 lordosis, the C2-C7 SVA, the T1 slope, and T1 slope minus C2-C7 lordosis (T1S-CL). Pearson correlation coefficients were calculated between the K-line tilt and each cervical parameter.Results: Of the 50 patients, 33 were men. The mean age of the patients was 70.84 ± 7.52 years. The mean K-line tilt was 11.28 ± 8.31°. The K-line tilt was correlated with the C2-C7 SVA (r = 0.813, P = 0.000) and T1S-CL (r = 0.315, P = 0.026).Conclusion: This study showed that the K-line tilt is also a useful parameter like the C2-C7 SVA and T1S-CL in cervical sagittal alignment. These slides can be retrieved under Electronic Supplementary Material. [ABSTRACT FROM AUTHOR]

Purpose: Although the T1 vertebra is considered as an important factor of cervical balance, little is known about its motion between flexion and extension. The purpose of present study was to analyze the T1 sagittal motion using kinematic magnetic resonance imaging (kMRI), and to identify factors that relate to T1 sagittal motion.Methods: We retrospectively analyzed 145 kMR images taken in weight-bearing neutral, flexion and extension positions. Cervical balance parameters were evaluated in each position. The degree of T1 sagittal motion was defined as [(T1 slope at extension) - (T1 slope at flexion)]. All patients were divided into three groups: Positive group (T1 followed the head motion, T1 sagittal motion > 5°), Stable group (5 ≥, ≥ - 5) and Negative group (T1 moved in the opposite direction from the head motion, > - 5). The groups were compared and multivariate logistic regression analysis was calculated.Results: There were 57 (40%) patients in the positive, 56 (39%) in the stable and 32 (22%) in the negative group. The positive group had the largest C2-7 sagittal vertical axis in flexion (p < 0.001) and the shortest in the extension (p = 0.023). Similar trends were seen in cranial tilt and cervical tilt. The value of T1 height < 27 mm was a significant independent factor for the negative group (p = 0.008, adjusted odds ratio = 5.958).Conclusion: Based on T1 sagittal motion, 40% of the patients were classified in positive group (the T1 vertebra followed the head motion in flexion and extension), and 20% were classified in the negative group (the T1 vertebra moved in the opposite direction from the head motion). T1 height < 27 mm was a potential predictor of negative group. [ABSTRACT FROM AUTHOR]

Study Design. Retrospective analysis of consecutive 45 radiographs and 120 kinematic magnetic resonance images (kMRI) Objective. The aim was to assess the visibility of C7 and T1 endplates on radiographs, and to verify the correlation between C7 or T1 slope and cervical balance parameters using kMRI. Summary of Background Data. Because the T1 slope is not always visible due to the anatomical interference, several studies have used C7 slope instead of T1. However, it is still unclear whether the C7 endplate is more visible on radiographs than T1, and if C7 slope has similarity with T1 slope. Methods. The endplate visibility was determined using weightbearing radiography. Subsequently, using weight-bearing MR images, the C7 slope of upper and lower endplate, T1 slope, C1 inclination, C2 slope, atlas-dens interval (ADI), C2-C7 lordotic angle, cervical sagittal vertical axis (cSVA), cervical tilt, cranial tilt, neck tilt, thoracic inlet angle (TIA) were measured, for the analysis of correlation between three types of slopes and cervical balance parameters. Results. 82% of the upper C7, and 18% of T1 endplate were clearly visible. The upper C7 endplate was significantly visible, whereas T1 endplate was significantly invisible (residual analysis, P<0.01). Linear regression analysis showed correlation between the upper C7 slope and T1 slope (R²=0.818, P<0.01) and, lower C7 slope and T1 slope (R²=0.840, P<0.01). T1 slope significantly correlated with neck tilt, TIA, C2-C7 angle, cSVA, cervical and cranial tilt, but not with the C1 inclination, C2 slope, and ADI. Upper and lower C7 slopes showed the close resemblance with T1 slope in terms of correlation with those parameters. Conclusion. Both, upper and lower C7 slope correlated strongly with T1 slope and showed similar relationship with cervical balance parameters as T1 slope. Therefore, C7 slope could potentially substitute T1 slope, especially upper C7 slope due to the good visibility. [ABSTRACT FROM AUTHOR]

Introduction: Cervical spine is part of the spine with the most mobility in the sagittal plane. It is important for surgeons to have reliable, simple and reproducible parameters to analyse the cervical.Material and Method: This study is a systematic review and a critique of current parameters to help improve the study of cervical spinal balance. We conducted a systematic search of PUBMED/MEDLINE for literature published since January 2014. Only studies written in English and containing abstracts were considered for inclusion. The search performed was: «C7 slope» OR «T1 slope» OR «C2C7 offset» OR «C2C7 lordosis» OR «cervical SVA (sagittal vertical axis)» OR «TIA (thoracic inlet angle)» (Lee et al., J Spinal Disord Tech 25(2):E41-E47, 2012) OR «SCA (spino-cranial angle)». Exclusion criteria were purely post-operative and cadaveric analysis, studies performed with CT scan or MRI, studies on adolescent idiopathic scoliosis, traumatology studies and no standing analysis of the cervical spine. Relevance was confirmed by investigators if cervical parameters was a major criteria of the study.Results: 138 articles were found by the electronic search. After complete evaluation 20 articles were selected. The large majority of papers used the same parameters C2_C7 lordosis, C2-C7 SVA, T1 slope or C7 slope and T1 slope/cervical lordosis mismatch. Janusz reported a new parameter using a retrospective cohort of patient with cervical radiculopathy: the TIA (thoracic inlet angle). Le Huec reported an other new parameter based on a prospective study of asymptomatic volunteer: the spino-cranial angle (SCA). This parameter is highly correlated with the C7 slope and the cervical lordosis. Other studies reported parameters that are more global balance analysis including the cervical spine than cervical spine balance itself.Conclusion: The most important parameters to analyse the cervical sagittal balance according to the literature available today for good clinical outcomes are the following: C7 or T1 slope, average value 20°, must not be higher than 40°. cSVA must not be less than 40°C (mean value 20 mm). SCA (spine cranial angle) must stay in a norm (83° ± 9°). Future studies should focus on those three parameters to analyse and compare pre and post op data and to correlate the results with the quality of life improvement. [ABSTRACT FROM AUTHOR]

Purpose: In this article, we summarize our work on understanding the influence of cervical sagittal malalignment on the mechanics of the cervical spine.Methods: Biomechanical studies were performed using an ex vivo laboratory model to study the kinematic and kinetic response of human cervical spine specimens in the setting of cervical sagittal imbalance. The model allowed controlled variations of C2-C7 Sagittal Vertical Alignment (C2-C7 SVA) and T1-Slope so that clinically relevant sagittally malaligned profiles could be prescribed, while maintaining horizontal gaze, and their biomechanical consequences studied.Results: Our results demonstrated that increasing C2-C7 SVA caused flexion of lower cervical (C2-C7) segments and hyperextension of suboccipital (C0-C1-C2) segments to maintain horizontal gaze. An increase in C2-C7 SVA increased the lower cervical neural foraminal areas. Conversely, increasing T1-slope predominantly influenced subaxial cervical lordosis and, as a result, decreased cervical neural foraminal areas. Therefore, we believe patients with increased upper thoracic kyphosis and radicular symptoms may respond with increased forward head posture (FHP) as a compensatory mechanism to increase their lower cervical neural foraminal area and alleviate nerve root compression as well as reduce the burden on posterior muscles and soft and bony structures of the cervical spine. Increasing FHP (i.e., increased C2-C7 SVA) was associated with shortening of the cervical flexors and occipital extensors and lengthening of the cervical extensors and occipital flexors, which corresponds to C2-C7 flexion and C0-C2 extension. The greatest shortening occurred in the suboccipital muscles, suggesting considerable load bearing of these muscles during chronic FHP. Regardless, there was no evidence of nerve compression within the suboccipital triangle. Finally, cervical sagittal imbalance may play a role in exacerbating adjacent segment pathomechanics after multilevel cervical fusion and should be considered during surgical planning.Conclusions: The results of our biomechanical studies have improved our understanding of the impact of cervical sagittal malalignment on pathomechanics of the cervical spine. We believe this improved understanding will assist in clinical decision-making. [ABSTRACT FROM AUTHOR]

Study Design: Retrospective study.Objective: To assess the long-term relationship between sagittal alignment of the cervical spine and patient-reported health-related quality-of-life (HRQOL) scores after multilevel posterior cervical fusion, and to explore whether an analog of T1 slope minus C2-C7 lordosis ('T1S-CL') impacts on patients' clinical outcomes.Background: A 6-month follow-up study demonstrated that, similar to the thoracolumbar spine, the severity of disability increases with sagittal malalignment after cervical reconstruction surgery.Methods: From 2007 to 2014, 31 consecutive patients having multilevel posterior cervical fusion for cervical stenosis, myelopathy, and deformities met inclusion criteria. To determine the true impact of the alignment on HRQOL, patients who have pseudarthrosis, a misplaced screw, junctional pathologies, or adjacent level disc herniation were excluded. Radiographic measurements included: C0-C2 lordosis, C2-C7 lordosis, C2-C7 sagittal vertical axis (SVA), T1 slope, and T1S-CL. Pearson correlation coefficients were calculated between pairs of radiographic measures and HRQOL.Results: C2-C7 SVA positively correlated with neck disability index (NDI) scores (r = 0.550). For significant correlations between C2-C7 SVA and NDI scores, regression models predicted a threshold C2-C7 SVA value of 43.5 mm, beyond which correlations were most significant. The T1S-CL also correlated positively with C2-C7 SVA and NDI scores (r = 0.827 and r = 0.618, respectively). Results of the regression analysis indicated that a C2-C7 SVA value of 43.5 mm corresponded to a T1S-CL value of 22.2°.Conclusion: This minimum 2-year follow-up study showed that disability of the neck increased with cervical sagittal malalignment after surgical reconstruction and a greater T1S-CL mismatch was associated with a greater degree of cervical malalignment. Specifically, a T1S-CL mismatch greater than 22.2° corresponded to severe disability (NDI>25) and positive cervical sagittal malalignment, defined as C2-C7 SVA greater than 43.5 mm.Level Of Evidence: 4. [ABSTRACT FROM AUTHOR]

Study Design: Retrospective study.Objective: To determine whether postoperative pseudarthrosis can be predicted from specific preoperative radiograph measurements.Summary Of Background Data: Various factors reportedly influence the occurrence of pseudarthrosis after anterior cervical discectomy and fusion (ACDF). However, to our knowledge, there are no reports on the relationships between preoperative radiographic parameters and pseudarthrosis.Methods: We analyzed 84 consecutive patients (45 males, 39 females, mean age, 58.9 ± 11.2 yrs) who underwent ACDF. In all patients, allografts filled with local chip bone were inserted after discectomy and anterior plating was performed. On preoperative plain radiographs, we analyzed C2-C7 sagittal vertical axis, T1 sagittal slope, segmental motion, global cervical motion, and location of fusion segments. Pseudarthrosis was diagnosed as interspinous motion >1 mm with superjacent interspinous motion ≥4 mm on magnified dynamic lateral radiographs. Multivariate logistic regression was used to analyze the risk factors for pseudarthrosis and the receiver operating characteristic (ROC) curve was used to define a cutoff value.Results: One hundred and twenty-five segments from 84 patients were included. The pseudarthrosis rate was 29% based on number of patients (24/84) and 20% based on number of segments (25/125). Multilevel surgery and segments at the lowest levels showed higher pseudarthrosis rates (P = 0.01). Per multivariate logistic regression analysis, greater preoperative segmental motion, greater preoperative T1 sagittal slope, and C6-7 segments were associated with a higher risk of pseudarthrosis (all P < 0.05). A segmental motion cutoff value of 12° demonstrated pseudarthrosis with sensitivity of 87%, specificity of 84%, and area under the curve of 0.899, indicating moderate accuracy.Conclusion: Greater preoperative segmental motion, greater preoperative T1 sagittal slope, and lower fusion levels could be risk factors for pseudarthrosis following ACDF. Preoperative segmental motion >12° is likely to be an important indicator of the development of pseudarthrosis.Level Of Evidence: 3. [ABSTRACT FROM AUTHOR]

Study Design: Comparative study of prospectively collected radiographic data.Objective: To predict physiological alignment of the cervical spine and study its morphology in different postures.Summary Of Background Data: There is increasing evidence that normal cervical spinal alignment may vary from lordosis to neutral to kyphosis, or form S-shaped or reverse S-shaped curves.Methods: Standing, erect sitting, and natural sitting whole-spine radiographs were obtained from 26 consecutive patients without cervical spine pathology. Sagittal vertical axis (SVA), global cervical lordosis, lower cervical alignment C4-T1, C0-C2 angle, T1 slope, C0-C7 SVA and C2-7SVA, SVA, thoracic kyphosis, thoracolumbar junctional angle, lumbar lordosis, sacral slope, pelvic tilt, and pelvic incidence were measured. Statistical analysis was performed to elucidate differences in cervical alignment for all postures. Predictive values of T1 slope and SVA for cervical kyphosis were evaluated.Results: Most patients (73.0%) do not have lordotic cervical alignment (C2-C7) upon standing (mean -0.6, standard deviation 11.1°). Lordosis increases significantly when transitioning from standing to erect sitting, as well as from erect to natural sitting (mean -17.2, standard deviation 12.1°). Transition from standing to natural sitting also produces concomitant increases in SVA (-8.8-65.2 mm) and T1-slope (17.4°-30.2°). T1 slope and SVA measured during standing significantly predicts angular cervical spine alignment in the same position. SVA < 10 mm significantly predicts C4-C7 kyphosis (P < 0.001), and to a lesser extent, C2-C7 kyphosis (P = 0.02). T1 slope <20° is both predictive of C2-C7 and C4-7 kyphosis (P = 0.001 and P = 0.023, respectively). For global cervical Cobb angle, T1 slope seems to be a more significant predictor of kyphosis than SVA (odds ratio 17.33, P = 0.001 vs odds ratio 11.67, P = 0.02, respectively).Conclusion: The cervical spine has variable normal morphology. Key determinants of its alignment include SVA and T1 slope. Lordotic correction of the cervical spine is not always physiological and thus correction targets should be individualized.Level Of Evidence: 3. [ABSTRACT FROM AUTHOR]

Background Context: T1 slope is a novel thoracic parameter used to assess cervical spine sagittal balance. Thoracic index (TI) parameters including T1 slope and cervical sagittal alignment parameters may play an important role in degenerative cervical spondylolisthesis (DCS). Current literature regarding the relationship between TI and cervical sagittal alignment parameters in patients with DCS is limited.Purpose: (1) To evaluate the T1 slope, cervical sagittal alignment, and thoracic inlet parameter in patients with DCS using kinematic magnetic resonance imaging (kMRI), and (2) to find a correlation between the T1 slope, TI, and other cervical sagittal parameters in patients with DCS.Design/setting: Retrospective kMRI study, Level III.Patient Sample: Fifty-two patients with DCS from 1,128 patients from a cervical kMRI database.Outcome Measures: T1 slope, C2-C7 angle, sagittal vertical axis C2-C7 (SVA C2-C7), cranial tilt, cervical tilt, neck tilt, and thoracic inlet angle (TIA).Methods: Cervical spine kMRIs of 52 patients with DCS (mean age 51.7±standard deviation) were analyzed in neutral, flexion, and extension positions. Patients with DCS were divided into two groups: anterolisthesis (N=33) and retrolisthesis (N=19). Each listhesis group was subclassified into grade 1 (slip 2-3 mm) and grade 2 (slip>3 mm).Results: Grade 2 retrolisthesis had the largest T1 slope followed by grade 1 retrolisthesis, grade 2 anterolisthesis, and grade 1 anterolisthesis. Significant differences were found between the anterolisthesis and the retrolisthesis groups in the neutral position (p=.025). The flexion position had the largest T1 slope and showed a significant difference with anterolisthesis in the neutral position (p=.041). Sagittal vertical axis C2-C7 showed strong correlation with cranial tilt in all DCS groups and all positions.Conclusions: In our study, T1 slope was larger in grade 2 DCS, and the retrolisthesis group had larger T1 slope than the anterolisthesis group. Presence of larger T1 slope was significantly correlated with larger cervical lordosis curvature. Furthermore, cranial tilt was strongly correlated with SVA C2-C7. [ABSTRACT FROM AUTHOR]

Purpose: To analyse pre-operative and post-operative changes of cervical sagittal alignment (CSA) in Scheuermann's kyphosis (SK) patients.Methods: 64 SK and 33 control patients were retrospectively reviewed. Whole spine X-rays obtained at pre-op, 3 months post-op and at latest follow-up were reviewed and ten separate CSA radiological parameters were measured. Patients were divided in three groups: thoracic SK (TK group, apex T6-T9, n = 40), thoracolumbar SK (TLK group, apex T10-T12, n = 24), and controls.Results: Pre-operative C2-C7 lordosis was 21.1° ± 8.1°(TK), 6.1° ± 5.0°(TLK), and 11.4° ± 8.3° in control group and correlated significantly with T1 slope in both SK groups (r = 0.640, r = 0.772). Pre-operative T1 slope was dependent on deformity type, thoracic kyphosis (TK, β = 0.445), and lumbar lordosis (LL, β = -0.354). At final follow-up C2-C7 lordosis decreased to 15.7° ± 5.5° in TK, and increased to 12.1° ± 4.1° in TLK group. C2-C7 lordosis changes linearly correlated with T1 slope changes post-operatively (r = 0.721). Post-operative T1 slope showed linear correlation with post-operative changes in TK (β = 0.728) and pelvic tilt (PT, β = 0.539) in TK, and LL (β = -0.669), thoracolumbar kyphosis (TLK, β = -0.434), and PT (β = 0.760) in TLK group.Conclusions: Our study suggests that SK is not a homogenous group of patients. Two patterns of pre- and post-operative CSA are demonstrated in TK and TLK groups. T1 slope is the most important parameter in determining pre-operative CSA and correlates with other regional anatomical parameters (TK and LL). Post-operative CSA adaptations also correlate with T1 slope post-operative changes. However, post-surgical T1 slope correlates with different parameters in the two SK groups (TK and PT in TK group; TLK, LL, and PT in TLK group). [ABSTRACT FROM AUTHOR]

Background: This retrospective study investigated an association between preoperative T1 slope and surgical and adjacent segment degeneration (SASD) after Bryan cervical disc arthroplasty (BCDA) in patients with cervical degenerative disc disease.Methods: Based on preoperative standing lateral radiographs, 90 patients were classified according to T1 slope that was higher or lower than the 50th percentile (high T1 or low T1, 28 and 62 patients, respectively). Patients were also classified as SASD or non-SASD (38 and 52 patients, respectively) determined by radiographs at final follow-up. Visual analog scale (VAS) and Neck Disability Index (NDI) scores for neck and arm pain were noted, and changes in the sagittal alignment of the cervical spine (SACS), functional spinal unit (FSU) angle, and FSU range of motion (ROM) were also noted. Univariate and multivariate logistic regression analyses were performed to determine the risk factors for SASD.Results: The overall rate of SASD was 42.2% (38/90). The SACS, FSU angle, FSU ROM, and SASD rates of the high T1 and low T1 slope groups were significantly different at the last follow-up. The NDI and VAS scores of the high T1 slope group were significantly greater than those of the low T1 slope. The multivariate logistic regression analysis showed that high T1 slope and endplate coverage discrepancy (ie, residual space behind the prosthesis) were significant risk factors for SASD after BCDA.Conclusion: High T1 slope and endplate coverage discrepancy were associated with SASD after BCDA. Patients with a high preoperative T1 slope have a smaller FSU angle and more neck pain after BCDA. [ABSTRACT FROM AUTHOR]

Background: The purpose of the research was to evaluate cervical sagittal parameters on magnetic resonance imaging (MRI) in patients with Modic changes and its impact on axial neck pain. Methods: This study consisted of 266 consecutive asymptomatic or symptomatic patients with Modic changes, whose average age was 50.9±12.6 years from January 2015 to December 2016. Cervical sagittal parameters included sagittal alignment of the cervical spine (SACS), T1 slope, thoracic inlet angle (TIA), and neck tilt (NT). The Modic changes group was compared with an asymptomatic control group of 338 age- and gender-matched adults. Results: In the Modic changes group, T1 slope was significantly higher (25.8°±6.3°) compared with that in the control group (22.5°±6.8°) (P=0.000). However, there was no significant difference of the NT, TIA, and SACS between the two groups. Patients in the Modic changes group were more likely to have experienced historical axial neck pain compared with the control group (P=0.000). With regard to the disc degeneration, it indicated that the disc in the Modic changes group had more severe disc degeneration (P=0.032). Conclusion: T1 slope in the Modic changes group was significantly higher compared to that of the control group. The findings suggested that a higher T1 slope with broken compensation of cervical sagittal mechanism may be associated with the development of Modic changes in the cervical spine. [ABSTRACT FROM AUTHOR]

Background: Many patients undergoing laminoplasty develop postoperative loss of cervical lordosis or kyphotic alignment of cervical spine despite sufficient preoperative lordosis. This results in poor surgical outcomes. Methods: Here, we reviewed the relationship between multiple radiological parameters of cervical alignment that correlated with postoperative loss of cervical lordosis in patients undergoing laminoplasty. Results: Patient with a high T1 slope (T1S) has more lordotic alignment of the cervical spine preoperatively and is at increased risk for the loss of cervical lordosis postlaminoplasty. Those with lower values of difference between T1S and Cobb's angle (T1S-CL) and CL-T1S ratio have higher risks of developing a loss of the cervical lordosis postoperatively. Alternatively, C2-C7 lordosis, neck tilt, cervical range of motion, and thoracic kyphosis had no role in predicting the postlaminoplasty kyphosis. Conclusion: Among various radiological parameters, the preoperative T1S is the most important factor in predicting the postoperative loss of the cervical lordosis/alignment following laminoplasty. [ABSTRACT FROM AUTHOR]

Study Design: A retrospective radiologic study., Objectives: To identify age-associated changes in T1 slope (T1S) and C7 slope (C7S), as well as the difference between T1S and C7S (△, which was defined as T1S minus C7S) and to explore the cervical morphology that C7S can be the most accurate alternative for the invisible T1S., Methods: 625 asymptomatic Chinese volunteers received cervical lateral radiographs from August 2021 to May 2022. Occipito-C2 angle (O-C2), C2-7 angle (C2-7), cranial arch, caudal arch, C7S, and T1S were examined. Thereafter, the △ was established. The correlations among T1S, C7S, △ and other cervical sagittal parameters, and between age and other cervical sagittal parameters were evaluated with the Pearson correlation coefficient analysis. Then, analysis of variance (ANOVA) was conducted to compare variations in cervical sagittal parameters among volunteers aged 40 to 59 years, 60 to 64 years, 65 to 69 years, 70 to 74 years, and ≥75 years of age, and among volunteers with 1 lordotic morphology, 2 lordotic morphology, straight morphology, kyphotic morphology, 1 sigmoid morphology, and 2 sigmoid morphology. Linear regression modeling of the correlation between C7S and T1S in various cervical alignment patterns was then established., Results: △ had the strongest correlation with caudal arch ( r = .646), and weakest correlation with cranial arch ( r = -.082). Age was significantly correlated with T1S ( r = .250), C7S ( r = .244), and △ ( r = .112). Among them, △ was stable until 74 years after which it showed an elevation from 3.3° in the group 70-74 years to 4.1° in the group over 75 years. Moreover, there was marked variation between T1S and C7S at 1 lordotic, 2 lordotic, straight and 2 sigmoid alignment patterns, but no difference was seen between T1S and C7S at kyphotic and 1 sigmoid alignment patterns., Conclusions: There was a progressive increase in T1S, C7S, and △ with age. Linear regression equations for accurate prediction of T1S were developed based on the C7S in 1 lordotic, 2 lordotic, straight and 2 sigmoid alignment patterns. C7S may be a reliable proxy for T1S in kyphotic and 1 sigmoid alignment patterns., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Study Design: A retrospective review.Objective: We investigated the longitudinal change of cervical alignment parameters including C2-7 lordosis, C2-7 sagittal vertical axis (SVA), T1 slope, and segmental angle (SA) after two-level anterior cervical discectomy and fusion (ACDF).Summary Of Background Data: Cervical alignment may influence postoperative clinical outcomes. Several studies have suggested that cervical alignment may serve as a parameter for assessing cervical deformities similar to those used to assess thoracolumbar spine deformities. However, to our knowledge, no studies have investigated the effect of ACDF on cervical sagittal alignment.Methods: We enrolled patients whom had ACDF, 23 patients with stand-alone cages and 22 with plate augmentation. Radiologic parameters including C2-7 lordosis, C2-7 SVA, T1 slope, and SA at the operated level were evaluated preoperatively and at 1 week and 6 months postoperatively. The differences between preoperative and 6-month postoperative parameter values were designated as Δvalues. T1S-CL was calculated as the T1 slope minus C2-7 lordosis. Clinical outcome were obtained by the Visual Analog Scale (VAS) and the Neck Disability Index (NDI).Results: ΔC2-7 SVA was significantly correlated with ΔT1S-CL and ΔC2-7 lordosis. ΔC2-7 lordosis was significantly correlated with ΔSA. ΔC2-7 lordosis had a significantly greater impact on ΔT1S-CL than did ΔT1 slope. The ΔSA and ΔC2-7 lordosis in the ACDF-plate were significantly higher than those in the in ACDF-cage. ΔT1S-CL and ΔC2-7 SVA in the ACDF-plate were significantly lower than those in the ACDF-cage.Conclusion: C2-7 SVA after two-level ACDF was affected more significantly by the SA and C2-7 angle than by the T1 slope. Two-level ACDF with plate restored more cervical lordosis by obtaining more segmental lordosis at the operated level and was more effective in terms of cervical alignment compared with ACDF using stand-alone cages.Level Of Evidence: 3. [ABSTRACT FROM AUTHOR]

Study Design: A retrospective study of surgical outcomes of adult spinal deformity (ASD) cases.Objective: The aim of the study was to investigate the effects of high T1 slope (T1S) on surgical outcomes in patients with ASD.Summary Of Background Data: Few studies have evaluated the surgical outcomes of patients with ASD with cervical deformities.Methods: Eighty-eight patients with ASD who underwent posterior spinal corrective fusion were assigned to either group A (T1S <40°) or group B (T1S ≥40°). Whole-spine standing radiographs of both groups were preoperatively assessed: at first standing after the surgery and at 1 and 2 years postoperatively.Results: There were 56 patients in group A and 32 in group B. The preoperative C7 sagittal vertical axis (SVA) improved from 61 to 41 mm in group A and from 161 to 64 mm in group B at first standing after the surgery. C7 SVA at 2 years after the surgery was, however, 57 mm in group A and 98 mm in group B because of correction loss (P = 0.003). T1S measurements before and immediately after the surgery and 2 years after the surgery were, however, 25°, 23°, and 27° in group A and 53°, 36°, and 41° in group B, respectively. There were no significant differences among measurements in group A. Those in group B were, however, significantly improved in the first standing, but T1S of 40° or higher deteriorated toward 2 years after the surgery.Conclusion: Among patients with T1S of 40° or higher, C7 SVA improved immediately after the surgery but worsened at 2 years after the surgery. These results suggested that cervicothoracic parameters were important predictors of correction loss.Level Of Evidence: 4. [ABSTRACT FROM AUTHOR]

Purpose: Recent studies suggest that cervical lordosis is influenced by thoracic kyphosis and that T1 slope is a key factor determining cervical sagittal alignment. However, no previous study has investigated the influence of cervical kyphosis correction on the remaining spinopelvic balance. The purpose of this study is to assess the effect of surgical correction of cervical kyphosis on thoraco-lumbo-pelvic alignment.Methods: Fifty-five patients who underwent ≥2 level cervical fusions for cervical radiculopathy or myelopathy were included. All patients had regional or global cervical kyphosis, which was surgically corrected into lordosis. Radiographic measurements were made using whole spine standing lateral radigraphs pre- and postoperatively to analyze various sagittal parameters. The visual analogue scale (VAS) for neck pain and the neck disability index (NDI) were calculated. The paired t test was used to compare pre- and post-operative radiographic measures and functional scores. Correlations between changes in cervical sagittal parameters and those of other sagittal parameters were analyzed by Pearson's correlation method.Results: Preoperative kyphosis (11.4° ± 8.3°) was corrected into lordosis (-9.3° ± 8.1°). The average fusion levels were 3.3 ± 1.0. With increasing C2-C7 lordosis after surgery (from -3.4° ± 10.0° to -15° ± 7.9°), C0-C2 lordosis decreased significantly (from -34.6° ± 8.2° to -27.7° ± 8.0°) (P < 0.001). Thoracic kyphosis (from 24.8 ± 13.9° to 33.5 ± 11.9°) and T1 slope (from 12.8° ± 7.9° to 20.4° ± 5.2°) significantly increased after surgery (P < 0.001). However, other parameters did not significantly change (P > 0.05). Neck pain VAS and NDI scores (31.8 ± 16.2) significantly improved (P < 0.001). The degree of increasing C2-C7 lordosis by surgical correction was negatively correlated with changes in both thoracic kyphosis and T1 slope (P < 0.01).Conclusions: Surgical correction of cervical kyphosis affects T1 slope and thoracic kyphosis, but not lumbo-pelvic alignment. These results indicate that the compensatory mechanisms to minimize positive sagittal malalignment of the head may occur mainly in the thoracic, and not in the lumbosacral spine. [ABSTRACT FROM AUTHOR]

Study Design: Retrospective study. Objective: To assess the relationship between sagittal alignment of the cervical spine and patient-reported health-related quality-of-life scores following multilevel posterior cervical fusion, and to explore whether an analogous relationship exists in the cervical spine using T1 slope minus C2-C7 lordosis (T1S-CL). Summary Of Background Data: A recent study demonstrated that, similar to the thoracolumbar spine, the severity of disability increases with sagittal malalignment following cervical reconstruction surgery. Methods: From 2007 to 2013, 38 consecutive patients underwent multilevel posterior cervical fusion for cervical stenosis, myelopathy, and deformities. Radiographic measurements included C0-C2 lordosis, C2-C7 lordosis, C2-C7 sagittal vertical axis (SVA), T1 slope, and T1S-CL. Pearson correlation coefficients were calculated between pairs of radiographic measures and health-related quality-of-life. Results: C2-C7 SVA positively correlated with neck disability index (NDI) scores (r = 0.495). C2-C7 lordosis (P = 0.001) and T1S-CL (P = 0.002) changes correlated with NDI score changes after surgery. For significant correlations between C2-C7 SVA and NDI scores, regression models predicted a threshold C2-C7 SVA value of 50 mm, beyond which correlations were most significant. The T1S-CL also correlated positively with C2-C7 SVA and NDI scores (r = 0.871 and r = 0.470, respectively). Results of the regression analysis indicated that a C2-C7 SVA value of 50 mm corresponded to a T1S-CL value of 26.1°. Conclusion: This study showed that disability of the neck increased with cervical sagittal malalignment following surgical reconstruction and a greater T1S-CL mismatch was associated with a greater degree of cervical malalignment. Specifically, a mismatch greater than 26.1° corresponded to positive cervical sagittal malalignment, defined as C2-C7 SVA greater than 50 mm. Level Of Evidence: 3. [ABSTRACT FROM AUTHOR]

Objective: To determine whether C 7 angles (C 7 slope, C 7 S) could replace T 1 angles (T 1 slope, T 1 S) by correlation analysis of T 1 S and C 7 S., Methods: A total of 442 patients from July 2015 to July 2020 in outpatient and inpatient department were enrolled retrospectively, and 259 patients who could identify the upper endplate of T 1 were screened out . Of them, there were 145 males and 114 females, aged from 20 to 83 years old with an average of (58.6±11.2) years, including 163 patients with cervical spine surgery and 96 non-surgical patients. Patients were stratified by sex, age, cervical kyphosis, cervical alignment imbalance, and cervical spine surgery. These 259 patients included 145 cases in the male group, 114 cases in the female group;76 cases in the youth group (<40 years old), 109 cases in the middle-aged group (40 to 60 years old), and 74 cases in the elderly group(>60 years old); 92 cases in the cervical kyphosis group, 167 cases in the non-kyphosis group;51 cases in the cervical sequence imbalance group, 208 cases in the non-imbalance group;163 cases in the cervical surgery group, 96 cases in the non-operation group. The correlations of C 7 S and T 1 S in various modalities groups were analyzed., Results: Of 442 patients, the recognition rate of upper endplate of T 1 was 58.6%(259/442), and that of C 7 was 90.7%. The mean T 1 S and C 7 S of the 259 patients were (24.5±8.0)° [(25.9±7.7)° in the male group and (23.7±6.9)° in the female group] and (20.8±7.3)° [(22.5±7.5)° in the male group and(19.7±5.8)° in the female group], respectively. The total correlation coefficient between C 7 S and T 1 S was r =0.89, R 2 =0.79, and the linear regression equation was T 1 S=0.91×C 7 S+4.35. In the above general information and the grouping of deformity factors, T 1 S was highly correlated with C 7 S( r value 0.85 to 0.92, P <0.05)., Conclusion: There is a high correlation between T 1 S and C 7 S in different factor groups. For cases where T 1 S cannot be measured, C 7 S can be used to provide guidance and reference for evaluating the sagittal balance of the spine, analyzing the condition, and formulating surgical plans.

Study Design: Retrospective cross-sectional study. Objective: Determine if pre-operative cervical alignment serves as an independent predictor of pre-operative disability as measured by the neck disability index (NDI). Summary Of Background Data: There is growing interest in the relationship between cervical sagittal alignment and clinical outcomes. While prior studies have shown that C2-C7 sagittal vertical axis (SVA) correlates with worse NDI scores in post-operative patients, no studies to date have examined the impact of cervical sagittal parameters on pre-operative disability in patients indicated for surgery. Methods: Patients with pre-operative standing cervical radiographs, no prior cervical spine procedures and a pre-operative NDI score were identified. Measurements were made by two observers at two different time points. Parameters measured were: Occiput-C2 angle, C1-C2 angle, C2-C7 angle (CL), T1 slope (TS), TS minus CL (TS-CL), C2-C7 SVA, and C1-C7 SVA. Intra- and inter-observer reliability was calculated. Subgroup analyses of myelopathy vs. radiculopathy and deformity vs. no deformity was performed. A multivariate linear regression was performed. Results: Ninety patients were included. Indications included cervical myelopathy (n = 63), cervical radiculopathy (n = 25), cervical stenosis (n = 9), and others (n = 5). CL averaged -13.7 ± 14.9 degrees. TS averaged 30.7 ± 10.4 degrees and C2-C7 SVA averaged 28.8 ± 13.2  mm. Intra- and inter-observer reliability was good to excellent (ICC > 0.8). Increasing CL (r = 0.277, P = 0.009), increasing TS (r = -0.273, P = 0.011) and increasing TS-CL (r = -0.301, P = 0.005) were correlated with decreasing NDI. CL, TS and TS-CL were also strongly correlated with each other (r > 0.65, P < 0.001 for all bivariate correlations). A multivariate regression adjusting for age and indication showed TS-CL (P = 0.040) and C2-C7 SVA (P = 0.015) were independent predictors of NDI. Conclusion: Increasing CL, increasing TS and increasing TS-CL are correlated with decreasing pre-operative NDI. Low TS-CL and high C2-C7 SVA are independent predictors of high pre-operative NDI. Level Of Evidence: 4. [ABSTRACT FROM AUTHOR]

Background Context: Laminoplasty is a major surgical method used to treat patients with cervical ossification of the posterior longitudinal ligament (OPLL). Sometimes, patients with cervical OPLL demonstrate postoperative kyphosis despite sufficient preoperative lordosis. Recently, the impact of T1 slope has emerged as a predictor of kyphotic alignment change after laminoplasty. However, the relationship between T1 slope and postoperative cervical alignment change is not yet fully established.Purpose: The goals of the present study were to investigate the relationship between T1 slope and loss of cervical lordosis (LCL), and to identify the role of T1 slope as a predictor of postoperative kyphosis after laminoplasty in patients with OPLL.Study Design: This is a retrospective case study.Patient Sample: Between January 2011 and January 2012, 64 consecutive patients who underwent cervical laminoplasty for OPLL were enrolled (male:female ratio=47:17; mean age=55.9 years). Cervical spine lateral radiographs in neutral, flexion, and extension were taken before surgery and at 2-year follow-up.Outcome Measures: The C2-C7 Cobb angle, cervical range of motion (ROM), T1 slope, neck tilt, and C2-C7 sagittal vertical axis (SVA) were measured from lateral radiographs of the cervical spine preoperatively and postoperatively at 2-year follow-up.Methods: Patients were divided into two groups according to preoperative T1 slope, and the postoperative cervical alignment change was compared between the groups. Postoperative kyphosis and LCL incidence were also evaluated at 2-year follow-up. The relationships between postoperative cervical alignment change and preoperative variables, including age, T1 slope, cervical ROM, C2-C7 SVA, and T1 slope minus C2-C7 Cobb angle (T1S-CL), were investigated.Results: Patients were divided into two groups above and below median preoperative T1 slope (23.2°). There were no differences in age, sex, type of OPLL, or operation level between the two groups. Patients with higher preoperative T1 slope demonstrated significantly more lordotic preoperative cervical alignment (p=.001). Patients with higher preoperative T1 slope were more likely to exhibit postoperative LCL (p=.03), and when it occurred the degree of LCL was greater (p=.06). In multiple linear regression analysis, higher T1 slope (B=0.414, p=.04) and lower T1S-CL (B=-0.412, p=.03) were significantly associated with more postoperative LCL. In spite of these results, postoperative kyphosis did not occur more frequently in patients with higher T1 slope (p=.64).Conclusions: Patients with higher T1 slope had more lordotic curvature before surgery and demonstrated more LCL at 2-year follow-up. Cervical alignment was compromised after laminoplasty, and the degree of LCL was correlated with preoperative T1 slope. After laminoplasty for cervical OPLL, patients with higher T1 slope tended to exhibit a greater LCL yet did not drift into frank postoperative kyphosis. [ABSTRACT FROM AUTHOR]

Study Design: A retrospective kinematic magnetic resonance imaging (kMRI) study. Objective: To evaluate the utility of kMRI in determining the relationship between cervical sagittal balance and TI alignment. Summary Of Background Data: Thoracic inlet parameters play an important role in cervical spine sagittal balance. However, most of the literature is based on lower resolution cervical X-rays or CT scans in the supine position. Methods: Cervical spine kMRI of 83 patients with degenerative cervical spine conditions (20-68 yr of age) was analyzed for: (1) cervical spine parameters: C2-C7 angle, C2-C7 sagittal vertical axis (SVA), cranial tilt, and cervical tilt; and (2) T1 parameters: thoracic inlet angle (TIA), T1 slope, and neck tilt (NT). Multiple logistic regression analysis and Pearson correlation coefficients were performed. Results: The mean TIA, T1 slope, and NT were 78.0, 33.2, and 44.8°, respectively. The mean C2-7 angle, SVA of C2-C7, cervical tilt, and cranial tilt were -15.4°, 22.0 mm, 18.1°, and 15.1°, respectively. The ratio of cervical:cranial tilt was maintained as 55:45%. A significant correlation was found between the C2-C7 angle and T1 slope (r = 0.731), TIA and C2-C7 angle (r = 0.406), cervical tilt with C2-C7 angle (r = 0.671), T1 slope with TIA (r = 0.429), TIA with neck tilt (r = 0.733), TIA with cervical tilt (r = 0.377), SVA C2-C7 with cervical tilt (r = -0.480), SVA C2-C7 with cranial tilt (r = 0.912), and C2-7 SVA with the ratio of cranial tilt to cervical tilt (r = 0.694). Conclusion: An individual with a large T1 slope required large cervical lordosis to preserve physiologic sagittal balance of the cervical spine. Cranial tilt was the cervical parameter most strongly correlated with SVA C2-C7, and thus may be a good parameter to assess decompensation of cervical sagittal balance. Level Of Evidence: 3. [ABSTRACT FROM AUTHOR]