Acceptable Chin–Brow Vertical Angle for Neutral Position Radiography: Preliminary Analyses Based on Parameters of the Whole Sagittal Spine of an Asymptomatic Chinese Population

Horizontal Gaze Assessment: An Extensive Narrative Review

OBJECTIVE

Bipedalism was a significant milestone in the evolutionary development of Homo sapiens sapiens, influencing neocortical evolution and subsequent behavioral changes. Coordinated visual and sensory inputs are crucial for posture, environmental interaction, and surgical planning, with horizontal gaze being a pivotal parameter. This narrative review aims to explore various geometric measures used to assess horizontal gaze in patients, highlighting their applications in surgical planning.

METHODS

A literature review was conducted in indexed databases using Mesh terms like "Cervical Vertebrae" and "Visual Fields" along with keywords such as "horizontal gaze" and "sagittal spine parameters." Among 477 initially identified articles, 41 were selected for inclusion after rigorous filtering.

RESULTS

The most recognized method for assessing horizontal gaze is the Chin Brow Vertical Angle (CBVA), initially described in patients with ankylosing spondylitis. Clinical photography is employed as a tool for CBVA calculation, while other measures like McGregor slope and Slope of the Line of Sight have been considered as alternatives to CBVA. Each method presents its unique advantages and limitations.

CONCLUSIONS

This review highlights the need for further research into horizontal gaze measurement methods. Developing novel approaches to determine horizontal gaze can significantly enhance surgical planning and, consequently, improve patient outcomes. The ongoing exploration of these geometric measures offers promising prospects for advancing the field and optimizing patient care.

Prevalence and risk factors of occupational neck pain in Chinese male fighter pilots: a cross-sectional study based on questionnaire and cervical sagittal alignment

Background

Neck pain (NP) is a common musculoskeletal disorder among fighter pilots and has become a rising concern due to its detrimental impact on military combat effectiveness. The occurrence of NP is influenced by a variety of factors, but less attention has been paid to the association of NP with demographic, occupational, and cervical sagittal characteristics in this group. This study aimed to investigate the prevalence and risk factors of NP in Chinese male fighter pilots using a questionnaire and cervical sagittal measurements.

Methods

Demographic and flight-related data, as well as musculoskeletal pain information, were gathered from Chinese male fighter pilots via a self-report questionnaire. Cervical sagittal parameters were measured and subtypes were classified using standardized lateral cervical radiographs. Differences in various factors between the case and control groups were analyzed using t-tests or chi-square tests. Binary logistic regressions were conducted to explore potential risk factors contributing to NP. Predictors were presented as crude odds ratios (CORs) and adjusted odds ratios (AORs), along with their respective 95% confidence intervals (CIs).

Results

A total of 185 male fighter pilots were included in this cross-sectional study. Among them, 96 (51.9%) reported experiencing NP within the previous 12 months. The multivariate regression analysis revealed that continuous flight training (AOR: 4.695, 95% CI: 2.226-9.901, p < 0.001), shoulder pain (AOR: 11.891, 95% CI: 4.671-30.268, p < 0.001), and low back pain (AOR: 3.452, 95% CI: 1.600-7.446, p = 0.002) were significantly associated with NP.

Conclusion

The high 12-month prevalence of NP among Chinese male fighter pilots confirms the existence of this growing problem. Continuous flight training, shoulder pain, and low back pain have significant negative effects on pilots' neck health. Effective strategies are necessary to establish appropriate training schedules to reduce NP, and a more holistic perspective on musculoskeletal protection is needed. Given that spinal integrated balance and compensatory mechanisms may maintain individuals in a subclinical state, predicting the incidence of NP in fighter pilots based solely on sagittal characteristics in the cervical region may be inadequate.

Relationship between gait parameter and spinal sagittal profiles in asymptomatic subjects

BACKGROUND

To study the gait parameters in asymptomatic volunteers and investigate the correlation between the gait and several radiographic sagittal profiles.

METHODS

Asymptomatic volunteers (20-50 years of age) were included and allocated into three subgroups depending on pelvic incidence (low, normal, and high). Standing whole spine radiographs and gait analysis data were obtained. The Pearson Coefficient Correlation was used to determine the relationship between the gait and radiographic profiles.

RESULTS

A total of 55 volunteers (28 male and 27 females) were included. The mean age was 27.35 ± 6.37 years old. The average sacral slope (SS), pelvic tilt (PT), pelvic incidence (PI), and PI-LL mismatch (PI-LL) were 37.78 ± 6.59, 14.51 ± 9.19 degrees, and 52.29 ± 10.87 degrees and - 0.36 ± 11.41, respectively. The mean velocity and stride of all the volunteers were 119.00 ± 30.12 cm/s and 130.25 ± 7.72 cm, correspondingly. The correlation between each of the radiographical and gait parameters was low (ranging from - 0.24 to 0.26).

CONCLUSION

Gait parameters were not differenced significantly between each of the PI subgroups in asymptomatic volunteers. Spinal sagittal parameters also showed a low correlation with gait parameters.

Clinical Impact and Correlations of Odontoid Parameters Following Multilevel Posterior Cervical Fusion Surgery

OBJECTIVE

C2 slope (C2S), a cervical parameter mathematically approximated as T1 slope minus cervical lordosis (T1S-CL), predicts functional improvement in cervical deformity patients. Nonetheless, C2S is a positional parameter based only on the horizontal axis. The current study aims to introduce novel odontoid parameters and establish their relationships with patient-reported health-related quality of life (HRQoL).

METHODS

Lateral plain radiographs of 32 adults who underwent multilevel posterior cervical fusion were analyzed. The odontoid parameters included odontoid incidence (OI), C2S, odontoid tilt (OT), and gravity line-C2 distance (GL-C2), while the cervical parameters were the Cobb angle at C0-1, C1-2, C0-2, C2-7, C2-7 sagittal vertical axis (cSVA), T1 slope, and T1S-CL. The range of motion (ROM) of the occipito-atlantoaxial complex was measured in flexion and extension plain radiographs. Scores on the Neck Disability Index (NDI) and visual analogue scale (VAS) for axial neck (VASn) and arm pain were measured.

RESULTS

Compared to asymptomatic subjects, patients had larger C2S, cSVA, and T1S-CL, and smaller OT. Preoperatively, OI was significantly correlated with the ROM of C1-2 (r = 0.37, p < 0.05) and C0-2 (r = 0.46, p < 0.01). OT and C2S had significant correlations with the C0-1, C1-2, and C0-2 angles, GL-C2, and T1S-CL. Postoperative NDI scores were significantly correlated with OI (r = -0.40, p < 0.05) and OT (ρ = -0.37, p < 0.05). VASn was significantly correlated with GL-C2 (r = -0.35, p < 0.05).

CONCLUSION

The odontoid parameters were significantly correlated with established cervical parameters and HRQoL measures. OI is a constant parameter representing the individual's compensatory reservoir at the upper cervical spine.

The Difference of Sagittal Correction of Adult Subaxial Cervical Spine Surgery According to Age: A Retrospective Study

Objective

At present, the true sagittal alignment of the cervical spine is uncertain, resulting in no standard reference for subaxial cervical surgery. So, we aimed to explore the age difference of normal cervical sagittal alignment and to further investigate the mid‐and long‐term changes of sagittal alignment after subaxial cervical spine surgery.

Materials and Methods

This was a retrospective study and 1223 asymptomatic volunteers and 79 patients undergoing subaxial cervical spine surgery were retrospectively reviewed in total. Asymptomatic volunteers and patients were divided into six subgroups: 20–29, 30–39, 40–49, 50–59, 60–69 and ≥70 groups. The age difference and trend with age of cervical sagittal parameters of asymptomatic volunteers were assessed by cervical lateral radiography and analyzed by ANOVA test, and the regression equation of C2‐7 Cobb was established via multiple linear regression. Based on the C2‐7 Cobb regression equations of different ages, the theoretical value, deviation value, loss value of the C2‐7 Cobb, and JOA recovery rate of patients were calculated, and the correlation among the loss value, deviation value of the C2‐7 Cobb, and JOA recovery rate of the 79 patients was evaluated by Pearson correlation analysis.

Results

For the asymptomatic volunteers, the C0‐2 Cobb decreased gradually with increasing age. The C2‐7 Cobb, C2‐7 SVA, T1S, NT, and TIA increased gradually with increasing age. The CBVA fluctuated with increasing age. T1S demonstrated a moderate correlation with C2‐7 Cobb (r = 0.60, p < 0.01); C0‐2 Cobb, C2‐7 SVA, CBVA, and TIA demonstrated a fair correlation with C2‐7 Cobb (r = −0.30, −0.33, 0.41, 0.40, p < 0.01); age demonstrated a poor correlation with C2‐7 Cobb (r = 0.19, p < 0.01). The regression equations of C2‐7 Cobb were established using C0‐2 Cobb, C2‐7 SVA, CBVA, and T1S. For the patients with subaxial cervical spine surgery, the loss of C2‐7 Cobb was moderately correlated with the deviation of C2‐7 Cobb (r = 0.33, p < 0.01).

Conclusion

The age difference of cervical sagittal alignment was obvious, and the C2‐7 Cobb increased with age especially. The closer the postoperative C2‐7 Cobb was to the theoretical value of corresponding age, the smaller the loss of correction angle was, and the better the mid‐ and long‐term outcomes. The personalized sagittal reconstruction should be performed according to age difference for subaxial cervical spine surgery.

Odontoid Incidence: A Novel Cervical Parameter Influencing Cervical Alignment From Top to Bottom

Objective

By using angulation of the axis itself, this study aims to define and analyze odontoid incidence (OI) and odontoid tilt (OT) as novel cervical alignment parameters and investigate their correlations with cervical alignment.

Methods

Novel and existing parameters were measured with whole-spine lateral plain radiographs and EOS images of 42 adults without cervical symptoms. The correlations of OI, OT, C2 slope (C2S), and T1 slope (T1S) were calculated.

Results

The OI, OT, and C2S showed significant correlations with C2–7 angle (r = 0.43, r = -0.42, r = 0.62, respectively) and C0–2 angle (r = -0.33, r = 0.48, r = -0.61, respectively). OI, OT, T1S were independent predictors of the C2–7 angle in univariate regression analysis (adjusted-R² = 0.17, R² = 0.15, R² = 0.28, respectively). OI, OT, and T1S were independent predictors in the multivariable regression analysis with estimated standardized coefficients of 0.36, -0.67, -0.69, respectively (adjusted- R² = 0.80, p < 0.001). Regarding the C0–2 angle, OI and OT were independent predictors in the univariate regression analysis (adjusted-R² = 0.08, R² = 0.21, respectively).

Conclusion

OI, OT, and C2S had significant correlations with cervical alignment. As the pelvic incidence, the OI is the only anatomical and constant parameter that could be used as a reference point related to the cervical spine from the rostral end. The study results may serve as baseline data for further studies on the alignment and balance of the cervical spine.

Global Sagittal Balance of Spine in Asymptomatic Controls: A Systematic Review and Meta-Analysis

OBJECTIVE

To assess the global sagittal balance of spine (GSBS) in asymptomatic controls.

METHODS

PubMed, Scopus, Cochrane library, and Web of Science searched up to July 2020. Studies were screened for the GSB parameters including T1 pelvic angle (TPA), spinosacral angle (SSA), sagittal vertical axis (SVA), C7/sacrofemoral distance ratio (Barrey index), odontoid hip axis (OD-HA), and Full Balance Index (FBI) as measured in asymptomatic participants. A meta-analysis was performed to synthesize pooled estimates. Heterogeneity and publication bias were assessed.

RESULTS

Overall, 76 studies were identified including 12,169 participants (54.7% female) with mean age ranges from 12.0 to 72.9 years old. We used the Newcastle-Ottawa Scale (NOS) to evaluate the quality of studies included in this review. Begg's test did not indicate obvious publication bias. The pooled analysis reveals that the mean (standard deviation) normative values were: 1) age ˃18 years, SSA (°), 127.6 (0.89); SVA absolute value (millimeters), 13.1 (1.13); TPA (°), 9.8 (1.13); T1SPI (°), -4.3 (0.57); and Barrey index absolute value, 0.51 (0.3). The mean value of the OD-HA (°) was reported 2.9 (1.6), and the FBI average value was less than 5°. 2) Age ≤18 years, SSA (°), 132.1 (8.3); SVA absolute value (millimeters), 11.9 (2.0); and Barrey index, -0.7 (8.3). A significant difference was observed between the 2 age groups based on SVA and SSA.

CONCLUSIONS

This paper presents normative data on TPA, SSA, SVA, Barrey index, OD-HA, and FBI as a reference for evaluating/measuring a GSB of spine in asymptomatic controls.

Sagittal balance of the cervical spine: a systematic review and meta-analysis

PURPOSE

The purpose of this systematic review and meta-analysis was to compare the cervical sagittal parameters between patients with cervical spine disorder and asymptomatic controls.

METHODS

Two independent authors systematically searched online databases including Pubmed, Scopus, Cochrane library, and Web of Science up to June 2020. Cervical sagittal balance parameters, such as T1 slope, cervical SVA (cSVA), and spine cranial angle (SCA), were compared between the cervical spine in healthy, symptomatic, and pre-operative participants. Where possible, we pooled data using random-effects meta-analysis, by CMA software. Heterogeneity and publication bias were assessed using the I-squared statistic and funnel plots, respectively.

RESULTS

A total of 102 studies, comprising 13,802 cases (52.7% female), were included in this meta-analysis. We used the Newcastle-Ottawa Scale (NOS) to evaluate the quality of studies included in this review. Funnel plot and Begg's test did not indicate obvious publication bias. The pooled analysis reveals that the mean (SD) values were: T1 slope (degree), 24.5 (0.98), 25.7 (0.99), 25.4 (0.34); cSVA (mm), 18.7 (1.76), 22.7 (0.66), 22.4 (0.68) for healthy population, symptomatic, and pre-operative assessment, respectively. The mean value of the SCA (degree) was 79.5 (3.55) and 75.6 (10.3) for healthy and symptomatic groups, respectively. Statistical differences were observed between the groups (all P values < 0.001).

CONCLUSION

The findings showed that the T1 slope and the cSVA were significantly lower among patients with cervical spine disorder compared to controls and higher for the SCA. Further well-conducted studies are needed to complement our findings.

The 3 Sagittal Morphotypes That Define the Normal Cervical Spine: A Systematic Review of the Literature and an Analysis of Asymptomatic Volunteers

BACKGROUND

Cervical alignment is vital for maintaining horizontal gaze and sagittal balance. The aims of this study were to summarize previously published descriptions of normative cervical alignment and to analyze a cohort of asymptomatic volunteers in order to identify natural clusters of normal radiographic parameters.

METHODS

We performed a systematic review of the literature on radiographic measurements of asymptomatic volunteers through a search of MEDLINE and ScienceDirect databases. We then performed an analysis of demographic and radiographic parameters of volunteers without back or neck complaints. Only subjects with a chin-brow vertical angle (CBVA) within previously published normal limits were retained for analysis. A 2-step cluster analysis was used to find natural groups of cervical alignment. Differences among groups were investigated with a post hoc analysis of variance (ANOVA).

RESULTS

We included 37 articles in our analysis. There was a broad spectrum of both C2-C7 lordosis-kyphosis and T1 slope across ages and sexes. Of the 119 asymptomatic volunteers who were available for analysis, 84 (with a mean age [and standard deviation] of 49.0 ± 17.1 years) had a CBVA ranging from -4.7° to 17.7°. The cluster analysis identified 3 alignment groups based on cervical lordosis-kyphosis and T1 slope (silhouette measure of cohesion, >0.6). Twenty-seven volunteers (32.1%) were identified as the "kyphotic curve cohort" (KCC) (mean C2-C7 Cobb angle, -8.6° ± 7.3°; mean T1 slope, 17.4° ± 6.6°), 43 volunteers (51.2%) were identified as the "medium lordosis cohort" (MLC) (mean C2-C7 Cobb angle, 8.7° ± 7.2°; mean T1 slope, 26.6° ± 4.0°), and 14 volunteers (16.7%) were identified as the "large lordosis cohort" (LLC) (mean C2-C7 Cobb angle, 21.2° ± 7.2°, mean T1 slope, 39.5° ± 6.4°) (p < 0.001 for both). Moving from KCC to LLC, there was a significant decrease in C0-C2 lordosis (p = 0.016). Examination of the cervical vertebral orientation demonstrated that C4 had a constant orientation relative to the horizontal (p = 0.665). Correlation analysis between C2-C7 and vertebral orientations again demonstrated that C4 orientation was independent of C2-C7 alignment.

CONCLUSIONS

We have identified 3 morphotypes of the cervical spine based on C2-C7 alignment and T1 slope. These findings demonstrate the broad definition of normal cervical alignment and the range of cervical lordosis-kyphosis that is acceptable.

No evidence of a correlation between lumbar spinal subtypes and intervertebral disc degeneration among asymptomatic middle-aged and aged patients

The aim of the present study was to identify whether lumbar spinal subtypes (LSS) were associated with lumbar disc degeneration (LDD) among asymptomatic middle-aged and aged subjects. A cohort of 158 asymptomatic Chinese adults aged >40 years was recruited and 97 volunteers that met the inclusion criteria with complete information available were selected for inclusion. According to spinal morphology, volunteers were divided into four subtypes based on the classification of Roussouly. After baseline information was collected and spinopelvic parameters were measured, the data were compared among the four groups. According to the Pfirrmann classification, the degree of LDD was evaluated at each level on the MRI. For grades I-V, LDD at each level was effectively compared. Each of the four LSS from I to IV according to Roussouly classification from types I to IV were comprised of 25 (25.8%), 19 (19.6%), 38 (39.2%) and 15 (15.5%) of volunteers, respectively. Lumbar lordosis, sacral slope and pelvic incidence were significantly different among the four sub-types (P<0.001 for each), but no difference in pelvic tilt was observed (P=0.21). From types I to IV LSS, the proportion of disc degeneration was found to be 44, 52, 50 and 48%, respectively, which exhibited no statistically significant difference among LSS. No correlation between LSS and intervertebral disc degeneration was obtained among the asymptomatic middle-aged and aged subjects. The present study provides a reference for spinal surgery and indicated that additional risk factors should be assessed in the asymptomatic population of this age group, particularly in terms of differentially expressed genes.