Internal Chain of Correlation of Sagittal Cervical Alignment in Asymptomatic Subjects

C4 constant vertebra: a novel benchmark of physiological cervical sagittal alignment

BACKGROUND

Cervical sagittal alignment is essential, and there is considerable debate as to what constitutes physiological sagittal alignment. The purpose of this study was to identify constant parameters for characterizing cervical sagittal alignment under physiological conditions.

METHODS

A cross-sectional study was conducted in which asymptomatic subjects were recruited to undergo lateral cervical spine radiographs. Each subject was classified according to three authoritative cervical sagittal morphology classifications, followed by the evaluation of variations in radiological parameters across morphotypes. Moreover, the correlations among cervical sagittal parameters, age, and cervicothoracic junction parameters were also investigated.

RESULTS

A total of 183 asymptomatic Chinese subjects were enrolled with a mean age of 48.4 years. Subjects with various cervical sagittal morphologies had comparable C4 endplate slope angles under all three different typing systems. Among patients of different ages, C2-C4 endplate slope angles remained constant. Regarding the cervicothoracic junction parameters, T1 slope and thoracic inlet angle affected cervical sagittal parameters, including cervical lordosis and C2-7 sagittal vertical axis, and were correlated with the endplate slope angles of C5 and below and did not affect the endplate slope angles of C4 and above. In general, the slope of the C4 inferior endplate ranges between 13° and 15° under different physiological conditions.

CONCLUSIONS

In the asymptomatic population, the C4 vertebral body maintains a constant slope angle under physiological conditions. The novel concept of C4 as a constant vertebra would provide a vital benchmark for diagnosing pathological sagittal alignment abnormalities and planning the surgical reconstruction of cervical lordosis.

Description of age-related changes in cervical sagittal alignment based on pelvic incidence classification in asymptomatic Chinese population

PURPOSE

To investigate the pelvic incidence (PI)- and age-related cervical alignment changes of Chinese healthy population.

METHODS

Six hundred and twenty-five asymptomatic adult subjects, who underwent the standing whole spinal radiograph, were recruited in this work. The sagittal parameters were measured, including Occipito-C2 angle (O-C2), C2-7 angle (C2-7), cranial arch, caudal arch, T1-slope (T1S), C2-7 sagittal vertical axis (C2-7 SVA), thoracic kyphosis (TK), lumbar lordosis (LL), pelvic tilt (PT), sacral slope (SS), PI, and sagittal vertical axis (SVA). All subjects were stratified into 5 age groups, namely 40-59 years, 60-64 years, 65-69 years, 70-74 years, and 75 years and above, with each age group further divided into 2 subgroups based on PI (deeming PI < 50° as low PI, and PI ≥ 50° as high PI). The correlations between PI or age, and other sagittal parameters were assessed. The age-related changes of sagittal parameters in each PI subgroup were also assessed, followed by one-way analysis of variance analysis for change comparison between age groups.

RESULTS

The average cervical sagittal parameters were as below: 18.2 ± 6.8° for O-C2, 10.4 ± 10.2° for C2-7, 3.9 ± 7.5° for cranial arch, 6.5 ± 7.1° for caudal arch, 23.6 ± 7.3° for T1S, and 21.0 ± 9.7 mm for C2-7 SVA. There was no obvious difference observed between PI and cervical sagittal parameters, excepting for caudal arch. While, C2-7, cranial arch, caudal arch, T1S, and C2-7 SVA increased remarkably with the age. Thereof, C2-7 exhibited great increases at the age of 60-64 years and 70-74 years, respectively, cranial arch increased notably at 60-64 years of age, and caudal arch developed obviously at 70-74 years of age, regardless of PI.

CONCLUSION

This study showed the PI- and age-related cervical alignment changes of Chinese healthy population. Based on the classification in our study, high or low PI apparently did not correlate with the occurrence of cervical degenerative disease.

Age-related changes in cervical sagittal alignment: based on 625 Chinese asymptomatic subjects

PURPOSE

This work aimed to provide a comprehensive description of cervical alignment including cranial arch and caudal arch according to age, thus offering a reference database for cervical deformity treatment.

METHODS

Total 150 males and 475 females aged at 48-88 were enrolled from August 2021 to May 2022. Radiographic parameters were measured, including Occipito-C2 angle (O-C2), C2-7 angle (C2-7), cranial arch, caudal arch, T1-slope (T1s), and C2-7 sagittal vertical axis (C2-7 SVA). Pearson correlation coefficient was employed in analyzing associations among sagittal parameters and between age and each parameter. Five groups were set according to different age stages, namely group with age 40-59 (N = 77), group with age 60-64 (N = 189), group with age 65-69 (N = 214), group with age 70-74 (N = 97), and group with age exceeding 75 (N = 48). An analysis of variance (ANOVA) test was applied to compare multi-sets of cervical sagittal parameters (CSPs). Chi-square test or Fisher's exact test was used in assessing the relationships of various cervical alignment patterns with age groups.

RESULTS

T1s exhibited the strongest correlation with C2-7 (r = 0.655) and caudal arch (r = 0.561), and moderately correlated with cranial arch (r = 0.355). The positive correlations between age and C2-7 angle (r = 0.189, P < 0.001), cranial arch (r = 0.150, P < 0.001), caudal arch (r = 0.112, P = 0.005), T1s (r = 0.250, P < 0.001), as well as C2-7 SVA (r = 0.090, P = 0.024) were observed. Moreover, two progressive growths of C2-7 were shown after 60-64 and 70-74 years old, respectively. Thereof, cranial arch increased greatly after the age of 60-64, followed by a relative stability in the degeneration. The notable growth of caudal arch was observed after the age of 70-74, and the growth remained stable when exceeding the age of 75. The difference between cervical alignment patterns and age groups was obvious (Fisher's exact test P < 0.001).

CONCLUSION

This work explored in detail the normal reference values of cervical sagittal alignment including cranial arch and caudal arch under different age groups. Age-related changes in cervical alignment depended on the increase in the cranial and caudal arches in different proportions with age.

Analysis of Components of Upper Cervical Lordosis in Asymptomatic Lordotic and Kyphotic Subjects

BACKGROUND

Upper cervical lordosis (CL) can be divided into 2 components: C2 slope (C2S) and McGregor slope (MGS) or C0-1 and C1-2 angles. The aim of this study was to investigate the components of upper CL in asymptomatic kyphotic and lordotic subjects.

METHODS

CL, C0-2 Cobb angle, MGS, C2S, C1 Slope, C0-1 Cobb angle, C1-2 Cobb angle, T1 slope angular parameters, and the C2-7 sagittal vertical axis distance of 78 asymptomatic subjects were measured.

RESULTS

Sixty subjects had lordotic curvature and 18 had kyphotic curvature. There was a significant difference between the kyphotic and lordotic groups in all parameters, except for C0-1 Cobb angle and C2-7 sagittal vertical axis. In lordotic subjects, MGS and C2S accounted for 58% and 42% of the C0-2 angle, whereas in kyphotic subjects, 86% of C0-2 was accounted for by C2S. There was a strong negative correlation between C2S and MGS.

CONCLUSIONS

In asymptomatic subjects, as CL decreases, MGS decreases, C2S increases, and the C0-2 angle turns down on the horizontal plane to maintain the horizontal gaze. Turning down the C0-2 angle is more important than its value for maintaining horizontal gaze; thus, the slopes (MGS and C2S) can better represent the upper and lower cervical alignment than angle values can. The relationship between upper and lower cervical alignment should be evaluated in terms of slope angles rather than simple angles. The lack of significant difference between the C0-1 angles in the kyphotic and lordotic groups suggests that only the C1-2 angle is involved in the compensatory mechanism for the horizontal gaze.