Correlation between the apex of lumbar lordosis and pelvic incidence in asymptomatic adult

Sagittal balance analysis and treatment rationale for young patients with symptomatic lumbosacral transitional vertebrae

Lumbosacral transitional vertebrae (LSTV) are a common anomaly in 7-36% of the population. LSTV can contribute to mechanical low back pain and increase the risk of early degeneration in cranial segments due to hypermobility and stress. This study analyzed sagittal balance in young symptomatic LSTV patients and tried to identify compensatory mechanisms that may explain early degeneration. Nineteen symptomatic and skeletally mature subjects with LSTV were retrospectively identified. Imaging included standing biplanar spine radiographs and supine lumbar MRI. Sagittal balance parameters were measured, and LSTV were classified using the Castellvi classification. Vertical mid-vertebral angle differences were calculated using MRI and lateral radiographs. The cohort included 17 females and 2 males (mean age 16 ± 3 years). Mean pelvic incidence was 67°±8°. L1-S1 lordosis averaged 61°±10°, L4-S1 lordosis was 10° lower than expected, and L4-L5 lordosis was higher than literature values. Thirteen patients had L4-L5 discopathy, with nine showing additional abnormalities such as interspinous ligament edema or posterior facet hypertrophy. In our study, LSTV was associated with L5-S1 disc hypoplasia and altered lumbar lordosis, leading to compensatory L4-L5 hyperextension. These findings suggest early degeneration may result from abnormal lordosis distribution. Treatment should aim to optimize lordosis distribution to reduce stress on adjacent segments.

The Impact of Spinopelvic Alignment on the Facet Joint Degeneration

STUDY DESIGN

Retrospective Cohort.

OBJECTIVES

This study aims to evaluate the relations between facet joint degeneration (FD) and sagittal spinopelvic parameters. Second, the association of FD with degenerative disc disease (DDD) and lumbar disc herniations (LDH) was assessed.

METHODS

The radiologic data of 192 patients was retrospectively analyzed. Total, proximal, and distal lumbar lordosis (LL, PLL, and DLL), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and sacral table angle (STA) were measured on lumbar x-ray plates. DDD and FD was graded on the MRI images. The apex of lumbar lordosis and PI-LL imbalance were noted in each patient. Correlation analyses were performed.

RESULTS

Age and body mass index (BMI) were correlated with FD. LL and DLL are positively associated with upper-level FDs (L1-2 and L2-3) (P < 0,05). PLL were positively associated with lower level FD (L5-S1) (P < 0,05). A significant increase in PI was associated with FD in L2-3 and L4-5. A larger PT was found in FD in L4. The PI-LL imbalance was not correlated with the FD. Correlation between DDD and LDH and FD was observed in each level (P < 0,01). The level of FD is not affected by the apex of the curve.

CONCLUSION

Age and BMI have a direct impact on FD. However, spinopelvic parameters influence the severity of FD rather than its occurrence. In addition to the effects of lumbar lordosis as a single entity, it is essential to consider separately the effects of proximal and distal lumbar lordosis at the FD level.

Lumbar Apex Position as an Independent Risk Factor for Adjacent Segment Diseases in Patients Undergoing Short-Level Transforaminal Lumbar Interbody Fusion

STUDY DESIGN

Retrospective study.

OBJECTIVE

To investigate whether lumbar apex position had an impact on the development of adjacent segment disease (ASD) following transforaminal lumbar interbody fusion (TLIF).

SUMMARY OF BACKGROUND DATA

Previous studies have demonstrated that solely concentrating on lumbar lordosis value is not suitable, and neglecting the significance of lumbar apex can lead to mechanical complications. However, the relationship between lumbar apex and ASD is still not well understood.

METHODS

In this retrospective study, 234 consecutive patients who underwent L3-5 or L4-5 TLIF for degenerative diseases were reviewed. The study evaluated the associations between sagittal parameters and pelvic incidence (PI). Patients were labeled "matched" when lumbar apex position aligned with the theoretical target, and "mismatched" when it did not. Multivariate analysis was applied to find the independent risk factors of ASD. In addition, a focused subanalysis was performed based on the lumbar apex position (ideal match, cranial from ideal, and caudal from ideal).

RESULTS

After an average follow-up period of 70.6 months, 68 cases were identified as having ASD. Postoperatively, 64.7% (44 of 68) of the patients with ASD exhibited a mismatched lumbar apex, compared with 41% (68 of 166) of those without ASD ( P < 0.001). PI correlated significantly with proximal lordosis (PL) and lordosis distribution index (LDI) but not with distal lordosis (DL). Multivariate analysis identified age, L3-5 fusion, postoperative DL, and postoperative mismatched lumbar apex as independent risk factors of ASD. Upon the subanalysis, it was discovered that there were unique compensatory strategies in the cranial and caudal groups, with notable variations in postoperative DL, PL, and LDI among three groups (all P value of <0.05).

CONCLUSION

Lumbar apex position significantly influenced the risk of ASD. To restore the lumbar apex to its ideal position, a proper value and distribution of DL should be attained.

LEVEL OF EVIDENCE

4.

Impact of pelvic anteversion on spinopelvic alignment in an asymptomatic population: a dynamic perspective of standing and sitting

BACKGROUND CONTEXT

A subgroup of patients with pelvic anteversion can present with an unusually large degree of lumbar lordosis (LL), a highly sloped sacrum, and a relatively small pelvic incidence (PI). Prior to lumbar surgery, it can be important to consider such unique sagittal alignment. However, until now, there has been a lack of a predictive model considering different pelvic alignments. Furthermore, the dynamic characteristics of an anteverted pelvis (AP) subgroup have also been unclear.

PURPOSE

To build linear predictive formulas for LL that take pelvic anteversion into consideration and to explore the dynamic characteristics of an AP subgroup.

STUDY DESIGN

Monocentric, cross-sectional study.

PATIENT SAMPLE

Five hundred sixty-five asymptomatic Chinese men and women between the ages of 18 and 80 years.

OUTCOME MEASURES

Sagittal parameters including LL, lumbar lordosis minus thoracic kyphosis (LL-TK), PI, pelvic tilt (PT), pelvic incidence minus lumbar lordosis (PI-LL), sacral slope (SS), sacral slope divided by pelvic incidence (SS/PI), sagittal vertical axis (SVA), thoracic kyphosis (TK), and T1 (first thoracic vertebra) pelvic angle (TPA) were measured on whole spine radiographs obtained with participants in standing and sitting positions.

METHODS

All participants underwent radiography in the standing position; 235 of them underwent additional radiography in the sitting position to allow measurement of sagittal parameters. The participants with pelvic anteversion were placed in an AP (anteverted pelvis) group. Sagittal parameters were compared between the AP group and the non-AP group, and predictive formulas for LL based on PI were created in both groups. In addition, changes in sagittal parameters from standing to sitting were compared in the AP group and a PI-matched control group.

RESULTS

Of the 565 participants, 171 (30.3%) had pelvic anteversion. In comparison with the non-AP group, the AP group presented with larger LL, a larger SS, and a smaller PT, with relatively small PI. The predictive formulas for LL were LL=0.60° × PI+21.60° (R2=0.268; p<.001) in the whole cohort, LL=0. 83×PI+18.75° (R2=0.427; p<.001) in AP group, and LL=0.79°×PI+9.66° (R2=0.451; p<.001) in the non-AP group. In moving from standing to sitting, the AP group presented with a larger decrease in SS and LL compared with the control group, indicating different patterns of spinopelvic motion.

CONCLUSIONS

In the cohort examined, 30.3% present with pelvic anteversion. Those with AP present with unique characteristics of spinopelvic alignment. In moving from standing to sitting, they exhibit different patterns of spinopelvic motion. We found that identifying the degree of anteversion in each person improves the accuracy of linear models for predicting the degree of LL, which in turn can make plans for spine surgery more accurate.

Predicting thoracic kyphosis morphology and the thoracolumbar inflection point determined by individual lumbar lordosis in asymptomatic adults

PURPOSE

The aims of this study were to explore the correlations between thoracic kyphosis (TK) and lumbar lordosis (LL) parameters and to build corresponding linear regressions to predict TK morphology and the thoracolumbar inflection point (IP) determined by individual LL parameters in asymptomatic adults.

METHODS

A total of 280 adult healthy volunteers were recruited, and full-spine X-rays were performed for each subject in a standing posture. The following sagittal parameters were measured: cumulative TK, LL, proximal LL (PLL), the apices of TK (TKA) and LL (LLA), the IP and the distance from the plumb line of the thoracic apex (TAPL) and the lumbar apex (LAPL) to the gravity line. The correlations between TK and LL parameters were analyzed, and the corresponding linear regressions were conducted.

RESULTS

Extensive variations existed in TK alignment, including angular and morphological parameters. In addition, there were statistical correlations of all cumulative TK angles with LL (r values from - 0.173 to - 0.708) and PLL (r values from - 0.206 to - 0.803), TKA and IP with LLA (rs = 0.359 and 0.582, respectively) and TAPL with LAPL (rs = 0.335). The common predictive formulas employed in ASD surgery could include T10-L1 = - 3.6-0.2*LL (R2 = 0.201), T4-L1 = 3.4-0.5*LL (R2 = 0.457), TKA = - 10.3 + 1.1*LLA (R2 = 0.180) and IP = - 12.7 + 1.6*LLA (R2 = 0.330).

CONCLUSION

There were intimate associations between TK and LL parameters in asymptomatic adults. Moreover, predictive models for thoracic alignment, particularly cumulative TK, based on LL parameters were proposed, which could better delineate anatomical relationships, guide thoracic construction during adult spinal deformity surgery and may help preventing proximal junctional failure.

Sex-based differences in clinical and radiological presentation of patients with degenerative lumbar scoliosis: a cross-sectional study

BACKGROUND

To evaluate the sex-based differences in clinical and radiological presentation of patients with degenerative lumbar scoliosis (DLS) and to explore whether the difference is helpful in investigating the etiology and progression of DLS.

METHOD

A retrospective review of 199 patients (41 males, 158 females) with DLS was included. Patient demographics including age, gender, bone mineral density were collected. Back and leg pain was assessed by visual analog scale, and general physical condition was assessed by Oswestry Disability Index. Cobb's angle was measured, and direction of scoliosis, position of the superior, inferior and apex vertebrae, number of vertebrae included in the scoliosis, rotation of apex vertebrae (Nash-Mo index), translation of apex vertebrae were recorded. Sagittal longitudinal axis, thoracolumbar kyphosis, lumbar lordosis (LL), pelvic incidence angle (PI), sacral slope, apex of lumbar lordosis and coronal balance distance were measured by whole spine lateral radiographs, and type of coronal imbalance was evaluated in all patients. Fat infiltration rate (FIR) of the paraspinal muscles at the vertebral apex was measured by MRI.

RESULT

Compared to female patients, male patients showed more back and leg pain on clinical presentation and smaller Cobb angle, less parietal rotation, larger LL, smaller PI-LL and lower paravertebral muscle FIR on radiologic features.

CONCLUSION

Gender differences do exist in DLS patients with regard to clinical and radiological presentation, low back pain was more pronounced in male patients, and scoliosis was more severe in female patients based on this cross-sectional study.

Variation in Functional Pelvic Tilt in Female Patients Undergoing Total Hip Arthroplasty With Acetabular Dysplasia

BACKGROUND

As the pelvis is a dynamic structure, the quantification of pelvic tilt (PT) should be done in different hip positions prior to total hip arthroplasty (THA). We sought to investigate functional PT in young female patients undergoing THA and explore the correlation of PT with the extent of acetabular dysplasia. Additionally, we aimed to define the PS-SI (pubic symphysis-sacroiliac joint) index as a PT quantifier on AP pelvis X-ray.

METHODS

Pre-THA female patients under the age of 50 years (n = 678) were investigated. Functional PT in 3 positions (supine, standing, and sitting) were measured. Hip parameters including lateral center-edge angle (LCEA), Tönnis angle, head extrusion index (HEI), and femoro-epiphyseal acetabular roof (FEAR) index were correlated to PT values. The PS-SI/SI-SH (sacroiliac joint-sacral height) ratio was also correlated to PT.

RESULTS

From the 678 patients, 80% were classified as having acetabular dysplasia. Among these patients, 50.6% were bilaterally dysplastic. The mean functional PT of the entire patient group was 7.4°, 4.1°, and -1.3° in the supine, standing and seated positions. The mean functional PT of the dysplastic group was 7.4°, 4.0°, and -1.2° in the supine, standing and seated positions. The PS-SI/SI-SH ratio was found to be correlated to PT.

CONCLUSION

Most of the pre-THA patients had acetabular dysplasia and exhibited anterior PT in the supine and standing positions, most pronounced in the standing position. PT values were comparable between the dysplastic and non-dysplastic group without change with worsening dysplasia. PS-SI/SI-SH ratio can be used to easily characterize PT.

Orientation of Osteotomized Vertebrae in 2-Level Pedicle Subtraction Osteotomy Plays a Crucial Role in the Remodeling of Harmonious Sagittal Curve for Severe Thoracolumbar Kyphotic Deformity Caused by Ankylosing Spondylitis

BACKGROUND

Few studies reported the remodeling of harmonious sagittal curve after 2-level pedicle subtraction osteotomy (PSO) for severe thoracolumbar kyphosis in ankylosing spondylitis (AS).

OBJECTIVE

To investigate how the orientation of osteotomized vertebrae (OV) affects the remodeling of harmonious sagittal curve in patients with AS undergoing 2-level PSO.

METHODS

Twenty-six patients treated with 2-level PSO were reviewed. Plumb lines of thoracic apex and lumbar apex, the superior/inferior endplate angle of OV, and OV tilt were measured. Patients with AS were grouped based on the postoperative lumbar lordotic apex (LLA, L3 or L4 vs L5 or others).

RESULTS

The level of thoracic kyphotic apex was positively correlated with that of superior OV postoperatively. Larger sacral slope, L1-L3 lordotic angle, and plumb lines of lumbar apex could be obtained in patients with LLA at L3 or L4, accompanied with larger superior endplate angle of OV and OV tilt of inferior OV ( P < .05). Besides, larger lumbar lordotic angle (LL) was observed in these patients (marginally significant, P = .057). For patients with relocated LLA at L5 or others, lower pelvic incidence was observed, accompanied with significant loss of correction ( P < .05) and worse Visual Analog Scale scores (marginally significant, P = .054) during follow-up.

CONCLUSION

Ventrally leaning inferior OV combined with dorsally leaning superior OV contributed to the most harmonious sagittal curve defined as thoracic kyphotic apex at T8 or above and LLA at L3 or L4. Sagittal curve with LLA at L5 could be acceptable in patients with more severe kyphosis, especially those with low pelvic incidence.

The effect of interlaminar Coflex stabilization in the topping-off procedure on local and global spinal sagittal alignment

PURPOSE

To investigate the effect of interlaminar Coflex stabilization (ICS) at various segments in the topping-off procedure on local and global spinal sagittal alignment.

METHODS

Eighty-nine consecutive patients with degenerative lumbar spinal stenosis (DLSS) who underwent ICS and transforaminal lumbar interbody fusion (TLIF) were retrospectively reviewed. They were divided into Group A (L4-L5 ICS + L5-S1 TLIF), Group B (L3-L4 ICS + L4-S1 TLIF), and Group C (L2-L3 ICS + L3-S1 TLIF) according to their fusion levels. The measured local sagittal parameters included the implanted segmental angle (ISA), intervertebral disc angle (IDA), intervertebral foreman height (IFH), and disc height. The assessed global sagittal parameters included thoracic kyphosis, lumbar lordosis (LL), the fused segment angle (FSA), the sacral slope, the pelvic tilt, pelvic incidence, and the sagittal vertical axis. The Oswestry Disability Index (ODI) and visual analog scales (VAS) were recorded to evaluate the clinical outcomes.

RESULTS

Regarding the local alignment parameters, the ISA and IDA decreased immediately after surgery in Groups A and B, followed by an increase at the last follow-up (all, P < 0.05). Conversely, the IFH of Groups A and B first increased after surgery and then decreased to approximately the original value (all, P < 0.05). No significant differences were evident between the local sagittal parameters at different time points in Group C. Regarding the global sagittal profiles, the LL and FSA exhibited a significant postoperative increase (both at P < 0.05) in all the groups. All three groups displayed significant improvements in the ODI, VAS-back pain, and VAS-leg pain. Furthermore, 4.5% (4/89) of the patients exhibited radiographic adjacent segment degeneration (ASD) at the last follow-up.

CONCLUSION

ICS during topping-off surgery led to a temporary loss of local lordosis, especially in the lower lumbar segment, while the intervertebral space realigned after middle-term follow-up. The topping-off procedure with ICS is a feasible and promising surgical option of DLSS since it reduces fusion levels and prevents ASD development.

Radiographic patterns and characteristics of sagittal profiles in normal spinopelvic curvatures: An explicit depiction of the distribution of lumbar vertebral bodies and discs

The current study aimed to investigate the sagittal morphology of the spinopelvic complex and the components of the lumbar spine in the normal population. In total, 132 adult volunteers were retrospectively evaluated and divided into four groups according to the Roussouly classification. Statistical analysis of radiological parameters, including lumbar lordosis (LL), thoracic kyphosis (TK), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), PI-LL, LL-TK, lumbar vertebral lordosis from L1 to L5 (L1L-L5L), the intervertebral angle from L1-L2 to L5-S1 (IVA1-2-IVA5-1), segmental lordosis from L1 to L5 (S1L-S5L), the proportion of L1-L5 (L1%-L5%), the proportion of the intervertebral angle from L1-L2 to L5-S1 (IVA1-2%-IVA5-1%), and proportion of segmental lordosis from L1 to L5 (S1L%-S5L%), was performed. Based on the classification, type II (n = 46) was the most common, followed by type I (n = 39), type III (n = 36), and type IV (n = 11). The quantitative values of the sagittal parameters of the four groups were obtained. Results showed a significant difference in terms of LL, PI, SS, and LL-TK. Further, L1%, L2%, L3%, IVA1-2%, IVA2-3%, S1L%, S2L%, and S3L% had an increasing trend. PI was positively correlated with LL, S1L, S2L, S3L, S4L, S1L%, and S2L%, but not with S5L%. In conclusion, pelvic parameters had a significant effect on lumbar curvature and lordosis distribution. Further, the abovementioned results were beneficial for individual surgical decision-making regarding targeted intervertebral angle, screw-insertion dimension, and rod contouring.

Predicting the ideal apex of lumbar lordosis based on individual pelvic incidence and inflection point in asymptomatic adults

Objective

The main aim of this study was to comprehensively explore the relationship among pelvic incidence (PI), inflection point (IP), and apex of lumbar lordosis (LLA), and establish a predictive formula for LLA based on individual PI and IP in asymptomatic Chinese adults.

Methods

A total of 385 asymptomatic adults with average age 38.3 ± 11.9 years (range 20–73 years) were recruited between November 2020 and October 2021. Full-spine, standing x-rays were then obtained from each participant. Next, the following sagittal parameters were measured: PI, IP, LLA, the horizontal offset between the plumb line of the lumbar apex and that of the posterosuperior corner of S1 (LASO), the upper lumbar lordosis (ULL) and lower lumbar lordosis (LLL), lumbar lordosis (LL), and thoracic kyphosis (TK). Moreover, the association among PI, IP, and the other sagittal parameters was evaluated, followed by linear regression analyses. A P-value of <0.05 was considered statistically significant.

Results

PI showed statistically significant correlations with LLA (r_s = −0.629; P < 0.01), LASO (r_s = 0.537; P < 0.01), LLL (r_s = 0.788; P < 0.01), and LL (r_s = 0.663; P < 0.01). On the other hand, IP also showed statistically significant correlations with LLA (r_s = 0.671; P < 0.01), LASO (r_s = −0.493; P < 0.01), LLL (r_s = −0.402; P < 0.01), and LL (r_s = −0.283; P < 0.01). The corresponding predictive formulae were displayed as follows: LLA = −0.03 * PI + 0.23 * IP + 14.45 (R²= 0.669); LASO = 0.38 * PI−2.09 * IP + 53.62 (R²= 0.460); and LLL = 0.58 * PI−0.88 * IP + 18.86 (R²= 0.659).

Conclusion

The specific lumbar shape should be modulated by pelvic morphology and IP level. In addition, we established predictive formulae for ideal sagittal lumbar profile based on individual PI and IP, with the overarching goal of helping surgeons to better comprehend the regulatory mechanisms of the individual sagittal lumbar alignment, and design a precise and personalized corrective plan.

Introduction of a Novel “Segmentation Line” to Analyze the Variations in Segmental Lordosis, Location of the Lumbar Apex, and Their Correlation with Spinopelvic Parameters in Asymptomatic Adults

Study Design

Cross-sectional study.

Purpose

This study aimed to understand the sagittal spinopelvic parameters, segmental lumbar parameters, and lumbar apex location in asymptomatic adults and analyze their correlations with each other.

Overview of Literature

Roussouly and his colleagues reported that pelvic incidence (PI) influences the lower arc of lumbar lordosis, whereas Pesenti and his colleagues reported that PI influences only the proximal part of lordosis and not the distal part. Both studies have their shortcomings.

Methods

One hundred asymptomatic adult volunteers (mean age, 29.1±7.9 years; 69 males, 31 females) who satisfied the selection criteria were enrolled in this study. Standing antero-posterior and lateral whole spine and pelvis X-rays were performed, and the radiographic parameters were analyzed. We introduced a “segmentation line” bisecting the apical vertebra/disk to divide the upper arc of lumbar lordosis (ULL) and lower arc of lumbar lordosis (LLL).

Results

The mean PI was 48.02°, ULL 29.12°, LLL 16.02°, total lumbar lordosis (TLL) 45.14°, lumbar tilt angle 4.73°, and location of the apex of lumbar lordosis (LLA) 4.11°. The location of the lumbar apex moved higher as the PI increased. The PI was strongly positively correlated with the LLL (r =0.582, p <0.001) and TLL (r =0.579, p <0.001) but not with the ULL (r =0.196, p =0.05). The LLA was strongly positively correlated with the ULL (r =0.349, p <0.001), negatively with the LLL (r =−0.63, p <0.001), and not correlated with the TLL (r =−0.177, p =0.078).

Conclusions

The PI influences the location of the lumbar apex, the LLL, and the TLL but not the ULL. The location of the lumbar apex significantly influences the segmental lordosis but not the TLL.

Automatic recognition of whole-spine sagittal alignment and curvature analysis through a deep learning technique

PURPOSE

Artificial intelligence based on deep learning (DL) approaches enables the automatic recognition of anatomic landmarks and subsequent estimation of various spinopelvic parameters. The locations of inflection points (IPs) and apices (APs) in whole-spine lateral radiographs could be mathematically determined by a fully automatic spinal sagittal curvature analysis system.

METHODS

We developed a DL model for automatic spinal curvature analysis of whole-spine lateral plain radiographs by using 1800 annotated images of various spinal disease etiologies. The DL model comprised a landmark localizer to detect 25 vertebral landmarks and a numerical algorithm for the generation of an individualized spinal sagittal curvature. The characteristics of the spinal curvature, including the IPs, APs, and curvature angle, could thus be analyzed using mathematical definitions. The localization error of each landmark was calculated from the predictions of 300 test images to evaluate the performance of the landmark localizer. The interrater reliability among a senior orthopedic surgeon, a radiologist, and the DL model was assessed using the intraclass correlation coefficient (ICC).

RESULTS

The accuracy of the landmark localizer was within an acceptable range (median error: 1.7-4.1 mm), and the interrater reliabilities between the proposed DL model and each expert were good to excellent (all ICCs > 0.85) for the measurement of spinal curvature characteristics.

CONCLUSION

The interrater reliability between the proposed DL model and human experts was good to excellent in predicting the locations of IPs, APs, and curvature angles. Future applications should be explored to validate this system and improve its clinical efficiency.

Restoring Theoretically Optimal Lumbar Lordosis Deduced from Pelvic Incidence and Thoracic Kyphosis has Advantages to Decrease the Risk of Postoperative Mechanical Complications in Adult Spinal Deformity

Objective

To establish a regression formula for LL based on individual PI and TK in asymptomatic population aged over 50 years and evaluate its predictive power for the occurrence of postoperative mechanical complications in patients with adult spinal deformity (ASD).

Methods

A total of 178 asymptomatic adults were recruited for the study. The association between LL and PI, LL and TK, was investigated to establish a predictive formula for ideal LL based on PI and TK. Additionally, 93 ASD patients undergoing posterior correction surgery were retrospectively analyzed. The absolute value of the gap between postoperative actual LL and theoretical LL was defined as ΔLL. Patients were classified into two groups depending on the presence or absence of mechanical complications. The demographic and radiological data of patients were compared between the two groups.

Results

A significant association was found between LL and PI (r = 0.599, P &lt; 0.001), LL and TK (r = 0.523, P &lt; 0.001). A novel formula was developed as follows: LL = 0.7*PI + 0.4*TK + 1 (R2 = 0.524). In the validation cohort, 29 patients developed mechanical complications. Postoperative ΔLL (12.5 ± 7.6° vs. 7.0 ± 5.4°, P = 0.001) significantly increased the incidence of mechanical complications. The most appropriate threshold of ΔLL for predicting mechanical complications was 9.8°. For patients whose ΔLL were &lt;9.8° and &gt;9.8°, the incidence of mechanical complications was 19.4% and 54.8%, respectively.

Conclusion

Ideal lumbar lordosis should be matched for PI and TK. The developed prediction formula for LL based on PI and TK in asymptomatic adults may help surgeons to understand the mechanisms of lumbar alignment generation and predict occurrence of mechanical complications after ASD surgery.

Predictive formulae of ideal lumbar lordosis determined by individual pelvic incidence and thoracic kyphosis in asymptomatic adults

BACKGROUND

The precise prediction of ideal lumbar lordosis (LL) has become increasingly important in clinical practice. The aim of this study was to explore the regulatory mechanisms of sagittal spinopelvic alignment and to predict ideal LL based on individual pelvic incidence (PI) and thoracic kyphosis (TK) parameters in asymptomatic adults.

METHODS

A total of 233 asymptomatic subjects older than 18 years were consecutively enrolled in our study between April 2017 and December 2019. A full-spine, standing X-ray was performed for each subject. The following parameters were measured in the sagittal plane: the apex of lumbar lordosis (LLA), the distance between the plumb line of the lumbar apex (LAPL) and the gravity plumb line, the inflection point (IP), LL, the upper arc and lower arc of lumbar lordosis (LLUA and LLLA, respectively), PI and TK. Stepwise multiple linear regressions were conducted, and the statistical significance level was P < 0.05.

RESULTS

Both PI and TK were two important predictive variables for LLA, LAPL, IP and LL. In addition, the LLUA was mainly explained by TK, while the LLLA was explained by PI. The corresponding predictive models are listed as follows: LLA = 17.110 - 0.040∗PI + 0.023∗TK (R² = 0.380), LAPL = 31.296 + 0.467∗PI - 0.126∗TK (R² = 0.309), IP = 10.437 + 0.091∗TK - 0.029∗PI (R² = 0.227), LL = 2.035 + 0.618∗PI + 0.430∗TK (R² = 0.595), LLUA = 0.893 + 0.418∗TK (R² = 0.598), LLLA = 3.543 + 0.576∗PI (R² = 0.433).

CONCLUSION

The specific sagittal lumbar profile should be regulated by both pelvic and thoracic morphology. Such predictive models for lumbar parameters determined by individual PI and TK parameters have been established, which are meaningful for surgeons to better understand the regulatory mechanisms of sagittal spinopelvic alignment and reconstruct a satisfactory lumbar alignment.

Sacral anatomical parameters varies in different Roussouly sagittal shapes as well as their relations to lumbopelvic parameters

PURPOSE

To study the normal variations in sacral anatomical parameters in different Roussouly sagittal shapes and the association between sacral anatomical parameters and lumbopelvic parameters in healthy adults.

METHODS

A cohort of 239 healthy volunteers between 18 and 45 years old was enrolled in this study. A full-spine, standing X-ray was taken for each volunteer. The following parameters were measured: the sacral table angle (STA), sacral kyphosis (SK), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), lumbar lordosis (LL), and lumbar lordosis apex (LLA). Two hundred and thirty-nine volunteers were classified into five groups according to the Roussouly classification. The differences in sagittal parameters among the five groups were evaluated by one-way analysis of variance. The correlations between lumbopelvic parameters and sacral anatomical parameters were analyzed, and simple linear regressions were simultaneously constructed.

RESULT

The sacral anatomical parameters vary in different Roussouly sagittal shapes. Correlation analysis revealed that the significant correlations between sacral anatomical parameters and lumbopelvic parameters. The STA correlated with PI (r = -.690, P <.001), PT (r = -.216, P = .001), SS (r = -.631, P <.001), LL (r = -.491, P <.001), and LLA (r = 0.515, P <.001). The corresponding regression formulae were as follows: PI = -0.991*STA + 143(R 2 = .476), LL = 0.870*STA-135.1(R 2 = .242), and LLA = 0.039*STA -0.087(R 2 = .265). The SK correlated with PI (r = .471, P <.001), PT (r = .445, P = .001), SS (r = .533, P <.001), LL (r = .438, P <.001), and the LLA (r = -.265, P <.001). The corresponding regression formulae were as follows: PI = 0.38*SK + 27.22(R 2 = .396), LL = -0.35*SK - 35.99(R 2 = .192), and LLA = -0.01*SK + 4.25(R 2 = .201).

CONCLUSIONS

The sacral anatomical parameters vary in different Roussouly sagittal shapes and have strong correlations with lumbopelvic parameters, which demonstrates that the specific lumbar shape can be affected by the sacral morphology. Moreover, the predictive models of lumbopelvic parameters based on SK and STA have been provided, which demonstrates constant sacral anatomical parameters could serve as good supplementary index of PI to predict ideal lumbar parameters.

Predictive model of global tilt (GT) determined by individual thoracic kyphosis, lumbar lordosis and pelvic incidence in the human degenerative spine

PURPOSE

Previous studies only investigated the simple linear relationships of global tilt (GT) with thoracic kyphosis (TK), lumbar lordosis (LL) and pelvic incidence (PI). This study aimed to establish multiple linear regressions of GT based on individual TK, LL and PI in patients with degenerative spines.

METHODS

Four hundred sixty-nine adult patients aged older than 35 years with various degenerative spinal diseases were enrolled in this two-centre study between January 2017 and December 2020. Full-spine X-rays were performed for all the subjects in a standing position. The following regional and global parameters were measured in the sagittal plane: TK, LL, PI, pelvic tilt (PT), sagittal vertical axis (SVA) and GT. The correlations of the GT, PT and SVA with the TK, LL and PI were analysed, and then multiple linear regressions were constructed.

RESULTS

GT was statistically correlated with TK, LL and PI. Additionally, TK, LL and PI were significant predictors for the GT, PT and SVA models. The relevant predictive formulae were as follows: GT = -9.60 + 1.09*PI + 0.89*LL + 0.42*TK (R² = 0.935), PT = -4.49 + 0.81*PI + 0.56*LL + 0.24*TK (R² = 0.792) and SVA = -25.68 + 2.98*LL + 2.37*PI + 1.67*TK (R² = 0.416).

CONCLUSION

The specific sagittal spinopelvic morphology, evaluated by GT parameters, should be determined by individual TK, LL and PI values in the degenerative spine. Surgeons can utilize such predictive models to better understand the degenerative evolution of sagittal alignment and recognize the relationships between regional parameters and global sagittal alignment to customize a precise correction strategy.

Optimized Surgical Strategy for Adult Spinal Deformity: Quantitative Lordosis Correction versus Lordosis Morphology

BACKGROUND

In surgical correction of adult spinal deformity (ASD), pelvic incidence (PI)-lumbar lordosis (LL) plays a key role to restore normal sagittal alignment. Recently, it has been found that postoperative lordosis morphology act as an important factor in preventing mechanical complications. However, there have been no studies on the effect of postoperative lordosis morphology on the restoration of sagittal alignment. The primary objective of this study was to evaluate the effect of postoperative lordosis morphology on achievement of optimal sagittal alignment. The secondary objective was to find out which radiographic or morphologic parameter affects sagittal alignment in surgical correction of ASD.

METHODS

228 consecutive patients with lumbar degenerative kyphosis who underwent deformity correction and long-segment fixation from T10 to S1 with sacropelvic fixation and follow-up over 2 years were enrolled. Patients were divided according to whether optimal alignment was achieved (balanced group) or not (non-balanced group) at last follow-up. We analyzed the differences of postoperative radiographic parameters and morphologic parameters between two groups. Correlation analysis and stepwise multiple linear regression analysis was performed to predict the effect of PI-LL and morphologic parameters on the sagittal vertical axis (SVA).

RESULTS

Of 228 patients, 195 (85.5%) achieved optimal alignment at last follow-up. Two groups significantly differed in postoperative and last follow-up LL (p < 0.001 and p = 0.028, respectively) and postoperative and last follow-up PI-LL (p < 0.001 and p = 0.001, respectively). Morphologic parameters did not significantly differ between the two groups except lower lordosis arc angle (=postoperative sacral slope). In correlation analysis and stepwise multiple linear regression analysis, postoperative PI-LL was the only parameter which had significant association with last follow-up SVA (R² = 0.134, p < 0.001). Morphologic parameters did not have any association with last follow-up SVA.

CONCLUSIONS

When planning spine reconstruction surgery, although considering postoperative lordosis morphology is necessary, it is still very important considering proportional lordosis correction based on individual spinopelvic alignment (PI-LL) to achieve optimal sagittal alignment.

Static and dynamic sagittal lumbar apex: a new concept for the assessment of lumbar lordosis distribution in spinal deformity

PURPOSE

Sagittal lumbar apex has been demonstrated to be a key parameter in sagittal plane morphology. Our aim was to understand its behavior with postural changes, analyzing two different concepts of lumbar apex.

MATERIALS AND METHODS

Prospective observational study with a cohort of patients presenting sagittal malalignment identified from a monocenter database of adult spinal deformities (ASD). Inclusion criteria were age > 30 years, SVA > 40 mm, and/or PT > 20. All patients had full-spine EOS radiographs in 2 different positions: (P1: natural position) and position 2 (P2: compensated position). Sagittal alignment, spinopelvic values, and two different methods of assessing lordosis apex location were analyzed in both P1 and P2 positions. Changes between P1 and P2 were compared using a paired t test with a significance level at p < 0.05.

RESULTS

Twenty-five patients were recruited (21 women and 4 men). The mean age was 64.8 years (range 21-79). The patient's main compensation was based on an increase in the femoral shaft angle, and pelvic retroversion, with a subsequent decrease in sacral slope, and therefore of the lower lumbar arc. When the lumbar apex was calculated as the most anterior point touching the vertical line in a lateral radiograph, postural compensation changes modified its location usually shifting it to a more caudal position. When the lumbar apex was assessed as the most distant point of the global lumbar lordosis, its position remained stable regardless of compensation.

CONCLUSIONS

Postural changes can modify the location of the lumbar apex when understanding its location as the cornerstone of sagittal plane harmonic distribution. This concept can be useful as an additional sign to assess compensation. However, if the lumbar apex was calculated as the angular point of the global lordosis, its position remained stable regardless of postural changes. This concept can help to mold lumbar lordosis in ASD surgery.

LEVEL OF EVIDENCE IV

Diagnostic: individual cross-sectional studies with consistently applied reference standard and blinding.

Pelvic incidence correlates to sagittal spinal morphology in lenke 5 adolescent idiopathic scoliosis and influences the proximal junctional kyphosis rate after correction surgery

PURPOSE

This study aimed to investigate the relationship between pelvic incidence and sagittal spinal morphology in Lenke 5 adolescent idiopathic scoliosis (AIS) and its impact on the proximal junctional kyphosis rate after surgery.

METHODS

The study enrolled a total of 52 cases of Lenke 5 AIS between September 2009 and December 2018. Sagittal spinal morphological parameters, pelvic incidence (PI) and the proximal junctional angle were measured on full-length spinal standing lateral x-ray films preoperatively, postoperatively and at the final follow-up. Pearson correlation analysis was performed to reveal the relationship between sagittal spinal morphology and PI. Multivariable regression analysis and receiver operating characteristic (ROC) curve analysis were performed to identify the risk factors for proximal junctional kyphosis (PJK).

RESULTS

A correlation was found between PI and sagittal spinal morphological parameters, but not between PI and lumbar lordosis. The PJK rate after surgery was 23% (12/52). PI was revealed as an independent risk factor for proximal junctional kyphosis according to multivariable regression analysis (OR = 0.902, p = 0.049). Both multivariable regression analysis and ROC curve analysis verified that restoring a rational postoperative PI-LL/PLL relationship reduced the rate of PJK, including PI-LL mismatch (OR = 0.743, p = 0.046; cutoff value = - 15.5°), the LL-PI ratio (OR = 5.756, p = 0.021; cutoff value = 1.09), and the PLL-PI ratio (OR = 2.116, p = 0.016; cutoff value = 0.40).

CONCLUSIONS

PI influences sagittal spinal morphology in Lenke 5 AIS, although it does not show an inherent relationship with lumbar lordosis. PI also correlates to the PJK rate after surgery. Restoring an ideal postoperative PI-LL relationship could decrease the PJK rate.

Lumbar lordosis morphology correlates to pelvic incidence and erector spinae muscularity

The retrospective study aimed to investigate the relationship between lumbar lordosis morphology, pelvic incidence and paraspinal muscle. It enrolled asymptomatic adult volunteers aged between 18 and 45 years old. Lumbar lordosis morphology, consisting of total lumbar lordosis (LL), proximal lumbar lordosis (PLL), distal lumbar lordosis (DLL), lumbar lordosis apex (LLA) and inflexion point, was evaluated, as well as pelvic incidence (PI) and muscularity of erector spinae (ES) and multifidus. Pearson correlation was performed to analyze the relationship between each other parameter. Cases were stratified according to pelvic incidence (very low < 30°, low 30°–45°, moderate 45°–60°, and high > 60°), comparison between groups was performed by univariance analysis. 87 asymptomatic adult volunteers (33 females and 54 males) were included in the study. PLL revealed a correlation with LLA (r = 0.603, p = 0.002) and inflexion point (r = 0.536, p = 0.004), but did not DLL with LL apex (r = 0.204, p = 0.058) or inflexion point (r = 0.210, p = 0.051). PI revealed a greater correlation with PLL (r = −0.673, p < 0.001) than with DLL (r = −0.237, p = 0.045). Linear stepwise regression analysis also exhibited the correlation between PI and PLL (R² = 0.452, PLL = 16.2–0.61 * PI, p < 0.001). ES muscularity correlated with LL apex (r = −0.279, p = 0.014) and inflexion point (r = −0.227, p = 0.047). Stratification by PI demonstrated PLL increased across groups (p < 0.001), but DLL was comparable between low and moderate PI group (p = 0.329). Lumbar lordosis morphology appears to accommodate to pelvic incidence and erector spinae muscularity. Proximal lumbar lordosis has a bigger correlation with pelvic incidence than the distal lumbar lordosis. The results are helpful for restoring a rational lumbar lordosis shape in long fusion surgery.

Revisiting thoracic kyphosis: a normative description of the thoracic sagittal curve in an asymptomatic population

PURPOSE

Thoracic kyphosis (TK) remained in the shadow of lumbar lordosis. Based on Berthonnaud and Roussouly segmentation, TK is divided into two arches: upper TK (UTK) and lower TK (LTK). The purpose of this study is to propose a normative description of the TK arches in an asymptomatic adults' population and their correlation with spinal and pelvic parameters.

METHODS

This is an observational study performed on asymptomatic healthy Caucasians volunteers aged between 18 and 45 years. Each patient had a standardized standing biplanar full spine X-rays. Using KEOPS^®, sacropelvic parameters and global spinal parameters (LL, TK) as well as the inflexion point location were measured. The upper lumbar lordosis angle (ULL) as well as LTK and UTK was calculated. Patients were classified according to Roussouly morphotypes of normal spine.

RESULTS

A total of 373 adults (F/M = 1.4/1) were enrolled with mean age of 27 years. Mean UTK averaged 25.8°, while mean LTK averaged 19.8° (p < 0.001). UTK angle values were statistically the same in the five different Roussouly spinal shapes (p > 0.05), while LTK values were variable among different Roussouly spine subtypes (p < 0.05). Finally, TK showed the highest correlation with the LL mainly with the ULL (Pearson = 0.66).

CONCLUSION

In asymptomatic young adults, thoracic kyphosis is composed by two unequal arches, a stable UTK and a variable LTK, with an apex around T8 and T9 vertebra, depending on the spinal morphotype according to Roussouly classification. This should be taken into consideration when analyzing spine sagittal compensation and preparing corrections to minimize risk of mechanical complications.