Global alignment taking into account the cervical spine with odontoid hip axis angle (OD-HA)

Parameters Used to Define Horizonal Gaze: A Systematic Review

Study designSystematic review.ObjectiveTo summarise the parameters available to measure horizontal gaze, provide their values in patients and/or asymptomatic individuals, and assess their reliability.MethodsA literature search was conducted on 9/9/2023 using Medline and Embase, applying the following keywords: "horizontal gaze" or "gaze line". Articles that reported on horizontal gaze were included.ResultsTwenty-six articles published between 2015 and 2023, were included, of which 15 reported on patients, 10 reported on asymptomatic individuals, and one reported on both. The three most reported horizontal gaze parameters were McGregor's slope (n = 20 studies, asymptomatic individuals range: -8.8-10.2°), C0-C2 angle (n = 18 studies, asymptomatic individuals range: -32.0-101.5°), and chin brow vertical angle (CBVA) (n = 12 studies, asymptomatic individuals range: -5.9-12.7°). The most frequently reported correlations were between McGregor's slope and C0-C2 angle (R,-0.390-0.676; P < 0.065; n = 4 studies), McGregor's slope and CBVA (R, 0.679-0.862; P < 0.0001; n = 3 studies), as well as CBVA and slope of the line of sight (R, 0.592-0.996; P < 0.001; n = 3 studies).ConclusionThe present systematic review identified 18 parameters used to measure horizontal gaze; however, there is no gold standard. Although parameters had good to excellent inter-observer reliabilities, there were large variations in measurements among asymptomatic individuals across studies, which may imply a limited clinical relevance. Therefore, there is a need for a gold standard parameter of horizontal gaze, which uses easily identifiable landmarks that are simple to measure (reliable), relates both orbital and cervical anatomical structures, and provides insight into compensatory mechanisms in deformative or degenerative conditions.

The influence of body posture on cervical alignment measured in the sagittal plane on conventional radiographs: A systematic review

BACKGROUND CONTEXT

Cervical sagittal balance parameters are an important aid in surgical decision-making and influence outcome in cervical spine surgery. In current literature, the normative values of these parameters vary highly within and between patients. This variability might be attributed to body posture.

PURPOSE

The primary aim is to review the literature on the influence of body posture, including studies that compare sitting or standing positions possibly varying in arm positions, on cervical alignment measured in the sagittal plane on X-rays.

STUDY DESIGN

A systematic review was performed.

METHODS

PubMed, Embase, Cochrane Library, Web of Science, and CINAHL were systematically searched for articles published up to and including May 2024. The primary outcome was variability in cervical alignment in the sagittal plane as measured in altering body postures on X-rays. Quality of the included articles was assessed with the QUADAS-2 tool.

RESULTS

Out of 17,628 screened articles, eight were eligible for inclusion. Articles were excluded based on irrelevant outcomes (n= 10,372), duplicates (n= 4,315), wrong study design (n= 1,462), or the influence of body posture was not described (n= 612). Overall cervical alignment ranged from 33.3 degrees lordosis to 3.5 degrees kyphosis. In all studies, statistically significant differences in T1 Slope (T1S), C2C7 Sagittal Vertical Axis (SVA), McGregor Slope (McGS), or C7 SVA were observed with respect to body posture. The observed differences between postures for cervical alignment ranged from 1 to 16.6 degrees.

CONCLUSIONS

Body posture significantly influences cervical alignment values measured in the sagittal plane on X-rays. Studies investigating this influence are scarce and vary highly in investigated body postures. Standardization of body posture is imperative to enable optimal comparison of cervical sagittal balance parameters within and between patients, but also between studies. Moreover, the high variability observed raises questions about the comparability of measured values in previously published studies.

A new 3D full-body scanner analyzing the sagittal and coronal balance of the adult spine: a preliminary prospective observational study

BACKGROUND

The degenerative spondylosis can cause the difficulty in maintaining sagittal and coronal alignment of spine, and X-ray parameters are the gold standard to analyze the malalignment. This study aimed to develop a new 3D full body scanner to analyze the spinal balance and compare it to X-ray parameters.

METHODS

Ninety-seven adult participants who suffer degenerative spondylosis underwent 3D full body scanning, whole spine X-rays, clinical questionnaires and body composition analyses. The 5 inflection points (ear, shoulder, hip, knee, ankle) of the 3D scanner in the sagittal plane were automatically labeled by an AI algorithm. Three concepts are created including "the angle between two points with respect to the plumb line", "the horizontal distances between two points in the sagittal plane" and "the angle between three points". For the coronal plane, the shoulder gradient was analyzed. X-ray parameters of cervical, thoracolumbar and whole spine sagittal balance and coronal balances were compared. The body composition data and clinical questionnaire scores were compared to x-ray and 3D scanner parameters.

RESULTS

The correlation coefficient (C.C.) of dAB_hor (horizontal distance between ear and shoulder in the sagittal plane) and C2-C7 SVA was 0.478 (p-value < 0.001). The C.C. of aAC_sag (sagittal angle of ear-hip from the plumb line) and ODHA was 0.336 (p < 0.001). About coronal balance, the C.C. of shoulder gradient and clavicle angle from x-ray was 0.373 (p < 0.001). The C.C.s were merely affected by body composition data. But in multiple regression analysis, BMI affected 3D scanner data. Clinical symptoms showed correlations with aBCD(shoulder-hip-knee) and aCDE(hip-knee-ankle angle), which may reflect a compensatory pelvic retroversion and knee flexion for positive sagittal imbalance.

CONCLUSIONS

This new 3D scanner has some strengths like radiation-free methods, correlation with x-ray parameters and clinical symptoms, independence to body composition data, and possibility of analyzing dynamic spine balance.

Sagittal spinal alignment measurements and evaluation: Historical perspective

Spinal alignment analysis play an important role in evaluating patients and planning surgical corrections for adult spinal deformity. The history of these parameters is relatively short with the first parameter, the Cobb angle, introduced in 1948 as part of an effort to improve scoliosis evaluation. New developments in the field were limited for nearly 30 years before better imaging technology encouraged new theories and later data about spinal alignment and the relationship between the spine and pelvis. These efforts would ultimately contribute to the creation of foundational spinal alignment parameters, including pelvic incidence, pelvic tilt, and sacral slope. By the 1990s, spinal alignment had become a sustained area of investigation for spinal surgeons and researchers. Novel alignment parameters have since been introduced as our knowledge has evolved and has allowed for valuable research that demonstrates the clinical and surgical value of alignment measurement. This manuscript will explore the history of spinal alignment analysis over the decades.

Artificial Intelligence Assistance for the Measurement of Full Alignment Parameters in Whole-Spine Lateral Radiographs

BACKGROUND

Measuring spinal alignment with radiological parameters is essential in patients with spinal conditions likely to be treated surgically. These evaluations are not usually included in the radiological report. As a result, spinal surgeons commonly perform the measurement, which is time-consuming and subject to errors. We aim to develop a fully automated artificial intelligence (AI) tool to assist in measuring alignment parameters in whole-spine lateral radiograph (WSL X-rays).

METHODS

We developed a tool called Vertebrai that automatically calculates the global spinal parameters (GSPs): Pelvic incidence, sacral slope, pelvic tilt, L1-L4 angle, L4-S1 lumbo-pelvic angle, T1 pelvic angle, sagittal vertical axis, cervical lordosis, C1-C2 lordosis, lumbar lordosis, mid-thoracic kyphosis, proximal thoracic kyphosis, global thoracic kyphosis, T1 slope, C2-C7 plummet, spino-sacral angle, C7 tilt, global tilt, spinopelvic tilt, and hip odontoid axis. We assessed human-AI interaction instead of AI performance alone. We compared the time to measure GSP and inter-rater agreement with and without AI assistance. Two institutional datasets were created with 2267 multilabel images for classification and 784 WSL X-rays with reference standard landmark labeled by spinal surgeons.

RESULTS

Vertebrai significantly reduced the measurement time comparing spine surgeons with AI assistance and the AI algorithm alone, without human intervention (3 minutes vs. 0.26 minutes; P < 0.05). Vertebrai achieved an average accuracy of 83% in detecting abnormal alignment values, with the sacral slope parameter exhibiting the lowest accuracy at 61.5% and spinopelvic tilt demonstrating the highest accuracy at 100%. Intraclass correlation analysis revealed a high level of correlation and consistency in the global alignment parameters.

CONCLUSIONS

Vertebrai's measurements can accurately detect alignment parameters, making it a promising tool for measuring GSP automatically.

Assessment of malalignment at early stage in adolescent idiopathic scoliosis: a longitudinal cohort study

INTRODUCTION

Our objective was to assess abnormalities of the odontoid-hip axis (OD-HA) angle in a mild scoliotic population to determine whether screening for malalignment would help predict the distinction between progressive and stable adolescent idiopathic scoliosis (AIS) at early stage.

MATERIALS AND METHODS

All patients (non-scoliotic and AIS) underwent a biplanar X-ray between 2013 and 2020. In AIS, inclusion criteria were Cobb angle between 10° and 25°; Risser sign lower than 3; age higher than 10 years; and no previous treatment. A 3D spine reconstruction was performed, and the OD-HA was computed automatically. A reference corridor for OD-HA values in non-scoliotic subjects was calculated as the range [5th-95th percentiles]. A severity index, helping to distinguish stable and progressive AIS, was calculated and weighted according to the OD-HA value.

RESULTS

Eighty-three non-scoliotic and 205 AIS were included. The mean coronal and sagittal OD-HA angles in the non-scoliotic group were 0.2° and -2.5°, whereas in AIS values were 0.3° and -0.8°, respectively. For coronal and sagittal OD-HA, 27.5% and 26.8% of AIS were outside the reference corridor compared with 10.8% in non-scoliotic (OR = 3.1 and 3). Adding to the severity index a weighting factor based on coronal OD-HA, for thoracic scoliosis, improved the positive predictive value by 9% and the specificity by 13%.

CONCLUSION

Analysis of OD-HA suggests that AIS patients are almost three times more likely to have malalignment compared with a non-scoliotic population. Furthermore, analysis of coronal OD-HA is promising to help the clinician distinguish between stable and progressive thoracic scoliosis.

Practical Methods of Assessing Coronal Alignment and Outcomes in Adult Spinal Deformity Surgery: A Comparative Analysis

STUDY DESIGN

Asymptomatic cohort: prospective, cross-sectional, multicenter. Symptomatic: retrospective, multisurgeon, single-center.

OBJECTIVE

To assess the association between cranial coronal alignment and adult spinal deformity (ASD) surgical risk and outcomes.

SUMMARY OF BACKGROUND DATA

ASD leads to decreased quality of life. Studies have shown that coronal malignment (CM) is associated with worse surgical outcomes.

MATERIALS AND METHODS

A total of 468 adult participants were prospectively enrolled in the asymptomatic cohort. Totally, 172 symptomatic ASD patients with 2-year follow-ups were retrospectively enrolled in the symptomatic cohort. Three cranial plumb line parameters: the positions of the plumb lines from the midpoint between the medial orbital rims (ORB-L5), the odontoid (OD-L5), and the C7 centroid (C7-L5) relative to the L5 pedicle, were measured. Each subject had plumb line medial (M), touching (T), or lateral (L) to either pedicle. The association between each group of patients and radiographic parameters, intraoperative variables, patient-reported outcomes, and clinical outcomes were analyzed.

RESULTS

In the asymptomatic cohort, OD-L5 was medial to or touching the L5 pedicle in 98.3% of volunteers. In the symptomatic patients, preoperative OD-L5-L exhibited higher mean age (56.2±14.0), odontoid-coronal vertical axis (OD-CVA) (5.5±3.3 cm), Oswestry disability index (ODI) score (40.6±18.4), pelvic fixation rate (56/62, 90.3%), OR time (528.4±144.6 min), median estimated blood loss (1300 ml), and durotomy rate (24/62, 38.7%). A similar pattern of higher CVA, preoperative ODI, intraoperative pelvic fixation rate, OR time, estimated blood loss, and durotomy rate was observed in ORB-L5-L and C7-L5-L patients. Final follow-up postoperative OD-L5-L was associated with higher rates of proximal junctional kyphosis (13.0%) and pseudarthrosis (17.4%).

CONCLUSION

Preoperative OD-L5, ORB-L5, and C7-L5 lateral to pedicles were associated with worse preoperative ODI and higher intraoperative complexity. Postoperative OD-L5-L was associated with higher rates of proximal junctional kyphosis and pseudarthrosis. Postoperative CM, approximated by the cranial plumb line lateral to the L5 pedicles, was associated with sagittal plane complications.

Gravity Line-Hip Axis Offset as a Guide for Global Alignment to Prevent Recurrent Proximal Junctional Kyphosis/Failure

BACKGROUND AND OBJECTIVES

Proximal junctional kyphosis/failure (PJK/F) is a potentially serious complication after adult spinal deformity (ASD) corrective surgery. Recurrent PJK/F is especially troublesome, necessitating fusion extension and occasionally resulting in irreversible neurological deficits. The gravity line (GL) offers valuable insights into global sagittal balance. This study aims to examine the postoperative GL-hip axis (GL-HA) offset as a critical risk factor for recurrent PJK/F.

METHODS

We retrospectively reviewed patients with ASD who had undergone revision surgery for initial PJK/F at a single academic center. Patients were categorized into 2 groups: nonrecurrent PJK/F group and recurrent PJK/F group. Demographics, surgical characteristics, preoperative and postoperative parameters of spinopelvic and global alignment, and the Scoliosis Research Society-22 scores were assessed. We examined these measures for differences and correlations with recurrent PJK/F.

RESULTS

Our study included 32 patients without recurrent PJK/F and 28 patients with recurrent PJK/F. No significant differences were observed in baseline demographics, operative characteristics, or Scoliosis Research Society-22 scores before and after surgery. Importantly, using a cutoff of -52.6 mm from logistic regression, there were considerable differences and correlations with recurrent PJK/F in the postoperative GL-HA offset, leading to an odds ratio of 7.0 (95% CI: 1.94-25.25, P = .003).

CONCLUSION

Postoperative GL-HA offset serves as a considerable risk factor for recurrent PJK/F in patients with ASD who have undergone revision surgery. Overcorrection, with GL-HA offset less than -5 cm, is associated with recurrent PJK/F. The instrumented spine tends to align the GL near the HA, even at the cost of proximal junction.

Establish a new parameter "horizontal view-axial angle" and explore its role in the treatment of atlantoaxial instability diseases

Objective

The objective of the study is to establish a new parameter that can be clearly measured on x-ray images to complement the description of the sagittal alignment of the craniocervical junction. The authors anticipate that this new parameter will enhance surgeons' understanding of the sagittal alignment of the craniocervical junction and play a positive role in the guidance of intraoperative reduction and in the evaluation of postoperative outcomes of patients with atlantoaxial instability.

Methods

From November 2018 to June 2020, a total of 159 asymptomatic subjects who underwent frontal and lateral cervical x-ray examination in the Second Affiliated Hospital of Soochow University were included in the study. Age, gender, previous spinal trauma, and disease history of each subject were recorded. After screening, 127 effective samples were finally obtained. When taking lateral cervical radiographs, all subjects placed their neck in a neutral position and looked straight ahead with both eyes. On the obtained lateral x-ray images, a straight line was drawn from the radix to the anterior clinoid process; another line was made along the posterior edge of the C2 vertebral body; and the angle between the two lines was measured, which was defined as the "horizontal view-axial angle." The angle formed by the tangent of the posterior edge of the C2 vertebra and C7 vertebral body is the "C2-C7 angle," which was used to describe the curvature of the lower cervical vertebra. The normal range of horizontal view-axial angle and its relationship with C2-7 angle were evaluated.

Results

The average C2-C7 angle of male subjects was (14.0° ± 7.4°), while that of female subjects was (11.09° ± 7.36°). The average horizontal view-axial angle of male subjects was (92.79° ± 4.52°), and that of female subjects was (94.29° ± 4.50°). Pearson correlation test showed that there was a significant negative correlation between horizontal view-axis angle and C2-C7 angle.

Conclusions

For patients with atlantoaxial instability diseases, the horizontal view-axis angle is expected to be a sagittal parameter to guide the intraoperative reduction and evaluate postoperative outcomes.

Spinopelvic measurements of sagittal balance with deep learning: systematic review and critical evaluation

PURPOSE

To summarize and critically evaluate the existing studies for spinopelvic measurements of sagittal balance that are based on deep learning (DL).

METHODS

Three databases (PubMed, WoS and Scopus) were queried for records using keywords related to DL and measurement of sagittal balance. After screening the resulting 529 records that were augmented with specific web search, 34 studies published between 2017 and 2022 were included in the final review, and evaluated from the perspective of the observed sagittal spinopelvic parameters, properties of spine image datasets, applied DL methodology and resulting measurement performance.

RESULTS

Studies reported DL measurement of up to 18 different spinopelvic parameters, but the actual number depended on the image field of view. Image datasets were composed of lateral lumbar spine and whole spine X-rays, biplanar whole spine X-rays and lumbar spine magnetic resonance cross sections, and were increasing in size or enriched by augmentation techniques. Spinopelvic parameter measurement was approached either by landmark detection or structure segmentation, and U-Net was the most frequently applied DL architecture. The latest DL methods achieved excellent performance in terms of mean absolute error against reference manual measurements (~ 2° or ~ 1 mm).

CONCLUSION

Although the application of relatively complex DL architectures resulted in an improved measurement accuracy of sagittal spinopelvic parameters, future methods should focus on multi-institution and multi-observer analyses as well as uncertainty estimation and error handling implementations for integration into the clinical workflow. Further advances will enhance the predictive analytics of DL methods for spinopelvic parameter measurement.

LEVEL OF EVIDENCE I

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

Assessment of dynamic balance during walking in patients with adult spinal deformity

PURPOSE

To assess dynamic postural alignment in ASD during walking using a subject-specific 3D approach.

METHODS

69 ASD (51 ± 20 years, 77%F) and 62 controls (34 ± 13 years, 62%F) underwent gait analysis along with full-body biplanar Xrays and filled HRQoL questionnaires. Spinopelvic and postural parameters were computed from 3D skeletal reconstructions, including radiographic odontoid to hip axis angle (ODHA) that evaluates the head's position over the pelvis (rODHA), in addition to rSVA and rPT. The 3D bones were then registered on each gait frame to compute the dynamic ODHA (dODHA), dSVA, and dPT. Patients with high dODHA (> mean + 1SD in controls) were classified as ASD-DU (dynamically unbalanced), otherwise as ASD-DB (dynamically balanced). Between-group comparisons and relationship between parameters were investigated.

RESULTS

26 patients were classified as ASD-DU having an average dODHA of 10.4° (ASD-DB: 1.2°, controls: 1.7°), dSVA of 112 mm (ASD-DB: 57 mm, controls: 43 mm), and dPT of 21° (ASD-DB: 18°, controls: 14°; all p < 0.001). On static radiographs, ASD-DU group showed more severe sagittal malalignment than ASD-DB, with more altered HRQoL outcomes. The ASD-DU group had an overall abnormal walking compared to ASD-DB & controls (gait deviation index: 81 versus 93 & 97 resp., p < 0.001) showing a reduced flexion/extension range of motion at the hips and knees with a slower gait speed and shorter step length. Dynamic ODHA was correlated to HRQoL scores.

CONCLUSION

Dynamically unbalanced ASD had postural malalignment that persist during walking, associated with kinematic alterations in the trunk, pelvis, and lower limbs, making them more prone to falls. Dynamic-ODHA correlates better with HRQoL outcomes than dSVA and dPT.