Correlations of Cervical Sagittal Alignment before and after Occipitocervical Fusion

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.

Recent Global Trends and Hotspots in Occipitocervical Fusion: A Bibliometric Analysis and Visualization Study

BACKGROUND

Occipitocervical arthrodesis has a variety of indications to treat craniocervical and atlantoaxial pathologies for which a selective cervical fusion would not provide sufficient stability. Over time, the indications for occipitocervical fusions (OCFs) have evolved, as new technologies and surgical techniques were developed. In this bibliometric analysis, we aim to explore the progression of OCF literature over time, analyzing the trends in publications and citations, publishing countries and authors, keywords, and topics.

METHODS

The Web of Science database was used for data retrieval on July 3, 2024, with the search "occipitocervical fusion" OR "occipito-cervical fusion" OR "occipitocervical arthrodesis" OR "occipital cervical fusion" OR "occipital cervical arthrodesis" OR ("OCF" AND "spine surgery"). Excel was used to create the citation analysis and publication trend figures, along with the publishing countries and author analysis. The bibliometric software VosViewer was used to generate the keyword co-occurrence network visualizations.

RESULTS

Overall, 762 articles were extracted. The number of pertinent publications and citations increased until 2020 before beginning to decrease. We found that Ehlers Danlos syndrome has become a more prevalent topic, as the association between Ehlers Danlos syndrome and craniocervical instability has received further scrutiny. "Dysphagia" continues to be a commonly cited topic, while, conversely, rheumatoid arthritis has decreased in publication frequency, possibly related to advances in medical management and surgical techniques. Overall, the United States, China, and Japan are the top publishing countries.

CONCLUSIONS

This analysis of OCF literature provides a helpful overview of emerging trends and clinician concerns, especially as seen through the perspective of time.

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.

Preoperative radiological indicators for prediction of difficult laryngoscopy in patients with atlantoaxial dislocation

Background

Difficult airway remains a great challenge in patients with atlantoaxial dislocation (AAD). Preoperative evaluation and reliable prediction are required to facilitate the airway management. We aimed to screen out reliable radiological indicators for prediction of difficult laryngoscopy in patients with AAD.

Methods

A retrospective nested case-control study within a single center longitudinal AAD cohort was conducted to investigate the radiological indicators. All the patients with difficult laryngoscopy from 2010 to 2021 were enrolled as the difficult laryngoscopy group. Others in the cohort without difficult laryngoscopy were randomly selected as the non-difficult laryngoscopy group by individually matching with the same gender, same surgery year, and similar age (±5 years) at a ratio of 6:1. Radiological data on preoperative lateral X-ray images between the two groups were compared. Bivariate logistic regression model was applied to screen out the independent predictive indicators and calculate the odds ratios of indicators associated with difficult laryngoscopy. Receiver operating characteristic curve and area under the curve (AUC) were used to describe the discrimination ability of indicators.

Results

A total of 154 patients were finally analyzed in this study. Twenty-two patients with difficult laryngoscopy and matched with 132 controls. Four radiological parameters showed significant difference between the two groups. Among which, ΔC1C2D (the difference of the distance between atlas and axis in the neutral and extension position), owned the largest AUC.

Conclusions

ΔC1C2D could be a valuable radiologic predictor for difficult laryngoscopy in patients with AAD.

Radiographic Predictors of Subaxial Subluxation After Atlantoaxial Fusion

STUDY DESIGN

A retrospective study.

OBJECTIVE

The aim of this study was to clarify preoperative radiographic predictors associated with the development of subaxial subluxation (SAS) after surgery.

BACKGROUND

The incidence of atlantoaxial fusion for atlantoaxial instability has been increasing. SAS can develop after surgery despite atlantoaxial fusion with the optimal C1-C2 angle. We hypothesized that preoperative discordant angular contribution in the upper and subaxial cervical spine is associated with the occurrence of postoperative SAS.

MATERIALS AND METHODS

Patients who underwent surgery for atlantoaxial instability with a minimum 5-year follow-up and control participants were included. The O-C2 angle, C2 slope (C2S), C2-C7 cervical lordosis (CL), and T1 slope (T1S) were measured. We focused on the angular contribution ratio in the upper cervical spine to the whole CL, and the preoperative C2/T1S ratio was defined as the ratio of C2S to T1S.

RESULTS

Twenty-seven patients (SAS=11, no-SAS=16; mean age, 60.7 y old; 77.8% female; mean follow-up duration, 6.8 y) and 23 demographically matched control participants were enrolled. The SAS onset was at 4.7 postoperative years. Preoperatively, the O-C2 angle, C2-C7 CL, and T1S were comparable between the SAS, no-SAS, and control groups. The preoperative C2S and C2/T1S ratio were smaller in the SAS group than in the no-SAS or control group (C2S, 11.0 vs. 18.4 vs. 18.7 degrees; C2/T1S ratio, 0.49 vs. 0.77 vs. 0.78, P <0.05). The receiver operating characteristic curve analysis demonstrated that the C2/T1S ratio had higher specificity and similar sensitivity as a predictor of postoperative SAS than C2S (specificity: 0.90 vs. 0.87; sensitivity: 0.73 vs. 0.73). The estimated cutoff values of the C2S and C2/T1S ratio were 14 degrees and 0.58, respectively.

CONCLUSIONS

The preoperative C2/T1S ratio was closely associated with postoperative SAS. Patients with a C2/T1S ratio <0.58 were at a high risk of SAS after atlantoaxial fusion.

LEVEL OF EVIDENCE

Level 4.

Comparison of three methods for measuring C0-1 angles and C0-2 angles

BACKGROUND

The mutual compensatory relationship between the upper cervical sagittal alignment and the lower cervical sagittal alignment has been repeatedly reported. However, the evaluation of the upper cervical sagittal parameters are varied in previous studies. This retrospective study was performed to compare three methods for measuring the upper cervical sagittal parameters.

METHODS

A total of 263 individuals with standing neutral lateral cervical radiographs were included in this study. The Frankfort horizontal line (FHL), foramen magnum line (FML), and McGregor line (ML) were separately used as the reference lines for measuring the C0-1 angle and C0-2 angle. Intraclass correlation (ICC) values were used to compare the consistency and repeatability of the three methods. Pearson's correlation analysis was used to analyze the correlation between the sagittal parameters of the upper and lower cervical spine.

RESULTS

The interobserver and intraobserver ICC values obtained from using the ML to measure the C0-1 angle and C0-2 angle were both higher than those obtained from using the FML or FHL. The C0-1 angle and C0-2 angle measured by the three methods were negatively correlated with the C2-7 angle. The upper sagittal parameters measured by the FHL were the most correlated with the C2-7 angle. The correlation between the C0-1 angle measured by the three methods and the C0-2 angle measured with the FHL or ML and the C2-7 angle increased with aging.

CONCLUSION

Use of the ML to measure the C0-1 angle and C0-2 angle has higher reliability. Use of the FHL to measure the sagittal alignment of the upper cervical spine is more suitable for evaluating the compensation mechanism between the upper and the lower cervical spine.

Feasibility of lateral mass screw insertion in patients with the risky triad of C1: evaluation of the over-the-arch technique

OBJECTIVE

The objective of this study was to evaluate the feasibility and complications of the over-the-arch (OTA) technique for screw insertion into the C1 lateral mass in patients in whom conventional techniques (i.e., posterior arch [PA] and inferior lateral mass [ILM]) are not feasible due to 1) PA with a very small height (< 3.5 mm), 2) a caudally tilted PA blocking the inferior part of the C1 lateral mass, or 3) loss of height at the ILM (< 3.5 mm).

METHODS

The authors reviewed the medical records of 60 patients who underwent C1 screw fixation with the OTA technique (13 screws) and the PA/ILM technique (107 screws) between 2011 and 2019. Vertebral artery (VA) injuries, screw malposition, and bony union were radiologically assessed. Clinical outcome measures, including Neck Disability Index (NDI), Japanese Orthopaedic Association (JOA) scale score, and occipital neuralgia, were recorded.

RESULTS

Thirteen OTA screws were successfully inserted without any major complications. NDI and JOA scale scores did not show significant differences between the two groups at final follow-up. No VA injuries were recognized during screw insertion. There was no evidence of ischemic damage to the VA or bony erosion in the occiput or atlas. Medial wall violation was observed in 1 screw (7.7%); however, no C0-1, C1-2, or lateral wall violations were observed. No patients developed new-onset neuralgia postoperatively after C1 fixation with the OTA technique.

CONCLUSIONS

The OTA technique was safe and useful for C1 screw fixation in patients in whom conventional techniques could not be employed.

Variation of cervical sagittal alignment parameters according to gender, pelvic incidence and age

PURPOSE

The aim was to describe radiographic cervical sagittal alignment variations according to age, gender and pelvic incidence (PI) and to investigate relationships with thoracic alignment.

METHODS

A total of 2599 individuals (5-93 years) without spinal deformity were studied. Cranial cervical parameters were: McGregor slope, occipita-C2 angle, McGregor-C2 lordosis and C1-C2 lordosis. Caudal cervical parameters were: C2-C7, cranial arch and caudal arch lordosis and C7- and T1-slope. A Bayesian inference compared parameter distributions. Correlations with spinopelvic and global alignment parameters were investigated.

RESULTS

Among cranial cervical parameters, variations of McGregor slope were non-significant. McGregor-C2 lordosis and C1-C2 lordosis were smaller in males and increased significantly during growth, whereas the occipito-C2 angle decreased (Pr > 0.95). The occipito-C2 angle was larger and McGregor-C2 lordosis was smaller in low PI (Pr > 0.95). Among caudal cervical parameters, C2-C7 lordosis and C7- and T1-slope were larger in males and increased after 50 years (Pr > 0.95). Lordosis changes were non-significant in the cranial arch, whereas values increased in the caudal arch after 35 years (Pr > 0.95). Caudal parameter differences were non-significant between PI groups. Strong correlations existed between C2-C7, caudal arch lordosis, C7-slope, T1-slope and thoracic kyphosis. The sagittal vertical axis C2 correlated with caudal arch lordosis and T1-slope (ρ > 0.5; Pr > 0.95).

CONCLUSION

Cervical alignment parameters vary according to age, gender and PI. In the cranial cervical spine, changes occur mainly during growth. In the caudal cervical spine, lordosis increases in the caudal arch, which is related to thoracic kyphosis increase with age. The caudal cervical arch acts as a compensatory segment by progressive extension, allowing horizontal gaze.

Sequential sagittal alignment changes in the cervical spine after occipitocervical fusion

BACKGROUND

There are few studies regarding sequential changes in the sagittal alignment of the upper and lower cervical regions of the spine after occipitocervical fusion (OCF). In addition, no comparisons of cervical sagittal alignment (CSA) between patients with craniocervical junction disorders (CJDs) and normal populations have been reported.

AIM

To compare the CSA of patients with CJDs with that of normal controls and investigate the sequential changes in the CSA of the upper and lower cervical spine after OCF.

METHODS

Eighty-four patients who underwent OCF (OCF group) and 42 asymptomatic volunteers (control group) were included. Radiographic parameters, including the occipital to C2 angle (O-C2a), occipital and external acoustic meatus to axis angle (O-EAa), C2–7 angle (C2-7a), and pharyngeal inlet angle (PIA), were measured and compared pre- and postoperatively. The correlations among the parameters were analyzed using Pearson’s correlation test.

RESULTS

The O-C2a and PIA of the OCF group were smaller than those of the control group, while their O-EAa and C2-7a values were larger than those of the normal controls. There were no significant differences in O-C2a, C2-7a, or PIA in the OCF group at baseline, 1 mo, or the final follow-up after surgery. The Pearson’s correlation results showed that there were significant correlations between the O-C2a and C2Ta, C2-7a, C2-7 sagittal vertical axis (SVA), and PIA at 1 mo after OCF surgery and between O-C2a and O-EAa, C2Ta, C2-7a, C2-7 SVA, and PIA at the final follow-up.

CONCLUSION

Patients with CJDs have a more kyphotic upper CSA and a more lordotic lower CSA than normal controls. The effectiveness of OCF surgery in restoring CSA may be limited by the realignment of the craniocervical junction being neglected. The reduction in O-C2a after OCF surgery may increase C2-7a and decrease PIA.

Understanding "Kyphosis" and "Lordosis" for Sagittal Balancing in Two Common Standing Postures

STUDY DESIGN

Cross-sectional radiographic comparison study.

OBJECTIVE

The aim of this study was to understand whole-body balancing in directed and natural standing postures, through comparison of kypholordotic ratios on whole-body radiographs of young, healthy subjects.

SUMMARY OF BACKGROUND DATA

Recent studies highlighted the importance of understanding whole-body balancing, proposing the use of the more physiological natural standing posture, together with the conventional directed standing posture, for imaging.

METHODS

Sixty healthy, 21-year-old subjects (36 males, 24 females) were recruited. EOS whole-body radiographs of subjects in directed and natural standing postures were obtained. Radiographic parameters compared include C2-sagittal vertical axis (C2-SVA), C7-SVA, C2-7-SVA, global cervical angles (C0-T1 and C2-C7), regional cervical angles (C0-C2, C2-C4, C4-C7), T1-slope, global thoracic angles (T1-T12 and T1-inflection vertebra [Inf]), thoracolumbar angle (T11-L2), global lumbar angles (T12-S1 and Inf-S1), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), spinocoxa angle (SCA), and femoral alignment angle (FAA). Kypholordotic ratios of T1-12/T12-S1, T1-Inf/Inf-S1, Tl-Inf/SCA, and (T1-Inf + FAA)/(T1-slope + SCA) were calculated and compared.

RESULTS

Compared to directed standing, natural standing has greater C2-SVA and C7-SVA, more lordotic global and regional cervical angles (except C0-2 angle), higher T1-slope, larger T1- T12 and T1-Inf kyphotic angles, smaller T12-S1 and Inf-S1 lordotic angles, larger PT, more lordotic SCA, and smaller SS and FAA angles. T1-12/T12-S1 and T1-Inf/Inf-S1 ratios in natural standing, and (Tl-Inf + FAA)/(T1-slope + SCA) ratio in both postures approximate 1. There were significant differences between postures for Tl-l2/Tl2-Sl, Tl-Inf/Inf-Sl and Tl-Inf/SCA ratios.

CONCLUSION

Whole-body balancing requires understanding of the balance between kyphosis and lordosis, which varies with the posture of patients. Analysis of kypholordotic ratios obtained in this study allude to the importance of performing whole-body imaging in the directed standing posture, and whole-spine or whole-body imaging in the natural standing posture, so as to fully understand spinal and whole body balancing for spinal realignment surgeries.Level of Evidence: Level 3.

[Relationship between O-EA angle and lower cervical curvature in patients with anterior atlantoaxial dislocation before and after occipitocervical fusion]

Objective

To investigate the relationship between O-EA angle and lower cervical curvature in patients with anterior atlantoaxial dislocation undergoing occipitocervical fusion, and to analyze the effect of O-EA angle on lower cervical curvature.

Methods

The clinical data of 61 patients with anterior atlantoaxial dislocation undergoing occipitocervical fusion who were admitted between April 2010 and July 2018 and met the selection criteria were retrospectively analyzed. There were 32 males and 29 females, with an age of 14-76 years (mean, 50.7 years). The fixed segment included 19 cases of C ₀-C ₂, 27 cases of C ₀-C ₃, 14 cases of C ₀-C ₄, and 1 case of C ₀-C ₅. The O-EA angle, C _2-7 Cobb angle, and T ₁ tilt angle were measured before operation and at last follow-up. According to the O-EA angle measured at last follow-up, the patients were divided into <95° group (group A), 95°-105° group (group B), and >105° group (group C), and compared the differences of gender, age, fixed segment (short segment was at C ₃ and above, long segment was beyond C ₃), and C _2-7 Cobb angle. Correlation analysis between the O-EA angle and C _2-7 Cobb angle before operation and at last follow-up, as well as the changes of O-EA angle and C _2-7 Cobb angle between before operation and at last follow-up were analyzed.

Results

All 61 patients were followed up 12-24 months, with an average of 22.4 months. There was no significant difference in O-EA angle, C _2-7 Cobb angle, and T ₁ tilt angle before operation and at last follow-up ( P>0.05). According to the last follow-up O-EA angle grouping, there were 14 cases in group A, 29 cases in group B, and 18 cases in group C. There was no significant difference in age, gender composition, and fixed segment composition among the three groups ( P>0.05); the differences in C _2-7 Cobb angles among the three groups were significant ( P<0.05), groups A, B, and C showed a gradually increasing trend. The O-EA angle was positively correlated with C _2-7 Cobb angle before operation and at last follow-up ( r=0.572, P=0.000; r=0.618, P=0.000); O-EA angle change at last follow-up was also positively correlated with C _2-7 Cobb change ( r=0.446, P=0.000).

Conclusion

The O-EA angle of patients with anterior atlantoaxial dislocation is positively correlated with C _2-7 Cobb angle. Too large O-EA angle should be avoided during occipitocervical fixation, otherwise it may accelerate the degeneration of the lower cervical spine.

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.

Occipitocervical Fixation: General Considerations and Surgical Technique

STUDY DESIGN

Narrative literature review.

OBJECTIVE

To review and present details on the occipitocervical fixation (OCF) technique as well as considerations for planning the procedure.

METHODS

We present the surgical technique of OCF in a step-by-step didactic and practical manner with surgical tips and tricks, including C1 and C2 screw fixation techniques. Additionally, we discuss complications, the extension of fusion, types of OCF, and how to avoid common side effects associated with OCF.

RESULTS

The complex and mobile anatomy of the craniocervical junction, when requiring fixation and fusion, warrants rigid instrumentation that can be achieve using a modern screw-plate-rod construct. Indications for OCF are craniocervical instability, and atlantoaxial instability when selective atlantoaxial fusion is not feasible. OCF generally involves occiput-C2 fusion. C1 fixation is generally unnecessary, since it increases the surgical time and is associated with the risk of vascular complications. Selective occiput-C2 fusion is recommended when there is no need for including the cervical subaxial region (eg, when stenosis or fractures coexist in the subaxial spine), and good fixation is achieved at C2. Most instrumentation systems now have occipital plates that are not pre-integrated to rods, making fixation much simpler. Surgical steps, from position to wound closure, are presented in detail, with pearls for practice and discussion of cervical alignment.

CONCLUSIONS

OCF is a challenging procedure, with potential risk of severe adverse effects. Understanding the surgical indications, as well as the nuances of the surgical technique, is required to improve patient outcomes and avoid complications.

Cranial Kyphotic Change After Multilevel Anterior Cervical Corpectomy and Fusion May Lead to Myelopathy Recurrence

OBJECTIVE

To determine the characteristic alignment change in patients with myelopathy recurrence after multilevel anterior cervical corpectomy and fusion (m-ACCF).

METHODS

We analyzed 52 patients who underwent m-ACCF, including 20 who underwent revision surgeries for myelopathy recurrence (R group) and 32 postoperative asymptomatic patients (A group). Classic alignment parameters (cervical lordosis angle, cervical sagittal vertical axis, and fusion area angle and length) and original alignment parameters (α-β, β-bone graft [BG], BG-γ, and γ-δ angles) were measured preoperatively, postoperatively, and at follow-up or before revision surgery. The difference in the amount of change in parameters between groups was analyzed. The relationship between distribution of restenotic lesions and characteristic alignment change in the R group was evaluated.

RESULTS

Cervical lordosis angle, fusion area angle, and fusion area length in the R group significantly decreased postoperatively compared with the A group (P < 0.01, P < 0.01, and P = 0.04). Compared with the A group, α-β and β-BG angles in the R group significantly decreased (P < 0.01), indicating kyphotic change on the cranial side. BG-γ and γ-δ angles in the R group significantly increased (P < 0.01), indicating lordotic change in the caudal fused area. Restenotic lesions significantly increased on the cranial side in the R group (cranial side, 19 levels; caudal side, 5 levels; P < 0.01).

CONCLUSIONS

In patients with myelopathy recurrence after m-ACCF, the cranial side has significant kyphosis and the caudal side has lordosis. Moreover, 79.2% of the restenotic lesions were significantly maldistributed on the cranial side. Surgeons should pay close attention to cranial kyphosis inducing myelopathy recurrence after m-ACCF.

Compensatory Mechanisms for Kyphotic Change in the Cervical Spine According to Alignment Analysis of the Cases after Anterior Cervical Corpectomy and Fusion

BACKGROUND

Compensatory mechanisms for cervical kyphosis are unclear. Few alignment analyses have targeted ongoing cervical kyphosis and detailed the effects of compensatory alignment changes.

METHODS

We analyzed the radiographic alignment parameters of 31 patients (21 men and 10 women) with postoperative kyphotic changes after anterior cervical corpectomy and fusion (ACCF) between 2006 and 2015. This analysis included lordotic angle of the fusion area, fusion area length, cervical lordosis angle (CL), O-C7 angle (O-C7a), and cervical sagittal vertical axis (cSVA) as basic parameters and occipito-C2 angle (O-C2a), adjacent cranial angle, adjacent caudal angle, and T1 slope as compensatory parameters at 2 time points after surgery.

RESULTS

Alignment analysis revealed that CL was significantly decreased by 5.0 ± 7.7° (P < 0.01) and O-C7a was changed by only -0.2 ± 6.8° (P = 0.75). An inverse correlation was found between ΔCL and ΔO-C2a (ρ = -0.40), with a nearly 1:1 relationship in the scatter diagram. ΔT1 slope had no direct compensatory correlation with ΔCL (P = 0.28) but was strongly correlated with ΔcSVA (ρ = 0.78). The scatter diagram of ΔcSVA and ΔT1 slope showed compensatory relevance and a shifted point to its collapse as the T1 slope lost control of cSVA; thereafter, both parameters incessantly increased, and ΔT1 and ΔcSVA became positive.

CONCLUSIONS

When CL decreased after ACCF, ΔO-C2 immediately compensated for the CL loss that could lead to failure to obtain horizontal gaze. If cSVA increased, Δcaudal adjacent angle and ΔT1 slope (extension below the kyphosis) compensated for the horizontal offset translation. The noncompensatory status (ΔcSVA and ΔT1 positive) may necessitate further correction surgery in which the caudal fused level is beyond T1.

Evaluating Cervical Sagittal Alignment in Cervical Myelopathy: Are Sitting Cervical Radiographs and Standing Whole-Spine Radiographs Equally Useful?

STUDY DESIGN

Retrospective review of medical charts and radiographic data.

OBJECTIVES

We aimed to clarify the differences in cervical alignment findings between sitting cervical lateral radiographs and standing whole-spine lateral radiographs with clavicle positioning in cervical spondylotic myelopathy (CSM) patients.

METHODS

We retrospectively evaluated the radiographs of 50 consecutive patients who underwent cervical surgery for CSM in our hospital. Cervical sagittal alignment was evaluated based on the C0-2 angles and C2-7 Gore and Cobb angles. Head position was evaluated in terms of the center of gravity of the head to C7 (CGH-C7) angle and the McGregor angle (ie, the angle between the McGregor line and a horizontal line). The T1-slope was also evaluated.

RESULTS

The mean values of the CGH-C7 angle and T1-slope were significantly lower, while the mean value of the McGregor angle was significantly higher on whole-spine lateral radiographs with clavicle positioning than on sitting cervical lateral radiographs. The mean values of the C0-2 and C2-7 angles did not differ significantly between the 2 radiographic positioning approaches.

CONCLUSIONS

Using whole-spine lateral radiographs with clavicle positioning may result in a significantly lower T1-slope and a posterior tilt of the head. In the absence of a compensatory change in cervical alignment, clavicle positioning may force patients to adopt an upward gazing position of the head. These compensatory mechanisms should be considered while evaluating cervical alignment on whole-spine lateral radiographs with clavicle positioning. Surgical planning should take into account the effect of posture on the radiographic appearance of cervical alignment.

Spinal alignment, surgery, and outcomes in cervical deformity: A practical guide to aid the spine surgeon

Compared to the thoracolumbar spine, the literature on cervical spine alignment is scarce. While a consistent number of articles have been published, few analyze the ideal surgical approaches for each type of deformity and the optimal amount of correction to achieve. This paper provides a comprehensive review of current literature on cervical spinal deformities (with or without myelopathy) and their surgical management; it is our goal to create a framework on which surgical planning can be made. A general assessment of the actually utilized parameters and correlation between the cervical and thoracolumbar spine alignment is presented. Moreover, we provide an analysis of cervical surgical approaches (anterior, posterior, or combined), techniques (laminoplasty, laminectomy and fusion, anterior cervical discectomy and fusion, corpectomy), and their indications. Finally, a complete evaluation of outcomes and postoperative health-related quality of life (HRQOL) measures based on questionnaires (NDI, VAS, SF-36, mJOA) is discussed. Several prospective studies would be useful in understanding how cervical alignment may be important in the assessment and treatment of cervical deformities with or without myelopathy. In particular, future works should concentrate on the correlation between cervical alignment parameters, disability scores, and myelopathy outcomes. We propose, via comprehensive literature review, a guide of practical key points on surgical techniques, cervical alignment, and symptom improvement goals surgeons should aim to achieve for each patient.

Late Subaxial Lesion after Overcorrected Occipitocervical Reconstruction in Patients with Rheumatoid Arthritis

Study Design

Retrospective case-control study, level 4.

Purpose

To clarify the risk factors for late subaxial lesion after occipitocervical (O-C) reconstruction. We examined cases requiring fusion-segment-extended (FE) reconstruction in addition to/after O-C reconstruction.

Overview of Literature

Patients with rheumatoid arthritis (RA) frequently require O-C reconstruction surgery for cranio-cervical lesions. Acceptable outcomes are achieved via indirect decompression using cervical pedicle screws and occipital plate–rod systems. However, late subaxial lesions may develop occasionally following O-C reconstruction.

Methods

O-C reconstruction using cervical pedicle screws and occipital plate–rod systems was performed between 1994 and 2007 in 113 patients with RA. Occipito-atlanto-axial (O-C2) reconstruction was performed for 89 patients, and occipito-subaxial cervical (O-under C2) reconstruction was performed for 24 patients. We reviewed the cases of patients requiring FE reconstruction (fusion extended group, FEG) and 26 consecutive patients who did not require FE reconstruction after a follow-up of >5 years (non-fusion extended group, NEG) as controls.

Results

FE reconstructions were performed for nine patients at an average of 45 months (range, 24–180 months) after O-C reconstruction. Of the 89 patients, three (3%) underwent FE reconstruction in cases of O-C2 reconstruction. Of the 24 patients, five (21%) underwent FE reconstruction in cases of O-under C2 reconstruction (p=0.003, Fisher exact test). Age, sex, RA type, and neurological impairment stage were not significantly different between FEG and NEG. O-under C2 reconstruction, larger correction angle (4° per number of unfixed segment), and O-C7 angle change after O-C reconstruction were the risk factors for late subaxial lesions on radiographic assessment.

Conclusions

Overcorrection of angle at fusion segments requiring O-C7 angle change was a risk factor for late subaxial lesion in patients with RA with fragile bones and joints. Correction should be limited, considering the residual mobility of the cervical unfixed segments.

An in vitro evaluation of sagittal alignment in the cervical spine after insertion of supraphysiologic lordotic implants

PURPOSE

Cervical spine malalignment can develop as a consequence of degenerative disc disease or following spinal surgery. When normal sagittal alignment of the spine is disrupted, further degeneration may occur adjacent to the deformity. The purpose of this study was to investigate changes in lordosis and sagittal alignment in the cervical spine after insertion of supraphysiologic lordotic implants.

METHODS

Eight cadaveric cervical spines (Occiput-T1) were tested. The occiput was free to translate horizontally and vertically but constrained from angular rotation. The T1 vertebra was rigidly fixed with a T1 tilt of 23°. Implants with varying degrees of lordosis were inserted starting with single-level constructs (C5-C6), followed by two (C5-C7), and three-level (C4-C7) constructs. Changes in sagittal alignment, Occ-C2 angle, cervical lordosis (C2-7), and segmental lordosis were measured.

RESULTS

Increasing cage lordosis led to global increases in cervical lordosis. As implanted segmental lordosis increased, the axial levels compensated by decreasing in lordosis to maintain horizontal gaze. An increase in cage lordosis also corresponded with larger changes in SVA.

CONCLUSION

Reciprocal compensation was observed in the axial and sub-axial cervical spine, with the Occ-C2 segment undergoing the largest compensation. Adding more implant lordosis led to larger reciprocal changes and changes in SVA. Implants with supraphysiologic lordosis may allow for additional capabilities in correcting cervical sagittal plane deformity, following further clinical evaluation.

C7 sagittal vertical axis is the determinant of the C5-C7 angle in cervical sagittal alignment

BACKGROUND CONTEXT

Previous studies have indicated that the T1 slope correlates with cervical lordosis. In contrast, the specific impact of the C7 sagittal vertical axis (C7SVA) on cervical lordosis remains unknown.

PURPOSE

This study aimed to investigate the specific role of C7SVA in cervical lordosis.

STUDY DESIGN/SETTING

This was a retrospective radiographic study.

PATIENT SAMPLE

Forty-eight consecutive patients who underwent lateral standing radiography of the entire spine were retrospectively reviewed.

OUTCOME MEASURES

Radiographic parameters included occipito (Oc)-C7, Oc-C2, C2-C7, C2-C4, and C5-C7 angles; T1 slope; C7SVA; T1 pelvic angle (TPA); pelvic incidence; pelvic tilt; and sacral slope.

METHODS

The radiographs of 96 consecutive patients who underwent lateral standing radiography of the entire spine in June 2015 in our hospital were retrospectively reviewed. Patients having cervical deformities, having undergone cervical fusion, and under 18 years of age were excluded. A total of 48 Asian patients (14 men and 34 women; mean age, 54.6 years) were eligible. Pathologies included scoliosis, myelopathy, thoracolumbar deformity, and spondylosis. Spearman rank correlation coefficients were used to examine correlations between the parameters. The relationship between C5-C7 lordosis and the radiographic parameters was calculated using the forward stepwise multivariate regression analysis. The authors do not have financial associations relevant to this article.

RESULTS

C7SVA correlated with the Oc-C7 (r=0.42) and C2-C7 (r=0.50) angles. However, the correlation coefficient was smaller than that between the T1 slope and Oc-C7 (r=0.83) or C2-C7 (r=0.76) angles. When the C2-C7 angle was divided into C2-C4 and C5-C7 angles, C7SVA correlated with the C5-C7 (r=0.63) angle but not with the C2-C4 angle. The correlation coefficient between the C5-C7 angle and C7SVA was higher than that between the C5-C7 angle and T1 slope (r=0.53) or the C5-C7 angle and TPA (r=0.60). Using radiographic parameters and age, multiple regression analysis revealed that only C7SVA affected the C5-C7 angle.

CONCLUSIONS

C7SVA was the only radiographic parameter that affected the C5-C7 angle. Both T1 slope and C7SVA are key to the shape of the cervical sagittal alignment. The results of this study can be a starting point to improve our understanding of cervical sagittal alignment.