Cervical spine alignment following lumbar pedicle subtraction osteotomy for sagittal imbalance

How does cervical sagittal profile change after the spontaneous compensation of global sagittal imbalance following one- or two-level lumbar fusion

PURPOSE

This study aimed to evaluate the cervical sagittal profile after the spontaneous compensation of global sagittal imbalance and analyze the associations between the changes in cervical sagittal alignment and spinopelvic parameters.

METHODS

In this retrospective radiographic study, we analyzed 90 patients with degenerative lumbar stenosis (DLS) and sagittal imbalance who underwent short lumbar fusion (imbalance group). We used 60 patients with DLS and sagittal balance as the control group (balance group). Patients in the imbalance group were also divided into two groups according to the preoperative PI: low PI group (≤ 50°), high PI group (PI > 50°). We measured the spinal sagittal alignment parameters on the long-cassette standing lateral radiographs of the whole spine. We compared the changes of spinal sagittal parameters between pre-operation and post-operation. We observed the relationships between the changes in cervical profile and spinopelvic parameters.

RESULTS

Sagittal vertical axis (SVA) occurred spontaneous compensation (p = 0.000) and significant changes were observed in cervical lordosis (CL) (p = 0.000) and cervical sagittal vertical axis (cSVA) (p = 0.023) after surgery in the imbalance group. However, there were no significant differences in the radiographic parameters from pre-operation to post-operation in the balance group. The variations in CL were correlated with the variations in SVA (R = 0.307, p = 0.041). The variations in cSVA were correlated with the variations in SVA (R=-0.470, p = 0.001).

CONCLUSION

Cervical sagittal profile would have compensatory changes after short lumbar fusion. The spontaneous decrease in CL would occur in patients with DLS after the spontaneous compensation of global sagittal imbalance following one- or two-level lumbar fusion. The changes of cervical sagittal profile were related to the extent of the spontaneous compensation of SVA.

Development and validation of a risk prediction model for cage subsidence after instrumented posterior lumbar fusion based on machine learning: a retrospective observational cohort study

Background

Interbody cage subsidence is a common complication after instrumented posterior lumbar fusion surgery, several previous studies have shown that cage subsidence is related to multiple factors. But the current research has not combined these factors to predict the subsidence, there is a lack of an individualized and comprehensive evaluation of the risk of cage subsidence following the surgery. So we attempt to identify potential risk factors and develop a risk prediction model that can predict the possibility of subsidence by providing a Cage Subsidence Score (CSS) after surgery, and evaluate whether machine learning-related techniques can effectively predict the subsidence.

Methods

This study reviewed 59 patients who underwent posterior lumbar fusion in our hospital from 2014 to 2019. They were divided into a subsidence group and a non-subsidence group according to whether the interbody fusion cage subsidence occurred during follow-up. Data were collected on the patient, including age, sex, cage segment, number of fusion segments, preoperative space height, postoperative space height, preoperative L4 lordosis Angle, postoperative L4 lordosis Angle, preoperative L5 lordosis Angle, postoperative PT, postoperative SS, postoperative PI. The conventional statistical analysis method was used to find potential risk factors that can lead to subsidence, then the results were incorporated into stepwise regression and machine learning algorithms, respectively, to build a model that could predict the subsidence. Finally the diagnostic efficiency of prediction is verified.

Results

Univariate analysis showed significant differences in pre-/postoperative intervertebral disc height, postoperative L4 segment lordosis, postoperative PT, and postoperative SS between the subsidence group and the non-subsidence group (p < 0.05). The CSS was trained by stepwise regression: 2 points for postoperative disc height > 14.68 mm, 3 points for postoperative L4 segment lordosis angle >16.91°, and 4 points for postoperative PT > 22.69°. If the total score is larger than 0.5, it is the high-risk subsidence group, while less than 0.5 is low-risk. The score obtains the area under the curve (AUC) of 0.857 and 0.806 in the development and validation set, respectively. The AUC of the GBM model based on the machine learning algorithm to predict the risk in the training set is 0.971 and the validation set is 0.889. The AUC of the avNNet model reached 0.931 in the training set and 0.868 in the validation set, respectively.

Conclusion

The machine learning algorithm has advantages in some indicators, and we have preliminarily established a CSS that can predict the risk of postoperative subsidence after lumbar fusion and confirmed the important application prospect of machine learning in solving practical clinical problems.

Global realignment after posterior vertebral column resection in severe thoracolumbar post-tubercular kyphosis: correlation with patient-reported outcomes

PURPOSE

To investigate spinal realignment in patients with severe post-tubercular kyphosis (PTK) who underwent posterior vertebral column resection (PVCR) and its correlation with patient-reported outcomes (PROs).

METHODS

Eighty-two patients were included in this study. Spinopelvic parameters (focal scoliosis (FS), coronal balance (CB), sagittal vertical axis (SVA), focal kyphosis (FK), C2-7 lordosis (CL), thoracic kyphosis (TK), lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT), pelvic incidence (PI), and pelvic incidence minus lumbar lordosis (PI-LL)) and PROs (Visual Analog Scale (VAS) and Oswestry Disability Index (ODI)) were analyzed. The correlation between spinopelvic parameters and PROs was evaluated.

RESULTS

FK, FS, CL, TK, LL, and PI-LL significantly changed after surgery. FK decreased from pre-operative 108.5 ± 16.4° to 31.8 ± 4.5° at three months after surgery and increased to 38.7 ± 6.6° at final follow-up (P < 0.001). FS decreased from pre-operative 20.9 ± 2.2° to 5.1 ± 2.2° at final follow-up (P < 0.001). CL decreased from pre-operative 7.2 ± 7.3° to 3.3 ± 8.3° at final follow-up (P = 0.002). TK improved from pre-operative - 5.6 ± 7.1° to 12.9 ± 8.2° at final follow-up (P < 0.001). LL decreased from pre-operative 75.5 ± 12.6° to 45.5 ± 7.9° at final follow-up (P < 0.001). PI-LL improved from pre-operative - 24.8 ± 13.4° to 4.8 ± 9.9° at final follow-up (P < 0.001). The improvement of PROs was found to be significantly correlated with the variations of FK, CL, TK, LL, and PI-LL. The multiple regression analysis revealed that FK was an independent predictor for the improvement of VAS and ODI.

CONCLUSIONS

PVCR is effective in treating severe PTK, which can significantly improve patients' clinical and radiographic outcomes. Spine surgeons should pay more attention to reducing the residual kyphosis.

Reciprocal Changes in the Whole-Body Following Realignment Surgery in Adult Spinal Deformity

The idea of the global balance of spine stems from Jean Dubousset, who first introduced the concept of cone of economy. Through the compensatory mechanisms, the human body maintains an upright posture and horizontal gaze in the setting of the spinal malalignment. Compensation takes place not only in the mobile spine segments, but also in the pelvis and lower extremities. Patients with a malalignment exhibit compensatory changes in the cervical hyper-lordosis, posterior pelvic shift, knee/ankle flexion, hip extension, and the pelvic retroversion. The advent of whole-body stereo radiography has yielded an improved understanding of global changes among the patients. Deformity-induced compensatory changes in the sagittal alignment could be resolved reciprocally after the surgical correction of the malalignment. Thoracolumbar realignment surgery restores the pathologic compensatory changes in the unfused spinal segments, pelvis, and the lower extremities. Similarly, reciprocal changes in the thoracolumbar spine may harmonize global sagittal alignment after the cervical reconstruction. This study reviews the compensatory mechanisms and reciprocal changes in global sagittal alignment caused by the surgical correction and highlights, the factors that should be considered while assessing a patient's compensatory status.

Global Spinal Realignment After Osteotomized Debridement in Active Lumbar Spinal Tuberculosis: Correlation with Patient-Reported Outcomes

OBJECTIVE

Osteotomized debridement (OD) has been proved to be highly effective in treating active thoracolumbar tuberculosis (TB); however, no research has investigated how OD affects spinal alignment. The goal of this study was to explore the global alignment compensatory mechanism after lumbar OD, as well as the correlation between spinopelvic parameters and patient-reported outcomes (PROs).

METHODS

Sixty-two patients with active lumbar spinal TB who underwent OD surgery were included. Spinopelvic parameters (C2-7 Cobb angle [C2-7 CA], sagittal vertical axis [SVA], proximal thoracic kyphosis, thoracic kyphosis, lumbar lordosis [LL], sacral slope [SS], pelvic tilt [PT], pelvic incidence [PI], spinosacral angle, and PI minus LL [PI-LL]) and PROs (Oswestry Disability Index [ODI] and Visual Analog Scale [VAS] score) were reviewed. The correlation between spinopelvic realignment and improved PROs was evaluated.

RESULTS

Compared with preoperative measurements, C2-7 CA, proximal thoracic kyphosis, thoracic kyphosis, LL, SS, and spinosacral angle significantly increased after OD, whereas SVA, PT, and PI-LL significantly decreased. ODI and VAS score significantly improved postoperatively. The improvement of VAS was observed to be correlated with variations of C2-7 CA, SVA, LL, and PI-LL. The improvement of ODI was found to be correlated with variations of SVA, LL, and PI-LL. The multiple stepwise regression analysis showed that LL was an independent predictor for ODI and VAS score.

CONCLUSIONS

The whole spine and pelvis are involved in realignment after lumbar spinal OD, which is closely related to PROs. More attention should be drawn to restoring an appropriate LL in lumbar TB surgery.

Systematic Review of Reciprocal Changes after Spinal Reconstruction Surgery : Do Not Miss the Forest for the Trees

The purpose of this review was to synthesize the research on global spinal alignment and reciprocal changes following cervical or thoracolumbar reconstruction surgery. We carried out a search of PubMed, EMBASE, and Cochrane Library for studies through May 2020, and ultimately included 11 articles. The optimal goal of a truly balanced spine is to maintain the head over the femoral heads. When spinal imbalance occurs, the human body reacts through various compensatory mechanisms to maintain the head over the pelvis and to retain a horizontal gaze. Historically, deformity correction has focused on correcting scoliosis and preventing scoliotic curve progression. Following substantial correction of a spinal deformity, reciprocal changes take place in the flexible segments proximal and distal to the area of correction. Restoration of lumbar lordosis following surgery to correct a thoracolumbar deformity induces reciprocal changes in T1 slope, cervical lordosis, pelvic shift, and lower extremity parameters. Patients with cervical kyphosis exhibit different patterns of reciprocal changes depending on whether they have head-balanced or trunk-balanced kyphosis. These reciprocal changes should be considered to in order to prevent secondary spine disorders. We emphasize the importance of evaluating the global spinal alignment to assess postoperative changes.

Use of iliac screw associated with more correction of lumbar lordosis than S2-alar-iliac screw for adult spinal deformity

Background

To date, there is a paucity of reports clarifying the change of spinopelvic parameters in patients with adult spinal deformity (ASD) who underwent long segment spinal fusion using iliac screw (IS) and S2-alar-iliac screw (S2AI) fixation.

Methods

A retrospective review of consecutive patients who underwent deformity correction surgery for ASD between 2013 and 2017 was performed. Patients were divided into two groups based on whether IS or S2AI fixation was performed. All radiographic parameters were measured preoperatively, immediately postoperatively, and the last follow-up. Demographics, intraoperative and clinical data were analyzed between the two groups. Additionally, the cohort was subdivided according to the postoperative change in pelvic incidence (PI): subgroup (C) was defined as change in PI ≥5° and subgroup (NC) with change < 5°. In subgroup analyses, the 2 different types of postoperative change of PI were directly compared.

Results

A total of 142 patients met inclusion criteria: 111 who received IS and 31 received S2AI fixation. The IS group (65.6 ± 26°, 39.8 ± 13.8°) showed a significantly higher change in lumbar lordosis (LL) and upper lumbar lordosis (ULL) than the S2AI group (54.4 ± 17.9°, 30.3 ± 9.9°) (p < 0.05). In subgroup (C), PI significantly increased from 53° preoperatively to 59° postoperatively at least 50% of IS cohort, with a mean change of 5.8° (p < 0.05). The clinical outcomes at the last follow-up were significantly better in IS group than in S2AI group in terms of VAS scores for back and leg. The occurrence of sacroiliac joint pain and pelvic screw fracture were significantly greater in S2AI group than in IS group (25.8% vs 9%, p < 0.05) and (16.1% vs 3.6%, p < 0.05).

Conclusions

Compared with the S2AI technique, the IS technique usable larger cantilever force demonstrated more correction of lumbar lordosis, and possible increase in pelvic incidence. Further study is warranted to clarify the clinical impaction of these results.

Variation patterns of cervical alignment in ankylosing spondylitis-related thoracolumbar kyphosis following pedicle subtraction osteotomy in the sitting position: an EOS-based investigation

OBJECTIVE

Both unchanged upper cervical lordosis combined with decreased lower cervical lordosis and decreased upper cervical lordosis combined with decreased lower cervical lordosis have been reported to occur after correction surgery for adult spinal deformity. However, variations in cervical alignment after correction surgery in patients with ankylosing spondylitis (AS) have not been investigated. The current study aimed to investigate the variations in cervical alignment following the correction surgery in AS patients with thoracolumbar kyphosis.

METHODS

Patients with AS who underwent pedicle subtraction osteotomy (PSO) for thoracolumbar kyphosis from June 2016 to June 2019 with a minimum of 1-year follow-up were reviewed. Patients were grouped according to the presence (ossified group) and absence (non-ossified group) of total ossification of the anterior longitudinal ligament (ALL) in the lower cervical spine. Radiographic parameters, including thoracolumbar, craniocervical, and global radiographic parameters, were measured on lateral sitting EOS images.

RESULTS

Thirty-two patients (27 males and 5 females) with a mean follow-up of 1.5 years were identified. There were 21 patients in the non-ossified group and 11 patients in the ossified group. After PSO, both groups showed a decrease in the occiput-C7 angle (p < 0.001 for both). In the non-ossified group, the C2-7 angle decreased significantly (p < 0.001), while the occiput-C2 angle remained unchanged (p = 0.570). In the ossified group, the occiput-C2 angle decreased significantly (p < 0.001), while C2-7 angle remained unchanged (p = 0.311). In addition, the change in occiput-C2 was correlated with the osteotomy angle in the ossified group (R = 0.776, p = 0.005).

CONCLUSIONS

The variation patterns of cervical alignment following correction surgery for AS-related thoracolumbar kyphosis were different based on patients with or without total ossification of ALL in the lower cervical spine. When planning PSO for patients in the ossified group, restoration of the physiological upper cervical lordosis angle could be achieved by adjusting the osteotomy angle.

Comparison study of clinical outcomes and sagittal alignment improvement between anterior and posterior fusion techniques for multilevel cervical spondylotic myelopathy

PURPOSE

To compare the sagittal alignment of different surgical approaches in patients with multiple levels cervical spondylotic myelopathy and explore the relationship between the cervical sagittal alignment and patient's health relative quality of life.

METHOD

A total of 97 multiple levels cervical spondylotic myelopathy patients who underwent surgery from January 2013 to January 2019 were collected in this study. Patients were divided into three groups: anterior cervical discectomy with fusion, anterior cervical corpectomy with fusion and laminectomy with fusion groups. Clinical outcomes and sagittal alignment parameters were compared preoperative and postoperative.

RESULTS

There were no significant differences in the average age and sex ratio among the groups. Sagittal parameters correlated to health relative quality of life were C7 slope, occipito-C2 angle, external auditory meatus tilt and cervical sagittal vertical axis. Both anterior cervical discectomy with fusion and anterior cervical corpectomy with fusion groups exhibited better sagittal alignment and clinical outcomes improvement postoperatively. Anterior cervical discectomy with fusion provided better clinical outcomes and the better improvement of cervical lordosis, C7 slope, occipito-C2 angle and cervical sagittal vertical axis compared with patients with Laminectomy with fusion.

CONCLUSION

C7 slope, occipito-C2 angle, external auditory meatus tilt and cervical sagittal vertical axis are the most important cervical sagittal parameters correlated to clinical outcomes in patients with multilevels cervical spondylotic myelopathy; anterior cervical discectomy with fusion and anterior cervical corpectomy with fusion provides more efficient to restoration of cervical sagittal alignment.

Changes in cervical sagittal alignment and the effects on cervical parameters in patients with cervical spondylotic myelopathy after laminoplasty

Objective:

To monitor changes in cervical parameters before and after laminoplasty surgery. Cervical parameters and health-related quality-of-life (HRQOL) values that may be affected after laminoplasty were examined before and after surgery. The clinical and radiological course of these values was monitored, and their interaction with all spinal radiological parameters was revealed.

Materials and Methods:

Nineteen patients who underwent clinical and radiological evaluation for 2 years were followed in this study. Neck disability index, visual analog scale, and short form 36 scores were determined to evaluate HRQOL. For radiological parameters, the C0-C2 angle, C2-C7 angle, cervical sagittal vertical axis, T1 slope angle, neck tilt (NT) and thoracic inlet angle were used. The results of the 4-month, 1 year and 2-year follow-ups were statistically evaluated.

Results:

Both the HRQOL and cervical radiological parameters deteriorated in the first 4 months and returned to normal in the 2^nd year. Statistically, all parameters were meaningful (P < 0.05), except for NT.

Conclusion:

Cervical parameters and HRQOL values, which deteriorated in the early period, recovered in the late period in the long-term follow-up of patients undergoing laminoplasty. The important point is that preoperative cervical parameters suitable for laminoplasty should be present, and spinopelvic parameters should be normal.

Radiographic and clinical evidence: osteoarthritic knee can change surgical result for lumbar degenerative disease patient undergone surgery for 3-year follow-up: a retrospective comparative clinical study

Background

There is a paucity of reports clarifying the implication of knee osteoarthritis (OA) on spinal sagittal alignment of patients undergone surgery for lumbar spine. This study aimed to analyze how osteoarthritic knee affects radiographic and clinical results of degenerative lumbar disease patients undergone lumbar fusion.

Methods

We retrospectively reviewed the medical records and radiographs of 74 consecutive degenerative lumbar disease patients who underwent posterior instrumentation and fusion surgery between May 2016 and June 2017 and were followed up for minimum 3 years postoperatively. The patients were divided into 2 groups according to the severity of knee OA by Kellgren-Lawrence grading (KLG) scale (group I, KLG 1 or 2 [n = 39]; group II, KLG 3 or 4 [n = 35]). Patient demographic data, comorbidities, spinal sagittal parameters and clinical scores were extracted and compared at preoperative, postoperative 1 month and the ultimate follow-up between the groups. In radiographic assessment, sagittal alignment parameters and sagittal balance were used. In clinical assessment, the scores of Oswestry disability index (ODI) and Scoliosis Research Society questionnaire (SRS-22) were used. For the frequency analysis of categorical variables across the groups, chi-square test was used and student t tests was used to compare the differences of continuous variables.

Results

In radiographic assessment, TLK (thoracolumbar kyphosis), LL (lumbar lordosis), PT (pelvic tilt), C7 SVA (sagittal vertical axis) in both groups improved significantly after surgery (p <  0.05). However, LL, PT, C7SVA improved at postoperative 1 month in the group II were not maintained at the ultimate postoperative follow-up. In clinical assessment, preoperative Oswestry disability index (ODI, %) and all SRS-22 subscores of the group I and II were not different (p > 0.05). There were significant differences between the groups at the ultimate follow-up in ODI (− 25.6 vs − 12.1, p <  0.001), SRS total score (%) (28 vs 20, p = 0.037), function subscore (1.4 vs 0.7, p = 0.016), and satisfaction subscore (1.6 vs 0.6, p < 0.001).

Conclusion

Osteoarthritic knee with KLG 3 or 4 have a negative influence on maintaining postoperative spinal sagittal alignment, balance, and the clinical outcomes achieved immediately by posterior instrumentation and fusion for lumbar degenerative disease.

Trial registration

This study was retrospectively registered with approval by the institutional review board (IRB) of our institution (approval number: 2018–11-007).

The differences in whole-body sagittal alignment between different postures in young, healthy adults

Study design

Prospective study.

Objective

To identify the radiographic differences between the standard upright position and the natural and comfortable upright position.

Methods

The radiographic data of 50 young and healthy adults were evaluated, and parameters including the global cervical angle (GCA), global thoracic angle (GTA), global lumbar angle (GLA) were used to depict the spine profile; the distance from the cranial center to the posterior corner of S1 (CSVA-S), the center of the hip (CSVA-H), the center of the knee (CSVA-K) and the center of the ankle (CSVA-A) were measured in both the standard and the natural and comfortable upright positions to assess whole-body balance.

Results

Significant differences were observed in the GCA (17.39 ± 6.90 vs. 10.90 ± 3.77, p < .001), GTA (25.63 ± 7.27 vs. 45.42 ± 8.15 p < .001), GLA (42.64 ± 8.05 vs. 20.21 ± 7.47 p < .001), CSVA-S (0.33 ± 2.76 cm vs. 8.54 ± 3.78 cm, p < 0.001), CSVA-H (1.53 ± 3.11 cm vs. 5.71 ± 3.26 cm, p < 0.001), CSVA-K (3.58 ± 2.47 cm vs. 5.22 ± 2.69 cm, p = 0.002) and CSVA-A (1.79 ± 1.92 cm vs. 4.79 ± 2.51 cm, p < 0.001) between the two different standing postures. Compared with the standard upright position, the natural and comfortable upright position results in a more kyphotic spine profile.

Conclusion

Significant differences in sagittal radiographic parameters were found between the standard upright position and the natural and comfortable upright position; the latter served as a marker for energy conservation during standing and revealed a more kyphotic spinal profile. The standard upright position and natural and comfortable upright position are equally important and should be addressed before a surgical plan is developed for patients who need surgery.

Cervical Deformity Arising From Upper Thoracic Malalignment

This study aims to describe the surgical management of cervical deformity arising from outside the cervical spine because of upper thoracic malalignment, using pedicle subtraction osteotomy (PSO). Cervical spine deformity is a complex topic and it can be generally divided into 2 categories, the first category is when the primary deformity is inside the cervical spine and the treatment will focus on the cervical spine itself, whereas the second category is when the primary deformity is outside the cervical spine usually in the adjacent upper thoracic area, the cervical deformity is a compensation for the adjacent malalignment, and thus in this situation, the management will occur in the upper thoracic area. Description of a single surgeon’s technique for performing PSO to treat rigid upper thoracic deformity. PSO in the upper thoracic spine is a safe and effective procedure and can result in satisfying clinical and radiological outcome with indirect correction of the compensatory cervical deformity. Cervical deformity arising from upper thoracic malalignment should be dealt with by treating the problem at its origin outside the cervical spine by performing a PSO in the upper thoracic spine.

The role of sagittal alignment in predicting major failure of lumbopelvic instrumentation: a biomechanical validation of lumbopelvic failure classification

STUDY DESIGN

Finite element analysis.

OBJECTIVES

To biomechanically validate the classification of lumbopelvic fixation failure using an in silico model. Even though major failure of lumbopelvic constructs has occurred more often in patients with suboptimal lumbar lordosis and sagittal balance, there has been no biomechanical validation of this classification.

METHODS

Finite element models (T10-pelvis) were created to match the average spinal-pelvic parameters of two cohorts of patients reported in Cho et al. (J Neurosurg Spine 19:445-453, 2013): major failure group (defined as rod breakage between L4 and S1, failure of S1 screws and prominence of iliac screws requiring removal) and non-failure group. A moment was applied at the T10 superior endplate to simulate gravimetric loading in a standing position.

RESULTS

Due to differences in the alignment of spinopelvic parameters between normal and failed spines in the presence of a fixed gravity line, the major failure cohort in this study observed a 20% higher load and 18% greater instability. As a result, the rod and screw stress in the major failure cohort increased by 20% and 42%, respectively, in comparison to the non-failure cohort.

CONCLUSIONS

The greater mechanical demand on the posterior rods in the lower lumbar spine in the major failure cohort further emphasizes the importance of proper sagittal alignment. This finite element analysis validates the classification of lumbopelvic fixation failure.

How Cervical Reconstruction Surgery Affects Global Spinal Alignment

BACKGROUND

There have been no reports describing how cervical reconstruction surgery affects global spinal alignment (GSA).

OBJECTIVE

To elucidate the effects of cervical reconstruction for GSA through a retrospective multicenter study.

METHODS

Seventy-eight patients who underwent cervical reconstruction surgery for cervical kyphosis were divided into a Head-balanced group (n = 42) and a Trunk-balanced group (n = 36) according to the values of the C7 plumb line (PL). We also divided the patients into a cervical sagittal balanced group (CSB group, n = 18) and a cervical sagittal imbalanced group (CSI group, n = 60) based on the C2 PL-C7 PL distance. Various sagittal Cobb angles and the sagittal vertical axes were measured before and after surgery.

RESULTS

Cervical alignment was improved to achieve occiput-trunk concordance (the distance between the center of gravity [COG] PL, which is considered the virtual gravity line of the entire body, and C7 PL < 30 mm) despite the location of COG PL and C7PL. A subsequent significant change in thoracolumbar alignment was observed in Head-balanced and CSI groups. However, no such significant change was observed in Trunk-balanced and CSB groups. We observed 1 case of transient and 1 case of residual neurological worsening.

CONCLUSION

The primary goal of cervical reconstruction surgery is to achieve occiput-trunk concordance. Once it is achieved, subsequent thoracolumbar alignment changes occur as needed to harmonize GSA. Cervical reconstruction can restore both cervical deformity and GSA. However, surgeons must consider the risks and benefits in such challenging cases.

Reciprocal change of sagittal profile in unfused spinal segments and lower extremities after complex adult spinal deformity surgery including spinopelvic fixation: a full-body X-ray analysis

BACKGROUND CONTEXT

Few studies have described reciprocal changes of pathologic compensatory mechanisms in the setting of spinopelvic fixation using full-body radiograph.

PURPOSE

To elucidate how sagittal alignment of unfused spinal segments and lower extremities change reciprocally following complex thoracolumbar realignment surgery including fusion to the sacrum in adult spinal deformity.

STUDY DESIGN

Retrospective cohort.

PATIENT SAMPLE

Thirty-four patients who underwent fusion from lower thoracic to the sacrum/pelvis and 49 patients with fusion from upper thoracic to the sacrum/pelvis.

OUTCOME MEASURES

The postoperative sagittal alignment change, and the correlation between the instrumented spinopelvic alignment change and reciprocal changes in unfused spinal segments/lower extremities.

MATERIALS/METHODS

This study included 34 patients who underwent fusion from lower thoracic to the sacrum/pelvis (LT-P group) and 49 patients with fusion from upper thoracic to the sacrum/pelvis (UT-P group). The postoperative sagittal alignment changes were evaluated after subdividing the two groups according to T1 pelvic angle (TPA) (aligned group: TPA<20 and malaligned group: TPA>20). The correlation between the instrumented spinopelvic alignment change (ΔTPA and ΔLL), reciprocal changes in unfused spinal segments and lower extremities, and the cranial sagittal vertical axis-hip/ankle change (ΔCrSVA-Hip/Ankle) were also analyzed.

RESULTS

At the baseline in both LT-P and UT-P groups, the patients in the malaligned subgroups showed greater C2-7 lordosis (C2-7L), sacrofemoral angle (SFA), and knee flexion angle (KA) than those in the aligned subgroups. At average 7.1 months postoperatively, these compensatory mechanisms were restored in accordance with instrumented TPA/LL change, especially in the UT-P group. The mid-thoracic alignment changed significantly kyphotic in the LT-P group. ΔTPA and ΔLL linearly correlated with ΔC2-7L, ΔKA, and ΔAA in the malaligned patients. The multivariate regression analysis revealed that change in lower extremity parameters (ΔSFA, ΔKA, and ΔAA) independently impacted ΔCrSVA-Hip/Ankle.

CONCLUSION

Adequate thoracolumbar realignment surgery results in restoration of the pathologic compensatory mechanisms in the unfused spinal segments and lower extremities, especially in patients fused from upper thoracic spine. A preoperative clinical evaluation of the lower limb joints, as well as a full-body radiographic evaluation, is paramount to achieve optimal global sagittal balance in thoracolumbar realignment surgery.

Impact of cervical range of motion on the global spinal alignment in ankylosing spondylitis patients with thoracolumbar kyphosis following pedicle subtraction osteotomy

BACKGROUND CONTEXT

The head's center of gravity (COG) plumb line (PL) and C7 PL could be simultaneously positioned over the pelvis in adult spinal deformity with normal cervical mobility. However, the position of the head in relation to the global spinal alignment has yet to be investigated in ankylosing spondylitis (AS) patients with thoracolumbar kyphosis.

PURPOSE

The objective of this study was to analyze the position of head in relation to the global spinal alignment in AS-related thoracolumbar kyphosis.

STUDY DESIGN/SETTING

Retrospective single-center study.

PATIENT SAMPLE

AS patients who underwent lumbar pedicle subtraction osteotomy for thoracolumbar kyphosis from January 2010 to August 2016 were reviewed. Only patients with a visible ear canal on the preoperative, immediate postoperative, and final follow-up radiographs were included.

OUTCOME MEASURES

The chin-brow angle, cervical range of motion (ROM), lumbar lordosis (LL), thoracolumbar angle, thoracic kyphosis (TK), L1 pelvic angle, pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), TK+LL+PI, PI-LL, maximal kyphosis (MK), deformity angular rate, T1 pelvic angle, T1 tilt, spinosacral angle, sagittal vertical axis (SVA) COG-C7, SVA COG-femoral head (FH), and SVA C7-S were evaluated. Data regarding the health-related quality of life, including the Oswestry disability index (ODI) and visual analogue scale (VAS)-back score, were also collected preoperatively, 2 years postoperatively, and at the latest follow-up.

METHODS

The cohort was divided into patients with occiput-trunk (OT) concordance or with OT discordance according to the SVA COG-C7 ≤30 mm or >30 mm, respectively. There was no funding in this study and there are no conflict of interest-associated biases.

RESULTS

A total of 43 patients (36 males and 7 females) with a mean age of 34.2 years (range, 18-59 years) were identified. There were 17 patients accompanied with OT concordance and 26 patients with OT discordance preoperatively. The cervical ROM was significantly lower (24.0° vs 56.1°, p<.001) and SVA COG-C7 was significantly larger (71.7 mm vs 7.4 mm, p<.001) in patients with OT discordance. Furthermore, the PT was larger (41.0° vs 33.5°, p=.010) in patients with OT discordance. After surgery, the whole cohort showed an improvement in LL (-8.6° vs -52.8°, p<.001). Moreover, the CBVA (25.4° vs 1.3°, p<.001) and SVA COG-C7 (46.2 mm vs 21.6 mm, p<.001) were significantly decreased following lumbar PSO. There were 13 patients accompanied with OT discordance postoperatively, and the cervical ROM was still lower (22.5° vs 42.8°, p=.024) in these patients. Postoperative PT was larger (26.5° vs 20.1°, p=.033) in the patients with OT discordance. At the latest follow-up, there were 17 patients accompanied with OT discordance. In these 17 patients, the cervical ROM was significantly lower (21.0° vs 47.0°, p=.001) and PT was significantly higher (26.2° vs 19.2°, p=.012). The ODI and VAS-back scores demonstrated no significant differences between the two groups preoperatively, 2 years postoperatively, or at the latest follow-up.

CONCLUSIONS

OT discordance in AS-related thoracolumbar kyphosis could be caused by the reduced cervical ROM. To maintain global spinal balance, the pelvis rotated further backward in response to the larger SVA COG-C7. Moreover, the larger SVA COG-C7 could be decreased after the lumbar PSO. Although there were radiographic differences between the patients with OT concordance and with OT discordance, there was no difference in clinical outcomes, and that a larger sample size and longer follow-up are needed.

Single Level Proximal Thoracic Pedicle Subtraction Osteotomy for Fixed Hyperkyphotic Deformity: Surgical Technique and Patient Series

BACKGROUND

Thoracic hyperkyphosis can display pathological deterioration, resulting in either hyperlordotic cervical compensation or sagittal malalignment. Various techniques have been described to treat fixed malalignment. Pedicle subtraction osteotomy (PSO) is commonly used in the lumbar spine and frequently limited to the distal thoracic spine. This series focuses on the surgical specificities of proximal thoracic PSO, with clinical and radiological outcomes.

OBJECTIVE

To report the surgical specificities and assess the clinical and radiological outcomes of proximal thoracic osteotomies for correction of rigid kyphotic deformities.

METHODS

This is a retrospective review of 10 consecutive patients who underwent single level proximal thoracic PSO (T2-T5). Preoperative and postoperative full-body EOSTM radiographs, perioperative data, and complications were recorded. The surgical technique and its nuances were described in detail.

RESULTS

Patients had mean age of 41.8 yr and 50% were female. The technique provided correction of segmental and global kyphosis, 26.6° and 29.5°, respectively. Patients reported reciprocal reduction in C2-C7 cervical lordosis (37.6°-18.6°, P < .001), significantly correlating with the reduction of thoracic hyperkyphosis (R = 0.840, P = .002). Mean operative time was 291 min, blood loss 1650 mL, and mean hospital stay was 13.8 d. Three patients reported complications that were resolved, including 1 patient who was revised because of a painful cross link. There were no neurological complications, pseudarthroses, instrumentation breakage, or wound infections at a minimum of 2-yr follow-up.

CONCLUSION

Proximal thoracic PSO can be a safe and effective technique to treat fixed proximal thoracic hyperkyphosis leading to kyphosis reduction and craniocervical relaxation.

Suboptimal Age-Adjusted Lumbo-Pelvic Mismatch Predicts Negative Cervical-Thoracic Compensation in Obese Patients

Background

Given the paucity of literature regarding compensatory mechanisms used by obese patients with sagittal malalignment, it is necessary to gain a better understanding of the effects of obesity on compensation after comparing the degree of malalignment to age-adjusted ideals. This study aims to compare baseline alignment of obese and nonobese patients using age-adjusted spino-pelvic alignment parameters, describing associated spinal changes.

Methods

Patients ≥ 18 years with full-body stereoradiographs were propensity-score matched for sex, baseline pelvic incidence (PI), and categorized as nonobese (body mass index < 30kg/m²) or obese (body mass index ≥ 30). Age-adjusted ideals were calculated for sagittal vertical axis, spino-pelvic mismatch (PI-LL), pelvic tilt, and T1 pelvic angle using established formulas. Patients were stratified as meeting alignment ideals, being above ideal, or being below. Spinal alignment parameters included C0-C2, C2-C7, C2-T3, cervical thoracic pelvic angle, cervical sagittal vertical axis SVA, thoracic kyphosis, T1 pelvic angle, T1 slope, sagittal vertical axis, lumbar lordosis (LL), PI, PI-LL, pelvic tilt. Lower-extremity parameters included sacrofemoral angle, knee flexion (KA), ankle flexion (AA), pelvic shift (PS), and global sagittal angle (GSA). Independent t tests compared parameters between cohorts.

Results

Included: 800 obese, 800 nonobese patients. Both groups recruited lower-extremity compensation: sacrofemoral angle (P = .004), KA, AA, PS, GSA (all P < .001). Obese patients meeting age-adjusted PI-LL had greater lower-extremity compensation than nonobese patients: lower sacrofemoral angle (P = .002), higher KA (P = .008), PS (P = .002), and GSA (P = .02). Obese patients with PI-LL mismatch higher than age-adjusted ideal recruited greater lower-extremity compensation than nonobese patients: higher KA, AA, PS, GSA (all P < .001). Obese patients showed compensation through the cervical spine: increased C0-C2, C2-C7, C2-T3, and cervical sagittal vertical axis (all P < .001), high T1 pelvic angle (P < .001), cervical thoracic pelvic angle (P = .03), and T1 slope (P < .001), with increased thoracic kyphosis (P = .015) and decreased LL (P < .001) compared to nonobese patients with PI-LL larger than age-adjusted ideal.

Conclusions

Regardless of malalignment severity, obese patients recruited lower-limb compensation more than nonobese patients. Obese patients with PI-LL mismatch larger than age-adjusted ideal also develop upper-cervical and cervicothoracic compensation for malalignment.

Level of Evidence

III.

Clinical Relevance

Clinical evaluation should extend to the cervical spine in obese patients not meeting age-adjusted sagittal alignment ideals.

Cervical spine alignment following surgery for adolescent idiopathic scoliosis (AIS): a pre-to-post analysis of 81 patients

Background

Several studies have emphasized the importance of restoring thoracic kyphosis (TK) in the setting of AIS, but very few have discussed changes in cervical spine alignment following surgery. Aim of this study was to evaluate reciprocal cervical alignment change after modification of global and regional thoracolumbar alignment with surgery in the setting of adolescent idiopathic scoliosis (AIS).

Methods

Baseline and 2-yrs follow-up radiographs of AIS patients (n = 81) were analysed measuring cervical parameters (upper cervical: C2-C0, McGregor Slope; lower cervical: C2-C7, C2-C7 sagittal vertical axis (SVA), C2-T3, C2-T3SVA, C2-T1Harrison (C2-T1Ha), T1 Slope (T1S)), thoracic, lumbar, pelvic and global alignment parameters. Post-operatively, patients were grouped twice; based on changes in TK and SVA. Cervical alignment was compared between groups. Pearson correlation was conducted to examine the relationship between changes in TK, SVA, and cervical alignment.

Results

Stratification by change in TK, revealed significant alteration of lower cervical alignment T1S [p < 0.001]), C2-T3 [p = 0.019], C2-T1Ha [p = 0.043]), but there was no reciprocal change in the upper cervical spine. Stratification by SVA revealed a significant coexisting change in the lower cervical spine (T1S [p < 0.001], C2-C7SVA [p = 0.034], C2-T3 [p = 0.023], C2-T3SVA [p = 0.001]). SVA change was not associated to a change in the upper cervical spine. The correlation analysis showed that with a post-operative increase in TK, the cervical spine became more lordotic. Changes in TK were significantly correlated with: ΔT1S, ΔC2-C7, ΔC2-T3, and ΔC2-T3SVA. Similarly, increased cervical kyphosis was found when SVA was decreased post-operatively. Furthermore, there was a significant correlation between change of SVA and both ΔC2-T3 and ΔC2-T3SVA.

Conclusions

In surgically treated AIS patients, changes in global and regional alignment of the thoracolumbar and cervical spinal segments exhibit interdependence. Thus, surgical planning with regard to sagittal deformity in AIS patients should account for the post-operative impact on cervical alignment.

Cervical and postural strategies for maintaining horizontal gaze in asymptomatic adults

PURPOSE

To investigate the different cervical strategies for maintaining horizontal gaze in asymptomatic subjects.

METHODS

One hundred and forty-four asymptomatic adults filled the SF-36 quality of life questionnaire and underwent full-body biplanar radiographs. Chin brow vertical angle (CBVA) and postural and cervical parameters were measured. Subjects were grouped according to cervical spine curvature (C2-C7 angle): kyphotic (< - 5°), straight [- 5°, 5°], lordotic (> 5°). Demographics, SF-36 component scores and CBVA were compared between groups. All other parameters were compared between groups, while controlling for confounding factors (ANCOVA). A correlation test was conducted between all cervical parameters.

RESULTS

32% of subjects had kyphotic (- 12° ± 7°), 27% straight (0° ± 3°) and 41% lordotic (12° ± 7°) cervical spines. While demographic and SF-36 data did not differ between groups, CBVA differed between lordotic and kyphotic groups (2° vs. 6.5°, p = 0.002). Sagittal vertical axis (SVA) and thoracic kyphosis (TK) were lower in the kyphotic group (SVA: K = - 26 ± 20 mm vs. L = - 2 ± 21 mm, p < 0.001; TK: K = 40° ± 6° vs. L = 51° ± 8°, p < 0.001). C2 slope (K = 29° ± 6° vs. L = 18° ± 6°, p < 0.001), C0-C2 (K = 42° ± 8° vs. L = 30° ± 8°, p < 0.001) and C1-C2 (K = 33° ± 6° vs. L = 28° ± 6°, p = 0.004) were higher in the kyphotic group. Significant correlations were found between almost all cervical parameters and C2-C7 angle.

CONCLUSIONS

Subjects with cervical kyphosis presented with more posterior global alignment and lower TK than subjects with lordosis. In order to maintain horizontal gaze, subjects with cervical kyphosis presented with a more lordotic upper cervical spine than subjects with cervical lordosis. Subjects with straight cervical curvature presented with an intermediate sagittal alignment. These slides can be retrieved under Electronic Supplementary Material.

Changes in Cervical Alignment after Multilevel Schwab Grade II Thoracolumbar Osteotomies for Adult Spinal Deformity

STUDY DESIGN

A retrospective cohort.

OBJECTIVE

The aim of this study was to describe changes in cervical alignment (CA) and cervical deformity (CD) after multilevel Schwab Grade II Osteotomies for adult spinal deformity (ASD).

SUMMARY OF BACKGROUND DATA

Reciprocal cervical and global changes after ASD surgery have not been previously described in the setting of multilevel osteotomy.

METHODS

Patients with long-segment (> five levels) fusion and osteotomy for ASD were radiographically evaluated. Pre- and postoperative cervical parameters evaluated included cervical lordosis (CL), C2-C7 sagittal vertical axis (C2-C7 SVA), and the T1 slope (T1S) minus the CL (T1S-CL). CD was defined as C2-C7 SVA >4 cm, CL < 0°, or T1S-CL ≥15°.

RESULTS

Eighty-five patients (mean age 64 ± 11.1) were identified. Preoperative lumbar lordosis (LL) was 28.7° ± 13.8°, thoracic kyphosis (TK) was 28.2° ± 17.0°, C7 plumbline (C7 SVA) was 7.54 ± 6.7 cm, pelvic tilt (PT) was 30.0° ± 8.96°, lumbopelvic mismatch was 32° ± 17.1°, and the T1 pelvic angle (TPA) was 26.8° ± 12.9°. The C7 SVA and TPA corrected to 3.90 cm (P < 0.0001) and 17.5°, respectively (P < 0.0001). CD increased from 41 (48%) to 47 (55%) patients. The mean CL changed from 16.5° to 11.9° (P < 0.013), C2 SVA from 10.1 to 6.37 cm (P < 0.0001), T1S-CL from 10.2° to 14.3° (P = 0.021), and TK from 28° to 39° (P < 0.0001). A correlation was observed between T1S and CL (ρ = 0.435, P < 0.0001) and C2-C7 SVA (ρ = 0.624, P < 0.0001). T1S was the only independent predictor of both the postoperative C2-C7 SVA and CL.In this study, the presence of any single preoperative CD criterion was noted to be a risk for persistent global deformity on postoperative radiograph [odds ratio (OR) = 2.5] and the development of PJK (OR = 2.1). The T1-CL < 15° may indicate an even greater risk for persistent global deformity (OR = 3.5).

CONCLUSION

Thoracolumbar fusion with multilevel Schwab Grade II Osteotomies was associated with a decreased CL and reciprocal increases in TK and T1S-CL.

LEVEL OF EVIDENCE

3.

Thoracolumbar Realignment Surgery Results in Simultaneous Reciprocal Changes in Lower Extremities and Cervical Spine

STUDY DESIGN

A retrospective, clinical, and radiographic single-center study.

OBJECTIVE

The aim of this study was to assess simultaneous cervical spine and lower extremity compensatory changes with changes in thoracolumbar spinal alignment.

SUMMARY OF BACKGROUND DATA

Full-body stereoradiographic imaging allows better understanding of reciprocal changes in cervical and lower extremity alignment in the setting of thoracolumbar malalignment. Few studies describe the simultaneous effect of alignment correction on these mechanisms.

METHODS

Patients aged ≥18 years undergoing instrumented thoracolumbar fusion without previous cervical spine fusion, hip, knee, or ankle arthroplasty were included. Spinopelvic, lower extremity, and cervical alignment were assessed from full-body standing stereoradiographs using validated software. Patients were matched for pelvic incidence and stratified on the basis of baseline T1-pelvic angle (TPA) as: TPA-Low <14°, TPA-Moderate = 14° to 22°, and TPA-High >22°. Perioperative changes between baseline and first postoperative visit <6 months in lower extremity alignment (pelvic shift: P Shift, sacrofemoral angle: SFA, knee angle: KA, ankle angle: AA, global sagittal axis: GSA) and cervical alignment (C0-C2 angle, C2-slope, C2-C7 lordosis and C2-C7 SVA:cSVA) were correlated with change in magnitude of TPA and sagittal vertical axis (SVA) correction.

RESULTS

After matching, 87 patients were assessed. Increasing baseline TPA severity was associated with a progressive increase in all regional spinopelvic parameters except thoracic kyphosis, in addition to increased SFA, P Shift, KA, GSA, and C2-C7 lordosis. As TPA correction increased, there was a reciprocal reduction in SFA, KA, P Shift, GSA, and C2-C7 lordosis. Change in SVA correlated most with change in GSA (r = 0.886), P Shift (r = 0.601), KA (r = 0.534), and C2-C7 lordosis (r = 0.467). Change in TPA correlated with change in SFA (r = 0.372), while SVA did not.

CONCLUSION

Patients with thoracolumbar malalignment exhibit compensatory changes in cervical spine and lower extremity simultaneously in the form of cervical hyperlordosis, pelvic shift, knee flexion, and pelvic retroversion. These compensatory mechanisms resolve reciprocally in a linear fashion following optimal surgical correction.

LEVEL OF EVIDENCE

3.

Postoperative Increase in Occiput-C2 Angle Negatively Impacts Subaxial Lordosis after Occipito-Upper Cervical Posterior Fusion Surgery

STUDY DESIGN

Retrospective case series.

PURPOSE

To elucidate the impact of postoperative occiput-C2 (O-C2) angle change on subaxial cervical alignment.

OVERVIEW OF LITERATURE

In the case of occipito-upper cervical fixation surgery, it is recommended that the O-C2 angle should be set larger than the preoperative value postoperatively.

METHODS

The present study included 17 patients who underwent occipito-upper cervical spine (above C4) posterior fixation surgery for atlantoaxial subluxation of various etiologies. Plain lateral cervical radiographs in a neutral position at standing were obtained and the O-C2 angle and subaxial lordosis angle (the angle between the endplates of the lowest instrumented vertebra (LIV) and C7 vertebrae) were measured preoperatively and postoperatively soon after surgery and ambulation and at the final follow-up visit.

RESULTS

There was a significant negative correlation between the average postoperative alteration of O-C2 angle (DO-C2) and the average postoperative alteration of subaxial lordosis angle (Dsubaxial lordosis angle) (r=-0.47, p=0.03).

CONCLUSIONS

There was a negative correlation between DO-C2 and Dsubaxial lordosis angles. This suggests that decrease of mid-to lower-cervical lordosis acts as a compensatory mechanism for lordotic correction between the occiput and C2. In occipito-cervical fusion surgery, care must be taken to avoid excessive O-C2 angle correction because it might induce mid-to-lower cervical compensatory decrease of lordosis.

Cervical sagittal deformity develops after PJK in adult thoracolumbar deformity correction: radiographic analysis utilizing a novel global sagittal angular parameter, the CTPA

PURPOSE

To describe reciprocal changes in cervical alignment after adult spinal deformity (ASD) correction and subsequent development of proximal junctional kyphosis (PJK). This study also investigated these changes using two novel global sagittal angular parameters, cervical-thoracic pelvic angle (CTPA) and the T1 pelvic angle (TPA).

METHODS

Multicenter, retrospective consecutive case series of ASD patients undergoing thoracolumbar three-column osteotomy (3CO) with fusion to the pelvis. Radiographs were analyzed at baseline and 1 year post-operatively. Patients were substratified into upper thoracic (UT; UIV T6 and above) and lower thoracic (LT; UIV below T6). PJK was defined by >10° angle between UIV and UIV + 2 and >10° change in the angle from baseline to post-op.

RESULTS

PJK developed in 29 % (78 of 267) of patients. CTPA was linearly correlated with cervical plumbline (CPL) as a measure of cervical sagittal alignment (R = 0.826, p < 0.001). PJK patients had significantly greater post-operative CTPA and SVA than patients without PJK (NPJK) (p = 0.042; p = 0.021). For UT (n = 141) but not LT (n = 136), PJK patients at 1 year had larger CTPA (4.9° vs. 3.7°, p = 0.015) and CPL (5.1 vs. 3.8 cm, p = 0.022) than NPJK patients, despite similar corrections in PT and PI-LL.

CONCLUSIONS

The prevalence of PJK was 29 % at 1 year follow-up. CTPA, which correlates with CPL as a global analog of cervical sagittal balance, and TPA describe relative proportions of cervical and thoracolumbar deformities. Patients who develop PJK in the upper thoracic spine after thoracolumbar 3CO also develop concomitant cervical sagittal deformity, with increases in CPL and CTPA.

A retrospective study to reveal the effect of surgical correction of cervical kyphosis on thoraco-lumbo-pelvic sagittal alignment

PURPOSE

Recent studies suggest that cervical lordosis is influenced by thoracic kyphosis and that T1 slope is a key factor determining cervical sagittal alignment. However, no previous study has investigated the influence of cervical kyphosis correction on the remaining spinopelvic balance. The purpose of this study is to assess the effect of surgical correction of cervical kyphosis on thoraco-lumbo-pelvic alignment.

METHODS

Fifty-five patients who underwent ≥2 level cervical fusions for cervical radiculopathy or myelopathy were included. All patients had regional or global cervical kyphosis, which was surgically corrected into lordosis. Radiographic measurements were made using whole spine standing lateral radigraphs pre- and postoperatively to analyze various sagittal parameters. The visual analogue scale (VAS) for neck pain and the neck disability index (NDI) were calculated. The paired t test was used to compare pre- and post-operative radiographic measures and functional scores. Correlations between changes in cervical sagittal parameters and those of other sagittal parameters were analyzed by Pearson's correlation method.

RESULTS

Preoperative kyphosis (11.4° ± 8.3°) was corrected into lordosis (-9.3° ± 8.1°). The average fusion levels were 3.3 ± 1.0. With increasing C2-C7 lordosis after surgery (from -3.4° ± 10.0° to -15° ± 7.9°), C0-C2 lordosis decreased significantly (from -34.6° ± 8.2° to -27.7° ± 8.0°) (P < 0.001). Thoracic kyphosis (from 24.8 ± 13.9° to 33.5 ± 11.9°) and T1 slope (from 12.8° ± 7.9° to 20.4° ± 5.2°) significantly increased after surgery (P < 0.001). However, other parameters did not significantly change (P > 0.05). Neck pain VAS and NDI scores (31.8 ± 16.2) significantly improved (P < 0.001). The degree of increasing C2-C7 lordosis by surgical correction was negatively correlated with changes in both thoracic kyphosis and T1 slope (P < 0.01).

CONCLUSIONS

Surgical correction of cervical kyphosis affects T1 slope and thoracic kyphosis, but not lumbo-pelvic alignment. These results indicate that the compensatory mechanisms to minimize positive sagittal malalignment of the head may occur mainly in the thoracic, and not in the lumbosacral spine.