The value of sitting radiographs: analysis of spine flexibility and its utility in preoperative planning for adult spinal deformity surgery

Spinopelvic Adaptations in Standing and Sitting Positions in Patients With Adult Spinal Deformity

Purpose

To describe spinopelvic adaptations in the standing and sitting positions in patients with adult spinal deformity (ASD).

Methods

Ninety-five patients with ASD and 32 controls completed health-related quality of life (HRQOL) questionnaires: short form 36 (SF36), Oswestry Disability Index (ODI), and visual analog scale (VAS) for pain. They underwent biplanar radiography in both standing and sitting positions. Patients with ASD were divided into ASD-front (frontal deformity Cobb > 20°, n = 24), ASD-sag (sagittal vertical axis (SVA) > 50 mm, pelvic tilt (PT) > 25°, or pelvic incidence (PI)-lumbar lordosis (LL) > 10°, n = 40), and ASD-hyper thoracic kyphosis (TK >60°, n = 31) groups. Flexibility was defined as the difference (Δ) in radiographic parameters between the standing and sitting positions. The radiographic parameters were compared between the groups. Correlations between HRQOL scores were evaluated.

Results

All participants increased their SVA from standing to sitting (ΔSVA<0), except for patients with ASD-sag, who tended to decrease their SVA (78-62 mm) and maximize their pelvic retroversion (27-40° vs 10-34° in controls, p<0.001). They also showed reduced thoracic and lumbar flexibility (ΔLL = 3.4 vs 37.1°; ΔTK = −1.7 vs 9.4° in controls, p<0.001). ASD-hyperTK showed a decreased PT while sitting (28.9 vs 34.4° in controls, p<0.001); they tended to decrease their LL and TK but could not reach values for controls (ΔLL = 22.8 vs 37.1° and ΔTK = 5.2 vs 9.4°, p<0.001). The ASD-front had normal standing and sitting postures. ΔSVA and ΔLL were negatively correlated with the physical component scale (PCS of SF36) and ODI (r = −0.39 and r = −0.46, respectively).

Conclusion

Patients with ASD present with different spinopelvic postures and adaptations from standing to sitting positions, with those having sagittal malalignment most affected. In addition, changes in standing and sitting postures were related to HRQOL outcomes. Therefore, surgeons should consider patient sitting adaptations in surgical planning and spinal fusion. Future studies on ASD should evaluate whether physical therapy or spinal surgery can improve sitting posture and QOL, especially for those with high SVA or PT.

Variations of Sagittal Alignment in Standing Versus Sitting Positions Under the Roussouly Classification in Asymptomatic Subjects

STUDY DESIGN

Prospective radiological analysis.

OBJECTIVE

To investigate the characteristics of the sagittal spinopelvic alignment in the standing and sitting positions under the Roussouly classification in a healthy population.

METHODS

This study using standing and sitting lateral radiographs included 143 volunteers whose spinopelvic parameters were measured. The parameters were compared in the standing and sitting positions. The lumbo-pelvic profile was identified according to the Roussouly classification. The differences in the values of the parameters between the standing and sitting positions were analyzed. The different frequencies of the unchanged apex were assessed.

RESULTS

All parameter values except the thoracolumbar angle (TLK) were significantly altered. With regard to the classification of the lumbopelvic profile, 15 (10.5%) subjects were excluded because they were evaluated as not belonging to any of the Roussouly types. The remaining 128 subjects were evaluated and classified as follows: 19 (14.8%), type 1; 53 (41.4%), type 2; 9 (7.0%), type 3 + anteverted pelvis (AP); 33 (25.8%), type 3; and 14 (10.9%), type 4. The differences in the pelvic tilt (PT), sacral slope (SS), and thoracic pelvic angle (TPA) values were significantly lower in types 1 and 2 than in other Roussouly types. Corresponding variations in the apical vertebra for the sagittal lumbar curves in the sitting position were observed.

CONCLUSIONS

Subjects with Roussouly type 1 and type 2 sagittal alignments were found to be less capable of performing changes in alignment when changing to the sitting position. The characteristics of the apical movement were also different.

Supine Imaging Is a Superior Predictor of Long-Term Alignment Following Adult Spinal Deformity Surgery

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To investigate correlations between preoperative supine imaging and postoperative alignment.

METHODS

A retrospective review was conducted of a single-institution database of patients with adult spinal deformity (ASD). Patients were stratified by fusion location in the lumbar or thoracic spine. Outcomes of interest were postoperative lumbar lordosis (LL) and thoracic kyphosis (TK). Sagittal alignment parameters were compared and correlation analyses were performed. Multilinear stepwise regression was conducted to identify independent predictors of postoperative LL or TK. Regression analyses were repeated within the lumbar and thoracic fusion cohorts.

RESULTS

A total of 99 patients were included (mean age 63.2 years, 83.1% female, mean body mass index 27.3 kg/m²). Scoliosis Research Society classification demonstrated moderate to severe sagittal and/or coronal deformity (pelvic tile modifier, 18.2% ++; sagittal vertical axis, 27.3% ++, pelvic incidence minus lumbar lordosis mismatch, 29.3% ++, SRS type, 29.3% N type curve and 68.7% L or D type curve). A total of 73 patients (73.7%) underwent lumbar fusion and 50 (50.5%) underwent thoracic fusion. Correlation analyses demonstrated a significant association between pre- and postoperative LL and TK. Multilinear regression demonstrated that LL supine and pelvic incidence were significant predictors of postoperative LL (r² = 0.568, P < .001). LL supine, TK supine, and age were significant predictors of postoperative TK (r² = 0.490, P < .001).

CONCLUSION

Preoperative supine films are superior to standing in predicting postoperative alignment at 1-year follow-up. Anticipation of undesired alignment changes through supine imaging may be useful in mitigating the risk of iatrogenic malalignment.

Pelvic and spinal postural changes between standing-sitting positions following lumbosacral fusion: a pilot study

Purpose

Prospective pre-operative and post-operative comparative analysis of radiographic spino-pelvic parameters between sitting versus standing positions of patients with LS fusion, to detect adaptation mechanisms around fused spinal segments.

Methods

Sixteen patients aged 53.9 ± 15.9 who underwent LS fusion between L3 and S1 were extracted from the database of an ongoing prospective study. Different spino-pelvic parameters were evaluated on full spine X-rays, standing, then sitting straight. Parameters were compared pre-operative versus post-operative, and on standing versus sitting X-rays.

Results

Preliminary results revealed a significantly greater pre-operative pelvic tilt (PT) in sitting than standing posture, (p = 0.020) but not in post-operative (p = 0.087). After surgery, PT was lower in sitting compared to pre-operative (p = 0.034) but not in standing (p = 0.245). L4–S1 lordosis was lower in sitting than standing in pre-operative (p = 0.014) and post-operative (p = 0.021). Surgery decreased segmental lordosis above the fusion (PSL, proximal sagittal lordosis) in sitting (p = 0.039) but not in standing (p = 0.193). No significant differences in thoracic kyphosis (TK) were observed. Fusions down to L5 versus S1 showed no significant differences for PT and PSL, neither in sitting versus standing, nor pre-operative versus post-operative.

Conclusion

Before fusion, compared to standing, PT increases in sitting straight posture (pelvic retroversion), and the lumbar spine adapts by decreasing its lordosis, mainly at L4–S1. After fusion, the segments adjacent to the instrumented section, adapt in flexion at lumbosacral and thoracolumbar junctions, i.e. just below and above (PSL). This might have mechanical implications for the occurrence of adjacent segment disease.

The sitting vs standing spine

Background

Planning of surgical procedures for spinal fusion is performed on standing radiographs, neglecting the fact that patients are mostly in the sitting position during daily life. The awareness about the differences in the standing and sitting configuration of the spine has increased during the last years. The purpose was to provide an overview of studies related to seated imaging for spinal fusion surgery, identify knowledge gaps and evaluate future research questions.

Methods

A literature search according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) extension for Scoping Reviews (PRISMASc) was performed to identify reports related to seated imaging for spinal deformity surgery. A summary of the finding is presented for healthy individuals as well as patients with a spinal disorder and/or surgery.

Results

The systematic search identified 30 original studies reporting on 1) the pre- and postoperative use of seated imaging of the spine (n=12), 2) seated imaging of the spine for non - surgical evaluation (n=7) and 3) seated imaging of the spine among healthy individuals (12). The summarized evidence illuminates that sitting leads to a straightening of the spine decreasing thoracic kyphosis (TK), lumbar lordosis (LL), the sacral slope (SS). Further, the postural change between standing and sitting is more significant on the lower segments of the spine. Also, the adjacent segment compensates the needed postural change of the lumbar spine while sitting with hyperkyphosis.

Conclusions

The spine has a different configuration in standing and sitting. This systematic review summarizes the current knowledge about such differences and reveals that there is minimal evidence about their consideration for surgical planning of spinal fusion surgery. Further, it identifies gaps in knowledge and areas of further research.

The standing T1-L1 pelvic angle: a useful radiographic predictor of proximal junctional kyphosis in adult spinal deformity

OBJECTIVE

Proximal junctional kyphosis (PJK), which can worsen a patient's quality of life, is a common complication following the surgical treatment of adult spinal deformity (ASD). Although various radiographic parameters have been proposed to predict the occurrence of PJK, the optimal method has not been established. The present study aimed to investigate the usefulness of the T1-L1 pelvic angle in the standing position (standing TLPA) for predicting the occurrence of PJK.

METHODS

The authors retrospectively extracted data for patients with ASD who underwent minimum 5-level fusion to the pelvis with upper instrumented vertebra between T8 and L1. In the present study, PJK was defined as ≥ 10° progression of the proximal junctional angle or reoperation due to progressive kyphosis during 1 year of follow-up. The following parameters were analyzed on whole-spine standing radiographs: the T1-pelvic angle, conventional thoracic kyphosis (TK; T4-12), whole-thoracic TK (T1-12), and the standing TLPA (defined as the angle formed by lines extending from the center of T1 and L1 to the femoral head axis). A logistic regression analysis and a receiver operating characteristic curve analysis were performed.

RESULTS

A total of 50 patients with ASD were enrolled (84% female; mean age 74.4 years). PJK occurred in 19 (38%) patients. Preoperatively, the PJK group showed significantly greater T1-pelvic angle (49.2° vs 34.4°), conventional TK (26.6° vs 17.6°), and standing-TLPA (30.0° vs 14.9°) values in comparison to the non-PJK group. There was no significant difference in the whole-thoracic TK between the two groups. A multivariate analysis showed that the standing TLPA and whole-thoracic TK were independent predictors of PJK. The standing TLPA had better accuracy than whole-thoracic TK (AUC 0.86 vs 0.64, p = 0.03). The optimal cutoff value of the standing TLPA was 23.0° (sensitivity 0.79, specificity 0.74). Using this cutoff value, the standing TLPA was the best predictor of PJK (OR 8.4, 95% CI 1.8-39, p = 0.007).

CONCLUSIONS

The preoperative standing TLPA was more closely associated with the occurrence of PJK than other radiographic parameters. These results suggest that this easily measured parameter is useful for the prediction of PJK.

The impact of preoperative supine radiographs on surgical strategy in adult spinal deformity

OBJECTIVE

Preoperative planning for adult spinal deformity (ASD) surgery is essential to prepare the surgical team and consistently obtain postoperative alignment goals. Positional imaging may allow the surgeon to evaluate spinal flexibility and anticipate the need for more invasive techniques. The purpose of this study was to determine whether spine flexibility, defined by the change in alignment between supine and standing imaging, is associated with the need for an osteotomy in ASD surgery.

METHODS

A single-center, dual-surgeon retrospective analysis was performed of adult patients with ASD who underwent correction of a thoracolumbar deformity between 2014 and 2018 (pelvis to upper instrumented vertebra between L1 and T9). Patients were stratified into osteotomy (Ost) and no-osteotomy (NOst) cohorts according to whether an osteotomy was performed (Schwab grade 2 or higher). Demographic, surgical, and radiographic parameters were compared. The sagittal correction from intraoperative prone positioning alone (sagittal flexibility percentage [Sflex%]) was assessed by comparing the change in lumbar lordosis (LL) between preoperative supine to standing radiographs and preoperative to postoperative alignment.

RESULTS

Demographics and preoperative and postoperative sagittal alignment were similar between the Ost (n = 60, 65.9%) and NOst (n = 31, 34.1%) cohorts (p > 0.05). Of all Ost patients, 71.7% had a grade 2 osteotomy (mean 3 per patient), 21.7% had a grade 3 osteotomy, and 12.5% underwent both grade 3 and grade 2 osteotomies. Postoperatively, the NOst and Ost cohorts had similar pelvic incidence minus lumbar lordosis (PI-LL) mismatch (mean PI-LL 5.2° vs 1.2°; p = 0.205). Correction obtained through positioning (Sflex%) was significantly lower for in the osteotomy cohort (38.0% vs 76.3%, p = 0.004). A threshold of Sflex% < 70% predicted the need for osteotomy at a sensitivity of 78%, specificity of 56%, and positive predictive value of 77%.

CONCLUSIONS

The flexibility of the spine is quantitatively related to the use of an osteotomy. Prospective studies are needed to determine thresholds that may be used to standardize surgical decision-making in ASD surgery.

The utility of supine radiographs in the assessment of thoracic flexibility and risk of proximal junctional kyphosis

OBJECTIVE

Supine radiographs have successfully been used for preoperative planning of lumbar deformity corrections. However, they have not been used to assess thoracic flexibility, which has recently garnered attention as a potential contributor to proximal junctional kyphosis (PJK). The purpose of this study was to compare supine to standing radiographs to assess thoracic flexibility and to determine whether thoracic flexibility is associated with PJK.

METHODS

A retrospective study was conducted of a single-institution database of patients with adult spinal deformity (ASD). Sagittal alignment parameters were compared between standing and supine and between pre- and postoperative radiographs. Thoracic flexibility was determined as the change between preoperative standing thoracic kyphosis (TK) and preoperative supine TK, and these changes were measured over the overall thoracic spine and the fused portion of the thoracic spine (i.e., TK fused). A case-control analysis was performed to compare thoracic flexibility between patients with PJK and those without (no PJK). The cohort was also stratified into three groups based on thoracic flexibility: kyphotic change (increased TK), lordotic change (decreased TK), and no change. The PJK rate was compared between the cohorts.

RESULTS

A total of 101 patients (mean 63 years old, 82.2% female, mean BMI 27.4 kg/m2) were included. Preoperative Scoliosis Research Society-Schwab ASD classification showed moderate preoperative deformity (pelvic tilt 27.7% [score ++]; pelvic incidence-lumbar lordosis mismatch 44.6% [score ++]; sagittal vertical axis 42.6% [score ++]). Postoperatively, the average offset from age-adjusted alignment goals demonstrated slight overcorrection in the study sample (-8.5° ± 15.6° pelvic incidence-lumbar lordosis mismatch, -29.2 ± 53.1 mm sagittal vertical axis, -5.4 ± 10.8 pelvic tilt, and -7.6 ± 11.7 T1 pelvic angle). TK decreased between standing and supine radiographs and increased postoperatively (TK fused: -25.3° vs -19.6° vs -29.9°; all p < 0.001). The overall rate of radiographic PJK was 23.8%. Comparisons between PJK and no PJK demonstrated that offsets from age-adjusted alignment goals were similar (p > 0.05 for all). There was a significant difference in the PJK rate when stratified by thoracic flexibility cohorts (kyphotic: 0.0% vs no change: 18.4% vs lordotic: 35.0%; p = 0.049). Logistic regression revealed thoracic flexibility (p = 0.045) as the only independent correlate of PJK.

CONCLUSIONS

Half of patients with ASD experienced significant changes in TK during supine positioning, a quality that may influence surgical strategy. Increased thoracic flexibility is associated with PJK, possibly secondary to fusing the patient's spine in a flattened position intraoperatively.

Preoperative and Postoperative Sitting Radiographs for Adult Spinal Deformity Surgery: Upper Instrumented Vertebra Selection Using Sitting C2 Plumb Line Distance to Prevent Proximal Junctional Kyphosis

STUDY DESIGN

Case-control study from a continuous series.

OBJECTIVES

To study the impact of perioperative sitting radiographs in adult spinal deformity (ASD) patients and determine whether proximal junctional kyphosis (PJK) can be prevented using preoperative sitting radiograph.

SUMMARY OF BACKGROUND DATA

Radiographic analysis of ASD comprises standing whole-spine radiography which cannot evaluate the relaxed posture without head-to-foot compensation.

METHODS

Preoperative and postoperative whole-spine standing and sitting radiographs and proximal mechanical complications in surgically treated spinal disorders with a minimum of 1-year follow-up were studied. Whole-spinal alignment was defined by cervical lordosis (CL), sagittal vertical axis (SVA), T1 slope (T1S), thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and level of kyphotic apex (KA). Proximal mechanical complication was described as a PJK (proximal junctional angle >20°) or reoperation due to proximal junctional failure.

RESULTS

Surgically treated 113 patients were prospectively investigated. Patients were divided into either the ASD (thoracic to ilium posterior corrective fusion), or non-ASD groups. In the ASD group, 10 patients had postoperative PJK, and three revision surgeries were carried out due to PJF with neurological deficit. Comparing standing with sitting positions, CL, TK, and PT became larger, SVA became frontal, LL and SS became smaller, and KA became caudal particularly in the ASD group. Logistic regression analysis demonstrated that the most influenced plumb line for PJK was the upper instrumented vertebra (UIV) to C2 plumb line distance, with a cutoff value of 115 mm for predicting PJK.

CONCLUSION

Our findings highlight the usefulness of sitting spinal alignment evaluation, particularly in ASD patients, with maximum effort of thoracic spine and lower extremity compensation at standing. Mechanical complications such as PJK could be predicted using the distance from the planned UIV to the C2 plumb line in preoperative sitting radiographs.

LEVEL OF EVIDENCE

3.

Sagittal Spinal and Pelvic Alignment in Middle-Aged and Older Men and Women in the Natural and Erect Sitting Positions: A Prospective Study in a Chinese Population

Background

This prospective study aimed to compare the sagittal spinopelvic parameters in the erect and natural sitting positions in healthy middle-aged and older men and women in a Chinese population.

Material/Methods

Ninety healthy middle-aged and older men and women underwent lateral whole spinal radiography in the natural and erect sitting positions. The radiographic sagittal spinopelvic parameters were measured. They included the sagittal vertical axis (SVA), the T1 pelvic angle (TPA), the pelvic incidence (PI), the pelvic tilt (PT), the sacral slope (SS), thoracic kyphosis (TK), thoracolumbar kyphosis (TLK), the T1 slope (T1S), cervical lordosis (CL), and lumbar lordosis (LL).

Results

In the natural sitting position, LL decreased by 14.5°, TK and TLK increased by 3.2° and 2.5°, respectively, PT increased by 10.3°, T1S increased by 6.9°, and CL increased by 3.4° compared with the erect position. In the natural sitting position, the mean forward-moving SVA was 33.4 mm, and the C2–C7 SVA was 6.1 mm. Men had a larger LL and smaller PT than the women when sitting in the erect position, and a greater TK, T1S, and C2–C7 SVA than women when sitting in the natural position.

Conclusions

In the natural sitting position, a reduction in LL was associated with TK, SVA and PT increased, and there were differences between men and women. The characteristics of spinopelvic alignment in healthy older adults should be considered when planning corrective spinal surgery.

Imaging in Spine Surgery: Current Concepts and Future Directions

OBJECTIVE

To review and highlight the historical and recent advances of imaging in spine surgery and to discuss current applications and future directions.

METHODS

A PubMed review of the current literature was performed on all relevant articles that examined historical and recent imaging techniques used in spine surgery. Studies were examined for their thoroughness in description of various modalities and applications in current and future management.

RESULTS

We reviewed 97 articles that discussed past, present, and future applications for imaging in spine surgery. Although most historical approaches relied heavily upon basic radiography, more recent advances have begun to expand upon advanced modalities, including the integration of more sophisticated equipment and artificial intelligence.

CONCLUSIONS

Since the days of conventional radiography, various modalities have emerged and become integral components of the spinal surgeon's diagnostic armamentarium. As such, it behooves the practitioner to remain informed on the current trends and potential developments in spinal imaging, as rapid adoption and interpretation of new techniques may make significant differences in patient management and outcomes. Future directions will likely become increasingly sophisticated as the implementation of machine learning, and artificial intelligence has become more commonplace in clinical practice.

The Impact of Adult Thoracolumbar Spinal Deformities on Standing to Sitting Regional and Segmental Reciprocal Alignment

Background

Regional and segmental changes of the lumbar spine have previously been described as patients transition from standing to sitting; however, alignment changes in the cervical and thoracic spine have yet to be investigated. So, the aim of this study was to assess cervical and thoracic regional and segmental changes in patients with thoracolumbar deformity versus a nondeformed thoracolumbar spine population.

Methods

This study was a retrospective cohort study of a single center's database of full-body stereoradiographic imaging and clinical data. Patients were ≥ 18 years old with nondeformed spines (nondegenerative, nondeformity spinal pathologies) or thoracolumbar deformity (ASD: PI-LL > 10°). Patients were propensity-score matched for age and maximum hip osteoarthritis grade and were stratified by Scoliosis Research Society (SRS)-Schwab classification by PI-LL, SVA, and PT. Patients with lumbar transitional anatomy or fusions were excluded. Outcome measures included changes between standing and sitting in global alignment parameters: sagittal vertical axis (SVA), pelvic incidence minus lumbar lordosis (PI-LL), pelivc tilt (PT), thoracic kyphosis, cervical alignment, cervical SVA, C2-C7 lordosis (CL), T1 slop minus CL (TS-CL), and segmental alignment from C2 to T12. Another analysis was performed using patients with cervical and thoracic segmental measurements.

Results

A total of 338 patients were included (202 nondeformity, 136 ASD). After propensity-score matching, 162 patients were included (81 nondeformity, 81 ASD). When categorized by SRS-Schwab classification, all nondeformity patients were nonpathologically grouped for PI-LL, SVA, and PT, whereas ASD patients had mix of moderately and markedly deformed modifiers. There were significant differences in pelvic and global spinal alignment changes from standing to sitting between nondeformity and ASD patients, particularly for SVA (nondeformed: 49.5 mm versus ASD: 27.4 mm; P&thinsp;< .001) and PI-LL (20.12° versus 13.01°, P < .001). With application of the Schwab classification system upon the cohort, PI-LL (P = .040) and SVA (P = .007) for severely classified deformity patients had significantly less positional alignment change. In an additional analysis of patients with segmental measurements from C2 to T12, nondeformity patients showed significant mobility of T2-T3 (-0.99° to -0.54°, P = .023), T6-T7 (-3.39° to -2.89°, P = .032), T7-T8 (-2.68° to -2.23°, P = .048), and T10-T11 (0.31° to 0.097°, P = .006) segments from standing to sitting. ASD patients showed mobility of the C6-C7 (1.76° to 3.45°, P < .001) and T11-T12 (0.98° to 0.54°, P = 0.014) from standing to sitting. The degree of mobility between nondeformity and ASD patients was significantly different in C6-C7 (-0.18° versus 1.69°, P = .003), T2-T3 (0.45° versus -0.27°, P = .034), and T10-T11 (0.45° versus -0.30°, P = .001) segments. With application of the Schwab modifier system upon the cohort, mobility was significant in the C6-C7 (nondeformed: 0.18° versus moderately deformed: 2.12° versus markedly deformed: 0.92°, P = .039), T2-T3 (0.45° versus -0.08° versus -0.63°, P = .020), T6-T7 (0.48° versus 0.36° versus -1.85°, P = .007), and T10-T11 (0.45° versus -0.21° versus -0.23°, P = .009) segments.

Conclusions

Nondeformity patients and ASD patients have significant differences in mobility of global spinopelvic parameters as well as segmental regions in the cervical and thoracic spine between sitting and standing. This study aids in our understanding of flexibility and compensatory mechanisms in deformity patients, as well as the possible impact on unfused segments when considering deformity corrective surgery.