Inter- and Intra-rater Agreement in Assessment of Adult Spinal Deformity Using the Scoliosis Research Society-Schwab Classification

Functional Alignment Within the Fusion in Adult Spinal Deformity (ASD) Improves Outcomes and Minimizes Mechanical Failures

STUDY DESIGN

Retrospective review of an adult deformity database.

OBJECTIVE

To identify pelvic incidence (PI) and age-appropriate physical function alignment targets using a component angle of T1-pelvic angle within the fusion to define correction and their relationship to proximal junctional kyphosis (PJK) and clinical outcomes.

SUMMARY OF BACKGROUND DATA

In preoperative planning, a patient's PI is often utilized to determine the alignment target. In a trend toward more patient-specific planning, age-specific alignment has been shown to reduce the risk of mechanical failures. PI and age have not been analyzed with respect to defining a functional alignment.

METHODS

A database of patients with operative adult spinal deformity was analyzed. Patients fused to the pelvis and upper-instrumented vertebrae above T11 were included. Alignment within the fusion correlated with clinical outcomes and PI. Short form 36-Physical Component Score (SF36-PCS) normative data and PI were used to compute functional alignment for each patient. Overcorrected, under-corrected, and functionally corrected groups were determined using T10-pelvic angle (T10PA).

RESULTS

In all, 1052 patients met the inclusion criteria. T10PA correlated with SF36-PCS and PI (R=0.601). At six weeks, 40.7% were functionally corrected, 39.4% were overcorrected, and 20.9% were under-corrected. The PJK incidence rate was 13.6%. Overcorrected patients had the highest PJK rate (18.1%) compared with functionally (11.3%) and under-corrected (9.5%) patients ( P <0.05). Overcorrected patients had a trend toward more PJK revisions. All groups improved in HRQL; however, under-corrected patients had the worst 1-year SF36-PCS offset relative to normative patients of equivalent age (-8.1) versus functional (-6.1) and overcorrected (-4.5), P <0.05.

CONCLUSIONS

T10PA was used to determine functional alignment, an alignment based on PI and age-appropriate physical function. Correcting patients to functional alignment produced improvements in clinical outcomes, with the lowest rates of PJK. This patient-specific approach to spinal alignment provides adult spinal deformity correction targets that can be used intraoperatively.

Toward the Development of a Comprehensive Clinically Oriented Patient Profile: A Systematic Review of the Purpose, Characteristic, and Methodological Quality of Classification Systems of Adult Spinal Deformity

BACKGROUND

Existing adult spinal deformity (ASD) classification systems are based on radiological parameters but management of ASD patients requires a holistic approach. A comprehensive clinically oriented patient profile and classification of ASD that can guide decision-making and correlate with patient outcomes is lacking.

OBJECTIVE

To perform a systematic review to determine the purpose, characteristic, and methodological quality of classification systems currently used in ASD.

METHODS

A systematic literature search was conducted in MEDLINE, EMBASE, CINAHL, and Web of Science for literature published between January 2000 and October 2018. From the included studies, list of classification systems, their methodological measurement properties, and correlation with treatment outcomes were analyzed.

RESULTS

Out of 4470 screened references, 163 were included, and 54 different classification systems for ASD were identified. The most commonly used was the Scoliosis Research Society-Schwab classification system. A total of 35 classifications were based on radiological parameters, and no correlation was found between any classification system levels with patient-related outcomes. Limited evidence of limited quality was available on methodological quality of the classification systems. For studies that reported the data, intraobserver and interobserver reliability were good (kappa = 0.8).

CONCLUSION

This systematic literature search revealed that current classification systems in clinical use neither include a comprehensive set of dimensions relevant to decision-making nor did they correlate with outcomes. A classification system comprising a core set of patient-related, radiological, and etiological characteristics relevant to the management of ASD is needed.

Reproducibility of the classification of early onset scoliosis (C-EOS)

STUDY DESIGN

Reproducibility study.

OBJECTIVES

Assess the agreement and reliability of the classification of early onset scoliosis (C-EOS). C-EOS is a promising tool for patients with early onset scoliosis (EOS). However, the reliability has only been examined without measuring radiographs and not including the annual progression rate (APR) modifier.

METHODS

We included a single-center consecutive cohort of patients diagnosed with EOS seen in our outpatient clinic. Patients had no previous spine surgery. Four raters rated 60 cases. Two anterior-posterior full-spine radiographs, taken minimum 6 months apart, and one sagittal radiograph were measured twice by all raters in a blinded test-retest setup. Results were assessed using crude frequency of overall agreement (OA), intra- and inter-rater Fleiss kappa (κ) statistics, and intraclass correlation coefficient (ICC). We calculated the 95% limits of agreement (LOA) for major curve angle (MCA), kyphosis, and APR using a linear mixed-effects model. Inter- and intra-rater LOA were analyzed for each etiology separately.

RESULTS

Mean age was 8.7 ± 3.4 years and the etiology were congenital/structural (n = 20), idiopathic (n = 19), neuromuscular (n = 13), or syndromic (n = 8). For etiology, OA was 75.8% and κ = 0.80. For major curve angle, OA was 84.2%, κ = 0.86, ICC = 0.97, and LOA = 12.8°. For kyphosis, OA was 55.8%, κ = 0.52, ICC = 0.87, and LOA = 20.6°. For APR, OA was 76.7%, κ = 0.61, ICC = 0.77, and LOA = 17.4°/year. Inter- and intra-rater LOA were generally largest for neuromuscular and smallest for idiopathic patients.

CONCLUSIONS

We found substantial agreement for etiology, however, with disagreement in certain cases. The reliability of MCA was excellent; however, somewhat lower for kyphosis and APR with less accuracy. The measurement errors of MCA, kyphosis, and APR depended largely on the etiology. Regarding APR, LOA exceeded the 10°/year increments proposed in the C-EOS, suggesting a revision of this optional modifier.

LEVEL OF EVIDENCE

Diagnostic study level 1.

Understanding Classification Systems in Spine Deformity

Classification systems provide organization for pathologic conditions and guide treatment for similar disease states. Spine deformity is a growing field with newer classification systems being developed as our surgical techniques and clinical understanding advances. The evolution of these classification systems reflects our current knowledge and are used to better understand the evolving field of spine surgery. Currently, classification systems in spine surgery range from describing deformity in different age groups and different regions of the spine to describing various osteotomies and the severity of proximal junctional kyphosis. This paper will describe what makes a successful classification system in spine deformity. Old classification systems will be briefly described and their limitations that necessitated the need for newer classification systems. Newer systems will also be reviewed and the importance of specific radiographic parameters. Finishing this review, clinicians will be able to pick which systems are ideal for their practice.

Moderate Interrater and Substantial Intrarater Reproducibility of the Roussouly Classification System in Patients With Adult Spinal Deformity

STUDY DESIGN

Reproducibility study of a classification system.

OBJECTIVES

To provide the inter- and intrarater reproducibility of the Roussouly Classification System in a single-center prospective cohort of patients referred for Adult Spinal Deformity.

SUMMARY OF BACKGROUND DATA

The Roussouly Classification System was developed to describe the variation in sagittal spine shape in normal individuals. A recent study suggests that patients' spine types could influence the outcome following spinal surgery. The utility of a classification system depends largely on its reproducibility.

METHODS

Sixty-four consecutive patients were included in a blinded test-retest setting using digital radiographs. All ratings were performed by four spine surgeons with different levels of experience. There was a 14-day interval between the two reading sessions. Inter- and intrarater reproducibility was calculated using Fleiss Kappa and crude agreement percentages.

RESULTS

We found moderate interrater (κ = 0.60) and substantial intrarater (κ = 0.68) reproducibility. All 4 raters agreed on the Roussouly type in 47% of the cases. The most experienced rater had significantly higher intrarater reliability compared to the least experienced rater (κ = 0.57 vs 0.78). The two most experienced raters also had the highest crude agreement percentage (75%); however, they also had a significant difference in distribution of spine types.

CONCLUSION

The current study presents moderate interrater and substantial intrarater reliability of the Roussouly Classification System. These findings are acceptable and comparable to previous results of reproducibility for a classification system in patients with Adult Spinal Deformity. Additional studies are requested to validate these findings as well as to further investigate the impact of the classification system on outcome following surgery.

Inter/Intraobserver Reliability of T1 Pelvic Angle (TPA), a Novel Radiographic Measure for Global Sagittal Deformity

STUDY DESIGN

Reliability analysis.

OBJECTIVE

To assess intra- and interobserver agreement of the T1 pelvic angle (T1PA), a novel radiographic measure of spinal sagittal alignment. Orthopedic surgeons of various levels of experience measured the T1PA in a series of healthy adult volunteers. The relationship of the TIPA to pelvic position was also assessed.

SUMMARY OF BACKGROUND DATA

Recent literature suggests that the T1PA is a more reliable measure of global sagittal alignment than traditional measurements (i.e., sagittal vertical axis). Previous research focuses on postoperative patients with known spinal deformity. No published research exists evaluating the use of T1PA on healthy subjects without spinal deformity. The purpose of this study is: (1) to assess the reliability of measurements of the T1PA, (2) to examine its relationship to pelvic position.

METHODS

Seven evaluators of varying orthopedic experience measured the T1PA in 50 healthy adult volunteers. Subjects were radiographed in each of three pelvic positions: resting, maximal anterior pelvic rotation, and maximal posterior pelvic rotation. After a washout period, the measurement was repeated. Using intraclass correlation coefficients, the intra- and inter-rater agreement for the T1PA was measured. The collected data was also used to determine the accuracy of this measurement and its relationship to pelvic position.

RESULTS

A very high level of agreement was found in measurements of the T1PA (intraclass correlation coefficients r = 0.98). At each pelvic position, all examiners had excellent intrarater reliability, > 0.85. The inter-rater reliability, compared with a gold standard, consistently measured the T1PA within ± 2°. The data also shows that the T1PA changes with pelvic rotation.

CONCLUSION

T1PA is a reproducible and reliable measure of global sagittal alignment regardless of the level of training. The T1PA varies based on pelvic rotation; this variation must be taken into account when assigning an absolute target for correction.

LEVEL OF EVIDENCE

4.

Pelvic incidence: a fixed value or can you change it?

BACKGROUND CONTEXT

There has been renewed interest in the pelvic vertebrae by spinal surgeons recently. Those involved in working with patients with adult spinal deformity focus on the position of the fused spine as it relates to the pelvis, and determine success or failure by specific numbers for given pelvic parameters. The pelvic parameters that are commonly measured for these patients are pelvic tilt, sacral slope, and pelvic incidence (PI). Out of the three, PI has always been considered to be the fixed measurement, whereas pelvic tilt and sacral slope have the capacity to change in relation to external forces. The assumption that the PI does not change has not been proven in a healthy, asymptomatic population.

PURPOSE

This study aimed to investigate the differences in PI between three pelvic positions used in common functional activities: resting baseline pelvic posture, maximal anterior pelvic rotation, and maximal posterior pelvic rotation.

STUDY DESIGN/SETTING

This was a randomized, prospective study of 50 healthy, asymptomatic, individuals who were recruited from the vicinity of our institution.

PATIENT SAMPLE

Fifty patients (16 men with a mean age of 26.5±12.1 years; 34 women with a mean age of 27.2±10.8 years) were recruited for this study. Initial screening occurred by telephone. The inclusion criteria consisted of participants being between 18 and 79 years of age, no previous history of spine, pelvic, or lower extremity pain which had lasted longer than 48 hours, or history of any disorder in the spine, pelvis, or lower extremity that had required medical care. Female patients could not be pregnant at the time of participation.

OUTCOME MEASURES

Changes in PI were assessed by examining the differences between the values of the PI with each change in pelvic position: resting to maximal anterior pelvic rotation and resting to maximal posterior pelvic rotation. Inter-rater reliability was assessed using Cronbach's alpha.

METHODS

This study was funded by a Small Exploratory Grant from the Scoliosis Research Society. All subjects had an initial posterior-anterior and lateral radiograph taken in their resting pelvic position. If no spinal deformity was noted, each subject was instructed to maximally rotate their pelvis anteriorly and an immediate lateral radiograph was taken. The subject was then instructed to maximally rotate their pelvis posteriorly and an immediate lateral radiograph was again taken. Radiographic measurements of PI were independently measured by a board-certified, fellowship trained orthopedic spine surgeon and a board-certified musculoskeletal radiologist after defining and agreeing to the specific manner of measurement.

RESULTS

Pelvic incidence values changed in 44 of 50 subjects (88%) when they maximally anteriorly rotated their pelvis from the resting pelvic position. The mean change was 2.9°, with 23 of 50 subjects (46%) changing ≥3°. Pelvic incidence values changed in 40 of 50 subjects (80%) when they maximally posteriorly rotated their pelvis from the resting position. The mean change was 2.82° with 27 of 50 subjects (54%) changing by ≥3°.

CONCLUSIONS

This study demonstrated that for a high percentage of the healthy subjects who participated, the PI changed when the subjects varied their pelvic position. This questions the assumption that PI is a fixed parameter and suggests a potential functional motion at the sacroiliac joint. It also supports the idea that intentionally changing one's posture could lead to a change in PI, an idea that could have ramifications in surgical cases.

Radiographic Predictors for Mechanical Failure After Adult Spinal Deformity Surgery: A Retrospective Cohort Study in 138 Patients

STUDY DESIGN

Retrospective cohort study at a single institution.

OBJECTIVE

We aimed at estimating the rate of revision procedures and identify radiographic predictors of mechanical failure after adult spinal deformity surgery.

SUMMARY OF BACKGROUND DATA

Mechanical failure rates after adult spinal deformity surgery range 12% to 37% in literature. Although the importance of spinal and spino-pelvic alignment is well documented for surgical outcome and ideal alignment has been proposed as sagittal vertical axis (SVA) < 5 cm, pelvic tilt < 20° and lumbar lordosis (LL) = pelvic incidence ± 9°, the role of radiographic sagittal spine parameters and alignment targets as predictors for mechanical failure remains uncertain.

METHODS

A consecutive cohort of adult spinal deformity patients who underwent corrective surgery with at least 5 levels of instrumentation between January 2008 and December 2012 at a single tertiary spine unit were followed for at least 2 years. Time to death or failure was recorded and cause-specific Cox regressions were applied to evaluate predictors for mechanical failure or death.

RESULTS

A total of 138 patients with median age of 61 years were included for analysis. Follow up ranged 2.1 to 6.8 years. In total 47% had revision and estimated failure rates were 16% at 1 year increasing to 56% at 5 years. A multivariate analysis adjusting for age at surgery showed increased hazard of failure from LL change > 30°, postoperative TK > 50°, and SS ≤30°. LL change was mostly because of 3-column osteotomy and ending the instrumentation at L5 or S1 increased the hazard of failure more than 6 fold compared with more cranial lumbar levels.

CONCLUSION

Mechanical failure rate was 47% after adult spinal deformity corrective surgery. LL change > 30°, postoperative TK > 50°, and postoperative SS ≤30° were independent radiographic predictors associated with increased hazard of failure.

LEVEL OF EVIDENCE

4.

A Comprehensive Analysis of the SRS-Schwab Adult Spinal Deformity Classification and Confounding Variables: A Prospective, Non-US Cross-sectional Study in 292 Patients

STUDY DESIGN

Cross-sectional analyses on a consecutive, prospective cohort.

OBJECTIVE

To evaluate the ability of the Scoliosis Research Society (SRS)-Schwab Adult Spinal Deformity Classification to group patients by widely used health-related quality-of-life (HRQOL) scores and examine possible confounding variables.

SUMMARY OF BACKGROUND DATA

The SRS-Schwab Adult Spinal Deformity Classification includes sagittal modifiers considered important for HRQOL and the clinical impact of the classification has been validated in patients from the International Spine Study Group database; however, equivocal results were reported for the Pelvic Tilt modifier and potential confounding variables were not evaluated.

METHODS

Between March 2013 and May 2014, all adult spinal deformity patients from our outpatient clinic with sufficient radiographs were prospectively enrolled. Analyses of HRQOL variance and post hoc analyses were performed for each SRS-Schwab modifier. Age, history of spine surgery, and aetiology of spinal deformity were considered potential confounders and their influence on the association between SRS-Schwab modifiers and aggregated Oswestry Disability Index (ODI) scores was evaluated with multivariate proportional odds regressions. P values were adjusted for multiple testing.

RESULTS

Two hundred ninety-two of 460 eligible patients were included for analyses. The SRS-Schwab Classification significantly discriminated HRQOL scores between normal and abnormal sagittal modifier classifications. Individual grade comparisons showed equivocal results; however, Pelvic Tilt grade + versus +  + did not discriminate patients according to any HRQOL score. All modifiers showed significant proportional odds for worse aggregated ODI scores with increasing grade levels and the effects were robust to confounding. However, age group and aetiology had individual significant effects.

CONCLUSION

The SRS-Schwab sagittal modifiers reliably grouped patients graded 0 versus + / +  + according to the most widely used HRQOL scores and the effects of increasing grade level on odds for worse ODI scores remained significant after adjusting for potential confounders. However, effects of age group and aetiology should not be neglected.

LEVEL OF EVIDENCE

3.

A Multicenter Comparison of Inpatient Resource Use for Adult Spinal Deformity Surgery

STUDY DESIGN

Multicenter, retrospective analysis, prospective database, consecutive case series.

OBJECTIVE

This study examines multicenter variability in patient-level surgical resource use, including implants, biologics, and length of stay (LOS), alongside health-related quality-of-life (HRQoL) improvements after adult spinal deformity (ASD) surgery.

SUMMARY OF BACKGROUND DATA

Efficiency in surgical resource use is critical to high-value health care. Decision makers and payers are placing increasing scrutiny on the costs and outcomes associated with complex spine surgery. Little is currently known regarding the variation in resources used and associated outcomes in complex spine surgeries.

METHODS

HRQoL outcomes were calculated from the Oswestry Disability Index, disease-specific 22-item Scoliosis Research Society questionnaire, and Medical Outcomes Study Short Form 36-question health survey domain scores. Changes in HRQoL were estimated as the difference between baseline and 2-year values. Patient-level surgical resources included blood use, bone morphogenetic protein volume, LOS, and implants. Patients were classified by mild, moderate, or severe sagittal modifier and analyzed across centers using analysis of variance and multivariable regression.

RESULTS

We analyzed 251 ASD patients, who were predominantly female (n = 207, 85%) with an average of 56 years (range 18-84 years). Significant differences were found in the average 2-year change in HRQoL across centers; however, this difference was found insignificant after controlling for patients within the same modifier groups (P > .05). However, significant differences were found across centers in average resources used per surgery (P < 0.05), with only LOS not reaching significance (P > 0.05). After accounting for clinical, demographic, and regional characteristics at the patient level, variation among centers persisted in resource use with no corresponding statistical differences in HRQoL outcomes.

CONCLUSION

The use of additional surgical resources does not appear to impact 2-year HRQoL outcomes after surgery for ASD. The estimated impact of physician preference on surgical resource utilization highlights the variation in current surgical practice and the opportunity for cost reductions via a more standardized approach.

LEVEL OF EVIDENCE

3.