Defining risk factors for adding-on in Lenke 1 and 2 AR curves

PURPOSE

To identify curve/correction characteristics associated with adding-on at 2 years after posterior spinal fusion (PSF) in Lenke 1/2 AR curves.

METHODS

A prospective multicenter registry was queried to identify patients with adolescent idiopathic scoliosis (AIS), Lenke 1/2 AR curves, who underwent PSF with a minimum of 2-year follow-up. Patient characteristics as well as pre- and post- operative radiographic variables were evaluated using Classification and Regression Tree (CART) analysis to determine which factors contribute to adding-on.

RESULTS

253 patients treated with PSF were assessed for adding-on, of which 50 met our adding-on criteria. Univariate analysis revealed adding-on was associated several factors including: post-operative thoracic and lumbar curve magnitude (p > 0.001), first erect (FE) end instrumented vertebra (EIV) angulation (p = 0.009) and EIV translation (p = 0.001), younger age (p = 0.027), Risser stage (p = 0.024), and a more proximal lowest instrumented vertebra (LIV) (p < 0.001). Multivariate CART analysis showed the chance of adding-on was more than 2 times greater (42 vs 16%) when the chosen LIV was translated more than 2.7 cm from the CSVL. When the LIV was within 2.7 cm, the post-op risk of adding-on was increased when the LIV was not perfectly leveled (> 0.5°).

CONCLUSION

In Lenke 1 and 2 AR curves, pre-operative LIV translation appears to be an independent risk factor for adding-on; and in those with < 2.7 cm of LIV translation, FE LIV angulation also seems to increase the risk of adding-on. These factors are relevant in determining appropriate LIV selection and aid in identifying patients at risk for developing adding-on.

What is the optimal cutoff value of the axis-line-angle technique for evaluating trunk imbalance in coronal plane?

BACKGROUND CONTEXT

Accurately evaluating the extent of trunk imbalance in the coronal plane is significant for patients before and after treatment. We preliminarily practiced a new method, axis-line-angle technique (ALAT), for evaluating coronal trunk imbalance with excellent intra-observer and interobserver reliability. Radiologists and surgeons were encouraged to use this method in clinical practice. However, the optimal cutoff value of the ALAT for determination of the extent of coronal trunk imbalance has not been calculated up to now.

PURPOSE

The purpose of this study was to identify the cutoff value of the ALAT that best predicts a positive measurement point to assess coronal balance or imbalance.

STUDY DESIGN/SETTING

A retrospective study at a university affiliated hospital was carried out.

PATIENT SAMPLE

A total of 130 patients with C7-central sacral vertical line (CSVL) >0 mm and aged 10-18 years were recruited in this study from September 2013 to December 2014.

OUTCOME MEASURES

Data were analyzed to determine the optimal cutoff value of the ALAT measurement.

METHODS

The C7-CSVL and ALAT measurements were conducted respectively twice on plain film within a 2-week interval by two radiologists. The optimal cutoff value of the ALAT was analyzed via receiver operating characteristic (ROC) curve. Comparison variables were performed with chi-square test between the C7-CSVL and ALAT measurements for evaluating trunk imbalance. Kappa agreement coefficient method was used to test the intra-observer and interobserver agreement of C7-CSVL and ALAT.

RESULTS

The ROC curve area for the ALAT was 0.82 (95% confidence interval: 0.753-0.894, p<.001). The maximum Youden index was 0.51, and the corresponding cutoff point was 2.59°. No statistical difference was found between the C7-CSVL and ALAT measurements for evaluating trunk imbalance (p>.05). Intra-observer agreement values for the C7-CSVL measurements by observers 1 and 2 were 0.79 and 0.91 (p<.001), respectively, whereas intra-observer agreement values for the ALAT measurements were both 0.89 by observers 1 and 2 (p<.001). The interobserver agreement values for the first and second measurements with the C7-CSVL were 0.78 and 0.85 (p<.001), respectively, whereas the interobserver agreement values for the first and second measurements with the ALAT were 0.91 and 0.88 (p<.001), respectively.

CONCLUSIONS

The newly developed ALAT provided an acceptable optimal cutoff value for evaluating trunk imbalance in the coronal plane with a high level of intra-observer and interobserver agreement, which suggests that the ALAT is suitable for clinical use.

Reliability of a new method for measuring coronal trunk imbalance, the axis-line-angle technique

BACKGROUND CONTEXT

Accurate determination of the extent of trunk imbalance in the coronal plane plays a key role in an evaluation of patients with trunk imbalance, such as patients with adolescent idiopathic scoliosis. An established, widely used practice in evaluating trunk imbalance is to drop a plumb line from the C7 vertebra to a key reference axis, the central sacral vertical line (CSVL) in full-spine standing anterioposterior radiographs, and measuring the distance between them, the C7-CSVL. However, measuring the CSVL is subject to intraobserver differences, is error-prone, and is of poor reliability. Therefore, the development of a different way to measure trunk imbalance is needed.

PURPOSE

This study aimed to describe a new method to measure coronal trunk imbalance, the axis-line-angle technique (ALAT), which measures the angle at the intersection between the C7 plumb line and an axis line drawn from the vertebral centroid of the C7 to the middle of the superior border of the symphysis pubis, and to compare the reliability of the ALAT with that of the C7-CSVL.

STUDY DESIGN/SETTING

A prospective study at a university hospital was used.

PATIENT SAMPLE

The patient sample consisted of sixty-nine consecutively enrolled men and women patients, aged 10-18 years, who had trunk imbalance defined as C7-CSVL longer than 20 mm on computed full-spine standing anterioposterior radiographs.

OUTCOME MEASURES

Data were analyzed to determine the correlation between C7-CSVL and ALAT measurements and to determine intraobserver and interobserver reliabilities.

METHODS

Using a picture archiving and communication system, three radiologists independently evaluated trunk imbalance on the 69 computed radiographs by measuring the C7-CSVL and by measuring the angle determined by the ALAT. Data were analyzed to determine the correlations between the two measures of trunk imbalance, and to determine intraobserver and interobserver reliabilities of each of them.

RESULTS

Overall results from the measurements by the C7-CSVL and the ALAT were significantly moderately correlated. Intraobserver assessments by measuring the C7-CSVL and by doing the ALAT failed to find any significant differences between the findings from the first and second assessments by the same radiologist. Interobserver assessments significantly differed between radiologists 1 and 2 for the first assessment measuring the C7-CSVL, and between radiologists 2 and 3 for the second assessment measuring the C7-CSVL. Interobserver assessments by doing the ALAT failed to find any significant differences among the three radiologists for either of the two assessments.

CONCLUSIONS

Our results indicated that using the ALAT, which is simple and convenient, is of great value in measuring trunk imbalance. For measuring trunk imbalance, the ALAT has essential advantages compared with measuring the C7-CSVL. We encourage spine surgeons to consider using the ALAT in evaluating trunk imbalance.