Predictors of spontaneous lumbar curve correction in thoracic-only fusions: 3D analysis in AIS

Stability of Idiopathic Lumbar Curves During Growth in Pediatric Patients After Instrumented Isolated Thoracic Fusion

INTRODUCTION

Isolated thoracic fusion (ITF) for idiopathic scoliosis preserves lumbar segment motion but risks lumbar curve progression. This study examined if Lenke classification, residual disc wedging, or tilting at the lowest instrumented vertebrae (LIV) are associated with lumbar curve progression or adding-on after ITF.

METHODS

A retrospective analysis of idiopathic scoliosis patients aged 8 to 12 years treated with primary ITF was conducted. Inclusion criteria were a diagnosis of idiopathic scoliosis, LIV T10-L1, and ≥2 years of postoperative follow-up. Growth, Lenke classification, lumbar magnitude, angle of disc wedging below the LIV, and LIV tilt were assessed preoperatively, at 6 weeks postoperative, and at final follow-up. Standard descriptive statistics and repeated measures ANOVA were performed, with significance set at P<0.05.

RESULTS

Fifty-seven patients were included, with a mean follow-up of 4.6 years (2 to 12 y). At surgery, 67% (38 patients) were Risser 0. There was no significant lumbar curve increase from the first (24 degrees±12) to the final follow-up (22 degrees±14, P=0.21). Patients with a lumbar curve ≥30 degrees at first follow-up (n=16) also showed no increase in curve magnitude (40 degrees±8 at first follow-up vs. 37 degrees±17 at final follow-up, P=0.47). Disc wedging ≥5 degrees and LIV tilt ≥5 degrees were not associated with lumbar curve progression (29 degrees±14 at first follow-up vs. 28 degrees±17 at final follow-up for disc wedging, P=0.52; and 30 degrees±12 at first follow-up vs. 27 degrees±16 at final follow-up for LIV tilt, P=0.28) or adding-on. Lenke classification was not associated with lumbar curve progression. However, Lenke 3 and 4 patients had larger curves immediately after surgery and final lumbar curves ≥45 degrees. Of 9 Lenke 3 and 4 patients, 3 had lumbar curves ≥45 degrees at the final follow-up. No Lenke 1 or 2 patients (0 out of 41) had lumbar curves ≥45 degrees at the final follow-up (P<0.01).

CONCLUSION

In pediatric ITF patients, disc wedging and LIV tilt were not associated with adding-on or lumbar curve progression.

LEVEL OF EVIDENCE

Level III.

Compensatory thoracic curve correction in lumbar anterior vertebral body tether (VBT) versus lumbar posterior spinal fusion (PSF)

PURPOSE

Anterior vertebral body tethering (VBT) is a non-fusion surgical option for skeletally immature patients with idiopathic scoliosis. Prior studies demonstrated compensatory correction of the thoracic curve after lumbar posterior spinal fusion (PSF); however, no studies have examined thoracic curve correction after lumbar VBT.

METHODS

Patients with Lenke 5 + 6 lumbar scoliosis who underwent VBT and at least 2 years' follow-up were compared to matched lumbar PSF patients. Groups were compared for major lumbar (L) and compensatory thoracic (T) curve correction, coronal/sagittal balance, and complications.

RESULTS

24 AVBT and 24 PSF patients were matched 1:1 for skeletal maturity and curve flexibility. There were no significant differences between VBT and PSF for average pre-operative or 2 year post-operative major L or compensatory T curves. Average final L curve correction was 50% VBT and 60% PSF (p = 0.08); average T curve correction was 17% VBT and 20% PSF (p = 0.18). Compared to pre-operative flexibility radiographs, the final post-op thoracic curves were 6° (VBT) and 5° (PSF) larger. PSF had better coronal balance by average of 17 mm (p < 0.0001). There were seven (24%) reoperations in the VBT group: two overcorrections relaxed, two T adding-on (extended to T by PSF-1, VBT-1), one broken tether converted to PSF. There was one (4%) reoperation in the PSF group (10-year post-op extension).

CONCLUSION

Compensatory thoracic correction was achieved to a similar degree for lumbar VBT and PSF patients. There was little change in thoracic curve magnitude over time, and, on average, the correction did not reach the pre-operative flexibility curve measurement. There was better coronal balance by PSF, and a higher rate of re-operation in VBT patients.

LEVEL OF EVIDENCE

III.

Prediction Model for Lumbar Curve Correction After Selective Thoracic Fusion in Lenke 1 and 2 Adolescent Idiopathic Scoliosis

STUDY DESIGN

A retrospective study.

OBJECTIVE

To identify independent risk factors and construct a prediction model for lumbar curve correction (LCC) after selective thoracic fusion (STF) in patients with Lenke 1 and 2 adolescent idiopathic scoliosis (AIS).

SUMMARY OF BACKGROUND DATA

STF has been widely applied to Lenke 1 and 2 AIS patients. However, LCC after STF is still controversial.

METHODS

One hundred twenty-eight patients undergoing STF with at least 2 years of follow-up were included. Cases were divided into a high-LCC group and a low-LCC group according to a rounded-up median of 65%. Forty-nine variables were taken into account. Logistic regression was applied to identify independent predictive factors. A prediction model was established by backward stepwise regression, and its evaluation was implemented on R.

RESULTS

Five parameters showed independent predictive value for low LCC: right shoulder higher before surgery (right shoulder higher versus balanced: odds ratio [OR]=0.244, P =0.014), postoperative Cobb angle of lumbar curve (LC) (OR=1.415, P =0.001, cutoff value=11°), lowest instrumented vertebra (LIV) distal to end vertebra (no vs. yes: OR=4.587, P =0.013), postoperative LIV tilt (OR=0.686, P =0.010, cutoff value=6.85°) and postoperative LIV+1 tilt (OR=1.522, P =0.005, cutoff value=6.25°). The prediction model included 6 variables: lumbar modifier, preoperative shoulder balance, postoperative Cobb angle of LC, LIV position, postoperative LIV tilt, and postoperative LIV+1 tilt. The model evaluation demonstrated satisfactory capability and stability (area under curve=0.890, 10-fold cross-validation accuracy=0.782).

CONCLUSION

Preoperative shoulder balance, Cobb angle of LC, LIV position, postoperative LIV and LIV+1 tilt could be used to prognosticate LCC after STF. A model with solid prediction ability was established, which could further our understanding of LCC and assist in making clinical decisions.

3D analysis of the preoperative deformity in AIS can be used to guide surgical treatment decisions for selective thoracic fusion

PURPOSE

To identify 3D measures of scoliosis from preoperative imaging that are associated with optimal radiographic outcomes after selective thoracic fusion (STF) for adolescent idiopathic scoliosis (AIS).

METHODS

Subjects with primary thoracic curves (Lenke 1-4, B or C modifiers) fused selectively (L1 or above) who had preoperative 3D reconstructions and minimum 2 years of follow-up were included. An optimal outcome at 2 years was defined as having 4 of 5 parameters previously defined in the literature: (1) lumbar curve < 26º, (2) deformity flexibility quotient < 4, (3) C7-CSVL < 2 cm, (4) lumbar prominence < 5º and (5) trunk shift < 1.5 cm. Univariate and CART analyses were performed to identify preoperative variables associated with achieving an optimal outcome 2 years postoperatively.

RESULTS

Ninety-nine (88F, 11 M) patients met inclusion. Mean age was 15 ± 2 years. Fifty-one subjects (52%) had an optimal outcome. Seven preoperative deformity measures representing smaller thoracolumbar/lumbar deformity in the optimal group were found to be significant on univariate analysis. CART analysis identified the following variables associated with optimal outcomes: difference in apical rotation > 30° = 27% optimal outcomes, difference in apical rotation ≤ 30° and coronal vertebral wedging of lumbar apex > 3° = 46% optimal outcomes, and difference in apical rotation ≤ 30° and coronal vertebral wedging of lumbar apex ≤ 3° = 80% optimal outcomes (p < 0.05).

CONCLUSION

Optimal outcomes after STF were associated with a preoperative difference in apical vertebral rotation in the axial plane less than 30° between thoracic and lumbar curves as well as coronal plane vertebral wedging of the lumbar apical vertebra less than 3°.

Breaking the Rules in Three Dimensions: What to Expect After a Thoracic-only Fusion With Structural Thoracic and Thoracolumbar Curves

OBJECTIVE

Despite guidelines to fuse both thoracic and thoracolumbar/lumbar (TH/L) curves in patients with structural curves in both regions, a thoracic-only fusion allows preservation of lumbar motion segments. The purpose of this study was to assess the 2-year postoperative three-dimensional (3D) radiographic and clinical outcomes of patients with double or triple major (thoracic curves >TH/L curves) structural curves who underwent a thoracic-only fusion.

METHODS

A prospective adolescent idiopathic scoliosis registry was queried for double or triple major curves undergoing thoracic-only posterior fusion and a minimum 2-year follow-up. 3D reconstructions were generated from bi-planar radiographs. Paired sample t tests were used to assess differences in the coronal, sagittal, and axial planes pre and postoperatively, as well as Scoliosis Research Society Questionnaire-22 scores. Pearson correlations were utilized to identify variables related to spontaneous lumbar derotation.

RESULTS

Twenty-two patients met the inclusion criteria. Both thoracic [61 ± 10 degrees to 20 ± 9 degrees ( P < 0.001)] and lumbar curves [41 ± 7 degrees to 22±7 degrees ( P < 0.001)] had significant coronal improvement and T5 to T12 kyphosis improved from 7 ± 14 degrees to 23 ± 8 degrees ( P < 0.001). The thoracic apical translation was significantly improved postoperatively (4.7 ± 1.5 to 0.5 ± 1 cm, P < 0.001), but the lumbar apical translation was unchanged (-1.7 ± 0.6 to -1.7±0.8 cm, P = 0.94). Scoliosis Research Society Questionnaire-22 scores significantly improved by 2 years postoperative.

CONCLUSIONS

Unlike the 3D correction observed in nonstructural TH/L curves after thoracic-only fusion, patients with double or triple major curves demonstrated only spontaneous coronal correction of the lumbar curve, whereas the sagittal and axial planes were not significantly improved. These radiographic parameters did not negatively affect subjective or clinical outcomes at minimum 2-year follow-up.

LEVEL OF EVIDENCE

Level IV-therapeutic.

Simultaneous Hypercorrection of Lowest Instrumented Vertebral Tilt and Main Thoracic Curve is Associated With Progression of Residual Lumbar Curve in Adolescent Idiopathic Scoliosis

STUDY DESIGN

A retrospective cohort study.

OBJECTIVE

To determine radiographic parameters, including the lowest instrumented vertebral (LIV) tilt, related to the postoperative magnitude and progression of residual lumbar curves (LCs) in adolescent idiopathic scoliosis patients who underwent posterior spinal fusion with LIV at or above L1.

SUMMARY OF BACKGROUND DATA

Although several guidelines have been proposed for thoracic curve fusion, factors related to the postoperative magnitude and potential progression of unfused LCs remained undetermined. The effect of the LIV tilt on residual LCs is also unclear.

MATERIALS AND METHODS

Patients with Lenke type 1 to 4 curves who underwent posterior spinal fusion with LIV at or above L1 with a minimum follow-up period of 2 years were evaluated. Prediction models for residual LCs were developed using multivariate linear regressions with selected radiographic parameters. Subgroup analyses, followed by sensitivity tests, were then performed for variables best predicting the progression of residual LCs.

RESULTS

A total of 130 patients were included. Multivariate linear regression analysis showed that the immediate postoperative LIV-tilt angle was associated with the immediate postoperative LCs and the prediction model for residual LCs, with high accuracy ( R =0.93 and 0.77, respectively). Sensitivity tests revealed immediate postoperative LIV-tilt angle <10° and correction rate of main thoracic curve Cobb angle >53% as predictors for progression of residual LCs, and they reached moderate discrimination when combined together as one criterion (odds ratio=16.3, 95% confidence interval=5.3-50.1; sensitivity=89%, specificity=67%, positive predicted value=51%, negative predicted value=94%).

CONCLUSION

The current study revealed that LIV tilt, as an operable factor during surgery, is not only a determinant in prediction models showing high correlation with the magnitude of postoperative LCs but a predictor for progression of residual LCs. "Immediate postoperative LIV-tilt angle <10° and correction rate of main thoracic curve Cobb angle >53%," as a united criterion, could serve as a predictor for progression of residual LCs.

Spontaneous Lumbar Curve Correction Following Vertebral Body Tethering of Main Thoracic Curves

BACKGROUND

Growth modulation through anterior vertebral body tethering (AVBT) has emerged as a fusionless option for the treatment of progressive scoliosis. When tethering the main thoracic curve, the compensatory thoracolumbar/lumbar curve must correct indirectly as a result. The present study evaluated the response of these lumbar curves following AVBT of the main thoracic curves.

METHODS

Patients who underwent thoracic AVBT and who had a minimum follow-up of 2 years were included. Magnitudes of the thoracic and lumbar curves were recorded preoperatively and at the first-erect and 2-year postoperative visits. Lumbar curves were further stratified according to their lumbar modifier (A, B, or C). Analysis of variance (ANOVA) and repeated-measures ANOVA were performed to compare correction rates, and the Pearson coefficient was utilized to determine the correlation between the tethered thoracic curve and uninstrumented lumbar curve magnitudes.

RESULTS

A total of 218 patients were included. Thoracic curve correction was 40% at the first-erect visit and 43% at 2 years (p = 0.012). Lumbar correction was 30%, 26%, and 18% at the first-erect visit (p < 0.001 for all compared with preoperatively) and minimally changed at 31%, 26%, and 24% at 2 years for lumbar modifiers A, B, and C, respectively. A total of 118 patients (54%) showed thoracic curve improvement between the first-erect and 2-year visits. In a subgroup analysis, these patients had a correction in lumbar curve magnitude from preoperatively to the first-erect visit of 30%, 22%, and 16% for lumbar modifiers A, B, C, respectively, that increased to 42%, 34%, and 31% at 2 years, with strong correlation to thoracic correction at 2-year follow-up (r = 0.557, p < 0.001).

CONCLUSIONS

Although there was immediate lumbar correction following AVBT of a main thoracic curve, further improvement following initial correction was only observed among patients with growth modulation of the thoracic curve. Considering all patients, the uninstrumented lumbar curve corrected 30% at 2 years and the instrumented thoracic curve corrected 40%. As indications for AVBT are refined, these data will provide insight into the response of the uninstrumented lumbar curve.

LEVEL OF EVIDENCE

Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.