Are Thoracic Curves With a Low Apex (T11 or T11/T12) Really Thoracic Curves?

Discovering the association between the pre- and post-operative 3D spinal curve patterns in adolescent idiopathic scoliosis

BACKGROUND

The advantage of considering the three-dimensional curve patterns, including the patterns of the vertebral position and alignment, in classification of adolescent idiopathic scoliosis (AIS) patients and whether such classification system relates to the surgical outcomes are not fully determined.

METHODS

A total of 371 AIS patients who received posterior spinal fusion surgery with 2-year follow-up were included retrospectively and consecutively. The 3D positions and orientations of the T1-L5 vertebrae were calculated from the 3D reconstructions of the spines at pre-operative and 2-year follow-up, a total of 102 variables per patient. A probabilistic clustering method was used to cluster the pre-operative and 2-year follow-up 3D spinal curve patterns separately. The distributions of the Lenke types and 3D pre-operative clusters in the post-operative clusters were determined.

RESULTS

A total of nine pre-operative clusters including, four right thoracic types, three left thoracolumbar/lumbar types, one low apex right thoracic/thoracolumbar, and one left thoracic/right lumbar were determined. Three post-operative 3D curve patterns were Type 1 with higher residual proximal Cobb angle, Type 2 with lower T5-T12 kyphosis and highest pelvic incidence-lordosis mismatch, and Type 3 with larger lumbar curve magnitude and rotation compared to the other two groups. More than 50% of patients in each of the 3D pre-operative clusters had the same post-operative group.

CONCLUSION

We developed a 3D classification of the AIS patients before and two-year after spinal fusion surgery. The link between the pre- and post-operative clusters lends itself to application of this classification system in developing predictive models of the AIS surgical outcomes.

Which thoracic curves are at the greater risk for distal adding-on: comparison between typical and atypical Lenke 1A curves

PURPOSE

To identify the characteristics and the incidence of adding-on (AO) in atypical Lenke 1A adolescent idiopathic scoliosis patients, and to investigate whether atypical and typical Lenke 1A curve should follow the same lowest instrumented vertebra (LIV) selection strategy.

METHODS

A total of 251 Lenke 1A patients who underwent posterior spinal fusion were analyzed. The minimum follow-up was 2 years. Curves were classified into two groups according to the apex. At last, 42 atypical Lenke 1A patients (apex at T10/11-T11/12) were identified and divided into atypical group (G1). Meanwhile, 42 age, gender, and Cobb angle-matched typical Lenke 1A patients (apex at T7/8-T10) were enrolled into the typical group (G2). The radiographic characteristics were evaluated, and the incidence of AO was compared between the 2 groups.

RESULTS

The incidence of atypical Lenke 1A curves was 16.7%. Patients in G1 were found to have more left thoracic curves (P = 0.029), better flexibility of thoracic (P = 0.011) and lumbar curve (P = 0.014), and more preoperative coronal imbalance (P = 0.001). At the final follow-up, G1 developed more AO (38.1% vs. 19.0%). Specificity, for patients with LIV proximal to last substantially touching vertebra (LSTV), the incidence of AO was significantly higher in G1 (82.4% vs. 42.9%, P = 0.022).

CONCLUSION

Atypical Lenke 1A curve had its own radiographic characteristics. It was more likely to develop AO when LIV was proximal to LSTV, which indicated different fusion levels should be considered in these two subtypes of Lenke 1A. We recommended LSTV as LIV in atypical Lenke 1A cases, while one level proximal to LSTV might be available in typical Lenke 1A curve.

LEVEL OF EVIDENCE

3.

Impact of multilevel facetectomy on segmental spinal flexibility in patients with thoracic adolescent idiopathic scoliosis

BACKGROUND

The aim of this study was to intraoperatively assess the effects of multilevel facetectomy on segmental spinal flexibility in patients with thoracic adolescent idiopathic scoliosis.

METHODS

Twenty patients who underwent posterior thoracic adolescent idiopathic scoliosis curve correction were evaluated. Compressive or distractive loaded force of 50N was applied on the handle of a compressor or distractor connected to the necks of pedicle screws inserted at T7 to T11. Segmental spinal flexibility rates were calculated based on the distance between screw heads under the loaded and unloaded conditions. In addition, the flexibility rates were obtained before and after multilevel facetectomy.

FINDINGS

Absolute flexibility rates of all segments significantly increased after multilevel facetectomy under both compressive and distractive forces (P < 0.01). The absolute change in the flexibility rate was significantly higher at the concave side than at the convex side under both compressive (P < 0.01) and distractive loaded forces (P = 0.046). No significant correlation was found between change in the flexibility rates and preoperative Cobb angle or preoperative curve flexibility.

INTERPRETATION

From a biomechanical point of view, multilevel facetectomy provides proper spinal flexibility to improve the correction rate of posterior adolescent idiopathic scoliosis surgery. The effects are higher at the concave side than at the convex side.

Comparison of Typical Thoracic Curves and Atypical Thoracic Curves Within the Lenke 1 Classification

STUDY DESIGN

Retrospective study.

OBJECTIVES

To examine the characteristics of Lenke type 1 curves based on the level of the apical vertebra.

SUMMARY OF BACKGROUND DATA

The Lenke classification is the most used system for adolescent idiopathic scoliosis, with approximately 50% of the curves falling into the Lenke 1 curve type category.

METHODS

A total of 611 Lenke 1 curves in a prospectively collected multicenter adolescent idiopathic scoliosis study were analyzed. Minimum follow-up was ≥ 2 years. Curves were subdivided into 3 groups according to their apex: the typical Lenke 1 curve group included apices from T7/8 to T10 (511 patients), the proximal group included apices from T4 to T7 (45 patients), and the distal group included apices from T10/11 to T11/12 (50 patients). Preoperative and postoperative radiographic and clinical outcomes were compared among the 3 groups.

RESULTS

The proximal and distal groups included significantly more left thoracic curves (proximal: 29%; typical: 1.8%; distal: 19%; p < .01). Flexibility of the main thoracic curve was significantly different among the 3 groups (proximal: 32% ± 17%; typical: 46% ± 18%; distal: 57% ± 18%; p < .001). The distal group included significantly more "A" lumbar modifiers (proximal: 29%; typical: 53%; distal: 96%; p < .01) and had curves characteristics similar to King type 4 curves (L4 tilted to the right: Lenke 1AR). The average lowest instrumented vertebra was significantly lower in the distal group (proximal: T12; typical: L1; distal: L2; p < .01). The proximal group had significantly greater thoracic kyphosis (proximal: 30° ± 18°; typical: 20° ± 13°, distal: 20° ± 10°; p < .001) and more fusion segments (proximal: 10; typical: 9; distal: 9; p < .03).

CONCLUSIONS

Curves categorized as Lenke 1 curves were less homogeneous than expected. Using only the Lenke type 1 designation to define a study population may introduce unintended bias to the study design.