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

Saturday, October 20, 2012: 3:27 PM
Melrose (Hilton Riverside)
Milad Alam1, Peter O. Newton2, Burt Yaszay2 and Tracey Bastrom2, (1)UCSD School of Medicine, San Diego, CA, (2)Orthopedics, Rady's Childrens Hospital, CA

Purpose

Curves with an apex at T11 and T11/T12 are classified by the SRS and Lenke classifications as thoracic curves. In this study, we wished to determine whether this classification is accurate or if curves with an apex at T11 or T11/T12 represent a combination of both “thoracic” and “thoracolumbar” curves or constitute their own class of curves.

Methods

A review of data collected on 1742 AIS cases from a multi-center study was performed. Based on an analysis of the most common curve apex levels (T9 for thoracic (TH) curves and L1 for thoracolumbar/lumbar (TL/L) curves), 2 comparison groups were created that represented “classic examples” of TH and TL/L curves. 66 cases with an apex at T11-T11/T12 were identified and compared to 320 cases with an apex at T9 and 126 cases with an apex at L1. A distribution analysis of the curve lengths and a Chi-square test comparing curve direction of the TH, TH/L, and T11 - T11/T12 curves was performed (p<0.05). Additionally, the three groups were compared with respect to the major Cobb magnitude, trunk shift, and age at time of surgery. Finally, a radiographic review of the T11-T11/T12 group was completed.

Results

The curve direction of the three groups was significantly different (TL/L: 84% Left, TH: 3% Left, and T11-T11/T12: 16% Left, p<.001). The mean number of vertebra in curves for the T11-T11/T12 group (7.1 ± 1.2) fell in between the value for the TL/L (5.7± 0.8) and TH (7.3 ± 1.0) groups. The T11-T11/T12 curve length distribution was a combination of a typical TH curve and a typical TL/L curve. The T11-T11/T12 curves have a greater trunk shift than both TL/L (p=0.002) and TH (p=0.011) curves. There was not a significant difference between the three groups in terms of major curve Cobb magnitude (p=0.09) or age at time of surgery (p=0.76). The radiographic review of the T11-T11/T12 curves revealed 3 curve patterns: 21 (32%) long single curves, 28 (42%) short single curves, which are more typical of a TL/L curves, and 17 (26%) double thoracic curves.

Conclusion

We suggest caution in lumping curves with an apex at either T11 or T11-12 disc together with other thoracic apices in studies that involve principally primary thoracic curves.