The RVAD in Infantile Scoliosis What does it

The RVAD in Infantile Scoliosis - What does it really represent? J. Sanders, G. Foley, H. Labelle, C. Johnston, J. d’Astous, S. Parent, C. E. Aubin

What is the RVAD anyway? � The angle between the actual vertebral body and the ribs? � A reflection of the spine’s rotation? � We know that in severe curves, the ribs really do slope. � But, phase II ribs probably represent rotation. � We really don’t know what to make of the RVAD as a physical entity or why it is related to prognosis.

Purpose Evaluate RVAD in 3 D to determine its physical significance because 2 D angles vary according to position of observer 90 ° 135 ° 90 ° Purpose Results Discussion & Conclusion

3 D Reconstructions Spine 3 D Introduction Material & Methods Results Discussion & Conclusion

Rib Vertebra Angle Difference (RVAD) � � RVAD (measured on coronal plane, Mehta’s method) b a RVAD 3 D: Computed in 3 D RVAD=b-a (concave - convex side) b Introduction Material & Methods Mehta, 1972 a Results Discussion & Conclusion 5

Rib Vertebra Angle Difference (RVAD) � Local RVAD ◦ 2 D measurement from reconstruction ◦ Measured in the local plane of the vertebra (Stagnara’s plan d’election, 1965)

Patient data � Age : 5. 4 ± 2. 3 years � 26 females, 16 males � Cobb : 43. 3 ± 19. 9 ° � 18 Phase I, 24 Phase II patients � 42 Early Onset Scoliosis patients Introduction Material & Methods Results Discussion & Conclusion

Results 200 � 42 (R² = 0. 02) associated with the 3 D RVAD 150 R 2 = 0. 4777 100 RVAD - Local RVAD Early Onset Scoliosis patients � The RVAD weakly associated with spinal axial rotation 50 � Strongly (R² = 0. 65) 0 R 2 = 0. 1089 R 2 = 0. 0515 0 10 20 30 40 -50 -100 Introduction R 2 = 0. 4345 Results Axial Rotation Discussion & Conclusion

Results 200 � 42 Early Onset Scoliosis patients � The RVAD weakly associated with spinal axial rotation � Strongly R 2 = 0. 6059 100 RVAD 3 D (R² = 0. 02) 150 associated with the 3 D RVAD -100 50 -50 (R² = 0. 65) Introduction 0 50 -100 Results 0 100 150 200 R 2 = 0. 7507 RVAD Rx Discussion & Conclusion

Conclusion: � RVAD is a projection of 3 D geometry of chest wall/spine ◦ Not true representation of 3 D nature of deformity ◦ Compound of factors : projection, axial rotation, chest wall/spine asymmetry � RVAD 3 D ◦ Deformation of rib cage in relation to spine Introduction Results Discussion & Conclusion

Discussion Thoughts: � RVAD is really a spine to rib (chest wall) and not a rotation measure � This still leaves us with the question of why is this chest wall to spine factor so important in curve prognosis.