1. R. Vazquez B.Ing. C.E. Aubin Ph.D., H. Labelle M.D.
25th Research Day of the POES, May 6, 2005
Effect of the rib cage on a surgical instrumentation of a scoliotic spine
R. Vazquez B.Ing.
C.E. Aubin Ph.D., H. Labelle M.D.

2. Introduction Adolescent Idiopathic Scoliosis (AIS):
3D deformation of the spine and the rib cage
Surgical treatment for severe scoliosis
Straighten the spine + Reducing the rib deformity
Additional stiffness with the rib cage?
Generated loads due to the presence of the rib cage?
Spinal surgery with thoracoplasty or not?
Rib hump: Cosmetical problem for the patient
Significant reduction of the rib hump of 21% without thoracoplasty using CDH instrumentation (Labelle et al., 1995)

3. Objectives Quantify the stiffening effect of the rib cage
Role of the rib cage during surgery of a scolitic spine?
Analyse the behavior of the rib cage and its effect on a scoliotic spine during a CDH instrumentation.
Evaluate necessary loads for the execution of surgical maneuvers

4. Modeling
Geometrical modeling (precision ≈ 3.3±3.8mm) (Delorme et al.,2003)
Mechanical modeling of the rib cage
Mechanical properties of: ● costal cartilages ● costo-vertebral articulations ● ribs ● intercostal ligaments based on experimental data (Schultz et al.,1974; Lemosse et al.,1998) y x z
Mechanical modeling of the spine (Luce, 2004)

5. 1st validation
Application of compressive loads to the sternum (Patrick et al.,1965; Nahum et al.,1970) and lateral squeezing loads on the rib cage (Agostoni et al.,1966)
Comparison with experimental data
100 N
100 N
100 N
Flexion, extension, longitudinal twist and lateral bending (Andriacchi et al.,1974)

6. Patient’s position during surgery
2nd validation
Simulation of CDH instrumentation:
Attach implants on the concavity side
Attach the 1st rod
Rotation of the 1st rod about 90°
Attach implants on the convex side
Attach the 2nd rod
Boundary conditions for the present model z x y
T1: Translations blocked in transverse plane (Tx – Ty)
L5: Only rotations in sagittal and frontal plane (Rx- Ry)
Sternum fixed
Patient’s position during surgery

7. 2nd validation Case studies of 6 AIS patients:
Comparison: with and without rib cage using clinical indices (Cobb, Kyphosis, Lordosis)
Evaluation of loads during surgery due to the rib cage (implants-vertebra links)
Patients
Type of curve
Cobb Angle
Kyphosis
Lordosis
Rib Hump (Apex)
Instrumented segment 1 RT
23°
82°
49° 6°
T2 to L1 2
52°
18°
46° 9° 3
77°
65°
41° 1°
T3 to L2 4 LT
37°
25°
28°
24°
T5 to L3 5
RT - LL
37° - 48°
20°
43°
T4 to L3 6
70° - 62°
30°
40°

8. Results (1st validation)
Compressions in agreement with experimental measures:
Compressive loads to the sternum
Lateral squeezing loads on the rib cage

9. Results (1st validation)
1.43
Intercostal ligaments and sternum responsible for this stiffening effect
1.35
1.35
1.37
The rib cage is stiffening the spine about:
43% in lateral bending
35% in flexion/extension
37% in axial rotation

10. Results (2nd validation)
CDH instrumentation simulations with and without the rib cage:
“en bloc” behavior of the rib cage
No additional forces due to the rib cage

11. Results (2nd validation)
CDH instrumentation simulations with and without the rib cage:

12. Discussion Rib cage few loaded Immediate passiv effect
1.a) Non-negligible stiffening effect of the rib cage on the spine
1.b) Slight influence of the rib cage on a surgery
Rib cage few loaded
1.c) No additional forces due to the rib cage
2. Preliminary model:
Immediate passiv effect
Generalized mechanical properties
3. Study in progress to increase the number of patients

13. Conclusion The rib cage doesn’t affect much:
the correction of the spine during a surgical instrumentation
the necessary loads for the execution of surgical maneuvers (preliminary results)

14. Acknowledgment QUESTIONS? LMBCAO / LIS3D Team Carl-Éric Aubin, Ph.D.
Hubert Labelle, M.D.
QUESTIONS?