Biomechanical analysis of rod contouring in posterior spinal instrumentation and fusion for 3D correction of adolescent idiopathic scoliosis.

Creator(s)

Marine Gay
Xiaoyu Wang
Todd Ritzman
Lorena Floccari
Richard M. Schwend, Children's Mercy HospitalFollow
Carl-Eric Aubin

Document Type

Article

Publication Date

11-2023

Identifier

DOI: 10.1007/s43390-023-00707-9

Abstract

PURPOSE: To biomechanically evaluate 3D corrective forces and deformity correction attributable to key parameters of rod contouring in posterior spinal fusion (PSF) for adolescent idiopathic scoliosis (AIS).

METHODS: Computerised patient-specific biomechanical models of six AIS cases were used to simulate PSF and evaluate the effects of 5.5-mm cobalt-chrome rod contouring angle (concave-convex angles: 30°-15°, 45°-15° and 60°-15°), length (spanning 4 and 7 vertebrae), and apex location (T7, T9). 3D correction and bone-implant forces were computed and analysed.

RESULTS: By increasing the concave rod contour from 30° to 60°, thoracic kyphosis (TK) increased from 18° ± 2° (15°-19°) to 24° ± 2° (22°-26°), apical vertebra rotation (AVR) correction increased from 41% (SD8%) to 66% (SD18%) whilst the main thoracic curve (MT) correction decreased from 68% (SD6%) to 56% (SD8%). With a contouring length of 4 vs. 7 vertebrae, the resulting TK, AVR and MT corrections were 22° ± 1° (19°-26°) vs. 19° ± 10° (15°-22°), 57% (SD18%) vs. 50% (SD26%) and 59% (SD1%) vs. 69% (SD35%), respectively. With the rod contouring apex at T7 (vs. T9), AVR corrections were 69% (SD19%) vs. 44% (SD9%), with no significant difference in TK and MT corrections, and with comparatively 67% of screw pull-out forces. Corrective forces were more evenly shared with fixation on 7 vs. 4 vertebrae.

CONCLUSION: Rod contouring of a greater angulation, over a shorter portion of the rod, and more centred at the apex of the main thoracic curve apex improved AVR correction and allowed greater restoration of TK, but resulted in significantly higher screw pull-out forces and came at the expense of less coronal plane correction.

Journal Title

Spine Deform

Volume

11

Issue

6

First Page

1309

Last Page

1316

Keywords

Adolescent idiopathic scoliosis; Posterior spinal fusion; Rod contouring

Comments

Grants and funding

• PCIPJ-346145-2011/Natural Sciences and Engineering Research Council of Canada

Recommended Citation

Gay M, Wang X, Ritzman T, Floccari L, Schwend RM, Aubin CE. Biomechanical analysis of rod contouring in posterior spinal instrumentation and fusion for 3D correction of adolescent idiopathic scoliosis. Spine Deform. 2023;11(6):1309-1316. doi:10.1007/s43390-023-00707-9