Single-rod versus dual-rod anterior instrumentation for idiopathic scoliosis: a biomechanical study.
METHODS
Anterior single- and dual-rod instrumented human and ovine thoracolumbar spines, with and without structural interbody support (SIS), were biomechanically tested and compared in flexion, lateral bending, and torsion.


OBJECTIVE
To determine significant differences in global stiffness of the constructs in an attempt to clarify specific indications for each in the treatment of spinal deformities.


BACKGROUND
Single- and dual-rod anterior systems have been used without any consensus as to indications for one versus the other. The potential added benefit of incorporating SIS and transverse connectors (dual-rod) with these constructs has also not been fully explored.


METHODS
Four human cadaveric and six ovine spines were instrumented in single- and dual-rod constructs and biomechanically tested intact, postdiscectomy with and without SIS, with single- and dual-rod constructs, and with and without transverse connectors (ovine only). Biomechanical testing modes were flexion, lateral bending, and torsion.


RESULTS
In the human cadaveric specimens, testing in flexion revealed that SIS was the major contributing factor for construct stiffness. In lateral bending, stiffness of single- and dual-rod constructs with and without SIS was equivalent. In torsion, both single- and dual-rod instrumentation and SIS appeared to contribute to global stiffness. In ovine specimens, dual rods were stiffer than single-rod constructs and SIS played only a minor role. Transverse connectors appeared to significantly stiffen dual-rod constructs in torsion only.


CONCLUSIONS
Dual-rod constructs with SIS appear to be the best combination for providing stiffness in anterior instrumentation. The addition of cross-links to anterior constructs does not appear to increase stiffness except in torsion.
Lowe
Thomas G
TG
Woodridge Spine Center, Denver, CO, USA. woodridgeortho@aol.com
Enguidanos
Stephen T
ST
Smith
David A B
DA
Hashim
Shukor
S
Eule
James M
JM
O'Brien
Michael F
MF
Diekmann
Molly J
MJ
Wilson
Lucas
L
Trommeter
Julie M
JM
D000328:Adult; D000818:Animals; D006801:Humans; D016268:Internal Fixators; D008875:Middle Aged; D023421:Models, Animal; D018583:Pliability; D012600:Scoliosis / Q000601:surgery*; D012756:Sheep; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D013314:Stress, Mechanical