An in vitro biomechanical comparison of single-rod, dual-rod, and dual-rod with transverse connector in anterior thoracolumbar instrumentation.
BACKGROUND
After thoracolumbar corpectomy, standard anterolateral instrumentation may consist of dual rods with cross-connectors. However, when the vertebral bodies are small or involved with disease, only 1 rod may be possible.


OBJECTIVE
To compare the biomechanics of an in vitro L1 corpectomy model using 1 rod, 2 rods, or 2 rods with 2 cross-connectors.


METHODS
Eight fresh frozen human cadaveric spines were potted from T9 to L3. Pure moments of 1.5, 3, and 4.5 Nm were applied, and the motion of the spine was measured using 3 infrared cameras. Loads were applied in flexion and extension, right and left lateral bending, and right and left axial rotation. Each spine was first tested in the intact state. After performing an L1 corpectomy and replacement with a carbon fiber reinforced polymer cage, 3 constructs were tested: single rod (1R), dual rod (2R), and dual rod with 2 transverse connectors (CC).


RESULTS
Analysis of variance suggests significant main effects of load (P < .0001), axis (P = .022), construct (P =.0019), and individual spine (P < .0001). Overall, the single-rod construct is significantly less rigid than the intact spine in axial rotation. There is no significant difference between the intact spine and either the dual-rod construct or the dual-rod cross-connector construct.


CONCLUSIONS
In our in vitro model of anterior spinal stabilization after corpectomy and grafting, a single-rod construct is significantly less rigid than the intact spine. Addition of a second rod returns the rigidity of the spine to the intact state. A dual-rod cross-connector construct is significantly more rigid than a single-rod construct.
Department of Neurosurgery, University of Iowa, Iowa City, Iowa, USA.
Chandan G
CG
Reddy
Michael
M
Magnetta
Nader S
NS
Dahdaleh
Matthew
M
Demmer
Kingsley Abode
KA
Iyamah
Tae-Hong
TH
Lim
James C
JC
Torner
Patrick W
PW
Hitchon
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000601:surgery; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D013904:Thoracic Vertebrae / Q000601:surgery