New rod-plate anterior instrumentation for thoracolumbar/lumbar scoliosis: biomechanical evaluation compared with dual-rod and single-rod with structural interbody support.
METHODS
A new rod-plate anterior implant was designed to provide plate fixation at the cephalad and caudal-end segments of a 5-level anterior spine construct. Biomechanical testing was performed on calf spines instrumented with 5-segment anterior scoliosis constructs. OBJECTIVES.: To analyze the initial and post-fatigue biomechanical performance of the new implant, and compare it to an anterior dual-rod construct and a single-rod construct with interbody cages.


BACKGROUND
Using single-rod anterior instrumentation for thoracolumbar and lumbar scoliosis, an unacceptable incidence of loss of correction, segmental kyphosis, and pseudarthrosis has been reported. Inadequate construct stiffness due to early postoperative bone-screw interface failure, especially at cephalad and caudal-end vertebrae, has been implicated as the cause of these complications.


METHODS
Thirty calf spines were instrumented over 5 segments with: (1) single-rod augmented with rod-plate implants, (2) dual-rod construct, and (3) single-rod with titanium mesh cages. Stiffness in flexion-extension and lateral bending modes was determined initially and post-cyclical loading by measuring segmental range of motion (ROM). Post-fatigue screw pullout tests were also performed.


RESULTS
In lateral bending, the caudal-end segmental ROM for rod-plate construct was 54% less than single-rod with cages construct (P < 0.05), with no difference between rod-plate and dual-rod constructs. In flexion-extension, the rod-plate construct showed 45% to 91% (initial test) and 84% to 90% (post-fatigue) less ROM than the single-rod with cages construct (P < 0.001). Again, there was no difference between rod-plate and dual-rod constructs at the cephalad and caudal-end segments. Post-fatigue screw pullout strengths of the rod-plate construct were significantly greater than those of the dual-rod and single-rod with cages constructs (P < 0.05).


CONCLUSIONS
The rod-plate construct was significantly stiffer and provided greater stability of bone-screw interface than the single-rod with cages construct. It achieved similar stiffness and improved bone-screw interface stability compared to dual-rod construct.
Zhang
Hong
H
Texas Scottish Rite Hospital for Children, 2222 Welborn Street, Dallas, TX 75219, USA. hong.zhang@tsrh.org
Johnston
Charles E
CE
Pierce
William A
WA
Ashman
Richard B
RB
Bronson
Dwight G
DG
Haideri
Nessie F
NF
D000818:Animals; D001696:Biomechanical Phenomena / Q000379:methods; D001858:Bone Nails / Q000592:standards; D001860:Bone Plates / Q000592:standards; D002417:Cattle; D008159:Lumbar Vertebrae / Q000502:physiology / Q000601:surgery*; D008422:Materials Testing / Q000379:methods / Q000592:standards; D012600:Scoliosis / Q000503:physiopathology / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods; D013904:Thoracic Vertebrae / Q000502:physiology / Q000601:surgery*