New rod-plate anterior instrumentation for thoracolumbar/lumbar scoliosis: Biomechanical evaluation compared with dual-rod and single-rod with structural interbody support

Hong Zhang, Charles E. Johnston, William A. Pierce, Richard B. Ashman, Dwight G. Bronson, Nessie F. Haideri

Research output: Contribution to journalArticle

4 Scopus citations


STUDY DESIGN. 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. SUMMARY OF BACKGROUND DATA. 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 interfacethan the single-rod with cages construct. It achieved similar stiffness and improved bone-screw interface stability compared to dual-rod construct.

Original languageEnglish (US)
Pages (from-to)E934-E940
Issue number25
StatePublished - Dec 1 2006



  • Biomechanical evaluation
  • Dual-rod anterior system
  • Rod-plate anterior system
  • Single-rod with cages
  • Thoracolumbar and lumbar scoliosis

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine
  • Clinical Neurology

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