Multiaxis cyclic biomechanical testing of Harrington, Luque, and Drummond implants

The performance characteristics of Harrington-Moe distraction rods, paired wired Luque rods and Drummond's system were evaluated and compared when subjected to nondestructive cyclic, multidirectional biomechanical testing. Twelve fresh, frozen swine spines with intact facet joints and anterior and posterior ligamentous complexes were instrumented and tested in a specially designed pneumatic testing machine. The instrumented spines were subjected to 207 kN/m2 compression and 49 N-m torsion. Each spine was cycled 28,000 times at 1 cycle per second. Linear and angular displacements were determined by digitizing photographs and video tapes made during testing. A computer program developed and refined for the project was used to complete the data analysis. Approximately 540 items of angular and linear displacement data were collected for each spine. Inspection of the spines after cyclic, multidirectional testing revealed no change in their osteoligamentous integrity compared with pre-testing. Pre- and post-testing radiographs showed no evidence of osseous failure, hook dislodgement or wire breakage. Erosion of laminal bone at the Harrington hook attachment sites was observed. Displacement of the Harrington hooks was seen during off-axis compression-torsion testing. Fretting and deposit of metal wear debris occurred between the sublaminal wires and "L" rods. There was no evidence of loosening of either the Drummond or Luque implants or fatigue failure of any component. Analysis of the linear and angular displacement data showed that the Luque and Drummond instrumented spines displaced less in axial compression, off-axis compression and off-axis compression-torsion than the single Harrington-Moe distraction rod.(ABSTRACT TRUNCATED AT 250 WORDS)