The importance of loading the periphery of the vertebral endplate

Commercial fusion cages typically provide support in the central region of the endplate, failing to utilize the increased compressive strength around the periphery. This study demonstrates the increase in compressive strength that can be achieved if the bony periphery of the endplate is loaded. Sixteen cadaveric lumbar vertebrae (L1-L5) were randomly divided into two even groups. A different commercial mass produced implant (MPI) was allocated to each group: (I) a Polyether-ether-ketone (PEEK) anterior lumber inter-body fusion (ALIF) MPI; and (II) a titanium ALIF MPI. Uniaxial compression at a displacement rate of 0.5 mm/sec was applied to all vertebrae during two phases: (I) with the allocated MPI situated in the central region of the endplate; (II) with an aluminum plate, designed to load the bony periphery of the endplate. The failure load and mode of failure was recorded. From phase 1 to phase 2, the failure load increased from 1.1±0.4 to 2.9±1.4 kN for group 1; and from 1.3±1.0 to 3.0±1.9 kN for group 2. The increase in strength from phase 1 to phase 2 was statistically significant for each group (group 1: P