Application of laser shock peening for spinal implant rods

The current industry standard rigid spinal implants suffer fatigue failures due to bending and torsion loads. The purpose of this program was to design novel prototype flexible titanium alloy spinal implant rod with machined features, and then apply the laser shock peening (LSP) process to restore the fatigue strength debit due to these features.

A flexible prototype rod was designed with flat section at the center of the rod. The flat section was laser shock peened. Static compression tests were conducted as per American Society of Testing Materials standards for three‐ and four‐point bending tests and “vertebrectomy” constructs. Finite element models were developed to aid in the design of LSP and also to guide the experiments.

The test results indicated a ∼3X improvement in flexibility and a reduction in fatigue load ratio, defined as applied load divided by the yield load; from 72 to 68 percent. This rod was LSP's on the flat sections, and tested again. The results indicated an increase in the fatigue load ratio from 68 to 75 percent without any further change in flexibility.

It has been demonstrated successfully that the current industry rigid spinal implant rod can be modified for flexibility and laser shock peened to increase fatigue strength. This enhancement will enable the use of the implant for longer periods and higher loads; and for surgical processes with and without fusion. This technology can be readily applied to all metals that are certified for human implant applications; thus can be implemented with minimal clinical trials.