Nitinol Implants in Orthopaedics: Review of past und current applications and concepts; discussion of boundaries for future applications

Although Nitinol has been used as an implant material in Orthopaedics for more than 20 years, it has never really penetrated the orthopaedic market like it did for vascular implants. Starting from early applications as osteosynthesis plates and staples, Nitinol implants underwent intensive clinical evaluations in China in the 80´s and early 90´s for spinal applications such as compression staples, intervertebral joints, scoliosis correction rods, anterior cervical fusion staples and posterior fixation devices.  These applications used predominantly the thermal shape memory effect of Nitinol. The success of current and future applications may hinge on whether they take advantage of the superelastic effect of Nitinol as well. The current commercial applications of Nitinol focus mainly on bone staples for the extremities and the spine.  The paper reviews the scientific and patent literature for the past 10 years which has been suggesting a broader use of the unique functional properties of the material: Examples include artificial spinal discs and spinal stabilization devices utilizing the superelastic transformation Austenite – Stress-Induced Marteniste), intervertebral annulus reinforcing  and nucleus augmentation devices using the enormous elastic deployment and porous Nitinol for spinal fusion and intervertebral body replacement making use of the excellent osteogenic cells integration and the low Elastic modulus. Finally the paper discusses boundaries for a broader use of Nitinol in the orthopaedics market including fatigue life, wear properties and corrosion behaviour.