Alloy for orthopaedic implants

Citation

(2001), "Alloy for orthopaedic implants", Anti-Corrosion Methods and Materials, Vol. 48 No. 3. https://doi.org/10.1108/acmm.2001.12848cad.004

Alloy for orthopaedic implants

Keywords Sandvik Steel, Sandvik Metinox, Stainless steel, Medical products

Technology developed through the experience of producing stainless steels, high alloy steels and special metals with exceptional demands on microcleanliness has enabled Swedish steelmaker, AB Sandvik Steel to produce a new nitrogen alloyed steel grade for use in orthopaedic implants and fracture fixation devices.

Called Sandvik Bioline High-N, the new steel grade is said to be an ultra-clean steel meeting all of the requirements of the governing international standard ISO 5832-9. In order to comply with stringent micro-cleanliness requirements, it is general steelmaking practice to employ a process of remelting, meaning the steel must be melted twice. Indeed, some manufacturers of medical implants consider remelting to be mandatory in ISO 5832-9 whereas the standard only makes a "recommendation" leaving room for technical innovation in the steelmaking process.

Sandvik reports that it has been able to meet all of the specification requirements without the need for further refining of the steel. By minimising the number of expensive operations during manufacturing, considerable cost savings can be made thereby increasing the competitiveness of the new material.

Most replacement hip stems are produced by hot forging which results in a fully annealed (softened) microstructure in the metal. In the annealed condition, Bioline High-N claims to exhibit a yield strength more than twice that of the standard 316LVM grade – the most widely used stainless steel for orthopaedic implants and fracture fixation devices. Work hardening, induced by cold working the material, results in an increase in yield strength. It is predominantly this property, combined with its corrosion resistance that makes High-N type steels the material of choice for stainless steel hip prostheses.

In addition to permanent implants such as hips, Sandvik Bioline High-N is being used increasingly to manufacture bone screws, pins, intra-medullary nails and other trauma products for fracture fixation.

All of these products require raw materials in different forms such as wire, strip, bar and tube. All are available from Sandvik Metinox.

Details available from: Sandvik Metinox. Tel +44 (0)114 263 3 100; Fax +44 (0)114 263 3111.