Additive Manufactured Hip Implant

Joint Reconstruction, Part 3 – Surface Finishing Standards

While choosing the right implant material is of utmost importance, as discussed in our previous Joint Reconstruction Series post, the significance of optimum surface treatment throughout the entire implant manufacturing process cannot be overstated.

This relates not only to the right surface finish – be it a high-gloss polish for low friction, a textured surface for easy osseointegration, or as preparation for subsequent coating, rounded edges, etc. – but also total compliance with the specified tight dimensional tolerances. The success of a joint implant is determined by the perfect match between the various implant components. This depends, to a large extent, on the surface treatment procedure(s).

With extensive experience in the medical industry, Rosler Metal Finishing is an expert in designing systems and solutions for the treatment of joint reconstruction implants utilizing shot blasting and mass finishing technologies.

Our Joint Reconstruction Series continues with an overview of the stringent finishing standards for endoprosthetic implants.

Finishing Requirements

For the comfort of patients and effectiveness of the components, joint replacement implants must be finished to precise specifications, including:

  • The removal of sharp edges and burs to prevent rupturing blood vessels and blood clots during implantation and the healing process.
  • An extremely smooth, polished surface on the implant areas that are interacting with each other with Ra readings of < 1.0 micro inches.
  • A textured, somewhat rougher surface finish on those areas that are implanted into the bone to promote osseointegration or as preparation for coatings.
  • Absolutely clean surfaces to remove contaminations and prevent infections.
  • Improved resistance against tensile and bending loads for longevity. This is achieved with shot peening and mainly applies to hip stems, but also knees and other implants.
  • Maintaining critical component dimensions during the various finishing operations.
The front side of the knee femoral must be extremely smooth as it interacts with the tibia, yet has a rougher underside (left). The hip stem section implanted into the bone and the backside of the acetabular cup must be textured to allow bone
growth (right).

Emerging Challenges

Additive manufacturing is rapidly evolving from a purely prototyping method into a full-fledged manufacturing system, bringing challenges and opportunities with it.

Hip implants as well as knee and other joint replacements are already made with additive manufacturing with great success.

While we expect the trend towards additive manufactured joint reconstruction implants to accelerate over the coming years, additive manufactured components pose enormous finishing challenges.

In addition to successfully removing support structures and sintered metal particles, these implants have significantly higher surface roughness to overcome. The initial surface roughness of an additive manufactured component can be as high as Ra 2,000 micro inches, while the initial surface roughness of a cast or forged part amounts to Ra 120-320 micro inches.

Since it promotes bone growth, the higher surface roughness associated with this material is an advantage for surface area implanted into the bone. For surfaces that must be extremely smooth however, additive manufactured pieces require additional processing and time compared to forged work pieces.

The Rosler Way

No matter what condition your joint reconstruction implants start in, Rosler Metal Finishing can help you find a better way and achieve the exact finish needed every time.  Contact us today to discuss your unique challenges.

Be sure to catch up on our previous posts in the series including:

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