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Machining knee implants

Knee implants undergo meticulous machining and finishing to meet required durability, functionality, and biocompatibility standards. The ultimate aim is to guarantee successful surgical procedures and a lasting improvement in patients’ quality of life.  

While knee arthroplasty has remained fundamentally the same since the 1970s, technological advances in manufacturing, materials development, the approach, and precision of implantation have improved it.

Extrude Hone has developed machining and finishing techniques for both the intercondylar zone (the central section of the box) and the cam zone with an efficiency that stays high against CNC milling for difficult-to-machine materials.

HOW ARE KNEE IMPLANTS MACHINED AND FINISHED ?

The process involves several stages, including machining, polishing, coating, and quality control testing. Here’s an overview of how knee implants are traditionally machined :

Machining knee implants

Knee implants are typically made from high-grade materials like cobalt-chromium alloys, titanium, or polyethylene (for the plastic components). 

The implant starts as a rough piece of material shaped through computer-aided machining (CNC milling). 

This step produces the basic shape of the implant, including the contours and features that must fit precisely into the knee joint.

 

Finishing the surfaces of the implant

Once the initial shape is created, the implant undergoes polishing to ensure a smooth surface, particularly for the metal components. 

Polishing is essential to reduce friction between the moving parts of the implant and the natural tissues of the body, reducing pain issues. Processes :

  • Mechanical polishing uses abrasive tools to smooth out the surface.
  • Electropolishing removes a thin metal layer to create an ultra-smooth finish and improve corrosion resistance.

A smooth, polished surface prevents implant wear and extends its longevity.

 

Surface coating of the implant

Depending on the type of implant, surface coatings may be applied to improve the performance and longevity of the knee surgery replacement. Common coatings include:

  • Porous coatings allow the bone to grow into the implant, promoting better fixation and stability. 
  • Hydroxyapatite (HA) coatings mimic natural bone and promote bone growth around the implant, often used for cementless implants.
  • Polymers (for plastic parts): Ultra-high molecular weight polyethylene (UHMWPE) is the most common material for the tibial insert (the plastic spacer between the metal components). 

Precision testing and inspection

After polishing and coating, the implants go through rigorous quality control checks to ensure they meet strict medical standards: dimensional inspection and surface roughness measurements

X-ray diffraction or similar techniques may be used to check for internal stresses or imperfections. Implants also undergo biocompatibility testing to ensure they will not react negatively with the body’s tissues.

 

Sterilization and packaging of knee implants

Once the knee implant is finished and passes all inspections, it is sterilized, typically using methods like ethylene oxide gas or gamma radiation. Sterilization ensures the implant is safe and ready for use in surgery.

Afterward, the implant is packaged in a sterile environment to maintain cleanliness until used.

 

Each of these finishing steps plays a crucial role in the overall performance of the knee implant, ensuring it is strong, durable, and capable of withstanding the demands of the human body for many years.

ECM MACHINING SOLUTIONS FOR KNEE IMPLANT INTERCONDYLAR AND CAM AREAS
A MORE EFFICIENT ALTERNATIVE TO CNC

The uniqueness of Extrude Hone’s technology means you can machine areas that are difficult to access appropriately with conventional methods.

The smoothness of the ECM operation, leveraging metal dissolution, allows us to stay away from common milling defects like shadows generated by tool path misshape, the axis ball screw wear, and the tooling wear.

ECM for knee implant box and cam machining

Extrude Hone offers a perfect electrochemical machining solution when strict dimensional tolerance and parallelism requirements are needed to finish the intercondylar zone (the central section of the box) and the cam zone.

ECM offers numerous advantages for achieving superior quality in a high-productivity environment with exacting requirements :

  • Targeted removal of material from precisely defined areas.
  • No mechanical or thermal loads on workpieces.
  • Roughing and finishing in a single operation.
  • Tolerances within 0.1mm (0.004in) and parallelism within 0.05mm (0.002in)
  • Surface finished to Ra 0.4µm ( 10 µinch) or better.
  • Suitable for deburring hard-to-reach areas and hardened or difficult-to-machine metals.
  • No secondary burrs and no risk of minor defects named as shadows.
  • Fast processing times 90 seconds per knee ( 4 knees simultaneously).
  • Multiple knees ( usually 4) can be processed simultaneously for improved productivity.
  • Running cost around  $1.6/pcs.
  • Superior process stability and robust process control.

Electrochemical Machining (ECM) offers several advantages when manufacturing knee implants, especially compared to traditional methods like CNC milling.

These benefits stem from ECM’s unique ability to machine complex shapes in hard materials with high precision and minimal stress on the workpiece: ECM’s efficiency compared to CNC milling remains high for difficult-to-machine materials.

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MACHINES AND CONTRACT SHOPS FOR KNEE IMPLANT MACHINING

Discover ECO+

With Extrude Hone, tailor your machine selection to specific needs.

 

With the new modular ECM entry-level machine concept ECO+, EXTRUDE HONE offers customers the flexibility to get the right equipment to engineer and run their ECM applications. 

One modular system with five packages helps you configure the machine to fit your requirements with enhanced surface finishing and high-precision ECM results.

Standardized packages reduce delivery time while offering high modularity. This means you don’t have to pay for unnecessary options without affecting the quality of your ECM parts.

Contract shop opportunity: accessing top machining technologies.

For those unwilling to invest, Extrude Hone provides contract shop services globally.

Benefit from trial and contract capabilities, extensive experience, and expert support to ensure quick turnaround and uncompromised quality.

At Extrude Hone, we are committed to providing an unparalleled experience. We use our knowledge to help your projects. We work hard to ensure the best solutions.

Our goal is to enhance efficiency and make your parts flawless.

LET US DO IT FOR YOU

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