The Crossover G3 Infinity Knee is a high-performance hybrid prosthetic knee developed by Leftside Industries, originally founded by inventor and adaptive athlete Brian Bartlett. It represents the evolution of a long line of “tendon-based” prosthetic designs created for extreme sports and high-activity amputees.

Origins and development history

The technology behind the Crossover knee did not start as a commercial medical product—it was born from sports performance engineering.

• Early origin (late 1990s–2000s):
  Brian Bartlett, a professional downhill mountain biker and skier, lost his leg in an accident and returned to extreme sports using early custom-built prosthetic concepts.
• BTK (Bartlett Tendon Knee):
  The first major innovation was the Bartlett Tendon Knee, a mechanical system that introduced elastic “tendon” elements alongside an air/oil shock system. This design aimed to mimic muscle and tendon behavior, giving the knee natural rebound and energy return instead of rigid hinge motion.  
• Military and high-performance adoption:
  The BTK system gained attention for durability in extreme environments and was tested and used with military and highly active users, especially for skiing, biking, and field operations.  
• Evolution into Leftside Industries systems:
  Over time, the design was refined into a more modular, adjustable platform with improved materials, shock tuning, and faster configuration changes for different activities.
• Crossover™ G3 Infinity Knee (current generation):
  The modern version of this technology is the G3 Infinity Knee, a third-generation platform designed to transition between everyday walking and high-impact sports use.

What the Crossover G3 Infinity Knee is today

The current system is a hybrid mechanical prosthetic knee built for users who want both mobility and athletic performance in one device.

Key characteristics include:

• Tendon-based energy system that stores and returns force for dynamic movement
• Air/oil shock absorption for impact control during sports
• Mechanical adjustability for different activities (walking, hiking, biking, snow sports)
• No electronics or batteries, improving reliability in harsh environments
• High durability design for dirt, water, snow, and heavy impact use
• Fast conversion between “everyday” and “sports” modes

Design philosophy

Unlike microprocessor knees that rely on sensors and software, the Crossover knee is built around a simple idea:
replicating muscle and tendon behavior mechanically rather than electronically.

This gives it:

• A more “connected” or responsive feel during sports
• Easier field maintenance
• Consistent performance in environments where electronics may fail

Item has been inspected and tested, with no functional issues only unless described above in the description or in the title. 

Look at all the pictures I would also recommend googling the item or go to the manufacture's website to find more detailed information about the item.

Product general overview

Prosthetic component is designed to enhance mobility, stability, and comfort for prosthetic limb users. Whether it is a prosthetic foot, knee, arm or specific component, it will assists with providing smooth, reliable motion and is engineered for daily use, rehabilitation, and long-term durability. 

Key Features

Durable Construction: Made from high-quality materials for long-lasting use

Lightweight & Comfortable: Reduces fatigue and enhances mobility

Professional-Grade: Ideal for rehabilitation and active use

Compatible: Designed to work with standard external prosthetic leg, arm, socket assembles. 

Domestic Ebay buyers

I have 3 day handling time. With most orders I can get the item out the next day or the following day (example if you order item Thursday morning it will most likely it will it get dropped off to the selected shipping carrier either friday or saturday or at the latest Monday). I hand delivery the items to the shipping carrier. If it is a holiday or the shipping carrier is closed I will not be able to drop off the item during the days they are closed

Shipping options usps or ups 

International buyers and shipping options 

Ebays international shipping program, international shipping is handled by eBay. Import charges are calculated and collected at checkout. If you are international buyer and do not see this option to ship the item, that most likely means the item is not eligible to be ship to your particular country with Ebay’s international shipping program. 

Ups is the fastest international shipping optional but also the most expensive. 

Disclaimer

Buyers must ensure item suits their medical  needs. Seller & eBay not responsible for improper use