As a below knee amputee you may require a much lower posterior (back) wall on your cycling socket to allow the knee to bend past 90 degrees to reduce discomfort at the back your knee. On your day to day prosthesis, this wall is kept at a certain height to prevent movement of your residual limb within the socket.
As an above knee or through knee amputee, you will require a knee that either has a cycling mode or allows for a free-swinging knee joint. There are some limitations with standard knees in these modes though, you won’t be able to stand and extend your knee to pedal and you will be heavily reliant on your sound leg to provide power to the drivetrain. There are however solutions to these issues. The CrossOver Extensible Knee, touted as the World’s First Extensible Knee, has a unit for shock absorption like what you would have on the rear suspension of your mountain bike. It has “tendons” that assist in extension of the knee allowing you to power through the leg to the drivetrain. Through Knee and Above Knee amputees may require some initial training in their pursuit of cycling.
As an above knee amputee, you might also have issues with your sockets on the bicycle seat. Modifications to the socket design or socket seat may be required for a more comfortable ride. Please speak to your prosthetist about these issues.