Advanced Knee Replacement



The Advanced Knee Replacement was a safety device introduced in Portal. The device was created by Aperture Science in order to keep Test Subjects from injuring themselves when falling from great heights.

These Knee Replacements were worn by Chell, the protagonist of Portal, until she is later fitted with the Long Fall Boots in Portal 2.

Overview
The Replacements serve the purpose of protecting human Test Subjects from even the slightest bit of harm regardless how far they have fallen, even from terminal velocity, and additionally to prevent the Handheld Portal Device from inflicting damage. This purpose was later succeeded by the Long Fall Boots introduced in the single-player campaign of Portal 2.

Prior to the events of Portal 2 in the Portal 2: Lab Rat comic, Chell was dragged back into the facility by the Party Escort Bot, breaking her Advanced Knee Replacements in the process. These were ultimately replaced by the Long Fall Boots.

Trivia

 * The idea for the Advanced Knee Replacement was recycled from a cut character from Half-Life 2, the Combine Assassin.
 * The necessity to add the Advanced Knee Replacement came when Beta testers believed it unfair that the player could survive falls from heights that would kill you in most other FPS games, specifically Half-Life.