Knee braces are mainly divided into three categories: 

Rehabilitation braces: Equipped with metal hinges and a hard shell, they extend from the middle of the thigh to the upper part of the calf. They are used for severe ligament injuries or postoperative fixation, providing the strongest support but with less flexibility. 

Sports braces: Made of elastic materials and combined with silicone pads or straps, they cover about 10 centimeters above and below the knee. They are suitable for protection during running and ball games. They have good breathability but relatively weak support. 

Adjustable postoperative brace: A plastic frame with multiple hinges, allowing the flexion angle to be controlled by a knob, helps gradually restore the joint's range of motion during rehabilitation training. 

According to the classification rules of medical devices in China, postoperative braces with joint angle adjustment functions are classified as Class II medical devices, while ordinary elastic knee supports are classified as Class I medical devices.