An 'unloader' is a device - like a brace - which changes the forces going through the knee in order to protect a damaged side.
The Unloader One brace is made by the company Ossur. The brace should be fitted by someone trained to do so.
An unloader brace may be useful when the joint space has collapsed on one side - perhaps due to an inadequate meniscal shock absorber - and also where the joint on one side needs protecting, such as after cartilage repair procedures. There is also a commercially available unloader implant which goes into the tibia bone and adjustments can be made from outside the joint.
Implantable joint-unloading prosthesis
An Update on Unloading Knee Braces in the Treatment of Unicompartmental Knee Osteoarthritis from the Last 10 Years: A Literature Review.. Mistry DA, Chandratreya A, Lee PYF. Surg J (N Y). 2018 Jul 2;4(3):e110-e118.