Custom knee braces are available through several popular orthopaedic companies, such as Breg, Donjoy, Ossur and Bledsoe.
They are indicated for people suffering with osteoarthritis (uni- or bi- compartmental) or sports related ligament injuries resulting in potential instability of the knee (ACL, PCL, etc.)
If a custom brace is out of reach, there are several off the shelf braces which can be measured to fit and produce good results for a fraction of the cost of a custom brace.