MEDICALLY CERTIFIED PROTECTION We learned a lot from developing our C-Frame and X-Frame knee braces, and we recognize the need for a great knee brace that won't break the bank. Not as stiff as the C-Frame or X-Frame, but a good chassis made from glass-filled nylon for comfort and a Carbon Injected knee for that rigidity which reduces the ACL, Meniscus, and MCL injury risk. The Z-Frame is also CE certified as a medical device and as impact protection, maybe it's time to get rid of your knee protectors and get yourself a knee brace? Next step up is the X-Frame for a stiffer chassis and our top line cage type brace or the C-Frame Pro Carbon knee brace, if you are looking for a single sided hinge.