Sometimes the term "immobilizer" and brace are used interchangeably. It may be necessary to know exactly what type of device is being called an immobilizer or a brace. A true immobilizer keeps the joint from moving at all.

An immobilizer may be used after ACL repair to keep the knee fully extended for the first few weeks after surgery. Some doctors think this kind of immobilization is needed to prevent loss of knee extension. The immobilizer can be removed and usually is taken off during physical therapy every day.

Braces usually have a metal hinge joint that allows the knee to bend and straighten. It keeps the joint stable and protects the healing ligament from too much strain or load during activity. In some braces, the joint can be set to allow some, but not all motion.