When knee ligaments are torn, a graft is made from a tendon in your leg. They put it in place of the torn ligament and put it under tension. However, that tension often disappears after surgery because of stress-relaxation.
A design application to relieve the stress-relaxation problem in ACL-reconstruction. It is a kind of rubber ring that helps to keep the tendon under tension. Similar to a hair-tie. Giving patients a more stable knee and needing no follow-up surgery