Maintaining Graft Tension After ACL RepairACL ligament repairs are done today using a tendon transplant from either the hamstrings muscle at the back of the knee or the patellar tendon from the front of the knee. The graft is an autograft because it's taken from the patient. In this article, researchers show how time and temperature affect the graft stiffness.
ACL tendon grafts must be prepared before placing them in the knee joint. First the tissue is harvested or removed from the body. It is preconditioned while in the operating room. Both the temperature and the amount of stiffness are preset. The idea is to increase the stiffness by lowering the tissue temperature.
However, when the graft is in the body, it returns to body temperature. This increase in temperature increases the length of the graft, a process called stress relaxation. In this study tendon grafts from the hamstring muscle of cadavers (bodies preserved after death for study) were tested. Each tendon graft was looped to make a double-strand graft and tested using a special hydraulic testing machine.
The authors report that the tendon grafts taken from the hamstring muscle lose tension and stiffness after implantation into the knee. They say it may help to keep the grafts at body temperature during the operation instead of cooling and then warming them again.
It appears that there is a wide range of stress relaxation that can occur. It's not possible for the surgeon to predict how much the graft will relax in stiffness or tension. This study shows that graft tension and stiffness will decrease after ACL repair. More study is needed to find a way to prevent knee laxity (looseness) after ACL repair.
William J. Ciccone II, MD, et al. VIscoelasticity and Temperature Variations Decrease Tension and Stiffness of Hamstring Tendon Grafts Following Anterior Cruciate Ligament Reconstruction. In The Journal of Bone and Joint Surgery. May 2006. Vol. 88-A. No. 5. Pp. 1071-1078.
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