title: Viscoelasticity and temperature variations decrease tension and stiffness of hamstring tendon grafts following anterior cruciate ligament reconstruction.
abstract: BACKGROUND
  Hamstring tendon grafts used for anterior cruciate ligament reconstruction are typically harvested early in the surgical procedure and are preconditioned prior to reimplantation. Postoperatively, the grafts undergo stress relaxation and warm from the temperature of the operating room to body temperature. The hypothesis of this study was that the tension within semitendinosus and gracilis tendon grafts and the stiffness of the grafts significantly decrease postoperatively because of both stress relaxation and an increase in temperature.
  
  
  METHODS
  Double-strand grafts were created from six semitendinosus tendons and six gracilis tendons harvested from cadaver specimens. The grafts were loaded to 65 N while at operating-room temperature (20 degrees C). After fifteen minutes of stress relaxation, graft tension was measured and the grafts were stretched by 0.1 mm to determine stiffness. The tension and stiffness measurements represented graft properties immediately following reconstruction. Additional tension and stiffness measurements were made following three hours of stress relaxation and after increasing the temperature to the body temperature at the knee (34 degrees C). Both types of graft were examined for differences in stiffness and tension due to stress relaxation and the temperature increase.
  
  
  RESULTS
  For both types of graft, the tension and stiffness decreased following stress relaxation to approximately 50% and 80%, respectively, of the value immediately after reconstruction. Increasing the temperature decreased the tension and stiffness further to approximately 40% and 70%, respectively, of the value after reconstruction for both types of graft. All changes in tension and stiffness were significant (p < 0.01).
  
  
  CONCLUSIONS
  Graft tension and stiffness achieved immediately following reconstruction are not maintained postoperatively because of stress relaxation and a temperature increase. This could lead to increased knee laxity.
authors.affiliation: The Medical Education and Research Institute of Colorado, 3920 North Union Boulevard, Suite 210, Colorado Springs, CO 80907, USA.
authors.forename: William J
authors.initials: WJ
authors.lastname: Ciccone
authors.forename: Derek R
authors.initials: DR
authors.lastname: Bratton
authors.forename: David M
authors.initials: DM
authors.lastname: Weinstein
authors.forename: John J
authors.initials: JJ
authors.lastname: Elias
mesh_terms: D000368:Aged; D016118:Anterior Cruciate Ligament / Q000601:surgery; D000070598:Anterior Cruciate Ligament Injuries; D002102:Cadaver; D004548:Elasticity; D006801:Humans; D008875:Middle Aged; D013314:Stress, Mechanical; D013696:Temperature; D013710:Tendons / Q000503:physiopathology* / Q000637:transplantation; D046509:Tissue Culture Techniques; D014783:Viscosity