title: Effect of cyclic tension on the biomechanical properties of flexor tendon grafts. Results of an ex-vivo porcine study.
abstract: BACKGROUND
  Autologous flexor tendons are widely used for anterior cruciate ligament (ACL) reconstruction. Pretension of the graft before fixation has been described as part of the surgical technique, nevertheless there is no consensus on the type and amount to tension needed to increase the stiffness without affecting its biomechanical properties.Our hypothesis is cyclic tension increases flexor tendon stiffness without affecting its ultimate failure at maximum loads (UFML).
  
  
  METHODS
  Forty-five flexor digitorum profundus tendons harvested from domestic pigs (Sus scrofa domestica) were randomly divided into three groups: E1 (n=15), E2 (n=15) and C (n=15). Groups E1 and E2 were subjected to 50 cyclic loads at a 1 Hz frequency, at 70N and 100N respectively, group C was not intervened. The three groups were then tested for UFML. Cyclic loads and measurements were performed using a Stress-Strain machine (SST 1.0 Kinetecnic). Results were analyzed using GrapgPad statistical software. Groups were compared using Mann-Whitney test with a 95% confidence interval.
  
  
  RESULTS
  Significant increased stiffness for group E1 (p=0.02) and group E2 ( p<0.01) when compared to group C. The stiffness of group E2 was also significantly higher than E1 (p=0.03). There was a significant reduction on the UFML between group E2 and C (p<0.01), which was not observed when comparing groups E1 and C.
  
  
  CONCLUSIONS
  Cyclic loads at 70N result in an increased stiffness of flexor tendons without affecting its ultimate failure at maximum loads. Cyclic loads at higher tensions might cause a deleterious effect on the biomechanical properties of flexor tendon grafts.
authors.affiliation: Department of Orthopedics, Faculty of Medicine, Universidad de los Andes, Santiago, Chile; Knee Surgery Unit, Clínica Dávila, Santiago, Chile; Knee Surgery Unit, Military Hospital, Santiago, Chile.
authors.forename: Mario
authors.initials: M
authors.lastname: Orrego
authors.affiliation: School of Kinesiology, Faculty of Medicine, Universidad de los Andes, Santiago, Chile; Knee Surgery Unit, Clínica Dávila, Santiago, Chile; Knee Surgery Unit, Clínica Meds, Santiago, Chile.
authors.forename: José
authors.initials: J
authors.lastname: Matas
authors.affiliation: Department of Orthopedics, Faculty of Medicine, Universidad de los Andes, Santiago, Chile. Electronic address: s.abusleme@gmail.com.
authors.forename: Sebastián
authors.initials: S
authors.lastname: Abusleme
authors.affiliation: School of Kinesiology, Faculty of Medicine, Universidad de los Andes, Santiago, Chile.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Guzmán-Venegas
authors.affiliation: Department of Orthopedics, Faculty of Medicine, Universidad de los Andes, Santiago, Chile; Knee Surgery Unit, Clínica Dávila, Santiago, Chile; Knee Surgery Unit, Military Hospital, Santiago, Chile.
authors.forename: Diego
authors.initials: D
authors.lastname: Amenabar
mesh_terms: D000818:Animals; D016118:Anterior Cruciate Ligament / Q000601:surgery*; D059549:Anterior Cruciate Ligament Reconstruction / Q000379:methods*; D001696:Biomechanical Phenomena; D004548:Elasticity / Q000502:physiology*; D034421:Sus scrofa; D013552:Swine; D013710:Tendons / Q000502:physiology* / Q000637:transplantation
keywords: ACL; Graft elongation; Stiffness; Tensioning; UFML