title: Does sterilization with fractionated electron beam irradiation prevent ACL tendon allograft from tissue damage?
abstract: OBJECTIVE
  Allografts are frequently used for anterior cruciate ligament (ACL) reconstruction. However, due to the inherent risk of infection, a method that achieves complete sterilization of grafts is warranted without impairing their biomechanical properties. Fractionation of electron beam (FEbeam) irradiation has been shown to maintain similar biomechanical properties compared to fresh-frozen allografts (FFA) in vitro. Therefore, aim of this study was to evaluate the biomechanical properties and early remodelling of grafts that were sterilized with fractionated high-dose electron beam irradiation in an in vivo sheep model.
  
  
  METHODS
  ACL reconstruction was performed in 18 mature merino mix sheep. Sixteen were reconstructed with allografts sterilized with FEbeam irradiation (8 × 3.4 kGy) and two with FFA. Eight FFA from prior studies with identical surgical reconstruction and biomechanical and histological analyzes served as controls. Half of the animals were sacrificed at 6 and 12 weeks, and biomechanical testing was performed. Anterior-posterior laxity (APL) was assessed with an AP drawer test at 60° flexion, and load to failure testing was carried out. Histological evaluation of mid-substance samples was performed for descriptive analysis, cell count, crimp and vessel density. For statistical analysis a Kruskal-Wallis test was used for overall group comparison followed by a Mann-Whitney U test for pairwise comparison of the histological and biomechanical parameters.
  
  
  RESULTS
  Biomechanical testing showed significantly decreased stiffness in FEbeam compared to FFA at both time points (p ≤ 0.004). APL was increased in FEbeam compared to FFA, which was significant at 6 weeks (p = 0.004). Median of failure loads was decreased in FEbeam grafts, with 12 reconstructions already failing during cyclic loading. Vessel density was decreased in FEbeam compared to FFA at both time points, with significant differences at 12 weeks (p = 0.015). Crimp length was significantly shorter in FEbeam compared to FFA at both time points (p ≤ 0.004) and decreased significantly in both groups from 6 to 12 weeks (p ≤ 0.025).
  
  
  CONCLUSIONS
  ACL reconstruction with fractionated Ebeam sterilization significantly alters the biomechanical properties and the early remodelling process of treated grafts in vivo. Therefore, this sterilization method cannot be recommended for clinical application. As substantial changes in the remodelling are inherent in this study, care in the rehabilitation of even low-dose sterilized allografts, used for ACL reconstruction, is recommended.
authors.affiliation: Charité-University Medicine Berlin, Julius Wolff Institute, Berlin, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Schmidt
authors.affiliation: Charité-University Medicine Berlin, Julius Wolff Institute, Berlin, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Grabau
authors.affiliation: Charité-University Medicine Berlin, Julius Wolff Institute, Berlin, Germany.
authors.forename: J H
authors.initials: JH
authors.lastname: Grotewohl
authors.affiliation: Leibniz Institute for Polymer Research, Dresden, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Gohs
authors.affiliation: Institute of Transfusion Medicine, Tissue Bank, Charité-University Medicine Berlin, Berlin, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Pruß
authors.affiliation: DIZG - German Institute of Cell and Tissue Replacement, Berlin, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Smith
authors.affiliation: Sporthopaedicum, Berlin, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Scheffler
authors.affiliation: Orthopedic Department, Center for Muskuloskeletal Surgery, Charité-University Medicine Berlin, Berlin, Germany. arnd.hoburg@charite.de.
authors.forename: A
authors.initials: A
authors.lastname: Hoburg
mesh_terms: D064591:Allografts; D000818:Animals; D016118:Anterior Cruciate Ligament / Q000382:microbiology / Q000473:pathology* / Q000528:radiation effects*; D059549:Anterior Cruciate Ligament Reconstruction; D001696:Biomechanical Phenomena; D018562:Disease Transmission, Infectious / Q000517:prevention & control; D004583:Electrons; D011829:Radiation Dosage; D012756:Sheep; D013242:Sterilization / Q000379:methods*; D013710:Tendons / Q000637:transplantation
keywords: ACL reconstruction; Allograft; Ebeam; Fractionation; Sterilization