title: Biomechanical strength of deep-frozen versus lyophilized large cortical allografts.
abstract: OBJECTIVE
  To compare biomechanical strength of deep-frozen versus lyophilized large cortical allografts.
  
  
  METHODS
  In vivo transplantation studies performed in tibia of adult cats using 4 cm deep-frozen and lyophilized, gamma-irradiated allografts to bridge large cortical defect model.
  
  
  BACKGROUND
  Bridging large cortical bone defect is a challenging problem. Options include autografts, allografts, bioceramics and prostheses. Allografts provide a suitable option.
  
  
  METHODS
  Forty mature cats were used. A large defect (4 cm) was created in mid-diaphysis of right tibia. In 16 cats, cortical defect was reconstructed using deep-frozen allografts (-80 degrees C) with intra-medullary rodding. In another 16 cats, lyophilized, gamma-irradiated allografts were used. Observation periods include 8, 12, 16 and 24 weeks. The specimens were procured together with unoperated legs as controls. Mechanical testing was performed using a materials testing machine with torsion test device of up to 500 Nm at speed of 0.18 rpm. Parameters studied included maximum torque, torsional stiffness and energy of absorption.
  
  
  RESULTS
  Deep-frozen allografts did not reach 100% strength, achieving only 64% at 6 months. In marked contrast, lyophilized allografts were significantly weaker with only 12% maximum torque strength at 6 months. Lyophilized allografts were significantly weaker than deep-frozen allografts in all observation periods (p < 0.05).
  
  
  CONCLUSIONS
  Deep-frozen allografts did not reach 100% normal strength and were significantly weaker than non-vascularised autografts. Lyophilized allografts were significantly weaker than deep-frozen allografts.
  
  
  CONCLUSIONS
  For the reconstruction of massive cortical bone defects, only deep-frozen cortical allografts should be used. Lyophilized allografts are not suitable.
authors.affiliation: Department of Orthopaedic Surgery, National University of Singapore, 5 Lower Kent Ridge Road, 119074 Singapore, Singapore. dosnathe@nus.edu.sg
authors.forename: A
authors.initials: A
authors.lastname: Nather
authors.forename: A
authors.initials: A
authors.lastname: Thambyah
authors.forename: J C H
authors.initials: JC
authors.lastname: Goh
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000379:methods; D002415:Cats; D015925:Cryopreservation / Q000379:methods; D017102:Fracture Healing / Q000502:physiology*; D005612:Freeze Drying / Q000379:methods; D005615:Freezing; D011859:Radiography; D013718:Tensile Strength; D013977:Tibia / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery / Q000637:transplantation*; D013978:Tibial Fractures / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery*; D014184:Transplantation, Homologous; D019737:Transplants; D016896:Treatment Outcome