Repeated Freeze-thaw Cycles Do Not Alter the Biomechanical Properties of Fibular Allograft Bone

• Published in: Clinical orthopaedics and related research 2012-03, Vol.470 (3), p.937-943
• Main Authors: Shaw, Joshua M., Hunter, Shawn A., Gayton, J. Christopher, Boivin, Gregory P., Prayson, Michael J.
• Format: Article
• Language: English
• Subjects: Adult; Aged; Basic Research; Biological and medical sciences; Biomechanical Phenomena; Biomechanics. Biorheology; Conservative Orthopedics; Cryopreservation; Diseases of the osteoarticular system; Female; Fibula - transplantation; Freezing; Fundamental and applied biological sciences. Psychology; Humans; Male; Medical sciences; Medicine; Medicine & Public Health; Middle Aged; Orthopedics; Sports Medicine; Stress, Mechanical; Surgery; Surgical Orthopedics; Tissue Preservation; Tissues, organs and organisms biophysics; Transplantation, Homologous
• ISSN: 0009-921X; 1528-1132
• DOI: 10.1007/s11999-011-2033-5

Background Allograft tissues can undergo several freeze-thaw cycles between donor tissue recovery and final use by surgeons. However, there are currently no standards indicating the number of reasonable freeze-thaw cycles for allograft bone and it is unclear how much a graft may be degraded with multiple cycles. Questions/purposes We therefore asked whether (1) the mechanical properties of fibular allograft bone would remain unchanged with increasing numbers of freeze-thaw cycles and (2) histologic alterations from increased numbers of freeze-thaw cycles would correspond to any mechanical changes. Methods Fibular allograft segments were subjected to two, four, and eight freeze-thaw cycles and compared biomechanically and histologically with a control group (one freeze-thaw cycle). Two freeze-dried treatments, one after being subjected to one freeze-thaw cycle and the other after being subjected to three freeze-thaw cycles, also were compared with the control group. Results For all segments, the average ultimate stress was 174 MPa, average modulus was 289 MPa, average energy was 2.00 J, and the average stiffness was 1320 N/mm. The material properties of the freeze-thaw treatment groups were similar to those of the control group: ultimate stress and modulus were a maximum of 16% and 70% different, respectively. Both freeze-dried treatments showed increased stiffness (maximum 53% ± 71%) and energy to failure (maximum 117% ± 137%) but did not exhibit morphologic differences. There were no alterations in the histologic appearance of the bone sections in any group. Conclusions Fibular allograft segments can be refrozen safely up to eight times without affecting the biomechanical or morphologic properties. Freeze-dried treatments require further study to determine whether the detected differences are caused by the processing. Clinical Relevance Cryopreserved cortical allografts are thawed by surgeons in preparation for procedures and then occasionally discarded when not used. Refreezing allograft tissues can result in a cost savings because of a reduction in wasted graft material.