Development of a novel method for the strengthening and toughening of irradiation-sterilized bone allografts.

Reconstruction of large skeletal defects is a significant and challenging issue. Bone allografts are often used for such reconstructions. However, sterilizing bone allografts by using γ-irradiation, damages collagen and causes the bone to become weak, brittle and less fatigue resistant. In a previous study, we successfully protected the mechanical properties of human cortical bone by conducting a pre-treatment with ribose, a natural and biocompatible agent. This study focuses on examining possible mechanisms by which ribose might protect the bone. We examined the mechanical properties, crosslinking, connectivity and free radical scavenging potentials of the ribose treatment. Human cortical bone beams were treated with varying concentration of ribose (0.06-1.2 M) and γ-irradiation before testing them in 3-point bending. The connectivity and amounts of crosslinking were determined with Hydrothermal-Isometric-Tension testing and High-Performance-Liquid-Chromatography, respectively. The free radical content was measured using Electron Paramagnetic Resonance. Ribose pre-treatment improved the mechanical properties of irradiation sterilized human bone in a pre-treatment concentration-dependent manner. The 1.2 M pre-treatment provided >100% of ultimate strength of normal controls and protected 76% of the work-to-fracture (toughness) lost in the irradiated controls. Similarly, the ribose pre-treatment improved the thermo-mechanical properties of irradiation-sterilized human bone collagen in a concentration-dependent manner. Greater free radical content and pentosidine content were modified in the ribose treated bone. This study shows that the mechanical properties of irradiation-sterilized cortical bone allografts can be protected by incubating the bone in a ribose solution prior to irradiation.

Elastic-plastic fracture toughness and rising JR-curve behavior of cortical bone is partially protected from irradiation-sterilization-induced degradation by ribose protectant.

OBJECTIVE: This study tested the hypothesis that pre-treating cortical bone with ribose would protect the rising fracture resistance curve behavior and crack initiation fracture toughness of both bovine and human cortical bone from the degrading effects of γ-irradiation sterilization. MATERIALS AND METHODS: A ribose pre-treatment (1.8 M for bovine, and 1.2 M for human, in PBS at 60 °C for 24 h) was applied to single-edge notched bending fracture specimens prior to sterilization with a 33 kGy dose of γ-irradiation. Fracture resistance curves were generated with a single specimen method using an optical crack length measurement technique. The effect of the treatment on overall fracture resistance behavior, crack initiation fracture toughness, and tearing modulus was compared with non-irradiated and conventionally irradiation sterilized controls. Hydrothermal isometric tension testing was used to examine collagen network connectivity and thermal stability to explore relationships between collagen network quality and fracture resistance. RESULTS: The ribose pre-treatment successfully protected the crack growth initiation fracture toughness of bovine and human bone by 32% and 63%, respectively. The rising JR-curve behavior was also partially protected. Furthermore, collagen connectivity and thermal stability followed similar patterns to those displayed by fracture toughness. CONCLUSIONS: This paper demonstrates that the fracture toughness of irradiation-sterilized bone tissue can be partially protected with a ribose pre-treatment. This new approach shows potential for the production and clinical application of sterilized allografts with improved mechanical performance and durability.

Periprosthetic supracondylar femoral fractures following knee arthroplasty: a biomechanical comparison of four methods of fixation.

PURPOSE: The aim of this study was to determine the biomechanical properties of four fixation options for periprosthetic supracondylar femoral fractures. METHODS: Fourth-generation composite femurs were implanted with a posterior-stabilizing femoral component of total knee arthroplasty. All femurs were osteotomized to produce a AO/OTA 33-A3 fracture pattern and four different constructs were tested: (1) non-locking plate; (2) polyaxial locking plate; (3) intramedullary fibular strut allograft with polyaxial locking plate; (4) retrograde intramedullary nail. The composite femurs underwent non-destructive tests to determine construct stiffness in axial and torsional cyclic loading. The final testing consisted of quasi-static axial loading until failure. RESULTS: Under cyclic torsional loading, the retrograde intramedullary nail was less stiff than non-locking plate, polyaxial locking plate and intramedullary fibular strut allograft with polyaxial locking plate (p = 0.046). No differences were detected in cyclic axial loading between the different constructs. During quasi-static axial loading to failure, the intramedullary nail achieved the highest axial stiffness while the non-locking plate showed the lowest (p = 0.036). CONCLUSIONS: The intramedullary fibular strut allograft with polyaxial locking plate did not prove to be significantly better to the polyaxial locking plate only in a periprosthetic distal femur fracture model.

γ-Irradiation sterilized bone strengthened and toughened by ribose pre-treatment.

OBJECTIVE: This study tested the hypothesis that a ribose-based pre-treatment would protect the strength, ductility and toughness of γ-irradiation sterilized cortical bone. METHODS: Experiment 1: The effects of ribose pre-treatment (1.8M in PBS at 60°C for 24h) prior to 33 kGy of irradiation on strength, ductility and toughness (beams in three-point bending) and fracture toughness (J-integral at instability in single edge notched (bending)) were tested against matched non-irradiated and irradiated controls from bovine tibiae. Experiment 2: Three-point bending tests were conducted using beams from human femora (males, 59-67 years). Bone collagen thermal stability and network connectivity were examined using hydrothermal isometric tension testing. RESULTS: Ribose pre-treatment protected the strength, ductility and toughness of irradiation sterilized bovine and human specimens to differing degrees. Their ultimate strength was not detectably different from non-irradiated control levels; toughness in bovine and human specimens was protected by 57 and 76%, respectively. Untreated human bone was less affected by irradiation and ribose pre-treatment was more effective in human bone than bovine bone. CONCLUSIONS: This paper presents the first proof-of-principle that irradiation-sterilized bone with improved mechanical properties can be produced through the application of a ribose pre-irradiation treatment, which provides a more stable and connected collagen network than found in conventionally irradiated controls.