Structural bone allografts are a viable option in reconstructing massive bone defects in patients following musculoskeletal (MSK) tumour resection and revision hip/knee replacements. To decrease infection risk, bone allografts are often sterilised with gamma-irradiation, which consequently degrades the bone collagen connectivity and makes the bone brittle. Clinically, irradiated bone allografts fracture at rates twice that of fresh non-irradiated allografts. Our lab has developed a method that protects the bone collagen connectivity through ribose pre-treatment while still undergoing gamma-irradiation. Biomechanical testing of bone pretreated with our method provided 60–70% protection of toughness and 100% protection of strength otherwise lost with conventional irradiation. This study aimed to determine if the ribose-treated bone allografts are biocompatible with host bone.

The New Zealand White rabbit (NZWr) radius segmental defect model was used, in which 15-mm critically-sized defects were created. Bone allografts were first harvested from the radial diaphysis of donor female NZWr, and treated to create 3 graft types: C=untreated controls, I=conventionally-irradiated (33 kGy), R=our ribose pretreated + irradiation method. Recipient female NZWr (n=24) were then evenly randomised into the 3 graft groups. Allografts were surgically fixed with a 0.8-mm Kirschner wire. Post-operative X-rays were taken at 2, 6, and 12 weeks, with bony healing assessed by a blinded MSK radiologist using an established radiographic scoring system. The reconstructed radii were retrieved at 12 weeks and analysed using bone histomorphometry and microCT. Kruskal-Wallis and Mann-Whitney tests were utilised to compare groups, with statistical significance when p<0.05.

Radiographic analysis revealed no differences in periosteal reaction and degree of osteotomy site union between the groups at any time point. Less cortical remodeling was observed in R and I grafts compared to untreated controls at 6 weeks (p=0.004), but was no longer evident by 12 weeks. Radiographic union was achieved in all groups by 12 weeks. Histologic and microCT analysis further confirmed union at the graft-host bone interface, with the presence of mineralising callus and osteoid. Histomorphometry also showed the bridging external callus originated from host bone periosteum and a distinct cement line between allograft and host bone was present at the union site.

Previous studies have shown that the presence of non-enzymatic glycation end products in bone can impair fracture healing. However, these studies investigated bony healing in the setting of diabetic states. Our findings showed that under normal conditions, ribose pretreated grafts healed at rates similar to controls via mechanisms also seen in retrieved human allografts clinically in use. These findings that grafts pretreated with our method are biocompatible with host bone in the rabbit help to further advance this technology for clinical trials.

Sprains and strains result from collagen fibre overextension. This study investigated changes in the molecular state of collagen due to overextension damage, thereby gaining insight into tissue degeneration and cellular detection of damage. Overextension results in intermolecular and intrafibrillar sliding, detected with x-ray diffraction. Tendon rupture results in increased susceptibility to proteolytic enzymes. These observations and contemporary theory concerning collagen fibre stability lead to the hypothesis that sub-rupture overextension should result in reduced thermal stability of fibrous collagen.

Tendons were harvested from steer tails. Each provided a specimen for control and for overextension. Sub-rupture overextension at 1%/s strain rate was accomplished on a mechanical testing system, under the control of custom software, until the slope of the force-deformation curve was approximately zero (before complete failure). Two loading treatments were tested: one-cycle and five-cycles. Two specimen types were tested: native tendons ± NaBH4 crosslink stabilization. Tendons in each of the four groups (2x2) were paired by originating tail. Thermal stability was assessed in terms of denaturation temperature (Td) using hydrothermal isometric tension testing. Specimens were held at constant length and heated from ambient temperature to 90degC. Td was defined as the temperature where load suddenly increased due to molecular unraveling and attempted shrinkage.

Overextension of native specimens reduced the thermal stability of the collagen (p< 0.0001) and five-cycles had a still greater effect (p=0.03). Td of controls was 64.5±1.0degC (mean±SD). After one-cycle, Td dropped to 63.2±1.0degC and, after five-cycles, Td dropped to 61.8±2.0degC. For stabilised tendons, the effect of multiple cycles was lost (p=0.08) but overstretching decreased Td by ~2degC (p< 0.0001).

This study confirms that the molecular state of collagen is altered by overextension damage, reducing Td by up to 10% of the expected range (37–65degC) in our experiments. This is thought to occur due to intermolecular sliding that liberates specific domains on the molecules, lowering the activation energy for uncoiling. These domains may also be key targets in degeneration and cell-collagen signaling.