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Enhanced healing of segmental tibial defects in sheep by a composite bone substitute composed of tricalcium phosphate cylinder, bone morphogenetic protein, and type IV collagen.

Diaphyseal segmental defects in the tibia of 18 sheep were used to evaluate the healing potential of a composite bone substitute device (CBS) composed of a tricalcium phosphate cylinder (TCP), naturally occurring sheep bone morphogenetic protein (sBMP), and type IV collagen. A total of 100 mg of sBMP and 20 mg of type IV collagen in the high-dose group (CBSH), and 13 mg of sBMP and 2.5 mg of type IV collagen in the low-dose group (CBSL) were adsorbed to TCP cylinders, respectively. TCP cylinders impregnated with type IV collagen alone (TCPC) were used as control. A significantly larger area and more highly integrated intensity of newly formed external callus between CBSH and CBSL or TCPC group were quantified by computerized image analyzer at both 3 and 6 weeks. A torsion test showed that the maximal torque capacity, maximal angular deformation, and bone stiffness of healed osteotomized tibia with implants recovered 117-125% in CBSH, 72-109% in CBSL, and 63-80% in TCPC, compared with the corresponding contralateral tibia at 16 weeks. A healing superiority of the segmental bone defects replaced by the implants was demonstrated in the CBSH group. Thus, the composite bone substitute device defined in this study was shown to possess osteoinductivity, osteoconductivity, and mechanical strength.