The Study Of A PLA/Nano-sized β-TCPbioabsorbable Self-retaining Cervical Spine Interbody Fusion Cage

Part Ⅰ:Degradation and osteogenic potential of a novel poly (lactic acid)/nano-sized β-tricalcium phosphate scaffoldObjective:The purpose of this study was to investigate the influence of nano-sized β-tricalcium phosphate (β-TCP) on the biological performance of poly (lactic acid)(PLA) composite scaffolds by using in vitro degradation and an in vivo model of heterotopic bone formation.Methods:Nano-sized β-TCP (nβ-TCP) was prepared with a wet grinding method from micro-sized P-TCP (mβ-TCP), and composite scaffolds containing0,10,30,50wt%nβ-TCP or30wt%mβ-TCP were generated using a freeze-drying method. Degradation was assessed by monitoring changes in microstructure, pH, weight, and compressive strength over26weeks period of hydrolysis. Composite scaffolds were processed into blocks, and implanted into muscular pockets of rabbits after loading with recombinant human bone morphogenetic protein-2(rhBMP-2). New bone formation was evaluated based on histological and immunohistochemical analysis2,4, and8weeks after implantation.Results:The in vitro results indicated the buffering effect of np-TCP was stronger than mβ-TCP, which was positively correlated with the content of nβ-TCP. The in vivo findings demonstrated that nβ-TCP enhanced the osteoconductivity of the scaffolds. Although composite scaffolds containing30%nβ-TCP exhibited similar osteoconductivity to50%nβ-TCP, they had better mechanical properties than the50%nβ-TCP scaffolds.Conclusions:This study supports the potential application of a composite scaffolds containing30%nβ-TCP as a promising scaffold for bone regeneration in cervical fusion. Part II:The biomechanical stability of a bioabsorbable self-retaining PLA/nano-sized β-TCP cervical spine interbody fusion device in single level ACDF sheep modelsPurpose:The aim of this study was to investigate the biomechanical stability provided by a novel PLA/nano-sized β-tricalcium phosphate (β-TCP) bioabsorbable self-retaining cervical fusion cage (BCFC).Methods:Quasistatic nonconstraining torques (maximum1.5NM) induced flexion, extension, lateral bending (±1.5NM), and axial rotation (±1.5NM) on32sheep cervical spines (C2-C5). The motion segment C3-C4was firstly tested intactly, the following groups were tested after complete discectomy:autologous tricortical iliac crest bone graft, Medtronic-Wego PEEK cage, Solis PEEK cage, and BCFC. Further, the group of autologous bone graft was tested with anterior plate. The mean range of motion (ROM) was calculated from the load-displacement curves.Results:BCFC significantly decreased ROM in lateral bending and axial rotation compared to other implants, and no significant difference in ROM between two types of PEEK cages and BCFC could be observed in flexion and extension. ACP significantly decreased ROM in flexion and extension, but no significant difference in ROM between BCFC and bone graft plus ACP could be determined in lateral bending and axial rotation.Conclusions:BCFC device showed better stability to autologous tricortical iliac crest bone graft and PEEK cages in single level ACDF models, it may be a potential alternative to the current PEEK cages. Part Ⅲ:Evaluation of a bioabsorbable self-retaining PLA/nano-sized β-TCP cervical spine interbody fusion device in goat cervical spine modelsPurpose:The aim of this study was to investigate the effect of a novel PLA/nano-sized β-tricalcium phosphate (β-TCP) bioabsorbable self-retaining cervical fusion cage (BCFC) in goat cervical spine models.Methods:Eighteen goats underwent C3-C4discectomy were randomely divided into3groups by the following methods:group A (n=6), autologous tricortical iliaccrest bonegraft; group B (n=6), Medtronic-Wego PEEK cage filled with autologous graft; group C (n=6), BCFC filled with autologous iliac bone. Radiography was performed pre-and post-operatively andl,4,8, and12weeks after operation, espectively. Disc space height (DSH), intervertebral angle (IVA), andlordosis angle (LA) were measuredin auterior, posterier and ateral viewat the sametimepoints. After12weeks, the goats were sacrificed and fused-segments were arvested, specimens were analyzed in histomorpholoy after the biomechamical study was performed.Results:The ROM of autologous tricortical iliac crest bone graft was significantly greater than that of the Medtronic-Wego PEEK cage and BCFC group (P<0.05). Rradiographic evaluations showed better result in Medtronic-Wego PEEK cage and BCFC group than autologous tricortical iliaccrest bone graft group.Conclusions:BCFC device showed better result to autologous tricortical iliac crest bone graft and PEEK cages in single level ACDF models in vivo, it may be a potential alternative to the current PEEK cages.