Effects Of Gamma Irradiation On Remodeling Of Disc Allografts In A Beagle Model

Objective To explore the feasibility of optimized Gamma irradiation to deal with discallografts, and meanwhile, to assess the property of decellularized disc allografts as thenatural disc scaffold for biological treatment aiming at disc degeneration. Method30mature beagles were used in the vitro and vivo study. Experiment in vitro: Discs wereharvested from6beagles and gradually frozen in RPMI-1640solution, and then dividedrandomly into four groups including a control group (discs with no irradiation) and threeirradiated groups (discs irradiated with doses of18-kGy,25-kGy and50-kGy,individually). The sample size in each group was12. Cell viability checking andbiomechanical test were performed to the discs, and the comparisons among variousgroups were also analyzed. Experiment in vivo:24beagles accepted single-level discallografting, and6discs in each group were transplanted. The study plain X-ray films andMRIs were taken before and after surgery, and at4,12, and24weeks postoperatively. Thespinal columns from L2to S1were harvested en bloc from the sacrificed beagles at theregulated study time, and the discs and columns were examined pathologically andbiomechanically in order to analyze the stability and degeneration of the treated segment.Results①The annulus fibrosus (AF) and nucleus pulposus (NP) cell viability in the control group was92.6%and90.7%, respectively. Accordingly,76.5%and70.6%in18-kGy group,52.7%and46.9%in25-kGy group, and18.3%and10.1%in50-kGygroup. There were significant differences among the various groups (P<0.01).②Therewere no obvious differences of the biomechanical properties among the four groups,whose axial forces and torsional torques were preserved at the normal level (P>0.05).③Radiography showed that the disc height and range of motion (ROM) decreasedsignificantly with time went on (P<0.05). At3months after disc allografting, the observedindexes in the treated groups were much smaller than those in the control group (P<0.05),and the indexes in18-kGy group were bigger than those in the other two treated groups(P<0.05). At6months after disc allografting, the disc height in18-kGy group approachedthe one in the control group (P>0.05), and ROM in18-kGy group was smaller than theone in the control group (P<0.05). Spontaneous fusion was observed at the transplantedsegments in25-kGy and50-kGy groups.④Based on MRI, macroscopic and microscopicfindings at three to six months postoperatively, the consistence among the three discdegenerative classifications was definite. The segmental degeneration in the control and18-kGy group was less severe than that in25-kGy and50-kGy groups.⑤No olisthesisand instability was observed at the treated segment, and the stability of the spine wasconfirmed by the biomechanical test. Conclusion①Optimized Gamma irradiation can beregarded as one the effective sterilization for disc allografts. There was a negativecorrelation between the disc cell viability and the irradiation dose.②The survival rate ofdisc cells correlates negatively with the velocity of disc degeneration. A certain amount ofviable cells are the prerequisite for the biological function of intervertebral disc (IVD).③Disc allografting can rebuild the stability of the spine, and meanwhile, as a naturalscaffold, grafted disc can provide an ideal physiological environment for disc cellproliferation though the long-term effect needs to be further studied.