Effects of Polyphosphate on the Fusion of Rabbit Lumbar Spine / 대한척추외과학회지

ABSTRACT

STUDY DESIGN: Posterior and posterolateral fusions were performed in rabbit lumbar spines. OBJECTIVES: To investigate the osteoinductive effect of polyphosphates. SUMMARY AND LITERATURE REVIEW Inorganic polyphosphates are known to be rich in osteoblasts and involved in the mineralization process in bone metabolism. However, no study has been undertaken to investigate the osteoinductive effect of polyphosphates. MATERIALS AND METHODS: Forty adult New Zealand white rabbits underwent monolevel lumbar fusions, and were divided into two groups according to the fusion beds twenty each between the laminae (posterior fusion group, PF group) and between the transverse processes (posterolateral fusion group, PLF group). In ten of twenty rabbits in the PF group, 0.8gm of autogenous iliac bone was grafted onto the right sides of the laminae, which were used as a control group (C1), with 0.4gm autogenous bone immersed in polyphosphate solution in the left sides as an experimental group (E1). In the other ten, 0.8gm of autogenous bone was grafted onto the right sides (C2) and 0.8gm of tricalcium phosphate porous blocks containing polyphosphate in the left sides (E2). The other twenty rabbits of the PLF group were similarly divided into C1, E1, C2 and E2 groups by grafting the same amount of materials between the transverse processes. The animals were sacrificed at the 16th postoperative week and the fusions evaluated grossly, radiologically and histologically. Statistical differences between the groups (C1 vs. E1, C2 vs. E2 and E1 vs. E2) in each of the PF and PLF groups were compared by chi-square tests. RESULTS: The fusions were finally determined by the gross finding using manual palpation. In the PF group, bony fusions were obtained in 90, 80, 90 and 70% of the C1, E1, C2 and E2 groups, respectively. In the PLF group, these were 80, 70, 60 and 0% of the C1, E1, C2 and E2 groups, respectively. Statistical analysis revealed differences only between C2 and E2 (p=0.005), and between E1 and E2 (p=0.002) of the PLF group. Histologically, beta-tricalcium phosphate particles containing polyphosphate were transformed into the osteoid in some areas of the PLF-E2 group, although only fibrous unions were obtained grossly. CONCLUSIONS: It is suggested that the polyphosphate may have an osteoinductive effect, even though the osteoinductive potency was very week in this fusion model of the rabbit lumbar spine. Therefore, further explorations, such as the threshold and optimal concentrations of polyphosphate in vivo and the best carrier material of polyphosphate, should be performed to obtain the optimal conditions for fusion.