Difference of Fusion Rate in Minimally Invasive Transforaminal Lumbar Interbody Fusion with Autobone and Hydroxyapatite according to Mixture Ratio and Amount of Bone Graft.

Purpose: The aim of this study is to analyze the fusion rate according to the mixture ratio and the amount of bone graft in minimally invasive transforaminal lumbar interbody fusion (MI-TLIF). Materials and Methods: This study included 92 subjects who underwent MI-TLIF. Patients were classified into either group I, in which patients received transplantation with only autogenous bone, group II, in which patients received transplantation with hydroxyapatite mixed with autogenous bone by more than 50%, or group III, in which patients received transplantation with hydroxyapatite mixed with autogenous bone by less than 50%. For analysis of the correlation of amount of bone graft with fusion rate, patients were divided into group A, having less than 12 ml of bone graft, and group B, having more than 12 ml of bone graft. Visual analogue scale and Oswestry disability index were used for clinical assessment, and Burkus' classification method was used for evaluation of bone fusion. Results: Fusion rates of groups I, II, and III according to the mixture ratio were 90.9%, 86.5%, and 86.2%, respectively. The fusion rate increased as the autobone ratio became higher; however, no significant difference was found (p=0.16). The fusion rates were 81.5% and 92.5% in group A and group B, respectively, which were classified according to the volume of bone graft, showing a significant increase in groups with bone graft volume more than 12 ml (p=0.03). Conclusion: A significantly high fusion rate was observed when bone graft volume was more than 12 ml in MI-TLIF. More than 12 ml of bone graft volume is essential for achievement of a satisfactory fusion rate [ABSTRACT FROM AUTHOR]