Fusion rate according to mixture ratio and volumes of bone graft in minimally invasive transforaminal lumbar interbody fusion: minimum 2-year follow-up

Abstract

Objectives: Hydroxyapatite (HA) is commonly used as bone substitute in clinical practices. However, only few studies have compared the relationship between the mixture ratio of bone graft in the actual clinical field and fusion rate according to bone graft volume. The study aimed 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).

Methods: A total number of 88 subjects who completed a 2-year follow-up after MI-TLIF participated in this study. Subjects were divided into three groups: Group 1 with local autograft, Group II with a mixture of HA and autobone of over 50%, and Group III with a mixture of HA and autobone of less than 50%. Subjects were also grouped into two groups: Group A with a graft volume of less than 12 ml and Group B with more than 12 ml. The correlation of mixture ratio and the graft volume with fusion rate was analyzed. For clinical analysis, visual analogue scale for pain and Oswestry Disability Index were used. Bone integration was evaluated based on the classification methods described in the Burkus study.

Results: Fusion rates are increased according to the ratio of autograft in all groups: 90.9% in Group I, 87.8% in Group II, and 85.7% in Group III. However, there were no significant differences between groups (p = 0.22). The fusion rates significantly increased as the amount of bone graft increased to over 12 ml, showing 81.5% in Group A and 92.0% in Group B (p = 0.03).

Conclusions: A high rate of fusion was achieved in MI-TLIF in graft volume of more than 12 ml. We therefore recommend at least 12 ml of bone graft volume for successful fusion.