Although the definition of nonunion of the spine is still controversial, many studies have defined it as failure of solid fusion at least 1 year post-surgery [[1], [2], [3]]. For lumbar spine fusion surgery, the reported nonunion rate varies from 0% to 56% [4]. Although some patients with nonunion are asymptomatic, nonunion is usually painful and, can change alignment, and cause instability in severe cases. Therefore, it is important to obtain a solid union during spinal fusion surgery.

Oblique lateral interbody fusion (OLIF) is a novel minimally invasive surgical technique widely used for the treatment of degenerative lumbar diseases [5]. OLIF can achieve a larger fusion bed with greater intervertebral space access, use of larger cages, more sufficient discectomy, and better end-plate preparation than posterior interbody techniques. Due to these advantages, it is expected that the fusion rate of OLIF is likely to be high; however, the actual fusion rate is not different from that of other interbody fusions [[6], [7], [8]].

Various factors such as old age, smoking, osteoporosis, revision surgery, and multiple operative level are known risk factors for nonunion in lumbar fusion surgery [[9], [10], [11], [12]]. However, the subjects of these studies were mostly patients who underwent posterolateral fusion or posterior approach interbody fusion, such as posterior lumbar interbody fusion or transforaminal lumbar interbody fusion, and there were few studies of factors affecting nonunion in OLIF. Therefore, this study aimed to identify the demographic, surgical, and radiological factors influencing nonunion following OLIF.