Radiological outcomes of static and expandable cage placement in minimally invasive oblique lumbar interbody fusion: a retrospective study

A single surgeon, retrospective case series. This study aimed to compare the radiological outcomes after using expandable versus static cages in oblique lumbar interbody fusion (OLIF). OLIF enables access to the spine while avoiding the anterior vessels and psoas muscles via a retroperitoneal corridor. Static cages have been used in this approach; however, they present with limitations, including repeated trialing, resulting in endplate violation and implant subsidence. Patients who underwent OLIF (n=86) were divided into expandable (n=39) and static cage (n=47) groups. Radiographic data were then analyzed preoperatively and postoperatively, including immediate, 3 months, and the most recent follow-up. Cage type predicted the incidence of subsidence, with expandable cages associated with 4.00 and 2.43 fewer instances of subsidence compared with static cages at the postoperative and most recent time points (p<0.05). Cage type was a significant predictor of the change in height in both the posterior disk and foraminal height (FH) models. Expandable cages were associated with improved posterior disk height (DH) expansion at all three time points (1.24 mm, 0.88 mm, and 1.85 mm, respectively; p<0.01), and with larger FH increases at the 3 months postoperatively and most recent follow-up (1.12 mm, 0.40 mm, and 1.28 mm, respectively; p=0.096, 0.016, and 0.030). The expandable cage type was associated with improvement (3.46°, 3.12°, and 3.36°; p<0.01, 0.05, and 0.08, respectively) at the postoperative and 3-month time points when predicting the change in segmental lordosis. No statistically significant differences were found between the groups in disk angle and lumbar lordosis measurements or baseline demographics. The results of this study indicate that both static and expandable cages result in radiographic improvement in posterior DH, segmental lordosis, and FH when used in OLIF. Expandable cages may demonstrate certain advantages over static cages due to lower implant subsidence instances and the greater posterior disk and FH expansion, thereby providing preliminary evidence to support the superiority of expandable cages in OLIF procedures.