Imaging-Based Quantitative Assessment of Cage Migration After Minimally Invasive Lumbar Interbody Fusion

Background/Objectives: Posterior cage migration is a clinically relevant complication after lumbar interbody fusion. Most reported risk factors are derived from open techniques, whereas evidence specific to minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) is limited. We evaluated factors associated with cage migration and symptomatic retropulsion in a large MIS-TLIF cohort. Methods: We retrospectively reviewed 650 consecutive patients undergoing MIS-TLIF, comprising 1126 fused motion segments. Cage migration was defined as posterior displacement > 3 mm compared with early postoperative radiographs. Demographic, clinical, surgical, and radiographic variables were compared between segments with and without migration. Cases with migration were further stratified by revision requirement. Results: Cage migration occurred in 27 of 1126 levels (2.4%). Seven cases required revision surgery for symptomatic cage retropulsion, corresponding to a level-based incidence of 0.6%. More posterior initial cage placement was significantly associated with subsequent migration. Age, body habitus, smoking, diabetes, endplate violation, and multilevel fusion were not associated with migration. Among migration cases, male sex was associated with higher odds of revision, and no radiographic or mechanical parameter predicted progression from radiographic migration to symptomatic retropulsion. In revision cases, the migrated cage was removed via the original approach, followed by contralateral placement of a new interbody cage using a minimally invasive technique. Conclusions: In this MIS-TLIF cohort, posterior initial cage placement was the primary factor associated with cage migration, consistent with prior open-series findings. Progression from migration to symptomatic retropulsion was not explained by mechanical parameters alone, suggesting a multifactorial process. These findings underscore the importance of meticulous cage positioning during MIS-TLIF and provide practical insights for postoperative surveillance and revision decision-making.