Fig. 4

A A 57-year-old man underwent L3–S1 fusion with screws and cages. An initial postoperative X-ray showed good locations of the implants. B One month after the surgery, a follow-up X-ray showed posterior migration of the L5–S1 cage and suspected concurrent S1 screw loosening. C, D, E Magnetic resonance imaging revealed large amount of fluid accumulation in the L3–S1 subfascial, epidural, posterolateral regions, and L4–L5 disc space. F, G Posterior-alone surgery with extension of the distal instrumented level, removal of the L5–S1 cage, and L5–S1 TLIDF with allograft were performed. An initial postoperative X-ray showed good alignment. H One year later, an X-ray revealed L5–S1 solid interbody union, and the infection was well controlled.