Subsidence induced recurrent radiculopathy after staged two- level standalone endoscopic lumbar interbody fusion with a threaded cylindrical cage: a case report

We report a case of subsidence induced recurrence of unilateral L5 and S1 radiculopathy six months following a successful staged two-level endoscopic standalone lumbar interbody fusion using the VARILIF-L^TM device. The patient was a 64-year-old female who first underwent outpatient endoscopic fusion L4/5 for failed non-operative care of Grade I spondylolisthesis. Within 11 months from the L4/5 index procedure, she developed symptomatic adjacent segment disease stemming from the L5/S1 level. A preoperative computed tomography before the planned L5/S1 endoscopic standalone VARILIF^TM fusion 15 months following her L4/5 VARILIF^TM procedure revealed fusion at the L4/5 level with minimal subsidence of the VARILIF-L^TM implant, and advanced degeneration of the L5/S1 motion segment with lateral recess and foraminal stenosis, reduced posterior disc height, and vacuum disc. The patient underwent uneventful L5/S1 endoscopic standalone fusion using the VARILIF-L^TM implant with successful clinical outcome and resolution of back and leg symptoms. Six months after the second endoscopic L5/S1 VARILIF^TM procedure she developed recurrent L5 and S1 radiculopathy. Computed tomography showed significant implant subsidence and formation of a large soft tissue bulge on the approach side behind the interbody fusion cage. The subsidence induced subsidence and loss of posterior disc height and the associated recurrence of nerve root compression of the traversing S1 and exiting L5 nerve root. The recurrent radiculopathy was eventually treated with another transforaminal endoscopic decompression which included a more generous foraminoplasty with resection of the remaining superior articular process including a partial S1 pediculectomy and additional resection of the posterior annulus as well as scar and bony tissue that had formed within the axillary hidden zone of Macnab. We concluded that recurrent radiculopathy might occur after standalone lumbar transforaminal endoscopic interbody fusion with an expandable threaded cylindrical cage as a result of vertical and angular subsidence.