Risk factors associated with cage retropulsion after lumbar interbody fusion

Cage retropulsion (CR) is a complication following lumbar interbody fusion (LIF). To date, few studies have concentrated on the relative risk factors associated with this complication. This study aimed to identify the CR-associated risk factors.Clinical data of patients who underwent LIF between January 2014 and December 2018 at three medical centers were retrospectively analyzed. Patients were divided into CR group and non-CR (NCR) group according to whether they experienced CR or not. This study analyzed radiological and surgical parameters to identify risk factors associated with CR.The enrolled 823 patients who underwent LIF had a total of 1205 disk levels. There were 387 men and 436 women, with a mean age of 58.8 (range, 33-86) years. The average follow-up time was 16.6 (range, 12-27) months. CR was found in 21 patients (9 men and 12 women, 21 levels). The incidence of CR was higher in patients with osteoporosis than those with a normal bone mineral density (BMD). The cages of retropulsion were all placed at the posterior of disk space by immediately postoperative X-ray or computed tomography (CT) scan. On the contrary, only 35.6% of cages were placed at the posterior of space in the NCR group. Pear-shaped disk was found in 10 of 21 patients in the CR group (47.6%), whereas it was noted in only 13.4% of cases in the NCR group. Furthermore, 13 out of 21 patients in the CR group experienced intraoperative endplate injury (61.9%), while only 13.4% of patients experienced that in the NCR group. Risk factors for CR were osteoporosis, posterior cage position, pear-shaped disk and intraoperative endplate injury.Intraoperative endplate injury, pear-shaped disk, osteoporosis, and posterior cage position were noted as CR-associated risk factors after LIF.