Risk Factors Associated with Cage Retropulsion After Lumbar Interbody Fusion

AIM: To identify the cage retropulsion (CR)-associated risk factors following lumbar interbody fusion (LIF). MATERIAL and METHODS: 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 the risk factors associated with CR. RESULTS: 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 old. 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). Besides, 14 patients complained of radicular pain postoperatively, of whom 10 patients were recovered after conservative treatment, while the remaining 4 patients further required revision surgery. The mean age was 62.3 +/- 8.1 (range, 44-74) years old in the CR group and 59.7 +/- 9.7 (range, 33-86) years old in the NCR group. The incidence of CR was higher in patients with osteoporosis than those with a normal bone mineral density (BMD). Moreover, 12 of 21 patients had osteoporosis (57.1%), however, only 29.2% of patients without CR had osteoporosis. The cages of retropulsion were all placed at the posterior 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 disk 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 [odds ratio (OR)=8.7, 95% confidence interval (CI) (3.42-34.6), P=0.01], posterior cage position [OR=5.8, 95%CI (2.12-24.6), p=0.03], pear-shaped disk [OR=9.9, 95%CI (6.21-46.42), p<0.001], and intraoperative endplate injury [OR=9.9, 95%CI (6.21-46.42), p<0.001]. CONCLUSION: Intraoperative endplate injury, pear-shaped disk, osteoporosis, and posterior cage position were noted as CRassociated risk factors after LIF.