Interbody cage subsidence after ACDF: a predictor of non-union and neck pain despite normal bone mineral density.

This study aimed to evaluate the association between preoperative bone mineral density (BMD) and cage subsidence following anterior cervical discectomy and fusion (ACDF), and to assess the impact of subsidence on fusion rates and clinical long term-outcomes.We retrospectively reviewed records of patients who underwent ACDF for degenerative cervical disc disease over an 11-year period. Preoperative cervical spine CT scans were analyzed to quantify BMD, while postoperative radiographs were used to identify cage subsidence. Binary logistic regression was used to identify association of radiographic and clinical outcome parameters. A total of 102 patients were included. Cage subsidence occurred in 19.6% of patients. Median BMD was 222.6 mg/cm3 among patients with cage subsidence and 232.6 mg/cm3 in the non-subsidence group (p = 0.505). Fusion was observed significantly more often in the non-subsidence group (p = 0.004). Binary logistic regression showed that cage subsidence was negatively associated with segment fusion in patients treated with stand-alone cages (OR 9.444; p = 0.0002) and was associated with overall higher revision surgery rates (OR 4.879; p = 0.012). Furhtermore, non-union of the segment was significantly associated with worsening neck pain (OR 3.182; p = 0.024), but had no effect on mJOA scores (p = 0.360) or arm pain (p = 0.243). Contrary to previous findings in the lumbar spine, bone mineral density was not associated with cage subsidence in ACDF. In stand-alone cage constructs, subsidence was linked to non-union, contributing to persistent neck pain and increased revision surgery rates.