Is disc height loss at 1 year predictive of pseudarthrosis and patient-reported outcome measures following anterior cervical discectomy and fusion with structural allograft?

OBJECTIVE The authors sought to determine if postoperative disc height loss is associated with pseudarthrosis following anterior cervical discectomy and fusion (ACDF). They also sought to determine if the amount of postoperative disc height loss is predictive of need for revision for pseudarthrosis, as well as the impact of postoperative disc height loss on patient-reported outcome measures (PROMs) following surgery. METHODS The authors retrospectively identified patients aged > 18 years who underwent primary one- to three-level ACDF with allograft at a single institution with 1-year postoperative lateral and flexion-extension cervical spine radiographs. Logistic regression models and receiver operating characteristic curves were used for analysis. Alpha was set at p < 0.05. RESULTS Anterior or posterior disc height loss >= 2 mm was found in 52.5% of patients. Patients with a loss >= 2 mm were more likely to develop pseudarthrosis (p = 0.021) but not to undergo revision surgery due to pseudarthrosis (p = 0.459). Multivariable analysis identified male sex (OR 1.66, p = 0.013), the number of levels fused (OR 2.09, p < 0.001), and fusion at C6-7 (OR 1.52, p = 0.043) as predictors of disc height loss. The analysis also revealed that levels at the top (OR 0.383, 95% CI 0.170-0.854, p = 0.020) and middle (OR 0.174, 95% CI 0.053-0.548, p = 0.003) of fusion constructs were significant independent predictors of lower pseudarthrosis rates while disc height loss was not. Patients with disc height loss had significantly less improvement in scores for the Neck Disability Index (p = 0.002), visual analog scale (VAS) for arm pain (p = 0.018), and VAS for neck pain (p = 0.011) at 1 year following surgery. CONCLUSIONS This study is, to the authors' knowledge, the largest study to date to assess the impact of postoperative disc height loss after ACDF. Disc height loss following ACDF was not predictive of revision surgery for pseudarthrosis or overall pseudarthrosis rates. However, pseudarthrosis was less likely to occur at the top and middle of fusion constructs. Loss in disc height postoperatively was significantly associated with less improvement in PROMs.