Risk factors for subsidence and loss of segmental lordosis segmental lordosisfollowing 1–3-level anterior cervical diskectomy and fusion for degenerative disease: A time-to-event analysis

BACKGROUND: Thousands of anterior cervical diskectomy and fusion (ACDF) procedures are performed annually. Increased interbody size offers better immediate segmental lordosis and disc height restoration but may increase the risk of subsequent subsidence. Our objective was to identify factors for subsidence and segmental lordosis loss following ACDF.

METHODS: The charts of patients undergoing 1-3 level ACDF at a single-institution were queried for demographics, pre- and postoperative radiographic alignment, bone health (Hounsfield units on CT), procedural details, and interbody characteristics. Outcomes of interest were subsidence ≥2 mm and ≥3° loss in segmental lordosis (SL).

RESULTS: 199 patients (median 61.5 yr; 52.8 % male) were included - 98 single-level; 70 two-level, and 31 three-level. Forty treated levels (12.1 %) ≥3° decrease in SLand 19 (5.7 %) experienced ≥2 mm subsidence. Levels showing ≥3° loss of correction occurred in older patients (p = 0.021) and those with greater postoperative C2-7 lordosis (p = 0.002), postoperative SL (p < 0.001), and perioperative change in SL (p < 0.001). Subsidence was associated with allograft spacer use, lower postoperative segmental lordosis (p = 0.022) and greater postoperative disc height (p = 0.023). Decreased time to loss of SL was predicted by greater postoperative C2-7 lordosis (HR 1.04 per °; 95 % CI [1.00, 1.08]; p = 0.041) and greater postoperative SL (HR 1.27 per °; [1.13, 1.43]; p < 0.001). Shorter subsidence time was predicted by allograft [versus titanium] spacer use (HR 21.40; [5.61, 81.54]; p < 0.001) and greater postoperative disc height (HR 1.63 per mm; [1.37, 1.94]; p < 0.001).

CONCLUSION: Greater disc height predicted subsequent subsidence and greater SL restoration predicted SL loss following 1-3 level ACDF. Matching the interbody to the "natural" disc height of adjacent levels and using titanium versus corticocancellous allograft spacers may reduce the risk of subsidence and loss of correction.