Purpose: To demonstrate the over-widening phenomenon (OWP) that can cause rod fracture (RF) when performing deformity corrective surgery using anterior column realignment (ACR) in patients with degenerative sagittal imbalance (DSI).

Materials and Methods: 199 patients diagnosed with DSI and underwent deformity correction using ACR were retrospectively analyzed. Finally, 35 patients with OWP (Group I) and 63 patients without ODP (Group

II) were compared. OWP was defined as the upper or lower endplate of the cage does not meet the endplate of the adjacent vertebral body at all. Demographic data, radiologic sagittal spinopelvic parameters, and perioperative factors were analyzed. Additional statistical analyses were performed to identify risk factor for the development of RF.

Results: The incidence of RF [I; 23 (65.7%) vs II; 24 (38.1%)] and subsequent revision surgery [I; 13

(56.5%) vs II; 3 (14.3%)] was significantly higher in patients in Group I than in patients in Group II. The postoperative L4-S1 lordosis was significantly greater in Group II patients than in Group I patients, and the postoperative lordosis distribution index (LDI) in Group I was confirmed to be 43.5%, which was lower than the ideal 50-80%, and this was significantly smaller than the postoperative LDI of 57.7% in Group

II. Logistic regression analysis showed that OWP was a significant risk factor for the development of RF (OR: 1.09, 95% CI: 1.01-1.19, p =0.028).

Conclusions: In patients with DSI, the suboptimal LDI after deformity correction using ACR causes an OWP, which is thought to be a risk factor for RF.