The validation study of preoperative surgical planning for corrective target in adult spinal deformity surgery with 5-year follow-up for mechanical complications

Purpose: We used the Hamamatsu formula as an indicator of correction goals in surgery for adult spinal deformity (ASD). However, it is reported that correction according to Global Alignment and Proportion (GAP) score and the Roussouly algorithm reduces implant-related complications. The purpose of this study was to validate three preoperative plannings for the incidence of complications.

Methods: Patients who underwent ASD surgery and followed up for 5 years were included. The Hamamatsu formula was also divided into three groups: ideal (I), moderate (M), and under (U). The GAP score was divided into three groups: proportioned (P), moderately disproportioned (MD), and severely disproportioned (SD). Patients who met the postoperative Roussouly classification algorithm were defined as the restored (R) group and those who did not were defined as the non-restored (NR) group. Proximal junctional kyphosis (PJK) and rod fractures were investigated.

Results: In the Hamamatsu formula, there were 51, 108, and 44 patients in Groups I, M, and U, respectively, with no significant differences in their complications. In the GAP score, there were 45, 71, and 87 patients in the P, MD, and SD group, respectively, with no significant differences in their complications. In the Roussouly classification, there were 102 and 101 patients in the R and NR group, respectively, with a significant difference in their complication rate (R/NR = 51%:70%; P = 0.005). PJK was significantly lower in the R group (R/NR = 15%:30%; P = 0.010).

Conclusion: Correction according to the Roussouly algorithm is useful for the prevention of mechanical complications, especially PJK.