For a study, the researchers sought to determine whether the number of screws per level and the material/diameter of the rod was linked to the development of proximal junctional kyphosis (PJF). Adult spinal deformity (ASD) surgery can cause PJF, a common and very harmful consequence. The stiffness of posterior spinal structures was linked to an increased incidence of PJF. Patients with ASD were enrolled in the research, with a minimum follow-up of 2 years. Patients with more than or equal to 5 levels of primary fusion with lower instrumented vertebrae (LIV) at the Sacro-pelvis were included. A cutoff of 1.8 (defined by receiver operating characteristic curve (ROC) analysis) was utilized to examine the number of screws per level fused. A total of 504 patients were enrolled in the research. PJF was found in 12.7% of cases. The average number of screws each level was 1.7, with 56.8% of patients having fewer than 1.8 screws per level. There were no differences in T1-pelvic angle or amount of lordosis correction between the low and high screw density groups (both P>0.15). PJF occurred in 17.0% of patients with more than or equal to 1.8 screws per level versus 9.4% of patients with fewer than 1.8 screws per level (P<0.05). Patients with less than 1.8 screws per level had a decreased risk of PJF (odds ratio (OR) 0.48, P<0.05), and a continuous variable for screw density was related with PJF (OR 3.87 per 0.5 screws per level, P<0.05). The likelihood of PJF was decreased in ASD patients receiving long-segment primary fusion to the pelvis with less than 1.8 screws per level. The discovery could have been linked to constructing rigidity. However, other patient and surgeon-specific factors might have caused residual confounding. More biomechanical and clinical research into this relationship was needed.