Reoperation Risk by Subtype in Proximal Junctional Kyphosis and the Impact of Osteoporosis Treatment in Adult Spinal Deformity Surgery

Purpose Proximal junctional kyphosis (PJK) is a common mechanical complication following adult spinal deformity (ASD) surgery. Although various preventive strategies exist, the clinical relevance of PJK subtypes and the impact of osteoporosis medications remain unclear. This study examined which PJK subtypes and grades are most associated with reoperation and evaluates whether osteoporosis treatment, particularly teriparatide, affects PJK incidence or severity. Methods This retrospective study included 189 patients who underwent long spinal fusion for ASD. PJK was classified by type (0–3) and grade (0–C). Osteoporosis medication use and bone mineral density (BMD) were recorded. Reoperation rates were compared across subtypes and treatment groups using the chi-square test and analysis of variance. Results Type 2 (vertebral fracture) and Type 3 (implant failure) PJK were significantly associated with higher reoperation rates (p < 0.0001). Patients with lower BMD exhibited a significantly higher prevalence of Type 2 PJK (p = 0.0082), whereas teriparatide users showed a significantly lower incidence of Type 2 PJK (p = 0.0141 vs. Type 0) as well as a trend toward fewer reoperations. Preoperative teriparatide administration was linked to the lowest revision rate among treatment groups. Conclusion PJK subtype and BMD strongly predicted reoperation after ASD surgery. Teriparatide may reduce structural PJK risk, especially when used preoperatively. Prevention strategies should be tailored to PJK subtype and bone quality.