Proximal Junctional Kyphosis in Degenerative Sagittal Deformity After Under- and Overcorrection of Lumbar Lordosis Does Overcorrection of Lumbar Lordosis Instigate PJK?

Study Design. Retrospective study. Objective. To analyze proximal junctional kyphosis (PJK) occurrence and surgical outcomes according to degree of lumbar lordosis (LL) correction relative to pelvic incidence (PI). In addition, risk factors of PJK including LL and sagittal vertical axis (SVA) correction were investigated. Summary of Background Data. PJK is a common complication after adult spinal deformity surgery, and many factors are known to be associated with PJK. However, the effect of degree of LL correction on PJK occurrence is not fully understood. Methods. Eighty-three degenerative sagittal imbalance patients treated with deformity correction and long instrumented fusion to the sacrum with a minimum follow-up of 2 years were studied. Patients were divided into three groups according to their postoperative LL angle relative to PI using the SRS-Schwab classification: Group A (undercorrection, PI-LL> 10(8)), Group B (ideal correction, -10(8)<= 10(8)), and Group C (overcorrection, PI-LL <=-10(8)). Prevalence, classification, and period of PJK occurrence were compared, and radiographic and clinical outcomes were analyzed. In addition, risk factors for PJK were evaluated. Results. Overall PJK prevalence was 36.1% (30/83), and ratio of optimal SVA at postoperative and last follow-up were significantly higher in Group C (P< 0.001, P< 0.001). Nevertheless, there was no significant difference in PJK prevalence among three groups (40% vs. 37.5% vs. 34.1%; P = 0.907). Group C had better clinical outcomes (last follow-up ODI, VAS of LBP) than Group A (10.0 vs. 18.4; P< 0.001 and 1.5 vs. 4.0; P< 0.001). The increases in LL or SVA correction degree were not associated with PJK occurrence (P = 0.304, P = 0.201). Conclusion. Overcorrection showed good surgical outcomes without increasing PJK prevalence. Degrees of LL and SVA correction do not act as risk factors for PJK. Therefore, in adult spinal deformity patients, LL correction greater than PI may be a good choice that can result in better clinical outcomes without increasing risk of PJK.