Study design:

A retrospective study.

Objectives:

To evaluate the impact of upper instrumented vertebra (UIV) orientation including the fused spinopelvic angle (FSPA) on proximal junctional kyphosis (PJK).

Summary of background data:

PJK is a challenging complication after adult spinal deformity (ASD) surgery. Some study proposed UIV orientation act as a risk factor of PJK, but there remain debates because UIV orientation is changed by position. Therefore, we investigated the relationship between the FSPA, a novel parameter for the relationship between UIV and pelvis which did not changed by position, and PJK.

Methods:

ASD patients underwent long-segment fusion to pelvis and followed-up for more than 2 years were included. Comparative analysis was performed on spinopelvic parameters including UIV orientation parameters (UIV slope angle and FSPA) between PJK and non-PJK group. Binary regression analysis was conducted to find out the risk factors for PJK. And correlation analysis was conducted to find out the parameters that affect the FSPA.

Results:

A total of 190 patients were included. PJK incidence was 13.2% (25/190). PJK group showed significantly greater postoperative UIV slope (21.3° vs. 18.8°, P=0.041) and significantly lesser postoperative FSPA (-0.9° vs. 4.5°, P<0.001). In binary regression analysis, only FSPA acted as a risk factor of PJK (odds ratio=0.920, P=0.004). The FSPA has strong positive correlation with pelvic incidence (PI) - lumbar lordosis (LL) (r=0.666, P<0.001) and negative correlation with lordosis distribution index (LDI) (r=-0.228, P=0.004).

Conclusion:

The FSPA is a fixed parameter which is not dependent on position. A reduction of the FSPA increases the risk for PJK. The FSPA can be adjusted through PI-LL and LDI. Thus, surgeons should increase the FSPA by adjusting the PI-LL and LDI during ASD surgery to prevent PJK.