Strengthening the Core to Reduce Risk: Can We Mitigate Proximal Junctional Kyphosis Through Central Sarcopenia Management?

Introduction: Success of adult spinal deformity (ASD) surgery is known to be impacted by demographics, spinopelvic parameters, and bone quality. Recently, studies have suggested central sarcopenia can predict development of proximal junctional kyphosis (PJK). This theory is understudied despite its potential utility in patient surgical candidacy assessment. We aimed to determine the impact of central sarcopenia in development of PJK following ASD surgery.

Methods: We conducted a retrospective review of all ASD surgeries at our tertiary care center from 2016-2023. Looking at axial MRI images, we used ImageJ to calculate the psoas and L4 vertebral index (PL4VI) as a measure of central sarcopenia. We also collected these measurements at the psoas upper instrumented vertebral index (PUIVI) if that level was flanked by the psoas muscles (i.e. L1-L4). PJK incidence was collected based on both radiology reports and post-operative clinic synopses. A Pearson correlation coefficient was calculated using SPSS.

Results: We collected data on 265 patients (average age 65±9.8 years), with 79 patients having fusions starting at L1-L3 for PUIVI measurement and 168 having available imaging for PL4VI measurement. In total, 24 patients developed PJK (9.1%) and 36 required revision surgery (13.8%). There was no significant relationship between the PUIVI (r=-0.099, p=0.373) or PL4VI (r= -0.018, p=0.801) and PJK. Additionally, while the calculated PUIVI (Pearson correlation -0.109, p=0.327) and PL4VI (r =0.002, p=0.981) did not significantly relate to the need for revision surgery, the L4 surface area (r = 0.187, p=0.009) and, L4 left psoas surface area (r = 0.158, p=0.029) were found to be significantly associated with an increased risk for a revision surgery. Lower UIV left psoas surface area (r =-0.968, p=0.032) was significantly associated with a decreased time to a revision surgery. The UIV surface area was significantly related to PJK (r = 0.25, p=0.02).

Conclusion : Although central sarcopenia calculations at the UIV nor L4 level significantly predicted PJK or the need for a revision surgery, there was a relationship between L4 surface area, UIV surface area, and L4 psoas surface area in patients that required revision surgery or developed PJK, suggesting both muscle and bone quality can impact PJK development.