Introduction: Proximal junctional kyphosis (PJK) is a common complication of adult spinal deformity (ASD) surgery. If symptomatic, it can broadly impact patient outcomes, resulting in pain and a spectrum of neurological deficits. The etiology of PJK is multifactorial and ill-defined, stemming from numerous surgical and patient-related variables. Poor bone quality, which has been suggested as a potential risk factor for PJK, is frequently measured by dual-energy X-ray absorptiometry (DEXA) scans and Hounsfield units (HU). This study aims to further elucidate the effect of bone quality, assessed through DEXA and HU, on the incidence of PJK.
Methods: This is a single institution retrospective review of patients who underwent surgery for ASD between 2016 and 2023. We collected data including patient demographics, DEXA T-scores, bone mineral density (BMD), and HU at the upper instrumented vertebra (UIV) and at the UIV+1. We then measured the incidence of PJK and performed independent sample t tests analysis using SPSS to determine risk factors for PJK.
Results: A total of 265 patients underwent ASD correction. HU measurements at the UIV and UIV+1 was available for 151 and 164 patients, respectively, while T-scores were available for 122 patients. HU at the UIV were lower in the PJK group when compared to the non-PJK group (150.9 vs 167.9 p = 0.187), although not statistically significant. In contrast, the difference in HU at the UIV+1 (142.8 vs 170.1, p=0.05) was significant. This trend, however, was not observed in DEXA scans or BMD values, with nearly identical average T-scores (-0.636 vs. -0.698, p = 0.425) and BMD values (0.948 vs. 0.957, p = 0.485) between those who did and did not develop PJK.
Conclusion : This study demonstrates that lower HU at the UIV+1 may be a risk factor for PJK development. While lower HU at the UIV showed a similar trend, it did not reach statistical significance. Further research involving larger, multicentric cohorts is needed to better define the role of HU and establish a threshold that may predict the risk of PJK.
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