Different characteristics between acute and delayed proximal junctional failure in elderly patients undergoing corrective surgery for adult spinal deformity: comparative analysis of risk factor, failure mode, and clinical consequences.

Background Context: While numerous studies have been conducted on proximal junctional failure (PJF), the clinical significance of acute and delayed PJF remains poorly understood.

Purpose: The primary object of this study is to investigate the risk factors separately for acute and delayed PJF. Secondly, we aim to assess the incidence of each failure mode and their clinical consequences in relation to acute and delayed PJF.

Study Design/setting: Retrospective comparative study.

Patient Sample: Patients aged ≥60 years who underwent deformity correction with ≥5-level fusion to sacrum.

Outcome Measures: Risk factor, failure modes, and patient-reported outcome measure (PROM).

Methods: Acute PJF is defined as PJF occurring within 6 months, while delayed PJF occurring after 6 months. Risk factors were analyzed by comparing various clinical and radiographic parameters among 3 groups: no, acute, and delayed PJF groups. The failure modes, including soft tissue failure, vertebral fracture, fixation failure, and myelopathy, were compared among these groups. The clinical subsequences after PJF development were evaluated by assessing the change in proximal junctional angle (PJA), revision rate, and patient-reported outcome measure (PROM).

Results: A study cohort of 363 patients was included in the analysis. Among them, 156 patients experienced PJF, with 87 patients (55.8%) in the acute PJF group and 69 patients (44.2%) in the delayed PJF group. Multivariate analyses showed that older age (Odds ratio [OR] = 1.057, 95% confidence interval [CI] = 1.002-1.118), osteoporosis (OR=2.149, 95% CI = 1.074-4.300), high American Society of Anesthesiology ASA score (OR=2.150, 95% CI = 1.089-4.245), and overcorrection relative to the age-adjusted pelvic incidence - lumbar lordosis target (OR=4.031, 95% CI = 1.962-8.280) were identified as risk factors for the development of acute PJF. On the other hand, a high body mass index (OR=1.150, 95% CI = 1.049-1.251) and an uppermost instrumented vertebra located at ≤T10 (OR=2.267, 95% CI = 1.205-4.268) were found to be associated with delayed occurrence of PJF. No radiographic parameters were found to be related to the development of delayed PJF. In terms of failure modes, vertebral fracture and fixation failure were more commonly observed in acute PJF, while soft tissue failure and myelopathy were more predominant in delayed PJF. The clinical course was more aggressive in the acute PJF group compared to the delayed PJF group, as evidenced by a greater increase in PJA, a higher revision rate, and worse PROM.

Conclusions: This study demonstrated different risk factors between the acute and delayed PJF. It was found that overcorrection relative to the age-adjusted PI-LL target increased the risk of acute PJF, but had no impact on the development of delayed PJF. Therefore, a different surgical strategy needs to be established to mitigate both acute and delayed PJF.