Dorsal spinal instrumentation in multiple myeloma: postoperative acute kidney injury is associated with mortality, morbidity, and deterioration of bone and muscle status.

backgroundPatients with multiple myeloma undergoing dorsal spinal instrumentation for malignant spinal lesions remain at high risk for postoperative complications and limited survival. Acute kidney injury (AKI) is common in myeloma and after major surgery, but its prognostic relevance in surgically treated myeloma patients and its association with subsequent CT-based body composition and bone density trajectories, remains insufficiently defined.

methodsWe performed a retrospective cohort study of consecutive multiple myeloma patients undergoing dorsal spinal instrumentation between 2011 and 2024 at a tertiary referral center. Postoperative AKI was defined and staged according to KDIGO criteria based on serum creatinine changes within 7 postoperative days. Clinical outcomes included overall survival (OS), surgical site infection (SSI), and length of hospital stay (LOHS). CT-based morphometry was assessed on non-contrast whole-body CT at L3 level on a preoperative baseline scan (tCT1) and a postoperative follow-up scan. The follow-up CT scan (tCT2) was obtained approximately 9 months postoperatively as part of routine oncologic follow-up or clinical indication rather than a fixed imaging schedule, reflecting real-world clinical practice. The mean interval between tCT1 and tCT2 was 9.1 ± 1.2 months. Analysis included skeletal muscle index (SMI), skeletal muscle density (SMD), visceral adipose tissue (VAT), and vertebral trabecular bone status assessed by Hounsfield Units (HU). Multivariable Cox regression, logistic regression, and log-linear regression were used to evaluate the independent association of AKI with OS, SSI, and LOHS, adjusting for clinically relevant covariates.

results59 patients were included (median age 69.0 years; 40.7% female); postoperative AKI occurred in 16 patients (27.1%). AKI was associated with significantly worse OS (median 224 vs. 396 days without AKI; log-rank p = 0.01), with progressively shorter OS across KDIGO stages. In multivariable Cox regression, AKI remained independently associated with worse OS (adjusted hazard ratio 2.35, 95% CI 1.22-4.54; p = 0.011). AKI was also associated with higher SSI rates (63% vs. 12%; p < 0.01) and longer LOHS (median 29 (IQR 8) vs. 19 (IQR 9) days; p < 0.001). After adjustment for age, sex, preoperative ECOG, and Charlson Comorbidity Index, AKI remained independently associated with higher SSI rates (adjusted odds ratio 3.20, 95% CI 1.11-9.26; p = 0.031) and prolonged hospitalization (LOS ratio 1.34, 95% CI 1.06-1.69; p = 0.014). Longitudinal CT analyses demonstrated significantly greater postoperative declines in the AKI group versus no AKI for SMI (median - 44.6% vs. -18.5%; p < 0.001), SMD (- 20.5% vs. -9.2%; p = 0.02), VAT (- 29.1% vs. -24.1%; p < 0.001), and HU (- 46.2% vs. -37.7%; p < 0.001).

conclusionsIn multiple myeloma patients undergoing dorsal spinal instrumentation, postoperative AKI is independently associated with reduced survival, increased postoperative morbidity, and accelerated loss of muscle quantity, muscle quality, visceral fat, and vertebral bone density. These findings highlight AKI as a clinically meaningful systemic event with downstream catabolic consequences and support intensified perioperative nephroprotective and multidisciplinary supportive strategies in this high-risk population.