Surgical stress and physiological reserve interact to drive postoperative outcomes after arthroplasty: a data-driven framework for risk stratification

Abstract Background Postoperative outcomes following total joint arthroplasty (TJA) vary widely, even amongst similar patients. Existing models often fail to integrate two key factors: surgical stress (procedural burden) and physiologic reserve (the patient’s inherent capacity to withstand stress). This study introduces a framework to quantify both using registry data and evaluates their combined effect on short-term arthroplasty outcomes. Methods We analyzed 187,849 TJA cases from ACS-NSQIP (2021–2023). Using principal component analysis, we derived two indices: a Hemodynamic Stress Index (HSI: operative time, RVUs, transfusions, bleeding, BMI, urgency) and a Physiologic Reserve Score (PRS: age, albumin, creatinine, dialysis, function, comorbidities). Patients were stratified into four quadrants: High Stress/Low Reserve (HS/LR), High Stress/High Reserve (HS/HR), Low Stress/Low Reserve (LS/LR), and Low Stress/High Reserve (LS/HR). Multivariable regression assessed complications (HS/HR as reference). Results Among 187,849 patients, 47,074 were classified as LS/HR, 46,851 as LS/LR, 46,850 as HS/HR, and 47,074 as HS/LR. The 30-day composite complication rate increased across cohorts from 2.89% in LS/HR patients to 5.14% in LS/LR, 5.60% in HS/HR, and 11.28% in HS/LR patients. Using LS/HR as the reference, adjusted odds of complications were higher in LS/LR (adjusted odds ratio [aOR], 1.98; 95% CI 1.85–2.12), HS/HR (aOR, 1.79; 95% CI 1.67–1.91), and HS/LR patients (aOR, 3.70; 95% CI 3.48–3.94; all p < 0.001). The HS/LR cohort also demonstrated increased risk across multiple individual complication domains. Bootstrap validation demonstrated stable PCA loadings and an optimism-corrected area under the receiver operating characteristic curve of 0.636, while temporal validation yielded similar discrimination in the development and validation cohorts (0.637 vs 0.635). Conclusion This quadrant-based framework provides an interpretable approach to perioperative risk stratification by jointly considering procedural stress and physiologic reserve. The observed risk gradients and internal validation support further investigation of this framework; prospective and external validation are required before clinical implementation.