An External Validation of the Pathologic Fracture Mortality Index for Predicting 30-day Postoperative Morbidity Using 978 Institutional Patients.

Introduction: Skeletal metastases increase the risk of pathologic fractures, causing functional impairment and pain. Predicting morbidity in patients undergoing surgical fixation for these fractures is challenging due to the complexity of metastatic disease. The Pathologic Fracture Mortality Index (PFMI) was developed to predict 30-day postoperative morbidity in long bone fractures caused by metastases. External validation is necessary for clinical use. This study aims to evaluate the following: (1) How well does the PFMI predict 30-day medical, surgical, utilization, and all-cause morbidity after pathologic fracture fixation in an external cohort of patients with long bone metastases? (2) How does the performance of the PFMI compare to established predictive indices including the American Society of Anesthesiologists (ASA) classification score, the modified 5-Item Frailty Index (mF-I5), and the modified Charlson Comorbidity Index (mCCI)?

Methods: We analyzed 978 patients who underwent internal fixation for pathologic fractures at two urban tertiary centers. The area under the receiver operating characteristic curve (AUC) was calculated for each predictive index to assess their accuracy in predicting 30-day morbidity across medical, surgical, utilization, and all-cause categories.

Results: All four predictive indices demonstrated suboptimal performance, with AUC values ranging from 0.51-0.62, 0.45-0.51, 0.51-0.62, and 0.50-0.57 for medical, surgical, utilization, and all-cause morbidity, respectively. The PFMI outperformed the ASA (P < 0.001), mF-I5 (P = 0.018), and mCCI (P = 0.034) in predicting utilization morbidity. It also better predicted medical (P = 0.021) and all-cause (P = 0.009) morbidity than ASA but did not outperform mF-I5 or mCCI in these areas. The PFMI did not surpass any indices in surgical morbidity.

Conclusion: None of the indices reached the ideal AUC of 0.80 for any morbidity type, emphasizing the need for refinement. Updating these tools with contemporary data and exploring new prognostic factors is critical to improve morbidity risk stratification in metastatic bone disease.