Prediction of Postoperative Outcomes Following Hip Fracture Surgery: Independent Validation and Recalibration of the Nottingham Hip Fracture Score

Abstract

Objectives: Independent validation of risk scores after hip fracture is uncommon, particularly for evaluation of outcomes other than death. We aimed to assess the Nottingham Hip Fracture Score (NHFS) for prediction of mortality, physical function, length of stay, and postoperative complications.

Design: Analysis of routinely collected prospective data partly collected by follow-up interviews.

Setting and participants: Consecutive hip fracture patients were identified from the Northumbria hip fracture database between 2014 and 2018. Patients were excluded if they were not surgically managed or if scores for predictive variables were missing.

Methods: C statistics were calculated to test the discriminant ability of the NHFS, Abbreviated Mental Test Score (AMTS), and American Society of Anesthesiologists (ASA) grade for in-hospital, 30-day, and 120-day mortality; functional independence at discharge, 30 days, and 120 days; length of stay; and postoperative complications.

Results: We analyzed data from 3208 individuals, mean age 82.6 (standard deviation 8.6). 2192 (70.9%) were female. 194 (6.3%) died during the first 30 days, 1686 (54.5%) were discharged to their own home, 211 (6.8%) had no mobility at 120 days, 141 (4.6%) experienced a postoperative complication. The median length of stay was 18 days (interquartile range 8-28). For mortality, C statistics for the NHFS ranged from 0.68 to 0.69, similar to ASA and AMTS. For postoperative mobility, the C statistics for the NHFS ranged from 0.74 to 0.83, similar to AMTS (0.61-0.82) and better than the ASA grade (0.68-0.71). Length of stay was significantly correlated with each score (P < .001 by Jonckheere-Terpstra test); NHFS and AMTS showed inverted U-shaped relationships with length of stay. For postoperative complications, C statistics for NHFS (0.54-0.59) were similar to ASA grade (0.53-0.61) and AMTS (0.50-0.58).

Conclusions and implications: The NHFS performed consistently well in predicting functional outcomes, moderately in predicting mortality, but less well in predicting length of stay and complications. There remains room for improvement by adding further predictors such as measures of physical performance in future analyses.

Keywords: Hip fracture; calibration; case mix; discrimination; risk score; validation.