Development of a data-driven case-mix adjustment model for comparison of hospital performance in hip fracture care

To compare hospitals' hip fracture patient mortality in a quality of care registry, correction for patient characteristics is needed. This study evaluates in 39,374 patients which characteristics are associated with 30 and 90-day mortality, and showed how using these characteristics in a case mix-model changes hospital comparisons within the Netherlands.

Mortality rates after hip fracture surgery are considerable and may be influenced by patient characteristics. This study aims to evaluate hospital variation regarding patient demographics and disease burden, to develop a case-mix adjustment model to analyse differences in hip fracture patients' mortality to calculate case-mix adjusted hospital-specific mortality rates.

Data were derived from 64 hospitals participating in the Dutch Hip Fracture Audit (DHFA). Adult hip fracture patients registered in 2017-2019 were included. Variation of case-mix factors between hospitals was analysed, and the association between case-mix factors and mortality at 30 and 90 days was determined through regression models.

There were 39,374 patients included. Significant variation in case-mix factors amongst hospitals was found for age ≥ 80 (range 25.8-72.1% p < 0.001), male gender (12.0-52.9% p < 0.001), nursing home residents (42.0-57.9% p < 0.001), pre-fracture mobility aid use (9.9-86.7% p < 0,001), daily living dependency (27.5-96.5% p < 0,001), ASA-class ≥ 3 (25.8-83.3% p < 0.001), dementia (3.6-28.6% p < 0.001), osteoporosis (0.0-57.1% p < 0.001), risk of malnutrition (0.0-29.2% p < 0.001) and fracture types (all p < 0.001). All factors were associated with 30- and 90-day mortality. Eight hospitals showed higher and six showed lower 30-day mortality than expected based on their case-mix. Six hospitals showed higher and seven lower 90-day mortality than expected. The specific outlier hospitals changed when correcting for case-mix factors.

Dutch hospitals show significant case-mix variation regarding hip fracture patients. Case-mix adjustment is a prerequisite when comparing hospitals' 30-day and 90-day hip fracture patients' mortality. Adjusted mortality may serve as a starting point for improving hip fracture care.