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. 2025 Feb 24:17:167-176.
doi: 10.2147/CLEP.S507252. eCollection 2025.

Interaction Between Multimorbidity and Hip Fracture Surgery Leads to Excess Risk of Infection: A Danish Registry-Based Cohort Study of 92,599 Patients With Hip Fracture

Cecilia Majlund Hansen  1 , Nadia R Gadgaard  1 , Christina Vandenbroucke-Grauls  1   2 , Nils P Hailer  3 , Alma Becic Pedersen  1   4
Affiliations

Interaction Between Multimorbidity and Hip Fracture Surgery Leads to Excess Risk of Infection: A Danish Registry-Based Cohort Study of 92,599 Patients With Hip Fracture

Cecilia Majlund Hansen et al. Clin Epidemiol. .

Abstract

Purpose: Infection in general is a frequent and serious complication after hip fracture (HF) surgery. Multimorbidity in HF patients is associated with elevated infection risk. It remains unclear whether multimorbidity interacts with HF surgery to increase infection risk beyond their individual effects.

Methods: Using Danish registries, we identified 92,599 patients ≥65 years surgically treated for HF 2004 to 2018 and an age- and sex-matched comparison cohort from the background population without HF (n=462,993). Multimorbidity was defined using the Charlson Comorbidity Index in categories no, moderate, or severe. We computed incidence rates (IR) of any kind of hospital-treated infection within 1 month and 1 year with 95% confidence intervals and estimated the attributable proportion (in %) based on differences in IRs.

Results: The IR of infection within 1 month was 181 (176-186) per 100 person years in HF patients with no multimorbidity and 9 (95% CI 8-9) in the comparison cohort with no multimorbidity. The IRs were 240 (234-246) and 302 (291-313) in HF patients with moderate and severe multimorbidity compared with 17 (16-18) and 31 (30-33) in the comparison cohort with same multimorbidity level. The attributable proportion indicates that 21% and 33% of the IR among HF patients with moderate and severe multimorbidity, respectively, was explained by interaction. Similar interactions were observed within 1 year.

Conclusion: Multimorbidity and HF surgery interact synergistically, which substantially increases the infection risk. The interaction effect increased with multimorbidity level. Our findings highlight the potential benefits of implementing more targeted and personalized preventive initiatives for multimorbid patients.

Keywords: comorbidity; epidemiology; hip fracture; infection; interaction; multimorbidity.

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Conflict of interest statement

CMH reports personal fees from Sygehus Lillebælt Orthopedic Department, outside the submitted work. NRG, CMVG and ABP are salaried employees as Aarhus University or Aarhus University Hospital. The Department of Clinical Epidemiology, Aarhus University, receives funding for other studies from companies in the form of research grants to and administered by Aarhus University. None of these studies have any relation to the present study. NPH reports contracts or grants from Swedish Research Council, Stiftelsen Promobilia, Skobranschens utvecklingsfond, and Waldemar Link and has affiliations with the Swedish National Board of Health and Welfare, Swedish Arthroplasty Register, Nordic Association of Arthroplasty Registers, and Biobank Sweden. No contracts, grants or affiliations reported by NPH present any conflict or have any relation to the present study. He also reports personal fees from DePuy Johnson Johnson, Warsaw, Indiana, USA, personal fees from Zimmer Biomet, Winterthur, Switzerland, personal fees from Heraeus Medical, Wehrheim, Germany, outside the submitted work. The authors report no other conflicts of interest in this work.

Figures

Figure 1
Figure 1
Interaction effect between Hip fracture surgery and multimorbidity on absolute scale based on stacked incidence rates.
Figure 2
Figure 2
Adjusted hazard ratios (HR) for risk of infection comparing Hip fracture patients with no, moderate and severe multimorbidity, as well as comparison cohort with moderate and severe multimorbidity with the comparison cohort with no multimorbidity as a reference, and attributable fraction (AF).
See this image and copyright information in PMC

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