# Preoperative rehabilitation and in-hospital mortality in delayed hip fracture surgery: a nationwide cohort study with stratification by kidney function

## TL;DR

Starting rehabilitation early in older patients with hip fractures who can't have surgery right away may lower their risk of dying in the hospital, especially if they have poor kidney function.

## Contribution

This study is the first to show that preoperative rehabilitation reduces in-hospital mortality in delayed hip fracture surgery, particularly in patients with impaired kidney function.

## Key findings

- Preoperative rehabilitation was linked to a 32% lower in-hospital mortality risk compared to no rehabilitation.
- The mortality benefit of rehabilitation was stronger in patients with lower kidney function.
- Results were consistent across multiple sensitivity analyses, including instrumental variable methods.

## Abstract

Early surgery within 24–48 h is recommended for hip fractures; however, the majority of older adults experience delays due to medical instability. Evidence is limited on interventions during this waiting period. In cardiovascular and acute care, rehabilitation initiated immediately after admission has been shown to improve outcomes. Whether similar early inpatient rehabilitation strategies could benefit orthopedic patients has not been well explored. We aimed to assess whether preoperative rehabilitation may reduce in-hospital mortality in patients undergoing delayed hip fracture surgery, and whether this association varies by kidney function.

In this nationwide retrospective cohort study using the JMDC hospital database (Tokyo, Japan), we identified patients aged ≥ 65 years who underwent delayed hip fracture surgery (≥ 3 days after admission) between 2014 and 2023. Patients were grouped by receipt of preoperative rehabilitation. We applied overlap weighting based on propensity scores to compare in-hospital mortality. A marginal standardization approach was used to assess effect modification by estimated glomerular filtration rate. Sensitivity analyses included multiple imputation, exclusion of patients with no rehabilitation during hospitalization, and instrumental variable analysis using day of admission.

Of 21,450 eligible patients, 9,486 received preoperative rehabilitation and 11,964 did not. After overlap weighting, in-hospital mortality was significantly lower in the rehabilitation group (1.51%) than in the non-rehabilitation group (2.19%) with an adjusted odds ratio of 0.68 (95% CI: 0.55–0.85). The marginal effects analysis showed a stronger protective association of preoperative rehabilitation in patients with lower kidney function (P for trend = 0.004). Sensitivity analyses yielded consistent results across all models, including the instrumental variable approach, supporting the robustness of the findings.

Preoperative rehabilitation was associated with lower in-hospital mortality in older adults undergoing delayed hip fracture surgery. This association was particularly pronounced in patients with impaired kidney function. These findings may help guide perioperative care strategies in frail older adults for whom early surgery is not immediately possible.

The online version contains supplementary material available at 10.1186/s12877-025-06415-5.