Relationship between short-term exposure to ambient sulfur dioxide and length of hospital stay after surgery for osteoporotic fractures: a distributed lag non-linear analysis.

BACKGROUND

While long-term air pollution is a known risk factor for fracture, its short-term impact on prognosis, particularly length of stay (LOS) in hospital following surgery, remains unclear.

OBJECTIVES

This study aimed to assess the relationship between short-term exposure to ambient sulfur dioxide (SO2) and LOS among patients undergoing surgery for osteoporotic fractures.

METHODS

A retrospective observational analysis of secondary hospital records from 3567 patients treated in Kunshan, China, between 2017 and 2024 was conducted. Individual clinical records were linked to daily area-level ambient SO₂ and meteorological data, and a distributed lag non-linear model was used to assess the association between short-term SO₂ exposure and LOS.

RESULTS

A non-linear, J-shaped association was identified between SO2 exposure and LOS, with an apparent inflection point around 8.1 µg/m3. However, the timing of the effects, namely, the lag structure, shifted according to the degree of exposure. Moderate levels (P75) were linked to a transient, inverted U-shaped impact that reached its peak at lag 5 (percentage increase: 1.03%; 95% CI: 0.46, 1.59). By contrast, high-intensity exposure (P95) appeared to trigger a more persistent form of toxicity, with risks peaking at lag 12 (percentage increase: 2.37%; 95% CI: 1.00, 3.76). Stratified analyses suggested higher susceptibility among female patients and those admitted in winter.

CONCLUSIONS

Short-term ambient SO₂ exposure was associated with prolonged LOS after osteoporotic fracture surgery, particularly at higher levels of exposure. These findings highlight the potential relevance of ambient air pollution to postoperative outcomes in vulnerable patient populations.