Combined effects of low temperature, hyperosmolarity and seawater-conditioned pathogens on open fracture healing in a rat model simulating circumpolar environments.

Objective: To investigate the factors influencing the healing of open fractures in circumpolar latitude region seawater immersion conditions.

Materials and methods: A femoral fracture model was established in ninety 6-to-8-week-old male Sprague-Dawley rats, randomly assigned to five groups (n = 18 per group): (1) fracture only, (2) fracture with circumpolar seawater immersion, (3) fracture with low-temperature isotonic solution immersion, (4) fracture with aseptic circumpolar seawater immersion, and (5) fracture with low-temperature aseptic circumpolar seawater immersion. Fractures were confirmed postoperatively by radiographs on days 7, 21, and 42. Micro-CT and H&E staining were performed on day 42 to assess bone healing. Bacterial cultures from internal fixation devices were analyzed on day 3. Blood samples were collected on days 3, 7, and 14 to assess leukocyte and neutrophil counts, and serum ALP and VEGF levels were measured on days 7, 14, and 21. Pathogenic microorganisms in the seawater were identified by metagenomic analysis. Fracture healing and callus formation rates were compared using the Log-rank test.

Results: X-ray, micro-CT, and histological analyses revealed significantly impaired fracture healing in the group exposed to circumpolar seawater immersion compared to the fracture-only group (P < 0.05). Bacterial colony counts on internal fixation devices were highest in the circumpolar seawater group (P < 0.05). Leukocyte and neutrophil levels were significantly elevated in this group on days 3 and 7 (P < 0.05), with no significant differences observed on day 14 (P > 0.05). Serum ALP and VEGF levels were significantly reduced on days 7, 14, and 21 (P < 0.05), although ALP levels on day 21 showed no significant difference (P > 0.05). Log-rank analysis indicated that the bone union and callus maturation rates were significantly lower in the circumpolar seawater group compared to the other four groups. Metagenomic analysis identified Flavobacterium, Rhodobacter, and Bacteroides as the dominant pathogens in circumpolar seawater.

Conclusions: This study demonstrates that hyperosmolarity, low temperature, and exposure to opportunistic pathogens under circumpolar seawater conditions collectively delay open fracture healing. Among these factors, opportunistic pathogens exert the most significant impact, highlighting microbial contamination as the primary barrier to bone regeneration in such environments and providing direction for future therapeutic strategies.

Clinical trial number: not applicable.