Effects of hypochlorous acid, povidone-iodine, and Carrel-Dakin solution irrigation on open fracture healing: a rat femur model.

BACKGROUND: Open fractures require immediate irrigation and debridement to minimize the risk of contamination and support subsequent wound management. However, antiseptic irrigants may also exert local cytotoxic or osteogenesis-impairing effects. The objective of this study was to conduct a comparative analysis of the effects of hypochlorous acid (HOCl), povidone-iodine (PI), and boric acid-buffered Carrel-Dakin solution (CD) on fracture healing in a rat model of open femur fracture, compared to physiological saline (PS) solution. METHODS: Thirty-two male Long-Evans rats underwent a standardized open femoral shaft fracture, followed by a 60-min contamination interval, intramedullary Kirschner-wire fixation, and irrigation with one of the following solutions: 0.9% PS, 0.5% PI, HOCl, or CD (n = 8/group). Animals received 10 mL of irrigant intraoperatively with a 4-min contact period before closure. Systemic antibiotics were intentionally omitted to isolate the local biological effects of the irrigants under standardized experimental conditions. Fracture healing was assessed using radiological, histopathological, immunohistochemical, and biomechanical methods. RESULTS: Radiological healing scores were similar among groups on postoperative day 14 (p = 0.89) but differed on day 28 (H(3) = 17.63, p = 0.000525). The median radiological scores on day 28 were lowest in PI and highest in CD. Composite histological healing scores were lower in the PI than in PS, HOCl, and CD. SPARC (osteonectin) expression was strongest in PS and HOCl, whereas weak staining was observed in PI. HOCl showed the highest level of BSP/SPP1 (osteopontin) expression compared to other groups, showing positive reactions in the chondro-osseous junction, mineralized osteoid, and osteoblasts. Conversely, bone morphogenetic protein (BMP2, BMP4, BMP6, BMP7, and BMP8A) expressions were highest in the CD group. Serum IL-1 levels were ranked according to groups as PS > PI> HOCL > CD. IL-12 and TNF-α levels were lowest in CD. Bone-specific-alkaline phosphatase (ALP) levels did not differ significantly among groups. The PI exhibited the highest lactate dehydrogenase (LDH) levels, indicating bone damage or metabolic changes. Collagen X and procollagen, the most sensitive biochemical turnover markers for bone matrix, were at the highest levels in PS. HOCl and CD exhibited a similar or better healing profile compared to PS. CONCLUSION: In this rat open femur fracture model, single intraoperative irrigation with HOCl or CD did not show the delayed healing pattern observed after PI irrigation. These findings provide preliminary preclinical evidence that HOCl and CD were biologically better tolerated than PI under the tested concentrations and exposure duration. However, the results should not be interpreted as proof of antimicrobial efficacy or as a direct clinical recommendation. Further studies using infected open-fracture models, microbiological endpoints, systemic antibiotic protocols, repeated-irrigation scenarios, serial time-point assessments, osteoblast cytotoxicity testing, and biomechanical validation are required before clinical application can be considered.