Effects of transcutaneous CO₂ application on fracture healing in a rat fracture model of disuse osteoporosis.

Abstract

Transcutaneous carbon dioxide (CO₂) therapy has been shown to accelerate fracture healing and osteogenesis by enhancing endochondral ossification and angiogenesis. We aimed to investigate the effects of this therapy on fracture healing in a rat hindlimb suspension model of disuse osteoporosis. Eleven-week-old male Sprague-Dawley rats were randomly assigned to three groups: 1) Control group (normal ambulation for 3 weeks, followed by femoral fracture with Kirschner-wire fixation); 2) Hindlimb suspension (HS) group (HS; 3 weeks of HS before fracture); 3) HS + CO₂ group (same as HS, followed by transcutaneous CO₂ therapy after fracture). HS was induced by tail suspension at a 30° head-down tilt to prevent hindlimb weight-bearing. Transcutaneous CO₂ therapy involved applying a CO₂-permeable hydrogel and enclosing both hindlimbs in polyethylene bags filled with 100% CO₂ for 20 min/day, 5 days/week. The HS + CO₂ group showed significantly higher modified Radiographic Union Score for Tibial fractures than did the HS group at weeks 3 and 4, as well as a significantly higher radiographic union rate at week 4. They also showed significantly higher Allen's histological grading scores at week 3. Compared with the HS group, the CO₂-treated animals showed significantly higher expression levels of runt-related transcription factor 2 and Osterix at weeks 1 and 2, respectively. These findings suggested that transcutaneous CO₂ therapy promoted osteogenic activation and accelerated radiological and histological fracture healing of disuse osteoporosis, supporting its potential as an adjunctive strategy for fragility fractures.