Objectives: Oxygen is an essential component for many aspects of tissue repair. However, the effect of oxygen levels on differentiation of stem cells into osteoblasts and chondrocytes during fracture healing is unknown, in part because of the difficulty in measuring oxygen during fracture healing. In this study we tested the feasibility of using electron paramagnetic resonance (EPR) oximetry to assess tissue oxygen partial pressure (pO(2)) after tibial fractures in mice.
Methods: Transverse tibia fractures were created by three-point bending in adult mice. Paramagnetic material, lithium phthalocyanine (LiPc), was implanted into the fracture site or adjacent to the periosteum in the contralateral leg immediately after fracture. Tissue pO(2) was assessed by EPR 90-110 minutes after implantation of the crystals. in a second experiment, LiPc was implanted into the fracture site and fracture repair and the bio-compatibility of LiPc were assessed at 14 and 28 days after injury.
Results: At the very early stage after fracture, injury significantly decreased tissue oxygenation at the fracture site. When animals were breathing 21% oxygen, pO(2) at the fracture site ((30.6 +/- 12.7 mmHg, n=7) was lower than that in contralateral legs (45.5 +/- 15.3 mmHg, n=7, p<0.01). breathing 100% inspired oxygen increased the pO(2) in both the fractured (72.8 +/- 28.2 mmHg; n=7) and contralateral legs (148.4 +/- 59.2 mmHg; n=7, p<0.01). in addition, LiPc crystals implanted into fracture sites did not interfere with normal fracture healing at 10 and 28 days post-injury.
Conclusions: EPR oximetry is a valuable tool for monitoring oxygen levels during fracture repair in mice.