Enhanced bone healing using local cryostimulation: In vivo rat study.

A short-term intense cooling through the skin causes a response of the body. Potentially, it can be used to enhance bone healing. The aim of this study is to evaluate an effectiveness of a bone defect cryostimulation in the Wistar rat model in vivo. Through holes with a diameter of 2.15 mm were formed in the cortical layer of the diaphysis of the hind paws of rats. Further animals were subjected to cryotherapy 1 and 2 times a week (up to 6 weeks). The local average skin surface temperature dropped from 28 to 14 °C. The decrease in temperature in a control point inside the biological tissue was 5.3 °C. Micro CT and histological analyses showed that cryostimulation twice a week is efficient treatment. In this case, there was an acceleration of maturation of the newly formed bone tissue replacing the defect region. In the control, the newly formed immature bone with a large number of osteocytes and vessels was detected. In the experiment, the newly formed bone had a more mature structure with signs of a compact bone (formation of Haversian canals, reduction in the number of osteocytes, appearance of gluing lines). Morphometric analysis has showed a 2-fold decrease of the relative vessels area near the defect region and an increase of 30% in the content of mast cells in the entire bone marrow and especially near the site of osteogenesis. Generally, the complete filling of the critical size defect and almost complete mineralization have been observed. This information is expected to be useful for understanding the effect-exposure correlation of the cryotherapy and in the design of the cryotherapy protocols.