Effect of hyperbaric oxygen on the ligament healing process in rats.

Animal experiments were done to investigate whether administration of hyperbaric oxygen promotes scar tissue formation, increases expression of the Type I procollagen gene, and improves the tensile properties of healing ligament. In 76 Sprague-Dawley rats, a 2-mm segment of the medial collateral ligament was removed. Thirty-eight rats were exposed to hyperbaric oxygen at 2.5 atmospheres absolute for 2 hours 5 days per week (Group H), whereas the remaining rats were exposed to room air (Group C). The animals were sacrificed at 3, 7, 14, and 28 days postoperatively. In situ hybridization histochemistry was done to examine the Type I procollagen gene expression in healing ligaments in 40 rats, whereas a tensile failure test was done in the remaining rats. The amount of scar tissue was greater in Group H than in Group C. Type I procollagen gene expression at 7 or 14 days was significantly greater in Group H than in Group C. The ultimate load and stiffness in Group H were significantly greater than in Group C at 14 days. Administration of hyperbaric oxygen promotes scar tissue formation and increases Type I procollagen gene expression in healing ligaments. These effects are associated with the improvement of their tensile properties.