Delayed healing of muscle after injection of bupivicaine and steroid.

The purpose of this study was to evaluate the histologic changes that occur in an area of rat skeletal muscle injected with a local anesthetic and steroid combination. Thirty adult male laboratory rats were assigned to one of six groups. Group 1 received bupivicaine injected into the right gastrocnemius muscle; Group 2 received procaine; Group 3 received bupivicaine and triamcinolone; Group 4 received procaine and triamcinolone; Group 5 received triamcinolone; and Group 6 received normal saline. Animals were sacrificed at 24 hours and at 1, 2, 3, and 4 weeks. The saline, steroid, and procaine groups showed minimal tissue reaction. The procaine/steroid group had focal areas of inflammation at 24 hours but none on subsequent evaluations. The bupivicaine group showed moderate localized necrosis of muscle fibers and a mild inflammatory cell response at 24 hours. Regeneration of muscle fibers was seen at 1 week, and at 3 weeks the tissue had returned to normal. The bupivicaine/steroid group showed extensive localized necrosis of muscle fibers with a heavy inflammatory cell response at 24 hours. These areas of necrosis persisted throughout the 4-week post-injection period, although some muscle fiber regeneration and fibrosis were also noted. This study shows that bupivicaine produces more tissue reaction than procaine and that the addition of steroid to bupivicaine increases the initial tissue damage and prolongs the healing phase.