Following skeletal muscle contusion injury, therapeutic ultrasound is one of the most commonly prescribed treatment modalities. To investigate the influence of ultrasound on the regeneration of skeletal muscle, it was necessary to establish a method to produce a repeatable contusion injury of sufficient magnitude.
The specific aims were to: a.) produce a contusion injury to the gastrocnemius (GTN) muscles of rats, via a drop mass technique, from three different heights; and b.) two hours post-injury evaluate the degree of injury (defined as width, depth, and length of the injury zone). To achieve the aims, we tested the hypothesis that compared with the degree of injury yielded by dropping a mass from 100 cm and 105 cm, the degree of injury would be greater from 110 cm.
Fifteen 3-mo male Wistar rats (3 groups of n = 5) were studied. Following administration of an inhalant anesthetic (isoflurane), the left (L) and right (R) hindlimbs were shaved. With the ankle flexed at 90 degrees, the mid-belly region of the L and R GTN muscles were marked 20.5 mm from the calcaneus. Each animal was positioned prone in the contusion injury device with the hindlimb to be injured fully extended and positioned such that the impact occurred on the mark over the mid-belly region. The bilateral contusion injury was administered by a 171 g mass falling a distance of either 100 cm, 105 cm, or 110 cm through a Lucite guide tube, which impacted a 6.4 mm radius head.
Animal mass (255.07 ± 2.40 g) did not differ between groups. Mean injury widths (mm) were not different at 100 cm or 105cm, but were 36% greater at the 110 cm height. Injury depths (mm) were 2.16 ± 0.52, 2.68 ± 0.41, and 3.58 ± 0.23 for the 100 cm, 105 cm and 110 cm groups, respectively. Mean injury lengths (longitudinal - mm) were not different between groups.
The hypothesis was partially supported as the greatest injury width was produced from a drop height of 110 cm, however, injury depth and length were not different. Supported by an OSU Seed Grant to STD.