A Muscle Contusion Injury Model

Abstract

We developed a reproducible muscle contusion injury and studied its effect on contractile function, histology, and passive failure. An instrumented drop-mass tech nique (mass, 171 g; height, 102 cm; spherical radius, 6.4 mm) delivered a single impact to the posterior sur face of the gastrocnemius muscle in one limb of 40 male Wistar rats. On Day 0, the impact significantly (N = 12, P < 0.01) decreased maximum tetanic tension to 63% of the contralateral control value. Histologic examina tion demonstrated extravasation of erythrocytes, edema, myofiber disruption, and vacuolation of myofi bers. Passive failure initiated at the site of injury. At 2 days, tetanic tension was 75% of controls (N = 11, P < 0.01). Histologically, acute inflammation and pha gocytosis were noted. Tetanic tension at 7 days was 81 % of controls (N = 8, P < 0.01). Vimentin staining indicated a dramatic increase in myoblast activity. Con tractile strength was near normal at 24 days. Histologic examination showed complete regeneration of normal striated muscle fibers. No vimentin activity was found. No passive failures initiated at the injury site. Contusion injury produced a significant deficit in contractile func tion that continually diminished with gross histologic evi dence of degeneration, regeneration, and normalization at the injured muscle fibers.