Evaluation of a new method to create a standardized muscle stretch injury

Abstract

Herein we describe a new test system to produce a standardized partial muscle-tendon junction (MTJ) stretch injury. In anesthetized rabbits the tibialis anterior (TA) muscle-tendon unit is unilaterally shortened using a custom designed clamp roller system. An angular displacement (average velocity of 450 degrees x s[-1]) is applied about the foot to plantarflex the ankle 90 degrees while the lower extremity is fixed. During ankle rotation the TA muscle is tetanically stimulated to generate an eccentric stretch injury at the MTJ. Forty-eight hours after injury, isometric torque deficit (injured/sham) was measured. Two groups of animals (N = 6 in each group) were tested with the only difference between the two groups being the initial tendon shortening. In Group 1 (tendon shortening = 1.2 cm. N = 6) the torque deficit was 36.7+/-5.9% (mean+/-SD). In Group 2 (tendon shortening = 1.5 cm. N = 6) the torque deficit was 58.7+/-7.4% (mean+/-SD). No order effect was suggested by the data (P = 0.6062), but the difference in torque deficit between the two groups was highly significant (P = 0.0001). For all tests in which the tendon was temporarily shortened before muscle stimulation and stretch (N = 12) there was a visible hematoma at the MTJ similar to the injury that is common in athletic injuries. Histological evaluation 48 h after injury revealed both fiber tearing and inflammation at the MTJ. In addition, there was focal fiber damage in the muscle belly for both groups. The damage and inflammatory process, however, were more severe in the group with greater initial tendon shortening.

Changes in Nitric Oxide and Inducible Nitric Oxide Synthase Following Stretch-Induced Injury to the Tibialis Anterior Muscle of Rabbit

“…Because injury was created by using a single stretch and stimulation of the muscle-tendon unit rather than repeated eccentric muscle contractions, this model can mimic the clinical injury pattern that occurs with a single stretch of the muscle-tendon unit, for example, the so-called "hamstring strain" [18]. However, we confirmed that this in vivo model of stretch injury showed a visible hematoma at the muscle-tendon junction, and that histological evaluation 48 h after injury revealed fiber tearing and inflammation at this junction [19].…”

“…The peroneal nerve was isolated through a 4 mm skin incision at the knee. The animal was placed supine in the test apparatus and the muscle-tendon unit shortened 1.3 cm [19]. With the muscle-tendon unit in the shortened position, the TA muscle was stimulated to tetany [19].…”

“…The animal was placed supine in the test apparatus and the muscle-tendon unit shortened 1.3 cm [19]. With the muscle-tendon unit in the shortened position, the TA muscle was stimulated to tetany [19]. Once muscle tetany was achieved, the ankle was plantar flexed through a 90° arc at 450°/s.…”

“…We employed an isokinetic injury apparatus that quantifies tibialis anterior (TA) muscle-tendon shortening according to the method previously reported [18][19][20]. This in vivo model of acute mechanical muscle stretch injury would be different from the injury observed with exhaustive exercise and reported eccentric muscle contractions.…”

Mesenchymal Stem Cells Improve Muscle Function Following Single Stretch Injury: A Preliminary Study

“…This work contributes to our understanding of muscle injuries most commonly seen clinically, involving an eccentric contraction or single stretch, evoking damage to the musculotendinous junction [19,48]. While the healing cascade is similar among all types of muscle injuries, it is unclear if the risk of reinjury is the same for contusion, ischemia-reperfusion, repeated eccentric contractions or a single stretch injury.…”