Functional and Neuromuscular Changes after Anterior Cruciate Ligament Rupture in Rats

Purpose: This study was designed to highlight the functional impairments and the neuromuscular adaptations following an anterior cruciate ligament (ACL) injury in rat. Methods: Animals were randomized into five groups: control (n = 8), SHAM-1wk (n = 6), SHAM-5wk (n = 8), ACL-1wk (n = 8), and ACL-5wk (n = 8). Rats performed three behavioral tests (the ladder-climbing test, the dynamic weight-bearing distribution, and the dynamic function assessment during locomotion) before the surgery (PRE) and at day (D) 1 (D1), D2, D3, D5, D7, D14, D21, D28, and D35 after ACL transection. Electrophysiological recordings, including responses of muscle metabosensitive afferents to a combination of specific chemical activators, namely, lactic acid and potassium chloride, and the quadriceps motor reflex activity, were performed at D7 (ACL-1wk) and at D35 (SHAM and ACL-5wk). Results: Behavioral results indicated an alteration of both weight-bearing distribution over the four paws and fine motor skills (ladder-climbing test) for the injured animals. Maximal motor reflex amplitude was higher after ACL injury compared with the other groups. Moreover, the regulation of motor reflex induced by metabosensitive afferents was perturbed from the first week after ACL transection, without affecting the response of these muscle afferents to their specific stimuli. Conclusions: This study brings some new evidence about the motor dysfunctions and spinal adaptations after ACL rupture in rats. Such information might be needed for assessing, in our animal model, the effectiveness of the diverse functional rehabilitation strategies used in human clinic after knee injuries.

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