Neuromuscular Recovery Pattern after Medial Collateral Ligament Disruption in Rats.

• Laurin Jérôme
• Dousset Erick
• Mesure Serge
• Decherchi Patrick

The medial collateral ligament (MCL) is one of the most injured ligaments during sport activities. The resulting joint damages effects on neuromuscular system remain unclear. Thus, this study was designed to assess the changes in neuromuscular properties of vastus medialis muscle after MCL transection. Complete rupture of MCL was performed on rats and dynamic functional assessment during locomotion was achieved before and once a week from 1 to 5 weeks post-lesion. Twitch properties, metabo- and mechanosensitive afferent fibers responses to specific stimuli were measured 1, 3 and 5 weeks after MCL transection. Results indicated that maximum knee angle measured during the stance phase of the gait cycle was decreased during 3 weeks following MCL injury and then recovered. Minimum knee angle measured during the stance phase was decreased during 2 weeks and showed compensatory effects at week 5. A stepwise decrease in MRR/A ratio (Maximum Relaxation Rate/Amplitude) concomitant with a stepwise increase in HRT (Half Relaxation Time) were observed following MCL injury. Variations in metabosensitive afferents response to chemical (KCl and lactic acid) injections were decreased at week 1 and recovered progressively from week 3 to 5 post-lesion. Recovery of the mechanosensitive afferents response to vibrations was not totally complete after 5 weeks. Our data indicate that alteration of the sensory pathways from the vastus medialis muscle could be considered as a source of neuromuscular deficits following MCL transection. Our results will be helpful in clinical purpose to improve the knowledge of the influence exerted by ligament rupture on motor system that permits building rehabilitation protocols and exercises more appropriated for recovery of functional stability. Key words: Mechanosensitivity, metabosensitivity, group III-IV afferent fibers, ligament transection.