Physiologic loading of the anterior cruciate ligament does not activate quadriceps or hamstrings in the anesthetized cat

Abstract

We attempted to elicit quadriceps and hamstring elec tromyographic responses in seven chloralose-anesthe tized cats by loading the ACL with controlled anterior displacement of the tibia on the femur using rigid fixa tion and an MTS testing machine. We did not detect reflex activity in the quadriceps or hamstring muscles of any of the cats in response to anterior tibial displace ments of up to 4 mm, with rise times ranging from 1.0 to 0.1 seconds. In four of the cats we loaded the ACL using a wire loop. Loads of up to 125 N (4 to 5 times body weight) produced no reflex activity in any of the four animals, although we consistently observed mono synaptic reflex responses to tendon taps. Whole nerve recordings from the posterior articular nerve revealed substantial activity from afferents in response to tug ging on the ACL, although we could not differentiate receptors in the ACL from those in other periarticular tissues. Thus, while traction on the intact ACL causes signals in the afferent nerves, those signals are not translated into direct monosynaptic reflexes.