NEURAL AND MUSCULAR ELECTRIC-ACTIVITY IN THE CATS KNEE - CHANGES WHENTHE ANTERIOR CRUCIATE LIGAMENT IS TRANSECTED

We studied the response of the normal and unstable knee to passive mot ion and anterior tibial displacement in the cat. 6 cats were anestheti zed and the deep level of anesthesia was controlled by electroencephal ograms. We recorded electric activity in the articular nerves (posteri or PAN and medial MAN) and periarticular muscles (quadriceps and hamst ring), while performing passive flexion, extension, internal and exter nal rotation. We then produced anterior displacement of the tibia at 3 0 degrees and 90 degrees of flexion, as in the Lachman and the anterio r drawer maneuvers, The anterior cruciate ligament was surgically sect ioned and the same series of passive displacements was performed. We o bserved statistically significant increased activity in the MAN, the P AN and the quadriceps muscle during knee flexion, in the MAN during ex tension, and in the PAN and hamstring during external rotation with th e knee 90 degrees flexed, Anterior cruciate transection caused anterio r displacement of the tibia during stress. This produced a significant increase in the MAN activity and a significant decrease in the hamstr ing electric activity at 30 degrees and 90 degrees of flexion, as in L achman and anterior drawer maneuvers. We conclude that electric activi ty in the articular nerves and periarticular muscles, in response to p assive motion and anterior tibial displacement, is altered in the cat' s knee after anterior cruciate transection, This suggests that various patterns of periarticular muscle reaction in the anterior cruciate-de ficient knee may be related to the unconscious perception of abnormal motion.