SENSORY INNERVATION OF THE ANTERIOR CRUCIATE LIGAMENT - AN ELECTROPHYSIOLOGICAL STUDY OF THE RESPONSE PROPERTIES OF SINGLE IDENTIFIED MECHANORECEPTORS IN THE CAT

In anesthetized cats, electrophysiological recordings were made from twenty-six single thick myelinated afferent fibers of the posterior articular nerve of the knee joint that had sensory endings in the anterior cruciate ligament. Most afferent fibers arising from the anterior cruciate ligament were activated by application of local pressure to discrete sites of the ligament, near the attachment to the femur. Afferent fibers from the anterior cruciate ligament did not fire when the knee was in the resting position at 30 degrees of flexion, but they were activated when the knee joint was extended and flexed and externally or internally rotated. Whereas responses were induced by movements in the working range of motion of the knee, activity was markedly increased when the joint was hyperextended and externally or internally rotated. These findings suggest that mechanoreceptors with myelinated axons provide information about tension of the anterior cruciate ligament. CLINICAL RELEVANCE: These data demonstrated directly the activation of sensory nerve fibers of the anterior cruciate ligament. Afferent fibers monitor tension during physiological and pathophysiological movements. The results of this study suggest that the sensory innervation is important for the stability of the joint and for the integrity of the ligament. Operations around the anterior cruciate ligament should be done in such a way that they preserve the ligament and the integrity of its mechanoreceptors and afferent nerves.