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.