Review of knee proprioception and the relation to extremity function afteran anterior cruciate ligament rupture

Several tests of human conscious knee proprioception have been described, b ut there is no consensus or reference standard established, Difficulties re main in the separation of information originating from muscles, tendons, an d joints, and the tests cannot discriminate between loss of afferent signal s or altered activity in the remaining receptors. There is convincing evide nce from several descriptive studies that the afferent information is alter ed after a knee ligament injury and severely disturbed in some patients wit h anterior cruciate ligament (ACL) injuries. However, an inherent inferior proprioceptive ability may also exist in some individuals, which makes them vulnerable to injuries. The deficits in proprioception have mostly been st udied and related to the consciously registered sense, whereas the extent o f possible disturbances of the unconscious or reflectory mechanisms is larg ely unknown. The latter may, at least from a theoretical point of view, be predominantly contributing to the overall afferent regulation, and a possib ility for major defects thus exists, since there is no knowledge of the qua ntified relation between the conscious and unconscious part. The clinical i mportance of the altered afferent information has not been evaluated proper ly, and the role of proprioception that contributes to function has yet to be investigated. A higher physiological sensitivity to detecting a passive joint motion closer to full extension has been found both experimentally an d clinically, which may protect the joint due to the close proximity to the limit of joint motion, Proprioception has been found to have a relation to subjective knee function, and patients with symptomatic ACL deficiency see m to have larger deficits than asymptomatic individuals. Little is known ab out whether training can restore defects in sensory information or by which mechanisms possible compensatory pathways are established, In rehabilitati on, each patient must, however, create muscle strength, alertness, and stif fness in harmony with the disturbed mechanics of the knee, which are presen t both after nonoperative treatment of the ACL and after a reconstruction o f the ACL.