Central nervous system modifications in patients with lesion of the anterior cruciate ligament of the knee.

Patients with traumatic lesion of the anterior cruciate ligament often experience knee instability, which, recent studies suggest, is probably due to reduced knee proprioception. We studied knee proprioception and somatosensory evoked potentials (SEPs) after stimulation of the common peroneal nerve at the knee above the articular branches subserving the sensory innervation of the anterior cruciate ligament, in 19 patients with traumatic anterior cruciate ligament lesion. Ten patients showed decreased position sense of the knee, and of these, seven presented loss of cortical P27 potential while preserving lemniscal P20 and spinal N14 responses to common peroneal nerve stimulation on the side of the anterior cruciate ligament lesion. All our patients had normal SEPs to stimulation of the posterior tibial nerve at both the ankle and the knee. We suggest that in patients showing SEP abnormalities, the dysfunction of the central somatosensory conduction is located above the medial lemniscus and is limited to common peroneal nerve somatosensory pathways. Therefore, it is likely that in the seven patients showing SEP abnormalities, the loss of the knee mechanoreceptors was followed by remodelling of the CNS above the medial lemniscus. In five patients with P27 absence after common peroneal nerve stimulation, we also recorded SEPs after stimulation of the peroneal nerve at the ankle and obtained a normal cortical positive response; moreover, in our healthy subjects, cortical responses were significantly higher in amplitude after peroneal nerve than after common peroneal nerve stimulation. These findings strongly suggest that proprioceptive afferent inputs from the knee are more effective than distal afferent inputs in generating the greater part of the common peroneal nerve cortical SEPs. Since common peroneal nerve stimulation probably allows selective recording of the responses produced by the activation of the cortical representation of the knee, minor lesions with a reduction in the number of knee mechanoceptors could result in SEP changes after common peroneal nerve stimulation.