[Instability of the cervical spine caused by arthrosis. An unusual form of degenerative spondylolisthesis].

A case of a patient with spondylolisthesis between C4 and C5 is reported. There were neurological signs of spinal cord involvement and the lesions were essentially those of a posterior degenerative arthrosis with disc degeneration at other levels. This severe instability was cured by an anterior interbody fusion.