Functional importance of degenerative spondylolisthesis in cervical spondylotic myelopathy in the elderly

Study Design. A correlation was studied between degenerative spondylolisthesis (DSL) of the cervical spine and spinal-evoked potentials intraoperatively recorded in elderly patients who had surgical treatment for cervical spondylotic myelopathy. Objective. To investigate the functional importance of cervical DSL in elderly patients with cervical spondylotic myelopathy. Summary of Background Data. Cervical DSL has received insufficient attention in contrast to the lumbar DSL. The authors are unaware of any journal article in which this condition has been evaluated electrophysiologically. Methods. This study investigated 47 patients with 68 DSL of 2 mm or more (3.1 +/- 0.9 mm; range, 2-6 mm) who underwent serial intervertebral recording of spinal-evoked potentials from either the intervertebral disc or the ligamentum flavum after epidural stimulation. Results. All the study patients had unequivocal evidence of a focal conduction block, with the area of negative evoked potential peak reduced to less than 60% that of the immediately caudal level: 31 at C3-C4, 12 at C4-C5, and 1 each at C1-C2, C2-C3, C5-C6, and C6-C7. The site of conduction block matched the level of DSL in 30 patients, but not in 17 patients. The DSL accompanied by conduction block had significantly greater displacement with greater angular mobility than that without conduction block. Conclusions. A significant association between DSL and conduction block in the face of a relatively wide canal indicates the functional importance of DSL in elderly patients with cervical spondylotic myelopathy. In this age group, a high incidence of both DSL (81%) and focal conduction block (91%) at the upper cervical level (C3-C4 or C4-C5) is of clinical interest.