Spondylolisthesis: indications for lumbar nerve root decompression and operative technique.

Pain mechanisms attributable to spondylolisthesis are discussed with particular regard to the anatomic relationships at the site of nerve root impingement where the exiting lumbar nerve root is noted to pass anterior to the pseudoarthrosis mass in the pars interarticularis portion of the posterior element of the vertebral body. Clinical findings support the fact that nerve root impingement is a definite factor in producing the pain and associated symptoms in root impingement further supports this hypothesis. The incidence of lower motor neuron deficit is determined by a combination of muscle testing and electromyography. Postoperative results are evaluated in terms of patients having arthritic changes associated with the spondylolisthesis and in those patients with absence of arthritic change. These changes distinguish the patients who might respond best to simple decompression of the nerve root impingement from those patients who might better benefit from spinal fusion. Operative techniques should include adequate decompression of the exiting lumbar nerve root by means of total laminectomy approach. Exision of the pseudarthrosis mass attached to the pedicle side of the pars interarticularis of the vertebra is necessary to relieve pressure on the shoulder of the exiting nerve root.