This report is the only prospective study to document the natural history of spondylolysis and spondylolisthesis from onset through more than 45 years of life in a population unselected for pain. Subjects with pars defects follow a clinical course similar to that of the general population. There appears to be a marked slowing of slip progression with each decade, and no subject has reached a 40% slip.

Patients with prolonged procedures (i.e., >5 hours) exposing more than three vertebral levels that include C2, C3, or C4 with more than 300-mL blood loss should be watched carefully for respiratory insufficiency.

The incidence of RLN symptoms after surgery was 2.7% (9 of 328). The incidence of RLN symptoms was 2.1% with anterior cervical discectomy, 3.5% with corpectomy (5 of 141), 3% with instrumentation (8 of 237), and 9.5% with reoperative anterior surgery (2 of 21). There was a significant increase in the rate of injury with reoperative anterior fusion. There was no association between the side of approach and the incidence of RLN symptoms.