We made a retrospective study of 149 children and adolescents with moderate spondylolisthesis (slip less than or equal to 30%), 77 treated by fusion and 72 conservatively at an average follow-up of 13.3 years. Both groups were fully comparable with regard to age at diagnosis, sex distribution (46% girls), and mean slip. The patients who were treated operatively had more pain before treatment and showed more initial progression of the slip. They had better clinical results and less pain at latest review, but the total progression of the slip over the whole follow-up showed no statistical differences between the two groups. Patients with a pseudarthrosis after attempted fusion had had a longer period of postoperative pain, but at the latest review had no more pain than those with sound fusion. None of those treated conservatively came to fusion later and the long-term results in 18 patients who had refused the advised operation were no worse than those for other conservatively treated patients. Our results suggest that a moderate grade of spondylolisthesis in adolescents usually has a benign course. It seems that spontaneous segmental stabilisation occurs as a result of degeneration of the disc at the level of the slip.

From 1948 to 1980, 93 children and adolescents had fusion in situ for severe spondylolisthesis with a slip of 50% or more, at a mean age of 14.8 years. Of these, 52 girls and 35 boys were reviewed after a mean follow-up of 13.8 years. The mean pre-operative slip was 76% and pain frequency correlated with the severity of the lumbosacral kyphosis but not with that of the slip. Posterior fusion was used in 54, posterolateral in 30 and anterior fusion in three patients. There were no major complications but 16 had re-operations for non-union or root symptoms. At follow-up there were three non-unions. After operation, 19 patients had 10% or more progression of the slip, but 10 showed correction by more than 10% as a result of remodelling. The lumbosacral kyphosis had increased by more than 10 degrees in 45%. Postoperative progression of the slip and of lumbosacral kyphosis was significantly more if the posterior element had been removed. At follow-up 77 patients were subjectively improved, four were unchanged, and one was worse. These results did not correlate with either the degree of the slip, or the angle of lumbosacral kyphosis. Fusion in situ is safe and gives good long-term clinical results. Secondary changes are associated with increased lumbosacral kyphosis, so reduction of this should be considered in severe cases.