Lumbar fusion for chronic low-back pain in isthmic spondylolisthesis

Abstract

Manifestation of isthmic spondylolisthesis (IS), with a prevalence of 5% in the general population, varies from totally asymptomatic to severe disability. Although fusion has positive short-term effects, the long-term outcome of such treatment, as well as possible accelerated degeneration of adjacent segment discs (ASD) and its clinical significance, are unknown. The primary objective of the present investigation was to provide this missing information. Additional aims were to identify factors of value in predicting the outcome of fusion with the ultimate goal of improving patient selection, and to determine the medium-term outcome of more extensive fusion including the anterior vertebral body, i.e., Posterior Lumbar Interbody Fusion (PLIF).

For all patients, the inclusion criteria were absence of previous spinal surgery, an age of 18-55 years, and at least 12 months of disabling symptoms due to IS. In a long-term randomized controlled trial (RCT), 111 patients were treated with a one-year exercise program (EX, n=34) or posterolateral fusion (PLF, n=77), with (n=37) or without (n=40) pedicle screw instrumentation. In a prospective investigation the outcome for 86 patients subjected to PLIF was assessed after two-year follow-up on the basis of the Pain Index (VAS), Disability Rating Index (DRI), Oswestry Disability Index (ODI), work status, and global self-assessment. In addition, quality of life was assessed with the SF-36 questionnaire; preoperative pain drawings (PD) obtained; and the long-term development of ASD quantified. In the prospective PLIF study, the two-year follow-up rate was 98%, while in the RCT, the 9- and 13-year rates, including radiographs, were 91% and 72%, respectively.

The two-year outcome for the PLIF group was virtually identical to the short-term outcome for the PLF patients in our previous RCT, although a larger number of major complications occurred following PLIF (12 (14%) versus 4 (5%); p=0.06). 54% of the patients whose PD were "organic"(O) and 33% of those with a "non-organic"(NO) PD rated themselves as much better (p=0.038) and, moreover, the mean pain index and DRI and ODI values for the O-group were also significantly better. Multivariate analysis revealed that working actively, male gender and regular exercise were associated with a more favourable outcome, but these factors could account for no more than 20% of the observed variability in outcome.

In the RCT involving patients treated by fusion or with exercise, 76% of the PLF group but only 50% of the EX patients rated their overall outcome as much better or better (p=0.015) after a mean of 9 years. All other assessments of outcome favoured the surgical group, but the differences were not statistically significant.

After a mean follow-up of 13 years, disc height was reduced by 2% in EX and 15% in PLF patients (p=0.0016). According to the UCLA grading scale, the discs of all patients in the EX group, but only 62% of the PLF group were normal (p=0.026). The only significant difference in outcome for PLF patients with and without ASD was the more favourable selfreported global outcome for the latter. No significant differences in long-term outcome or frequency of radiologically verifiable ASD in instrumented and non-instrumented patients were observed. Finally, laminectomised patients developed ASD more often than those not laminectomised (p=0.015).

We conclude that treatment of IS patients with either PLF or PLIF results in similar shortterm outcomes. PLF, with or without pedicle screw fixation, is associated with a long-term outcome that is modestly better than that obtained by natural healing processes. This study also shows that fusion, particularly in combination with laminectomy, accelerates degenerative changes at the adjacent level, with a consequent minor negative effect on outcome.