Posterior lumbar fusion with and without interbody fusion in isthmic spondylolisthesis: a systematic review and meta-analysis

Background Isthmic spondylolisthesis is caused by a lesion in the pars articularis resulting in forward slippage of the vertebral segment relative to the caudal vertebral segment. Patients can develop neurogenic claudication or radiculopathy in case degeneration progresses. Nerve decompression is usually accompanied by spondylodesis: two frequently performed procedures are posterolateral fusion (PLF) and posterior lumbar interbody fusion (PLIF). Methods Studies from four databases (PubMed, Embase, Web of Science, COCHRANE Library and Emcare) were included that compared clinical outcomes of posterolateral fusion (PLF) versus posterior lumbar interbody fusion in patients with isthmic spondylolisthesis. For Oswestry Disability Index (ODI) pooled point estimate and the 95% confidence interval (CIs) was derived using the random-effects model. Results Fourteen studies met the inclusion criteria of which four were randomized controlled trials (RCT), six were retrospective, and four were prospective cohort studies (two with historical control). The pooled results for ODI yielded no difference between PLF and PLIF with an estimated pooled mean difference of -0.29 (95% CI [-0.83, 0.26], P = 0.45). A significant difference in favour of PLIF was demonstrated regarding SF-36 (1/3 studies) and VAS back pain (1/7 studies). None of the studies reporting Roland Disability Scores, Visual Analogue Scale (VAS) leg pain and (adjusted) Japanese Orthopedic Association score displayed a significant difference. Fusion rate was reported in favour of PLIF (2/6 studies). Conclusions Our results suggest that both PLF and PLIF are adequate options for the treatment of isthmic spondylolisthesis. However, included studies gave insufficient data on possible confounding factors like age, degeneration status, grade of slippage, disc height, smoking, and facet joint condition. Therefore, there is not enough evidence to support either PLF or PLIF as the best treatment option. Large multicentre RCTs with proper adjustment for confounding factors and clearly defined inclusion and exclusion criteria should determine whether the two treatment modalities are indeed comparable.