Despite a large number of patients with lumbar spondylolisthesis treated surgically worldwide, it remains controversial whether reduction of the slip is advantageous and what type of fusion offers the best outcome to surgical candidates (1,2,3).

Good or acceptable results are described for simple posterolateral fusion (4,5), posterior instrumented fusion (6), and anterior and circumferential procedures (7) without slip reduction. The aim of contemporary surgical treatment is, however, not only fusion, but also fusion in physiologic position.

Interbody location has some theoretical advantage over posterolateral fusion. The Wolf law says that osteointegration potential is superior in grafts placed under compression. Interbody position of the bone graft is therefore ideal because the anterior and middle spinal columns bear 80% of the spinal load, compared to 20% borne by the posterior elements. Interbody location further provides 90% of the vertebral osseous contact area; also, the vascular bed, mandatory for osteoinduction, is more abundant in the interbody region. Higher potential to form solid bone mass is not the only advantage of interbody grafts and spacers. They also help to further restore disc space height, optimize sagittal balance, and in some cases also adjust coronal alignment (8,9,10,11). Posterolateral fusion has only very limited potential to do this.

The commonest methods of achieving lumbar interbody fusion are anterior lumbar interbody fusion (ALIF) with or without posterior instrumentation and posterior lumbar interbody fusion (PLIF) or transforaminal lumbar interbody fusion (TLIF) supplemented by transpedicular stabilization. Advocates of anterior approach argue that it provides a better anterior column support and a superior contact for osteointegration (11,12). Opponents are defending one-stage posterior surgery with good nerve root decompression and posterior lumbar interbody fusion (13). The type of olisthesis appears to be important in determining both the type of fusion that should be implemented and the desirability of slip reduction. The status of sagittal profile of the lumbopelvic junction seems to be of a major importance in determining the risk of further slip progression (14), especially in cases with insufficiency of the hook and catch posterior retaining mechanism (15). Surgical indication is usually based on intractable pain that has failed to respond to conservative management and/or neurologic deficit in adults. However, in adolescents with dysplastic types of spondylolisthesis, the risk of slip progression can be sufficient to warrant surgical intervention (3,4,5,6,7,8,9,10,11,12,13,14,15,16). Inability to walk or work under load and cosmetic consequences should not be underestimated when considering surgery (17).

We reviewed our series to assess the outcome of different methods with further subgroup analysis of isthmic spondylolisthesis treated with instrumented PLIF and reduction of slip.