Unilateral Approach for Microsurgical Decompression

Abstract

The article by Sasai and colleagues in this issue (“Microsurgical bilateral decompression via a unilateral approach for lumbar spinal canal stenosis including degenerative spondylolisthesis”) examines the use of a minimally invasive unilateral approach to address lumbar spinal canal stenosis in patients presenting with symptoms related primarily to neurogenic claudication. The authors noted good relief of symptoms and a high degree of satisfaction in patients with degenerative stenosis as well as in those with spondylolisthesis. Symptomatic lumbar stenosis recalcitrant to nonoperative treatment often responds satisfactorily following an adequate decompression. It is encouraging that the authors of this study have shown similar results using a minimally invasive approach. In carefully selected patients with lumbar stenosis a limited bilateral medial facetectomy often provides adequate symptomatic relief without resultant instability. Well-designed prospective studies have shown that in the setting of a degenerative spondylolisthesis, outcomes following decompression are better with an adjunctive posterolateral fusion.1–3 The authors of this paper present a retrospective series of patients with degenerative spondylolisthesis who had a statistically significant increase in the degree of listhesis at follow-up, but without any apparent deleterious effect on outcomes. The reported increased slip progression in patients with spondylolisthesis could be considered a negative outcome, as the literature to date suggests that slip progression is associated with worsening back pain and possible symptomatic foraminal stenosis.4 It is not possible from this study to infer why these patients did not have a worse functional outcome compared with their counterparts (those with stenosis without slip progression). Certainly there is a concern that outcomes may worsen over a longer followup period in those patients with slip progression. Palmer and associates5 examined a small cohort of 8 patients who underwent a similar minimally invasive procedure in the setting of spondylolisthesis and found no slip progression at the 3-month follow-up. Proponents of minimally invasive decompression hypothesize that by lessening the disruption of the posterior musculoligamentous complex and facet joints, greater stability is preserved compared with an open traditional decompressive procedure. This may be the case, but as evidenced by the results of the study by Sasai and colleagues, slip progression may be inevitable regardless of the degree of bony ligamentous decompression. It is encouraging that the authors noted positive outcomes at longer-term follow-up after a minimally invasive decompression. Any effort to minimize the established morbidity of a traditional, posterior midline open decompressive approach deserves careful consideration. However, prospective studies with appropriately selected control groups are necessary to establish the long-term efficacy of such procedures. Consideration of the morbidity related to the learning curve, duration of surgery, and expense must all be taken into account. A prospective study comparing microsurgical decompression to an open approach in the presence or absence of a listhesis is needed. In the setting of a listhesis 3 different surgical cohorts should be examined: microsurgical decompression, an open decompression preserving the medial facet joints as best as possible, and an adjunctive fusion procedure. Only with such a prospective study can we adequately determine if a minimally invasive decompressive procedure alone adequately improves outcomes while preventing instability in this spinal disorder. In the absence of such data, the finding of documented slip progression (which to date has been shown to portend worse outcomes) suggests cause for concern in utilizing this procedure in the setting of a degenerative spondylolisthesis.