Clinical benefits of minimally invasive spinal fusion appear to “diminish” as a function of fusion length

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Virginie Lafage

A recent study has concluded that the clinical benefits of a minimally invasive surgical technique appear to “diminish” as a function of fusion length. The data, which examined the relationship between open versus minimally invasive lumbar fusion and the number of levels fused, were presented by Virginie Lafage (Hospital for Special Surgery, New York, USA) at the North American Spine Society (NASS) annual meeting (24–29 September, Los Angeles, USA).

Lafage pointed to sources that examined single-level minimally invasive lumbar interbody fusion, all of which concluded that single-level fusion was beneficial in terms of reduced blood loss, morbidity and preservation of soft tissue, in comparison to open fusion. Additionally, she presented sources suggesting that multi-level minimally invasive fusion resulted in shorter length of stay and decreased post-operative pain compared to open fusion, however the procedures were limited to one- or two-level fusions.

According to Lafage, the relationship between the number of levels fused and clinical outcome in patients undergoing an open and minimally invasive lumbar fusion procedure is somewhat unexplored. For instance, little work has been done to investigate minimally invasive outcomes as a function of fusion length, especially in multi-level fusions.

To address this gap in the literature, Lafage and colleagues aimed to compare the outcomes of open versus minimally invasive surgical techniques in lumbar fusion procedures as a function of the number of levels fused. A total of 440 patients undergoing no more than four level lumbar interbody fusion were examined; with 62% undergoing open fusion (157 patients underwent one-level fusion, 56 patients underwent two-level and 35 patients had three or four levels), and 38% undergoing minimally invasive fusion (122 patients had one-level, 36 patients two-level and eight patients had three or more).

Demographic analysis indicated that on average, open fusion patients were older (mean age: 58.2 vs. 55.2 years), had more comorbidities (1.48 vs. 0.96, as indicated by the Charlson Comorbidity Index), had more levels fused (1.7 vs. 1.3) and experienced more blood loss (766±830 vs. 293±311) compared to the minimally invasive cohort.

In terms of the peri-operative complication rates, Lafage reported that no significant differences were found in the majority of complications measured (including cardiac, neurological, pulmonary, ileus, immobility, anaemia and infection) between the open and minimally invasive cohorts in relation to the level of fusion. However, open patients had significantly higher rates of blood loss anaemia in single-level fusions compared to minimally invasive fusions. Yet, the latter cohort developed higher rates of ileus compared to the open patients that underwent three or more level fusions.

Regarding the outcomes per level, Lafage noted that for one-level fusion, the minimally invasive cohort of patients experienced significantly less peri-operative complication rates (16% vs. 29% for open surgery) as well as a shorter length of stay. Additionally, no difference in operative time was observed for either cohort undergoing one-level fusion, while the open fusion patients had significantly higher rates of blood loss anaemia.

In terms of two-level fusion procedures, the minimally invasive patient cohort displayed a trend of lower peri-operative complications (14% vs. 30% for open fusion), as well as a trend toward longer operative time. However, lower intraoperative blood loss occurred in patients that underwent minimally invasive two-level fusion.

Lastly, for three or more level fusions, no difference in peri-operative complications was observed between the two cohorts. The only significantly different complication rate was that the minimally invasive patient cohort experienced higher rates of ileus; 13% versus 0% for patients that underwent open fusion.

In light of these findings, Lafage concluded that for patients undergoing multi-level lumbar interbody fusion, the clinical benefits of a minimally invasive surgical technique appear to “diminish” as a function of fusion length.

Specifically, one and two level minimally invasive procedures showed significantly lower peri-operative complication rates compared to open procedures of similar length. However, while three (or more) level minimally invasive procedure showed no significant difference in complication rates, future studies—with larger sample sizes—are necessary to confirm the current findings, especially as multi-level minimally invasive fusion procedures are relatively rare.

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