"Minimally invasive spine surgery" is frequently requested by patients and lauded by surgeons, but it has lacked a concrete definition. Until now, there has been no standardized way to compare just how invasive one procedure is relative to another.
Dr. Roger Härtl, Hansen-MacDonald Professor of Neurological Surgery, Director of Spinal Surgery at Weill Cornell Medicine and Neurosurgical Director, Och Spine at NewYork-Presbyterian/Weill Cornell Medical Center set out to change that. In a recent study published in Global Spine Journal, Dr. Härtl and an international team of spine surgeons introduce the Minimally Invasive Spine Surgery Invasiveness Classification, or MISS-INC (L). MISS-INC (L) is a new consensus-based scoring system created to quantify surgical invasiveness for degenerative lumbar spine procedures.
Defining "minimally invasive"
"Minimally invasive" is shorthand for smaller incisions and a better recovery, but the term has never had a clear definition.
"This term, minimally invasive, has been used for many years, and nobody really knows exactly what that means," Dr. Härtl said. "There's no real way to compare invasiveness between what one surgeon does versus another."
That ambiguity makes it hard to compare outcomes across studies or to provide patients with a true idea of what a procedure looks like with different surgeons or at different institutions.
Building consensus, one factor at a time
To develop the classification, the team, including former Weill Cornell Medicine fellow Dr. Rachel Bratescu, convened an international panel of 45 spine surgeons. They ran a modified Delphi process, a method for reaching expert consensus, over three years and multiple rounds of review. The surgeons began with 16 factors drawn from the literature and existing invasiveness indices. The next step was to refine the list with discussions, internal and external review and case-based testing.
The panel agreed on nine factors to best capture surgical invasiveness for degenerative lumbar procedures:
Operative time
Number of approaches
Blood loss
Instrumentation (pedicle screws or interspinous spacers)
Muscle dissection and access
Anesthesia type
Number of levels
Fusion technique
Revision status
Each factor is scored from zero to two points, and the points are added together for a total invasiveness score. A score under five indicates a truly minimally invasive procedure, a score of five to ten is considered less invasive and a score above ten is considered more invasive. In the study's final consensus survey, every factor cleared the predefined threshold of 75 percent agreement among panelists, with agreement ranging from 80 to 100 percent.
"The main benefit is that you can actually quantify invasiveness now," Dr. Härtl said. "Now we can compare invasiveness — before, you couldn't do that."
What does MISS-INC (L) mean for research and patient care?
MISS-INC (L) is primarily a research tool that allows invasiveness to be quantified and compared across procedures. In the future, it will hopefully lead to studies correlating invasiveness with outcomes such as complication rates and patient satisfaction, helping answer a question that has long been assumed but never rigorously tested: is minimally invasive surgery actually safer?
"We can now compare across a spectrum and come up with a correlation between outcomes and the invasiveness of procedures,” Dr. Härtl explained.
Looking ahead, Dr. Härtl also sees a way the classification could be helpful in conversations with patients. When weighing treatment options, a surgeon could use MISS-INC (L) scores as a starting point for explaining relative invasiveness, alongside the fuller discussion that guides any treatment decision.