How Much Does BMI Affect MIS-TLIF Outcomes?

Answer: Significantly. Here are the details.

A research team from both the U.S. and Germany set out to calculate and quantify the effect of a high BMI (body mass index, >35) on minimally invasive transforaminal lumbar interbody fusion (TLIF) outcomes. Their work, “Class 2/3 obesity leads to significantly worse outcomes following minimally invasive transforaminal lumbar interbody fusion,” was published in the September 2024 edition of The Spine Journal.

“Minimally invasive spine surgery [MISS] is increasingly being utilized and offers benefits such as less postoperative pain, shorter hospital stay, and faster recovery,” said co-author Pratyush Shahi, M.B.B.S., M.S.(Ortho) to OTW.

A past minimally invasive spine surgery research fellow at Hospital for Special Surgery in New York, Dr. Shahi explained, “Obese patients form a significant subset of patients undergoing spine surgery. However, there is little evidence on how obesity, especially class 2/3 obesity defined as a body mass index >35, impacts outcomes after surgery.”

“The purpose of this study was, therefore, to analyze clinical outcomes, return to activities, fusion rates, and complication/reoperation rates following minimally invasive transforaminal lumbar interbody fusion (minimally invasive spine surgery – transforaminal lumbar interbody fusion) in class 2/3 obese patients and compare them with the other body mass index groups.”

Methodology

The researchers divided 390 patients into four groups based on their body mass index:

• normal (18.5 to <25),
• overweight (25 to <30),
• class 1 obesity (30 to <35), and
• class 2/3 obesity (BMI >35).

There were 119 patients in the normal body mass index group, 160 who were overweight, 67 in the class 1 obesity group, and 44 with class 2/3 obesity.

Under 6 Months, Little Difference.  More Than 6 Months, Big Difference

Although no significant difference was seen between the groups in patient reported outcome measures at less than 6 months, at more than 6 months, the 2/3 obesity patients reported significantly worse outcomes, lower patient acceptable symptomatic state achievement rates, and lower minimal clinically important difference achievement rates in Visual Analog Score leg and Short Form-12 Physical Component Summary.

Other study findings were:

• No significant differences in the minimal clinically important difference achievement rates in the Oswestry Disability Index and Visual Analog Scores (back) and responses on the Global Rating of Change scale.
• The class 2/3 obesity group had a lower fusion rate (67% vs. >87% in other groups), but it was not statistically significant.
• The class 2/3 obesity group had significantly higher postoperative length of stay (62 hours vs. <50 hours in other groups) and
• Took significantly greater number of days to return to driving (74 days vs. <40 days in other groups).
• No significant difference was found in return to work and discontinuation of narcotics. The groups had similar complication and reoperation rates.

A minimally invasive and endoscopic spine surgery fellow at Wooridul Spine Hospital in Seoul, South Korea, Dr. Shahi told OTW, “We found that although class 2/3 obese patients showed significant clinical improvement following minimally invasive spine surgery – transforaminal lumbar interbody fusion, the magnitude of improvement was less compared to the other body mass index groups. They also took longer to be discharged from the hospital and return to driving following surgery. No significant difference was seen in fusion rates and complication/reoperation rates.”

“The findings of the study suggest that morbidly obese patients are likely to have poorer outcomes and slower recovery compared to other body mass index groups after minimally invasive spine surgery—transforaminal lumbar interbody fusion,” stated Dr. Shahi to OTW.

“This does not preclude these patients from undergoing minimally invasive spine surgery – transforaminal lumbar interbody fusion as they still improve significantly compared to before surgery, but this highlights the possible need of preoperative optimization through weight loss for better outcomes.”

“These findings can help in preoperative patient education, setting of realistic expectations, and shared decision-making. The study also lays the background for future cohort studies to analyze the impact of preoperative optimization of obesity on clinical outcomes after elective spine surgery.”