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BMI and Complications in Spine Surgery

Published November 9, 2018
| Written By Jerry Nichols, MD   | Medically Reviewed by Jerry Nichols, MD

Can excess weight result in worse outcomes following spine surgery? According to the results of a study published in The Spine Journal in July 2018, the answer may be “yes.”

In the article, entitled “Body mass index predicts risk of complications in lumbar spine surgery based on surgical invasiveness,” the study authors performed a retrospective review of outcomes from over 31,000 spine surgeries. Their findings indicate that an increasing degree of obesity directly correlated with an increased risk of complications.

In this study, Body Mass Index (BMI) was used to define Obesity per World Health Organization WHO criteria (Table 1).

Body Mass Index (BMI)

Nutritional Status

Below 18.5 kg/m2


18.5-24.9 kg/m2

Normal weight

25.0-29.9 kg/m2


30.0-34.9 kg/m2

Obesity Class 1

35.0-39.9 kg/m2

Obesity Class 2

40.0 and above

Obesity Class 3

Table 1: World Health Organization (WHO) Obesity Categories

Obesity Class 2, defined as a body mass index (BMI) of 35.0 - 39.9 kg/m2, was associated in this study with an increased risk of several complications including:

  • Increased blood loss
  • Increased risk of deep venous thrombosis (DVT, another name for blood clots, typically in the legs)
  • Pulmonary embolism (blood clots in the lungs)
  • Superficial wound infections.

Obesity Class 3 (BMI > 40) was additionally associated with:

  • Kidney failure
  • Urinary tract infections
  • Sepsis (life-threatening organ dysfunction in response to infected tissue or infection in the blood).

This study also specifically looked at surgical invasiveness and BMI and to what extent these correlated with surgical complications. The data demonstrated a significantly higher incidence of superficial infection with more invasive surgeries among individuals with Obesity Class 3.

Additionally, obesity was found to increase the likelihood of requiring a repeat operation within 30-days after initial spine surgery. Obesity is also associated with other medical issues which can complicate surgery (high blood pressure, diabetes, heart disease).

The authors of this study pointed out several potential limitations to the results of their study. For one, the database used (the National Surgery Quality Improvement Program ,or NSQIP) is large and lacks significant granularity (detail). Secondly, there was no follow-up data available beyond 30-days post-op. Additionally, the data did not include details on the severity of the spine conditions or associated disability. Finally, the study data did not include any radiographic information (x-rays, CT scans, MRIs) for review.

Despite these limitations, the study does suggest that even relatively modest weight reduction from one BMI level to another before undergoing spine surgery (e.g., dropping from Obesity Class 3 to Obesity Class 2) may significantly reduce the risk of post-operative complications.

Obesity affects nearly 35% of adults of the US population, and nearly 80% of individuals who get surgery on their spines are overweight or obese. Obesity also contributes to low back pain and greater rates of degenerative spine conditions. While BMI is sometimes argued not to be the best measure of obesity, the information presented in this study may still be useful to patients and their surgeons when discussing potential risks of spine surgery.

(Want to know your BMI? Click here for a BMI calculator.)

Updated: February 13, 2020

Information provided within this article is for educational purposes and is not a substitute for medical advice. Those seeking specific medical advice should consult his or her doctor or surgeon. If you need to consult with a specialist, you may be able find a health care provider in our Specialist Finder. SpineNation does not endorse treatments, procedures, products or physicians.

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Contributors and Experts

Jerry Nichols, MD is board certified in Physical Medicine and Rehabilitation with Carilion Clinic.