Patients with morbid obesity more likely to develop complications after spinal fusion surgery

Patients with morbid obesity are at nearly twice the risk of developing complications after spinal fusion surgery, reports a study in the May 15 issue of Spine. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.

Patients in the most severe category of obesity also have higher hospital costs for spinal fusion, according to the new research by Dr P.S.A. Kalanithi and colleagues of Stanford University. They write, "Morbid obesity was associated with $20,000 more per admission in charges, and a 97 percent higher complication rate."

Morbid Obesity Increases Costs and Complications of Spinal Surgery
The researchers analyzed data on nearly 85,000 hospital admissions for spinal fusion—an increasingly common operation for spinal pain—in California between 2007 and 2008. Two percent of the patients were classified as morbidly obese, with a body mass index (BMI) of 40 or greater. Patients with morbid obesity are generally 50 to 100 percent over their ideal body weight, or 100 pounds overweight.

Patients with morbid obesity had an overall complication rate of 13.6 percent, compared to 6.9 percent in other patients. This represented a 97 percent relative increase: nearly double the risk of complications. The greatest increases were in lung-related complications and problems with wound healing. But severe obesity was also linked to increases in heart- and kidney-related complications, among others.

Morbidly obese patients also had higher average hospital costs: approximately $109,000 versus $85,000. In addition to the increase in complications, the higher costs reflected a longer hospital stay: 4.8 versus 3.5 days.

Although the overall risk of death after spinal fusion was low, it was somewhat higher for morbidly obese patients. The difference became significant for one type of spinal surgery: posterior lumbar (lower spine) fusion, with a mortality rate of 0.56 percent for morbidly obese patients versus 0.16 percent for other patients.

With adjustment for other factors, morbid obesity was the most important risk factor for complications of spinal fusion surgery—even stronger than older age or accompanying (comorbid) medical problems.

Spinal surgeons can expect to see increasing numbers of morbidly obese patients—not only because their number is increasing in the population, but also because severe obesity is an important risk factor for back pain and spinal degeneration. Morbidly obese patients are known to be at increased risk of complications of other kinds of surgery.

The new study provides important information on the additional risks and costs of spinal fusion surgery in patients with severe obesity. "Hospital charges, length of stay, and mortality were all increased in morbidly obese patients," Dr Kalanithi and coauthors write.

And yet, they emphasize that—while surgeons and patients should be aware of the excess risks—the results do not mean that spinal fusion should not be performed in patients with severe obesity, when indicated. "Indeed, in-hospital mortality in morbidly obese patients in this study was less than one percent, and in-hospital complication rates…were under fifteen percent," according to the authors. Dr Kalanithi and colleagues call for further studies to evaluate the impact of morbid obesity and improve the safety of spinal surgery for this group of patients—possibly including new minimally invasive surgical approaches.