Low BMI May Be More Problematic than High BMI for TSA Patients

    A high body mass index (BMI) is typically a red flag for orthopaedic surgeons evaluating patients for total shoulder arthroplasty (TSA), with the literature identifying high BMI as a potential risk factor for complications after the procedure.

    A study from the Yale School of Medicine suggests that surgeons should be just as concerned with outcomes in underweight patients, who have a higher risk of adverse events and infection following TSA than any other BMI category, including the morbidly obese.

    The study findings were presented at the 2019 Annual Meeting of the American Academy of Orthopaedic Surgeons.

    “In the past, the literature has predominantly stated that overweight patients are at risk of adverse outcomes,” said Jonathan Grauer, MD, professor and interim chair, Department of Orthopaedics and Rehabilitation at Yale School of Medicine. “However, more recently, studies have started to show a more mixed picture.

    “Although there are many studies investigating the effect of obesity on outcomes, underweight patients on the other end of the BMI spectrum are often not considered in these studies and have largely been underrepresented.”

    For this study, the researchers identified nearly 16,000 TSA patients in the National Surgical Quality Improvement Program database. Patients were categorized by BMI as defined by the World Health Organization:

    • Underweight: BMI less than 18.5
    • Normal weight: BMI 18.5 to 24.9
    • Overweight: BMI 25.0 to 29.9
    • Obese: BMI 30.0 to 39.9
    • Morbidly obese: BMI 40.0 to 49.9
    • Super morbidly obese: BMI over 50

    Prior studies focused on BMI have used broader categories and have been inconsistent with how they defined “obese.” That could be problematic, said lead author Taylor Ottesen, BS, a medical student in the class of 2020 at Yale School of Medicine.

    “Some studies considered anyone with a BMI of over 35 as obese,” he said. “However, someone with a BMI of 35 is very different from someone with a BMI of 55. Yet they were being put into the same group. We felt these groups needed to be more granular, so we decided to take the World Health Organization categories of BMI and then run the analysis based on their striations of multiple tiers of obesity.”

    The researchers found that super morbidly obese patients were not more likely to experience adverse events, consistent with some of the newer literature. Further, overweight patients actually had the lowest rate of adverse events across all 6 BMI categories, which has been shown in a variety of general surgery papers, including in the emergency, cardiac, and vascular surgery literature.

    Underweight patients, however, were more likely to experience a major adverse event, such as cardiac arrest, or a major postoperative infection following TSA. Compared with normal-weight patients, underweight patients experienced more adverse events within 30 days after surgery: 12.07% for underweight patients versus 3.82% for normal-weight patients.

    Underweight patients were also:

    • 4.01 more likely to develop postoperative infections
    • 2.11 times more like to be readmitted to the hospital within 30 days following surgery
    • More likely to need revision surgery

    The researchers concluded that the risk of adverse events should be carefully considered when underweight patients are evaluated for TSA. In addition, obesity is a scale that should be more carefully assessed when determining eligibility for surgery.


    Ottesen T, Hsiang W, Malpan R, Varthi AG, Rubin LE, Grauer JN. Underweight Patients are the Greatest Risk Body Mass Index Group for Perioperative Adverse Events Following Total Shoulder Arthroplasty (Paper 829). Presented at the 2019 Annual Meeting of the American Academy of Orthopaedic Surgeons, March 12-16, Las Vegas, Nevada.