Underweight Patients Are the Greatest Risk Body Mass Index Group for 30-Day Perioperative Adverse Events After Total Shoulder Arthroplasty

Taylor D. Ottesen, BS; Walter R. Hsiang, BS; Rohil Malpani, BS; Allen D. Nicholson, MD; Arya G. Varthi, MD; Lee E. Rubin, MD; Jonathan N. Grauer, MD


J Am Acad Orthop Surg. 2021;29(3):e132-e142. 

In This Article

Abstract and Introduction


Introduction: Existing literature investigating the correlation of body mass index (BMI) with surgical complications has focused on those with elevated BMI. These investigations have reported mixed conclusions, possible because of insufficient power, poor controlling of confounding variables, and inconsistent definitions of BMI categories (eg, underweight, overweight, and varying classifications of obese). Few studies have considered complications of patients with low BMI. The aim of the current study was to analyze the spectrum of categories for BMI with 30-day perioperative adverse events after primary total shoulder arthroplasty (TSA) to better assess where along the BMI spectrum patients are at risk for complications.

Methods: Patients undergoing elective TSA were abstracted from the National Surgical Quality Improvement Program (NSQIP) databases from 2005 to 2016. Patients were then aggregated into BMI categories, and 30-day adverse events were normalized to average risk of normal-weight subjects (BMI 18.5 to 24.9 kg/m2). Risk-adjusted multivariate regressions were performed, controlling for demographic variables and overall health.

Results: In total, 15,717 patients met the inclusion criteria. Underweight TSA patients (BMI < 18.5 kg/m2) had the greatest odds for multiple perioperative adverse events compared with any other BMI category. By multivariate analysis, underweight patients were more likely to experience any adverse event (odds ratio [OR] = 2.22, P = 0.034), serious adverse events (OR = 3.18, P = 0.004), or have postoperative infections (OR = 2.77, P = 0.012) within 30 days when compared with normal-weight patients. No significant difference was observed in these complications for elevated BMI categories when compared with normal-weight patients.

Conclusions: Only underweight TSA patients were found to have higher rates of 30-day perioperative adverse events than normal BMI patients, unlike any overweight/obese category including the super morbidly obese. Underweight TSA patients were thus identified as an at-risk subpopulation of TSA patients who had not previously been described. Physicians and healthcare systems should give additional consideration to this fragile cohort because they often already do for those at the other end of the BMI spectrum.

Level of Evidence: III


Over the past two decades, the incidence of total shoulder arthroplasty (TSA—anatomic and reverse) has rapidly increased in the United States, given the demonstrated success of such procedures to treat glenohumeral arthritis and rotator cuff arthropathy in an aging cohort.[1] However, complications have been reported in approximately 10% of patients undergoing TSA.[2] Therefore, orthopaedic surgeons must develop a well-rounded understanding of risk factors for perioperative complications to better conduct patient risk factors, counseling, and how to optimize quality improvement measures.

Elevated body mass index (BMI) has frequently been cited as a risk factor for adverse events after orthopaedic interventions,[3–5] including TSA.[6–10] However, other studies have questioned this correlation for both nonorthopaedic interventions[11–14] and orthopaedic surgeries alike,[15] including TSA.[16–19]

One possible explanation for the varied results of the effect of BMI on TSA perioperative complications is the diverse cutoff values used for various categories of BMI definitions by different studies. For example, some studies define obesity as all patients BMI >30 kg/m2 in one aggregated group.[9,17] This has the potential to have patients with BMI of 31 kg/m2 dilute those with BMI of 41 kg/m2 or even 51 kg/m2, which might have a different risk stratification. Other studies have defined obese as those having a BMI >35 kg/m2 [6] or 40 kg/m2.[7,8,10,19] With any of these definitions, differences of different BMI groups might not be appreciated.

On the other end of the BMI spectrum, none of the previous TSA studies striate nonoverweight/nonobese categories to specifically investigate underweight patients.[6,8,10,16,18,19] This deficit is notable because studies in general surgery,[11] surgical oncology,[12] vascular surgery,[13] and cardiac surgery[14] have demonstrated underweight patients have a higher risk of mortality and postoperative complications compared with normal weight.[3,4,6,8,15,16] Thus, by failing to separate the underweight subpopulation for analysis, a potentially at-risk group may not be noted, and the subpopulation might sway the results of the group previously labeled "normal weight."

To address the abovementioned potential gaps, the current study used the large American College of Surgeons National Surgical Quality Improvement Program (NSQIP) database to evaluate the effect of incremental BMI categories, as defined by the World Health Organization (WHO), on TSA 30-day perioperative complications. The aim of this work was to more definitively determine the association of BMI on perioperative adverse events after TSA.