Sunday, October 6, 2013

The not infrequent complications after reverse total shoulders - influence of body mass index

Reverse total shoulder arthroplasty in patients of varying body mass index

This article analyzes the association of one element (BMI) of the characteristics of the patient and the rate of complications within a minimum of 90 days after a primary reverse total shoulder. They classified the patients into 3 groups: normal BMI (BMI <25 kg/m2) (30 patients), overweight or mildly obese (BMI 25-35 kg/m2) (65 patients), and moderately or severely obese (BMI >35 kg/m2) (24 patients).

Complications occurred in 30 patients (25%), major in 11 (9%), minor in 19 (16%), surgical in 21 (18%), and medical in 14 (12%). The most common surgical complications were acute blood loss anemia requiring transfusion (8.4%) and dislocation (4.2%). The most common medical complications were atelectasis (2.5%) and acute renal insufficiency (2.5%).

Patients with a BMI exceeding 35 kg/m2 had a significantly higher overall complication rate (P < .05) and intraoperative blood loss (P = .05) than the other groups. Patients with BMI of less than 25 kg/m2 had a greater overall complication rate than those with a BMI of 25 to 35 kg/m2 (P < .05).

While the increased complication rate in patients that are moderately to severely obese makes some intuitive sense, it is difficult to understand an increased complication rate in those of normal BMI. 

It is important to keep in mind that this analysis took a continuous variable, BMI, and converted it into a  categorial variable (normal, overweight and obese). The result is obvious: a patient with a BMI of 24.9 is "normal", while a patient with a BMI of 25 is "overweight"; a patient with a BMI of 35 is "overweight" while a patient with a BMI of 35.1 is "obese". It would have been more interesting to plot the rate of complications (a continuous variable) against the BMI (a continuous variable). This may have helped shed some light on the apparent anomaly of increased complications in the "normal" group.

The authors collected a lot of data on their patients, including age, gender, diagnosis, prior shoulder surgery, comorbidity score, operating time, blood loss as well as BMI. Perhaps a better way to have done the analysis would have been to conduct a univariate analysis of each of these for their association with the complication rate and then a multivariate analysis to see which were independent.

Perhaps the most important result from this study is that 25% of the patients having primary reverse total shoulders had complications within a minimum of 90 days (we could not find the average followup days for this patients listed in the article).  This is a real caveat to surgeons and patients alike.

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