Abstract
Introduction
Body Mass Index (BMI) is an essential tool for orthopaedic surgeons in regards to preoperative risk stratification as well as assessment of overall health and nutritional status. Patient's self-awareness of their height, weight and BMI is crucial in maintaining a healthy lifestyle. The purpose of our study was to determine the accuracy of orthopaedic patient's reported height and weight. We hypothesized that a patient's age, sex and/or BMI may affect the accuracy of these reported values.
Methods
After IRB approval, we performed a prospective, observational study in the setting of our orthopaedic clinic. Patients were asked to report their predicted height and weight and then were weighed and measured using a single standardized scale. All values, including age and sex, were recorded. Differences were then calculated. Patients were categorized based on their age (younger than 65 vs older than 65), sex, and actual BMI (less than 30 vs greater than 30). Student t-test was used to calculate significance (p <0.05 conferred significance).
Results
A total of 211 patients participated in our study (127 females, 84 males). Females had an average height discrepancy of 2.21cm, whereas males had an average height discrepancy of 1.56 cm (p=0.22). Females had an average weight discrepancy of 2.46 kg compared to 2.13 kg in males (p=0.58). The average height discrepancy in patients less than 65 years old was 2.09 cm compared to 1.76 cm in patients older than 65 (p=0.81). The average weight discrepancy in patients less than 65 years old was 2.50 kg compared to 2.12 kg in patients older than 65 (p=0.54). The average height discrepancy in the high BMI group was 2.29 cm compared to 1.42 in the low BMI group (p=0.11). The average weight discrepancy in the high BMI group was 2.71 kg compared to 1.72 kg in the low BMI group. This difference approached statistical significance (p=0.094).
In regards to BMI changes based on values reported, 64 patients had a lower actual BMI than reported (range −0.015 to −5.29 kg/cm2), 6 patients had no change in BMI, and 141 had an increase in BMI (range 0.0006 to 16.6 kg/cm2). Average BMI of those patients with less than 1 kg/cm2 change in BMI was 30.9 kg/cm2, whereas those with greater than 1 kg/cm2 change in BMI had an average of 35.18 kg/cm2 (p=2.27×10−5). There were 9 patients' whose reported weights gave them a BMI of less than 40 kg/cm2, whereas their actual weight put their BMI over 40 kg/cm2
Conclusion
There was a trend towards higher BMI patients (BMI >30 kg/cm2) being less accurate in predicting their height and weight compared to a lower BMI population. Patients who had a more likely chance of inaccurate weight estimation leading to a greater change in BMI had a statistically higher BMI. In 9 instances, patients' reported weights kept them below the recommended threshold for receiving a total joint replacement, whereas their actual weight put them over the recommended threshold.
