Correcting calf girth discriminates the incidence of falling but not bone mass by broadband ultrasound attenuation in elderly female subjects

Abstract

Calf circumference has been cited as an independent risk factor for hip fracture. Correcting this measured girth for subcutaneous adipose tissue or fluid accumulation provides a more valid estimate of lean tissue, but has not been reported in elderly populations. Two hundred eighty-eight randomly selected female volunteers, aged ≥70 years, were assessed by quantitative ultrasound (QUS) and clinical risk factors as part of a larger screening study for hip fracture risk. This involved measuring broadband ultrasound attenuation (BUA) and administering a structured risk factor questionnaire that included estimated daily skeletal loading (time standing or walking). Body mass index (BMI) was estimated using current body mass and height at age 25 years. Calf girth was measured using a standard anthropometric tape, the medial calf skinfold (a vertical fold at the point of maximum calf girth) was measured, and corrected calf girth (CCG) was calculated by subtracting the skinfold (in centimeters) multiplied by π from calf girth. Subjects were aged 76.9 ± 5.0 years, had BMIs of 24.3 ± 3.9 kg/m2, and spent an average of 5.5 ± 2.0 h on their feet each day. Age, current body mass, BMI calf girth, and CCG all correlated with BUA (p < 0.01). CCG correlated with hours on the feet (p < 0.05), whereas calf girth did not (p > 0.05). Dividing the sample into tertiles by these correlates of BUA and predicting BUA using stepwise regression revealed different predictors for each tertile. Of the total sample, 93 had fallen in the last 12 months, whereas 195 had not. Independent t-tests showed these groups to be similar in age, BMI, and calf girth (p > 0.05), but fallers spent less time on their feet each day, and had smaller CCG (p < 0.05). This suggests that larger calf muscles may be protective against falling—possibly as a result of enhanced stability or greater neuromuscular control.