Validity of footprint analysis to determine flatfoot using clinical diagnosis as the gold standard in a random sample aged 40 years and older.
BACKGROUND
Research is needed to determine the prevalence and variables associated with the diagnosis of flatfoot, and to evaluate the validity of three footprint analysis methods for diagnosing flatfoot, using clinical diagnosis as a benchmark.


METHODS
We conducted a cross-sectional study of a population-based random sample ≥ 40 years old (n = 1002) in A Coruña, Spain. Anthropometric variables, Charlson's comorbidity score, and podiatric examination (including measurement of Clarke's angle, the Chippaux-Smirak index, and the Staheli index) were used for comparison with a clinical diagnosis method using a podoscope. Multivariate regression was performed. Informed patient consent and ethical review approval were obtained.


RESULTS
Prevalence of flatfoot in the left and right footprint, measured using the podoscope, was 19.0% and 18.9%, respectively. Variables independently associated with flatfoot diagnosis were age (OR 1.07), female gender (OR 3.55) and BMI (OR 1.39). The area under the receiver operating characteristic curve (AUC) showed that Clarke's angle is highly accurate in predicting flatfoot (AUC 0.94), followed by the Chippaux-Smirak (AUC 0.83) and Staheli (AUC 0.80) indices. Sensitivity values were 89.8% for Clarke's angle, 94.2% for the Chippaux-Smirak index, and 81.8% for the Staheli index, with respective positive likelihood ratios or 9.7, 2.1, and 2.0.


CONCLUSIONS
Age, gender, and BMI were associated with a flatfoot diagnosis. The indices studied are suitable for diagnosing flatfoot in adults, especially Clarke's angle, which is highly accurate for flatfoot diagnosis in this population.
Clinical Epidemiology and Biostatistics Research Group, Instituto de Investigación Biomédica de A Coruña (INIBIC), Complexo Hospitalario Universitario de A Coruña (CHUAC), SERGAS, Universidade da Coruña.
Salvador
S
Pita-Fernández
Cristina
C
González-Martín
Teresa
T
Seoane-Pillado
Beatriz
B
López-Calviño
Sonia
S
Pértega-Díaz
Vicente
V
Gil-Guillén
D000328:Adult; D000368:Aged; D000886:Anthropometry / Q000379:methods*; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D005413:Flatfoot / Q000175:diagnosis* / Q000453:epidemiology; D005528:Foot / Q000033:anatomy & histology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D013030:Spain / Q000453:epidemiology