The validity and reliability of various footprint analysis in flatfoot diagnosis of competitive athletes

Abstract

Background: Foot morphology is an essential intrinsic factor in athlete performance. Therefore, abnormality of the foot morphology, such as flatfoot, can affect the foot biomechanics, reduce motor performance, and increase the risk of injury. Assessment of flatfoot in the competitive athlete is essential to decide on the appropriate management; however, the imaging evaluation method needs special equipment and experience. Footprint analysis using Clarke's angle (CA), Chippaux Smirak Index (CSI), and Staheli Index (SI) offers a cheaper, faster, more effective, and easier method for flatfoot diagnosis. This study aims to determine the validity and reliability of various footprint analysis with calcaneal inclination angle (CIA) from the radiographic image as the standard examination. Method: This is an analytic observational study with a retrospective cohort design. The data of CIA, CA, CSI, and SI were collected from 70 athletes' medical records from 6 different sports that met inclusion criteria. The validity, reliability, diagnostic performance, and determination of the cut-off point were performed. Results: The correlation test and intraclass correlation coefficient showed that CSI and SI were valid and reliable in diagnosing flatfoot, while CA was invalid but reliable in diagnosing flatfoot. Area under the curve of the ROC curve and the cut–off point of CA were 0.427 (p=0.403) and 39.32o; CSI was 0.446 (p=0.537) and 33.58; and SI was 0.418 (p=0.347) and 73.59, respectively. The sensitivity and specificity of CA were 26.78% and 100%; CSI was 10.71% and 100%; and SI was 78.57% and 78.57%, respectively. Conclusion: Footprint analysis using CA is not valid but reliable in diagnosing flatfoot, while CSI and SI are valid and reliable in diagnosing flatfoot. The Staheli Index has the best diagnostic performance compared to others.