Intra- and interobserver reliability of Achilles tendon resting angle: A simple and affordable clinical tool

Abstract

Objective: To evaluate the intra- and interobserver reliability of the Achilles tendon resting angle (ARTA) measurement, using a standardized protocol. Methods: Observational study with 50 volunteers (100 feet), evaluated by two independent observers. The ATRA was measured with an analog goniometer, with the patient prone and the knee flexed to 90°. Two measurements were performed by each evaluator, with a minimum interval of 10 minutes between them. Statistical analysis included Pearson’s correlation coefficient and intraclass correlation coefficient (ICC). Results: Mean ATRA was 39.64° (± 7.18), with a significant difference between the sexes (p = 0.0004), lower in men and equivalent between the right and left sides. Intraobserver reliability was excellent, with ICCs of 0.980 for evaluator A and 0.971 for evaluator B. Interobserver reliability was also excellent, with an ICC of 0.934 in the first measure and 0.936 in the second measure. Conclusion: Clinical Achilles tendon resting angle measurement with an analog goniometer showed excellent intra- and interobserver reliability, making it a simple, accessible, and reproducible method. Level of Evidence III; Retrospective Case Series