Intrarater and interrater reliability of digital calipers in assessing Achilles tendon thickness in patients with knee osteoarthritis.

Objective: This study aimed to evaluate the intrarater and interrater reliability of measuring Achilles tendon (AT) thickness using a digital caliper in patients with knee osteoarthritis.

Methods: A cross-sectional survey was conducted at the Physiotherapy Department of Rabia Moon Hospital, involving the recruitment of 61 patients with knee osteoarthritis. Measurements were taken in millimeters at a 90-degree angle, approximately 5 cm from the attachment to the calcaneus, precisely where the ankle joint joins the medial malleolus. Two physical therapists conducted two testing sessions, separated by 7 days, to assess both the intrarater and interrater reliability of the digital caliper. During the second session, two raters simultaneously assessed the patients' responses on the digital caliper. The study analyzed reliability indices, including the Intraclass Correlation Coefficient (ICC) and Bland-Altman plot.

Results: The study found high intrarater reliability for the digital caliper, with an ICC of 0.96 (95% confidence interval: 0.22, 0.99). For interrater reliability, the ICC was 0.98 (95% CI: 0.96, 0.98) in patients with knee OA. Additionally, both interrater and intrarater agreement for measuring AT thickness with the digital caliper fell within acceptable limits on 95% of occasions, as indicated by the Limits of Agreement values: 0.32 to -0.53 mm for interrater agreement and -0.35 to -0.04 mm for intrarater agreement.

Conclusions: Digital Calipers have been found to provide excellent intrarater and interrater reliability when used to measure AT thickness in patients with knee osteoarthritis (OA).