Ultrasound measurement of muscle thickness at the anterior thigh level in rheumatology setting: a reliability study

Ultrasound (US) is a promising tool for assessing sarcopenia. We aimed to test in the rheumatology setting two US scanning protocols to measure muscle thickness (MT) at the anterior thigh level and to assess their feasibility and reliability. In the first phase of the study, three rheumatologists performed a US examination on 19 consecutive patients adopting two scanning protocols, namely the anterior superior iliac spine (ASIS) and the greater trochanter techniques. After consensus was obtained on the easiest scanning protocol to perform, two rheumatologists adopted only the ASIS technique in 40 consecutive patients. MT measurements were recorded as well as the time needed to complete each scanning protocol bilaterally. The median time needed to complete the US examination was under 5 minutes for each of the two techniques, with no significant difference between them (p = 0.64). In the first phase, we found an excellent inter-observer reliability of the proposed scanning protocols, with a higher but nonstatistically significant intraclass correlation coefficient (ICC) for the ASIS technique compared with the greater trochanter technique (ICC 0.97 vs. ICC 0.92, p = 0.05). The ASIS technique had a significantly higher intra-observer reliability (ICC 0.97 vs. ICC 0.92, p < 0.01). In the second phase, the ASIS technique confirmed on a larger sample its excellent inter-observer reliability, with an ICC of 0.96. The present study presents a novel tool for assessing sarcopenia and provides evidence in favor of feasibility and reliability of US measurement of MT at the anterior thigh level in rheumatology setting. Key Points • This study demonstrates that ultrasound (US) measurement of muscle thickness at the anterior thigh level is highly reliable, especially for the "anterior superior iliac spine (ASIS)" technique. • The short time needed to complete the US assessment highlights the feasibility of the proposed scanning protocols. • The simplicity and conciseness of the proposed techniques will allow other researchers and clinicians to use it for a fast assessment of sarcopenia.