Reliability of point-of-care ultrasound for measuring quadriceps femoris muscle thickness

BACKGROUND: Point-of-care ultrasound can be used to assess muscle thickness. However, its reliability has not been fully evaluated. AIM: This study aimed to assess the intrarater and inter-rater reliability of point-of-care ultrasound for the estimation of quadriceps and rectus femoris thickness in patients from a rehabilitation setting. DESIGN: This is a cross-sectional study. SETTING: This study was conducted at the Department of Physical Medicine and Rehabilitation of a tertiary care hospital. POPULATION: Twenty-nine inpatients consecutively selected after admission. METHODS: Four observers, two trained and two untrained, used point-of-care ultrasound to measure quadriceps femoris and rectus femoris thickness. Each observer performed two measurements followed by a second set of two measurements three hours later. Intraclass correlation coefficients (ICC) were then calculated. RESULTS: Both intrarater and inter-rater ICC were higher than 0.888 for both quadriceps and rectus femoris measurements. Reliability was high-est when ICC were calculated based on the average of two measurements, with the intrarater ICC being of 0.956 (95% CI: 0.937-0.970) for rectus femoris and of 0.966 (95% CI: 0.951-0.976) for quadriceps femoris; and with the inter-rater ICC being of 0.919 (95% CI: 0.863-0.957) for rectus femoris and 0.945 (95% CI: 0.907-0.971) for quadriceps femoris. Trained and untrained observers did not have significantly different ICC values. CONCLUSIONS: These results suggest that point-of-care ultrasound is a reliable option to measure muscle thickness of knee extensors by the same or different observers. CLINICAL REHABILITATION IMPACT: Measuring knee extensors thickness may aid to adequately modulate treatment choices in patients with disability. This study suggests that quadriceps and rectus femoris muscle thickness measured after a short training course, by either an experienced or inexperienced clinician, presents high reliability. Reliability can be increased if the average of two measurements is used. Be-sides being inexpensive and portable, point-of-care ultrasound is a reliable tool for measuring knee extensors' thickness, rendering it potentially adequate to be used in clinical practice.