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 highest 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. Besides 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.