Intra-rater reliability of rehabilitative ultrasound imaging of the cervical multifidus muscle in healthy subjects

Introduction
The multifidus muscle is a deep muscle and the main stabiliser of the spine. Ab normal activity and morphology of this muscle can provoke cervical spinal pain. One way to as sess the morphology of deep stabilising muscles is ultrasonography. There is limited evidence on the reliability of measuring the multifidus muscle in the cervical region of the spine using rehabili tative ultrasound imaging (RUSI).

Aims
This study aimed to evaluate the reliabili ty of measuring the cross-sectional area, surface area, and circumference of the multifidus muscle in the cervical region of the spine.

Material and methods
The study involved 10 heal thy subjects, including 7 women and 3 men, aged 23–62 years. The cross-sectional area, circumfe rence, and surface area of the multifidus musc le in the cervical section of the spine were me asured in the subjects using RUSI. The intraclass correlation coefficient (ICC) was used for each measurement (3.1–3.3) as recommended index for the intra-rater reliability assessment.

Results
Taking measurements twice, with a 15-minute interval between them, increased the reliability of measurements of the cross-sectio nal area, surface area, and circumference of the multifidus muscle in the cervical section of the spine to ICC > 0.9, which indicates excellent relia bility. The mean of the three measurements de creased the ICC value to 0.8–0.9, showing good reliability of the measurements. The ICC 3.3 va lues for measurements of the area and circum ference of the multifidus muscle in the cervical region of the spine performed after seven days were lower, in the range of 0.48–0.55, which sug gests questionable reliability of measurements. The value of ICC 3.3 of the cross-sectional area also decreased, although it remained in the upper limit (0.85), demonstrating good reliability of the measurement.

Conclusions
The RUSI is a reliable tool for asses sing the morphology of the multifidus muscle in the cervical spine region.