Three-dimensional freehand ultrasonography to measure muscle volume of the lumbar multifidus: Reliability of processing technique and validity through comparison to magnetic resonance imaging.

There is a growing interest in muscle characteristics of the lumbar multifidus related to low back pain, but findings between studies are inconsistent. One of the issues explaining these conflicting findings might be the use of two-dimensional measures of cross-sectional area and thickness of the lumbar multifidus in most studies, which might be a suboptimal representation of the entire muscle volume. A three-dimensional volumetric assessment, combined with standardized imaging and processing measurement protocols, is highly recommended to quantify spinal muscle morphology. Three-dimensional freehand ultrasonography is a technique with large potential for daily clinical practice. It is achieved by combining conventional two-dimensional ultrasound with a motion-tracking system, recording the position and orientation of the ultrasound transducer during acquisition, resulting in a three-dimensional reconstruction. This study investigates intra- and interprocessor reliability for the quantification of muscle volume of the lumbar multifidus based on three-dimensional freehand ultrasound and its validity, in 31 patients with low back pain and 20 healthy subjects. Two processors manually segmented the lumbar multifidus on three-dimensional freehand ultrasound images using Stradwin software following a well-defined method. We assessed the concurrent validity of the measurement of multifidus muscle volume using three-dimensional freehand ultrasound compared with magnetic resonance imaging in 10 patients with low back pain. Processing reliability and agreement were determined using intraclass correlation coefficients, Bland-Altman plots, and calculation of the standard error of measurement and minimal detectable change, while validity was defined based on correlation analysis. The processing of three-dimensional freehand ultrasound images to measure lumbar multifidus volume was reliable. Good to excellent intraclass correlation coefficients were found for intraprocessor reliability. For interprocessor reliability, the intraclass correlation coefficients were moderate to good, emphasizing the importance of processing guidelines and training. A single processor analysis is preferred in clinical studies or when small differences in muscle volume are expected. The correlation between magnetic resonance imaging and three-dimensional freehand ultrasound measurements of lumbar multifidus volume was moderate to good but with a systematically smaller multifidus volume measured on three-dimensional freehand ultrasound. These results provide opportunities for both researchers and clinicians to reliably assess muscle structure using three-dimensional freehand ultrasound in patients with low back pain and to monitor changes related to pathology or interventions. To allow implementation in both research and clinical settings, guidelines on three-dimensional freehand ultrasound processing and training were provided.

Reliability and agreement of lumbar multifidus volume and fat fraction quantification using magnetic resonance imaging.

INTRODUCTION: Magnetic resonance imaging (MRI) is the standard to quantify size and structure of lumbar muscles. Three-dimensional volumetric measures are expected to be more closely related to muscle function than two-dimensional measures such as cross-sectional area. Reliability and agreement of a standardized method should be established to enable the use of MRI to assess lumbar muscle characteristics. OBJECTIVES: This study investigates the intra- and inter-processor reliability for the quantification of (1) muscle volume and (2) fat fraction based on chemical shift MRI images using axial 3D-volume measurements of the lumbar multifidus in patients with low back pain. METHODS: Two processors manually segmented the lumbar multifidus on the MRI scans of 18 patients with low back pain using Mevislab software following a well-defined method. Fat fraction of the segmented volume was calculated. Reliability and agreement were determined using intra-class correlation coefficients (ICC), Bland-Altman plots and calculation of the standard error of measurement (SEM) and minimal detectable change (MDC). RESULTS: Excellent ICCs were found for both intra-processor and inter-processor analysis of lumbar multifidus volume measurement, with slightly better results for the intra-processor reliability. The SEMs for volume were lower than 4.1 cm³. Excellent reliability and agreement were also found for fat fraction measures, with ICCs of 0.985-0.998 and SEMs below 0.946%. CONCLUSION: The proposed method to quantify muscle volume and fat fraction of the lumbar multifidus on MRI was highly reliable, and can be used in further research on lumbar multifidus structure.