Rehabilitative ultrasound imaging of the lumbar multifidus muscle: measuring morphology

Stokes, Maria (2006) Rehabilitative ultrasound imaging of the lumbar multifidus muscle: measuring morphology. Rehabilitative Ultrasound Imaging Symposium, San Antonio, United States. 08 - 10 May 2006. A10-A11 . (doi:10.2519/jospt.2006.0301).

Record type: Conference or Workshop Item (Paper)

Abstract

What Is Known?

The lumbar multifidus muscle has been characterized using rehabilitative ultrasound imaging (RUSI) in normal populations, and people with spinal pathology. The reliability1, and validity of the technique have been demonstrated. Morphological features quantified for multifidus include cross-sectional area (CSA), linear dimensions (muscle depth/thickness and width) and shape ratios, with normal reference ranges established. Multifidus shape at the fourth lumbar vertebra (L4) is usually round or oval but a triangular muscle may indicate hypertrophy. At L5 the muscle usually appears triangular due to the shape of adjacent bony
surfaces.

Linear dimensions are predictive of CSA but the strength of this relationship is influenced by regularity of shape and wasting. The CSA is symmetrical sides) in normal populations and marked asymmetry occurs with acute low back pain (LBP)5 and idiopathic scoliosis.6 Recovery of size after LBP is not automatic and requires specific rehabilitation of multifidus. Size measurements and description of shape are potentially useful for clinical evaluation, and research into the effects of pathology and interventions.

What Is Unknown?

While data on multifidus morphology are increasing, different normal populations need to be studied to document the effects of factors such as ethnicity and habitual physical activity, particularly in sporting groups.

Size is highly correlated with strength in some muscles but this relationship is difficult to quantify in multifidus, as isolated force cannot be measured. The relationship between changes in muscle thickness and electrical activity is also unknown. The quality of the image can be poor in the presence of spinal pathology and in older people, possibly due to infiltration of fat and other noncontractile tissue, which needs to be quantified. The mechanism of wasting and whether it is a cause or effect of injury are unknown.

What Are the Future Directions and Research Priorities?

If RUSI is to become a routine aid to physical therapy practice and a robust research tool, standardized protocols for obtaining measurements are needed. The validity of using linear measurements to assess the CSA of irregularly shaped muscles requires attention. Comprehensive studies of different normal populations are needed to generate reference databases for assessing changes due to pathology and effects of interventions. Longitudinal epidemiological studies of multifidus are needed to determine those at risk of developing LBP, whether wasting occurs before the onset of injury/pain and to help elucidate the mechanisms of wasting. The contribution of noncontractile tissue to CSA needs to be quantified to determine true muscle size, particularly with pathology and aging. The sonographic technique of elastography is potentially useful for distinguishing the biomechanical behavior of these tissues.

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