Measurement of Muscle Size and Excursion

Ultrasound imaging devices have built-in software that allows for linear and elliptical (cross sectional area or circumference) measurements to be made.  Sonography provides a direct view of multifidus in cross section.  A comparison of multifidus size can be made between sides and between vertebral levels.  A validation study found no significant difference in measurements when using ultrasound imaging vs. magnetic resonance imaging (MRI) of multifidus cross sectional area. 

These measurements are important because a naturally occurring side effect of acute low back pain is sudden onset of lumbar multifidus atrophy.  This muscle wasting is related to recurrence of symptoms and is likely to lead to a chronic condition.  In one study, a 31% difference from right to left side of multifidus cross sectional area (CSA) was found in acute lower back pain patients.  In these patients, the smaller muscle was on the painful side and this was also confined to one vertebral level.

Multifidus measurements are documented in an initial evaluation if atrophy is present.  This can be documented as a percentage loss compared to the contralateral side or between segments.  After specific training of these muscles we expect to see muscle hypertrophy (or at least a regain of fluids within the muscle).  So periodic multifidus measurements may be taken using the same ultrasound imaging procedure.  Then progress can be documented in re-evaluation, progress, or discharge notes.

Ultrasound imaging measurements can be acquired showing the change in muscle depth upon isometric contraction of the transversus abdominis and multifidus.  A measurement of the excursion of transversus abdominis can also be obtained using ultrasound imaging.