Rehabilitative Ultrasound Imaging of the Posterior Paraspinal Muscles

journal of orthopaedic & sports physical therapy | volume 37 | number 10 | october 2007 | 581

[ CLINICAL COMMENTARY ]

The role of muscles in joint protection and stabilization has beenof increasing interest to researchers and clinicians involved inspinal pain and rehabilitation. Evidence for the importance ofdeep posterior muscles of the spine in the management of people

with low back pain (LBP) has been provided by biomechanical7,60,80,82

and neurophysiological46,48 investigations. Imaging studies have furtherallowed denition of both normal morphology and impairments

in paraspinal muscles.22,27,32,33 Rehabili-tative ultrasound imaging (RUSI) is apotentially useful tool in physical thera-py for the assessment and treatment ofthese muscles. The advantages of RUSIover other imaging techniques have beendiscussed in a recently published related

cles can be incorporated into neuromus-culoskeletal rehabilitation. The mainapplications of RUSI for measurementof morphological characteristics (mor-phometry) and visualization of musclecontraction for biofeedback are dis-cussed. The lumbar multidus is themost widely studied paraspinal muscle,in both healthy populations68 and peoplewith spinal pain and injury.22,26,27 Stud-ies of different cervical muscles are alsoemerging.37,39,61-63 In the thoracic region,the lower trapezius is the rst muscle tobe measured with ultrasound imaging.53

Quantitative evaluation of the posteriorparaspinal musculature using static anddynamic imaging has been used to studymuscle morphology and behavior dur-ing contraction.34,39,64,74,76 In this context,behavior relates to level of contraction(change in thickness), changes in sizeover time and with respect to othermuscles, as well as observation of con-traction as a biofeedback tool for the pa-tient or therapist. In this commentarywe review what is known about RUSI asapplied to the paraspinal musculature,propose guidelines for standardizingthe imaging and measurement tech-niques in clinical and research applica-tions, and propose future directions forresearch.

T SYNOPSIS: Interest in rehabilitative ultra-sound imaging (RUSI) of the posterior paraspinalmuscles is growing, along with the body ofliterature to support integration of this techniqueinto routine physical therapy practice. This clinicalcommentary reviews how RUSI can be used asan evaluative and treatment tool and proposesguidelines for its use for the posterior muscles ofthe lumbar and cervical regions. Both quantita-tive and qualitative applications are described,as well as measurement reliability and validity.Measurement of morphological characteristics ofthe muscles (morphometry) in healthy populationsand people with spinal pathology are described.Preliminary normal reference data exist for mea-surements of cross-sectional area (CSA), linear

dimensions (muscle depth/thickness and width),and shape ratios. Compared to individuals withoutlow back pain, changes in muscles size at rest andduring the contracted state have been observedusing RUSI in people with spinal pathology. Visualobservation of the image during contractionindicates that RUSI may be a valuable biofeed-back tool. Further investigation of many of theseobservations is required using controlled studiesto provide conclusive evidence that RUSI enhancesclinical practice. J Orthop Sports Phys Ther2007;37(10):581-595. doi:10.2519/jospt.2007.2599

T KEY WORDS: cervical muscles, lumbarmuscles, lumbar spine, neck, morphometry,sonography

1Professor of Neuromuscular Rehabilitation, Director of Research, School of Health Professions and Rehabilitation Sciences, University of Southampton, UK; Visiting Professor,Department of Physiotherapy, Trinity College, Dublin, Ireland. 2Senior Lecturer, Division of Physiotherapy, School of Health and Rehabilitation Sciences, University of Queensland,Brisbane, Australia; Clinical Director, UQ/Mater Back Stability Clinic, Mater Health Services, Brisbane, Australia. 3Assistant Professor, Department of Physical Therapy, RegisUniversity, Denver, CO; Doctoral Candidate, Division of Physiotherapy, School of Health and Rehabilitation Sciences, University of Queensland, Brisbane, Australia. 4AssistantProfessor, Department of Physical Therapy, University of Evansville, Evansville, IN; Assistant Professor, University of Kentucky, Lexington, KY. 5Professor and NHMRC PrincipalResearch Fellow, Director, Division of Physiotherapy, School of Health and Rehabilitation Sciences, University of Queensland, Brisbane, Australia. Address correspondence toDr Maria Stokes, Professor of Neuromuscular Rehabilitation and Director of Research, School of Health Professions and Rehabilitation Sciences, University of Southampton,Higheld Campus, Southampton, Hants SO17, 1BJ, UK. E-mail: [email protected]

manuscript.79

The primary purpose of this clinicalcommentary is to review the currentscientic literature on RUSI related tothe posterior paraspinal muscles andto increase the understanding of howRUSI of the posterior paraspinal mus-

Rehabilitative Ultrasound Imagingof the Posterior Paraspinal Muscles

MARIA STOKES, PhD, MCSP1 JULIE HIDES, PhD, MPhtySt, BPhty2

JAMES ELLIOTT, PT, MS3 KYLE KIESEL, PhD, MPT, ATC, CSCS4 PAUL HODGES, PhD, MedDr, BPhty (Hons)5

582 | october 2007 | volume 37 | number 10 | journal of orthopaedic & sports physical therapy

[ CLINICAL COMMENTARY ]ANATOMY OF THEPARASPINAL MUSCULATURE

Interpretation of RUSI is depend-ent on an understanding of the ana-tomical features and function of the

musculoskeletal structures of the spine.This section presents an overview of theanatomical and biomechanical propertiesof the paraspinal musculature, focusingon the lumbar and cervical muscles inrelation to RUSI. The reader is referredto the following manuscripts for furthermore specic details of anatomy andfunction.2-4,6,8,52,55,60

Posterior Lumbar Spine MusculatureThe lumbar paraspinal muscles, lyingbehind the transverse processes, havebeen divided into 3 groups by Bogduk.3

The rst and deepest group includes thedeep intersegmental muscles, interspi-nales, and intertransversarii mediales.These muscles are short and too small toprovide sufficient clarity of their bordersfor adequate visualization by ultrasoundimaging (USI). The second group com-prises the polysegmental muscles, whichattach directly to the lumbar vertebrae

and include the multidus and lumbarportions of the erector spinae (ES), lon-gissimus, and iliocostalis muscles (TABLE1). The third and most supercial groupof muscles consists of long, polysegmen-tal muscles, which traverse the lumbarregion from the thoracic levels. Thesemuscles attach to the ilium and sacrum,and include the thoracic portions of the

ES muscles.Lumbar Multidus This is the most me-dial of the lumbar muscles and Macin-tosh et al44 have described it as a large,multifascicular muscle composed of 5overlapping layers, with its size increas-ing in a caudal direction (FIGURE 1, TABLE1). The morphometry of the lumbar mul-tidus muscle can be assessed with RUSI

TABLE 1 Anatomy of Selected Lumbar and Cervical Posterior Paraspinal Muscles

Muscle Origin Insertion

Lumbar multidus44 Laminae and spinous processes of each lumbar vertebra Descend in a caudal direction to cross 3 to 5

vertebrae

Deep laminar bers: inferior edge of a lamina Mamillary bodies and zygapophyseal joint capsule

of the vertebra 2 levels caudal

Supercial bers: along the spinous process Cross up to 5 levels: attach to the mamillary

processes of the caudal vertebra, sacrum, and

posterior superior iliac spine

Erector spinae43

Longissimus Lumbar transverse and accessory processes Ventral surface of posterior superior iliac spine

Iliocostalis Tips of lumbar transverse processes and adjacent middle layer of Ventral edge of iliac crest

the thoracolumbar fascia

Cervical multidus2 Laminae and spinous processes of cervical vertebrae Capsules of cervical facet joints81

Semispinalis cervicis2 Transverse processes of the upper 5 or 6 thoracic vertebrae Cervical spinous processes of C2 to C5

Splenius capitis2 Spinous processes of C7 and T3 or T4 Just deep to sternocleidomastoid into the mastoid

process and occipital bone just below lateral third of

superior nuchal line

Semispinalis capitis2 Tips of transverse processes of T6 and T7, and C1-C3 articular processes Mastoid process

FIGURE 1. Cadaver dissection of lumbar multidus (M), rotatores (R), and the semispinalis (SS) musculature,showing fascicles passing down in a caudal direction over the lumbar spine.


using either a transverse or parasagittalimage. On the transverse section, lumbarmultidus can be identied as a singleregion of muscle and separate fasciclesare not often visible (FIGURES 2 and 3).The advantage of imaging using a trans-verse section is that the cross-sectionalarea (CSA) of the muscle can be mea-sured.21,68 Conversely, in a parasagittal(longitudinal) image, muscle fasciclescan be identied from the connectivetissue between muscle bers (FIGURE 4).

Parasagittal views are easier to interpretthan transverse views, both for measur-ing muscle thickness34 and for providingbiofeedback of changes in the muscleduring contraction.24,74

Researchers using biomechanicalmodels based on anatomical data havesuggested that the supercial bers oflumbar multidus create a posteriorsagittal rotation (extension) of the lum-bar spine, in addition to intervertebralcompression,43,4 while the deeper bersprimarily generate compressive forces,with minimal associated torque.4,47 It hasbeen proposed that the intersegmentalnature of the deep lumbar multidusprovides an advantage to the neuromus-

cular system for controlling the stabilityof the motion segment.55 For this rea-son, clinicians aim to include voluntarycontraction of the deep bers in theirexercise (or rehabilitative) programs.24

Electromyographic (EMG) studies ofarm movement suggest differential ac-tivation of the deep (earlier onset) andsupercial bers.51 This nding suggeststhat different exercises may be neces-sary for selectively re-educating the deepversus the supercial bers, but this re-quires investigation.

There is consistent evidence that thelumbar multidus muscle controls spi-nal motion, contributing to interverte-bral stiffness.31,55,80 Lumbar multidusRUSI studies have identied reducedCSA in people with acute LBP,26,27 andEMG evidence suggests that changes inmotor control may be more localized tothe deep bers.42 However, it is impor-tant to consider that all lumbar mus-cles contribute to stability of the lumbarspine.7,8,12,18,47,48,80

Lumbar ES The lumbar ES lie lateralto multidus and consist of longissimusthoracis pars lumborum and iliocostalislumborum pars lumborum (TABLE 1).43

In the upper lumbar region, research-ers have demonstrated that the longis-simus muscle overlaps the bers of themultidus muscle.43 Various studies haveshown that the ES muscles contribute tolateral exion, extension, and rotationof the lumbar spine, as well as stabil-ity.7,8,12,18,47,48,80 Regarding imaging, theES muscles are too large to allow CSAmeasurements using RUSI. However,Watanabe et al78 have measured thick-ness successfully in the sagittal plane byplacing the transducer longitudinally.Their technique illustrates the use of theechogenic (reective, white) transverseprocesses and subcutaneous tissue-mus-cle border as landmarks to assess thick-ness of the ES muscles.

Posterior Cervical Spine MusculatureThe posterior musculature of the cervi-cal spine is commonly divided into 4 lay-ers (FIGURE 5). The most supercial layer

FIGURE 2. Schematic diagram of a cross section at the level of the fourth lumbar vertebra (L4). The lumbarmultidus muscle (M) lies lateral to the spinous process, superior to the lamina (L), and medial to erector spinae(ES). Abbreviations: AT, adipose tissue; IL, iliocostal ligament; S, skin; SP, spinous process; TP, transverse process;VB, vertebral body.

FIGURE 4. Parasagittal ultrasound image of thelumbar multidus muscle, taken lateral to the spinousprocess using a 5-MHz curvilinear transducer. Thefacet joints (F) can be used as landmarks for thelower border of the muscle.

FIGURE 3. Bilateral transverse ultrasound image atL4, using a 5-MHz curvilinear transducer, showingthe spinous process (SP) in the center of the imageand the echogenic laminae (L) appearing as brightwhite horizontal landmarks, either side of the baseof the SP and beneath the lumbar multidus (M)muscle. The lateral borders are not clear enoughto enable measurement of area and require thetransducer to be angled more appropriately for eachside separately.



consists of the upper trapezius muscles,the second layer consists of the spleniuscapitis muscle,62 the third layer consistsof the semispinalis capitis63 and semispi-nalis cervicis muscles,71 while the deepestlayer contains the multidus and rotatoresmuscles. Some studies place semispinaliscervicis in this deepest layer,61 while othersalso include the suboccipital muscles ofrectus capitis posterior minor (RCPmin)and major (RCPmaj).71 We have limitedthe description of anatomical features ofcervical muscles to those described by re-searchers using RUSI.37,39,61-63

Cervical Multidus and Semispinalis Cer-vicis Winkelstein et al81 have suggestedthat the ability of the multidus muscle tocontrol cervical segmental motion couldbe compromised by its insertion directlyinto the capsules of the facet joints (TABLE1), which have been widely implicated inneck pain and injury.41,56,65,82 Degenerativechanges in the deep cervical paraspinalmusculature have been found in studiesusing RUSI and magnetic resonance im-aging (MRI) in patients with persistentneck pain following trauma.15,19,37,73 Thesemispinalis cervicis muscle (along withthe capitii musculature) is considered aprimary cervical spine extensor.52

Splenius Capitis and Semispinalis Capi-tis These muscles have been describedas broad and at, extending upward andlateral to their attachment on the mastoidprocess (TABLE 1).62,63 The main functionof these muscles is neck extension,46,71

and they are more active during large,fast movements of the neck11 than duringsustained postural activity.

QUANTITATIVE EVALUATION

The procedures described arebased on developmental studies byHides et al,21,26,27 Kiesel et al,34 and

a relatively large population study byStokes et al,68 and reect the suggestionsof the team of authors of this commen-tary. Both static and dynamic techniquesfor quantitative evaluation of muscles aredescribed.

Imaging Procedure for Lumbar MultidusImages of lumbar multidus have eitherbeen obtained from transverse (FIGURE3)21,22,26,27,68 or parasagittal (FIGURE 4)34

orientations.Positioning As originally suggested byHides et al,21 the subject is usually relaxedin a prone lying position. But this is notalways possible, as Coldron et al10 realizedwhen attempting to scan lumbar mul-tidus in women who had recently givenbirth. Researchers have shown that theside-lying position can be used to obtainimages without affecting muscle size atrest.10 But this is not the case when im-aging with the subject in a standing pos-ture.40 Lee et al40 found that in healthycontrol subjects, lumbar multidus CSAincreased from prone lying to uprightstanding, then gradually decreased dur-ing forward exion. In patients with LBP,CSA also increased from prone to uprightstanding, but forward exion produced afurther increase in CSA, suggesting al-tered function of lumbar multidus.40

As suggested by Hides et al,21 we recom-mend that, in prone lying, 1 to 2 pillows

be placed under the hips to minimize thelumbar lordosis, so that the muscles lie ashorizontally as possible along the spine.Inclinometers were used by Hides et al25

and Kiesel et al34 to ensure the lumbarspine was within 10 of horizontal.

Positioning of the operator relative tothe subject is important for standardiza-tion of the technique to achieve correctimage interpretation. So, with the subjectprone, we recommend that the scannerand operator be situated to the left of theprone subject (the opposite to imaginganterior structures in the supine subject),in keeping with standardized protocols inradiology.9,79

The lumbar spinous processes are pal-pated and their position located on theskin with an indelible marker, such asan eye liner pencil, which is water insol-uble but easily removed with an alcoholswab.54 In most individuals, the spinousprocess of L5 is a deep, small, bluntedbony point lying at the center of the lum-bosacral depression and can be found bypalpating cranially from the sacrum.5 Onprogression in a cranial direction is thecomparatively large spinous process ofL4. The remaining lumbar spinous pro-cesses are then identied by continuingpalpation cranially. These locations canbe veried with USI by including thesacral base in the image and counting thespinous processes cranially.Transducers Various transducers havebeen used for imaging the lumbar mul-tidus muscle, but we suggest the use ofa curved transducer with a frequency of5 MHz, which is used for transverse im-aging in the majority of studies (TABLE 2).This is because more of the sound wavesemitted by a curved transducer are likelyto be perpendicular to the rounded bor-der of multidus than those from a lineartransducer. For parasagittal imaging, weconsider transducer shape less impor-tant, so curvilinear34 or linear25 arrays canbe used. Regarding transducer frequency,the depth of lumbar multidus is moresuited to 5 MHz21,68 for image clarity thanlower or higher frequencies, such as 3MHz or 7 to 10 MHz, respectively.79 The

FIGURE 5. Magnetic resonance images: (A) sagittal cross section of the C6 vertebral level; (B) the correspondingaxial scan at the C6 level showing the cervical multidus (M), semispinalis cervicis (SEC), semispinalis capitis(SCP), splenius capitis (SC), and trapezius (T) muscles.


size of the transducer varies with differ-ent ultrasound machines (TABLE 2), but wesuggest using as large a footprint (lengthof array surface) as possible, with a mini-mum of 5 cm, to ensure sufficient contactwith the skin to enable a wide eld of viewon the scan. For further details on select-ing transducers, see a related publica-tion by Whittaker et al,79 which discussesthe relationships between muscle shape,depth, and transducer specications.Imaging Technique We endorse thetechnique used by a number of research-ers,21,25,27,68 in which the transducer wasrst placed longitudinally and centrallyover the lower lumbar spine to orientand conrm the marks on the skin. The

indicator mark on the side of the trans-ducer (either a line or light) was directedcranially, producing a scan showing thespinous processes, as seen in FIGURE 6. Forparasagittal imaging, researchers havedescribed moving the transducer later-ally to image lumbar multidus,34,74 usingthe facet joints inferiorly as a landmark(FIGURE 4). For transverse imaging, thetransducer was rotated from the central

longitudinal orientation through 90, tolie transversely in the midline with its in-dicator mark towards the operator,21,68 sothat the right side of the anatomy wouldappear on the right side of the screen.This produced an image in which the spi-nous process and laminae could be seen,with lumbar multidus muscles visibleon both sides of the spine (FIGURE 3). Ifthe muscles were too large for bilateralimaging, they were scanned individuallyby moving the transducer laterally, to theleft and right (FIGURES 7 and 8). As in thesepreviously cited studies, we recommendthat the echogenic (bright) vertebrallaminae be used as landmarks to identifythe muscles deep border, which is impor-tant when measuring CSA, as there is alarge difference in CSA over the span of1 vertebral level if a consistent landmarkis not used.

The lateral border of the lumbar mul-tidus muscle is often difficult to dis-tinguish from the lumbar longissimusmuscle, and strategies to produce musclecontraction can help to identify the bor-der during real-time imaging (TABLE 3).However, if a test movement is used, it isimportant that the subject relaxes beforemeasurements are taken. Off-line mea-surements on stored images do not havethe advantage of dynamic (real-time) im-aging for locating muscle borders and itmay me more of a matter of extrapolatingbetween identiable areas of a border.

TABLE 2Transducers for Ultrasound Imagingof the Posterior Lumbar and Cervical

Paraspinal Muscles*

Muscles Transducer Researchers Footprint Size (cm)

Lumbar

Multidus

Transverse image 5.0 MHz curvilinear Van et al74 5.5

Stokes et al68 5.0

Parasagittal image 5.0 MHz curvilinear Kiesel et al34 7.0

7.5 MHz linear Hides et al25 7.5

Cervical (Transverse)

Semispinalis capitis 7.5 MHz linear Rankin et al61 8.0

Deep posterior group 5.0 MHz curvilinear Rankin et al61 5.0

Multidus 10.0 MHz linear Lee et al39 3.8

7.5 MHz linear Kristjansson37 7.0

* Transducers with a large footprint (>5 cm) are preferable for sufficient contact with the skin to enablea wide eld of view. Transducer size and frequency depend on availability with a particular scanner.The preferable transducer for transverse imaging of lumbar multidus is 5 MHz curvilinear. Not reported in paper cited (detail gained from authors). The deep posterior cervical group comprises the semispinalis cervicis, multidus, and rotatores.

FIGURE 6. Ultrasound image showing a sagittal viewof the lumbar spine. The 5-MHz linear transducer wasplaced centrally over the spinous processes (SP).

FIGURE 8. Transverse ultrasound image of the rightlumbar multidus muscle at L5, using a 5-MHzcurvilinear transducer. The spinous process (SP) isshorter and the lateral edge less steep than at L4(Figure 7). (Reproduced from Stokes et al,68 withpermission).

FIGURE 7. Transverse ultrasound image of a leftlumbar multidus (M) muscle at L4, using a 5-MHzcurvilinear transducer. The oval shape of the muscleis evident and is bordered inferiorly by the lamina (L),medially by the spinous process (SP), and laterally bylongissimus (Lo).



Static Measurement of Lumbar MultidusThe CSA (cm2) of multidus is measuredby tracing around the muscle borderwith the on-screen cursor or off-line us-ing an image-processing package such asImageJ (http://rsb.info.nih.gov/ij/docs/index.html). For consistency, the precisepart of the border needs to be traced eachtime and the inner edge of the border isoften used.68 Two linear dimensions areoften measured, dened as the great-est depth (anteroposterior [AP]) andthe greatest width (lateral dimension[Lat]), lying perpendicular to the APdimension.21 Hides et al21 described theshape of the lumbar multidus muscle asa ratio of the linear measurements, withthe AP divided by the lateral dimension(AP/Lat). Stokes et al68 made anthropo-metric measurements on ultrasound im-ages to examine their relationships withCSA, including the length (cm) of thespinous process (SPL) and the horizontaldistance (cm) between the lateral edgeof each lamina (bilateral lamina width).Researchers have also used whole-bodymeasurements and characteristics to as-sess their predictive value for estimat-ing lumbar multidus size, includingheight, age, body mass, and body massindex (BMI).21,27,68 Relationships alludedto here, particularly between muscle di-mensions, will be discussed later in thecommentary.

Dynamic Measurement of LumbarMultidusReal-time RUSI can be used to assessmuscle during active movements. Dy-namic measures are described for theposterior cervical39 and the lumbar mul-tidus,34,74,75 as well as muscular fatigue.64

The most common RUSI measurementof the paraspinal muscles to representmuscle contraction is change in musclethickness. Watanabe et al78 measuredthickness change of the lumbar ES mus-cles in the sagittal plane. Signicantdifferences were found in measures ob-tained in neutral, exed, and extendedstatic postures. Kiesel et al34 used gradedresistance of contralateral upper extrem-ity lifts, performed in prone, to produceincremental activation of lumbar mul-tidus and demonstrated a positive re-lationship between increases in musclethickness and ne-wire EMG signals (seevalidity section below). Vasseljen et al75

used high-speed motion mode (M-mode)ultrasound, compared with ne-wireEMG, to identify movement of the deepbers of the lumbar multidus muscleduring rapid arm lifting. Lee et al39 foundsignicant increases in thickness of cervi-cal multidus during contractions, whichwere similar at 3 levels from C4 to C6.

It is clear that RUSI can be used tomeasure thickness of the posterior trunkmusculature.34 Preliminary studies of as-

ymptomatic subjects comparing RUSI tothe gold standard of intramuscular EMGare encouraging and suggest that RUSImay be used to measure both magni-tude34,39 and timing75 of activation in theparaspinal muscles.

Morphometry of the Lumbar MultidusThe lumbar multidus muscle, in the ab-sence of pathology, has been described asgenerally round or oval in shape, and itssize varies among the vertebral levels.25

Studies with similar methodology andsubject groups provide consistent data,as summarized in TABLE 4.Cross-sectional Area At the level of thefourth lumbar vertebra (L4), the meanCSA of multidus has been reported tobe approximately 8 cm2 in males and ap-proximately 6 cm2 in females (TABLE 4).The muscle becomes larger at L5 (ap-proximately 9 cm2 in males and approxi-mately 7 cm2 in females). The CSAs at L4and L5 are highly correlated (r = 0.82 formales, 0.80 for females), so one could bereasonably well estimated from the otherusing predictive equations.68 A multilevelanalysis of the entire lumbar spine indi-cated that multidus CSA increases fromL2 to L5 and then decreases at S1.25 Meandata from a group of 10 young femaleswere approximately 2.0 cm2 at L2, 3.3cm2 at L3, 4.9 cm2 at L4, 7.1 cm2 at L5,and 6.4 cm2 at S1.Linear Dimensions The thickness orAP dimension of lumbar multidus isapproximately 2.6 cm and the lateraldimension is approximately 2.8 cm inhealthy males (TABLE 4). In females, themean values are approximately 2.2 cmfor the AP dimension and 3.0 cm for thelateral dimension.Muscle Shape The linear dimensions in-dicate that the muscle is almost round inmales but more oval in a horizontal di-rection in females (ie, atter).21,68 A studyof 120 healthy subjects reported round,oval, and triangular lumbar multidusmuscle shapes.68 Gender, age, vertebrallevel, and physical activity accounted forthese different shapes.

The shape of the lumbar multidus

TABLE 3Strategies for Identifying the LateralBorder of Lumbar Multifidus During

Transverse Imaging

Maneuver by the Subject

Raise (extend) the ipsilateral lower limb slightly24

Shorten ipsilateral limb gently

Raise the contralateral upper limb34

Imagine the muscles are sausages on either side of the spine and try to shorten and fatten the sausages

Note: ensure that movements are minimal to maintain the test position and avoid movement of the transducer

from the scanning site

Observe on Transverse Image

Movement of multidus and adjacent erector spinae muscle (longissimus) in relation to each other. Fascicles

of multidus move in a swirling motion, sliding round against each other, which differs from the movements

of longissimus

Although a lateral border may not be visible, the relative motions of the muscles will indicate the boundary


muscle is not always regular, particularlyin subjects with relatively large muscles,where it can appear more triangular68

(FIGURE 9). The medial and inferior (deep)borders of the multidus are conned bythe spinous process and lamina, so themultidus can only hypertrophy in a lat-eral or superior (supercial) direction,which may explain the more triangularshape of hypertrophied muscles.68 Insuch cases, the shape ratio is mislead-ing as it would tend to suggest a roundshape. Stokes et al68 suggested that it maybe more appropriate to describe a trian-gular-shaped muscle using 3 measure-ments (the superior, medial, and lateralborders), but this requires investigation.The clinical relevance of lumbar multi-dus shape and whether or not it reectsmuscle tone have yet to be explored.

Prediction of CSA From Linear Mea-surements Researchers have shown that

linear measurements can reect CSA ac-curately.21,27,68 Linear measurements canbe made more quickly and easily thantracing the muscle border to measurearea (an option not available on all ultra-sound apparatus). Linear measurementsare therefore more applicable for clinicaluse than CSA, provided they predict CSAaccurately. The combined linear measure-ments (AP Lat) were highly correlatedwith CSA at L4 and L5 (range in males,r = 0.95 to 0.98; range in females, r =0.93 to 0.95) in 3 studies (TABLE 4).21,27,68

However, it is known that this correla-tion for resting muscle weakens whenmuscle becomes atrophied (r = 0.75 and0.85 in males and females, respectively27)and cannot be assumed in all situations.Thus the clinical utility of the predictionof CSA from resting linear measures may

TABLE 4Lumbar Multifidus Morphometry From Images

in Prone Lying in Healthy Populations

Abbreviations: AP, anteroposterior; CSA, cross-sectional area; L, left; NR, not reported; R, right.* Mean 1 SD, range.

CSA VersusLinear

AP Dimension Lateral DimensionsPopulation Age (y)* Researchers CSA (cm2)* Shape Ratio* Thickness (cm)* Dimension (cm)* Multiplied (r)

Fourth Lumbar Vertebra

Males

n = 21 18-35 Hides et al21 6.15 0.93 (4.35-8.5) 0.91 0.12 (0.68-1.19) 2.55 0.3 (2.03-3.35) 2.82 0.23 (2.50-3.31) 0.98n = 52 40 13 (20-69) Stokes et al68 7.78 1.85 (4.24-11.5 [95%]) 1.02 0.15 (0.72-1.33) NR NR 0.96n = 19 41.7 (35-47) Lee et al40 R, 7.68 1.29; L, 7.62 1.38 NR NR NR NR

Females

n = 27 18-35 Hides et al21 5.6 0.8 (4.18-7.23) 0.75 0.13 (0.42-0.98) 2.24 2.98 (1.63-2.75) 3.05 3.25 (2.35-3.96) 0.93n = 10 25.5 (21-31) Hides et al27 4.87 1.22 NR NR NR NRn = 68 34 13 (20-64) Stokes et al68 5.55 1.28 (3.03-8.06 [95%]) 1.05 0.21 (0.64-1.47) NR NR 0.95

Fifth Lumbar Vertebra

Males

n = 45 39 13 (20-69) Stokes et al68 8.91 1.68 (5.62-12.30 [95%]) 1.03 0.17 (0.70-1.36) NR NR 0.95n = 19 41.7 (35-47) Lee et al40 R, 7.25 2.11; L, 7.14 1.55 NR NR NR NR

Females

n = 10 25.5 (21-31) Hides et al27 7.12 0.68 NR NR NR NRn = 46 32 12 (20-64) Stokes et al68 6.65 1.0 (4.69-8.60 [95%]) 0.95 0.17 (0.62-1.28) NR NR 0.94

L4/5

Males and 28 5.6 Kiesel et al34 NR NR 2.48 0.19 NR NRfemales,

n = 5

FIGURE 9. Transverse ultrasound image of atriangular shaped left lumbar multidus muscleat L4, taken using a 5-MHz curvilinear transducer.(Reproduced from Stokes et al,68 with permission.)


[ CLINICAL COMMENTARY ]be limited, as in most cases comparisonof atrophied and nonatrophied musclesis the objective of the assessment. Dur-ing contraction, however, Kiesel et al33

found that the AP linear measurementof lumbar multidus was consistentlydecreased by induced pain, indicatingthat this simple, time-efficient measuremay be clinically useful for assessment ofcontraction capability. Correlations werefound to be poor between muscle size andbody anthropometry.68

Muscle thickness (AP dimension) wasalso highly correlated with CSA at L4(males, r = 0.8; females, r = 0.7). Howev-er, at L5, although statistically signicant(P.001), the relationship was not strongenough to be of clinical value (males, r =0.66; females, r = 0.54), assuming thatcorrelation coefficients above 0.70 arerequired to be clinically signicant.36 Wesuggest that multiplication of the lineardimensions, although not representativeof a round or oval shape, is preferable toa single measurement when area cannotbe measured, based on evidence of itshigh correlation with lumbar multidusCSA.21,27,68

Symmetry Mean between-side differ-ence in lumbar multidus muscle sizein healthy individuals without pain orpathology has been found to be below10% (mean SD, 3 4%27; 9.6% 8% in males,68 8.1% 6% in females68).Marked asymmetry can occur with acuteLBP27 and be a useful clinical indicator ofabnormality.Effect of Age Researchers have not founddifferences in lumbar multidus musclesize among different age groups.68 How-ever, the quality of the muscle may be-come altered, as changes in water andfat content that occur with age producechanges in signal intensity on MRIscans.72 Inltration with fatty or broustissue increases the echogenicity of mus-cle, making it appear whiter than usual,as observed in some of the older subjects(up to age 69 years) studied by Stokes etal.68 But a reliable method for quantica-tion of these changes in ultrasound im-ages has yet to be developed.

Imaging Procedure for the PosteriorCervical MusclesThere are limited published data on RUSIof the cervical muscles. Those studiedinclude splenius capitis,62 semispinaliscapitis,61,63 multidus,37,39 and the deepposterior cervical muscle group compris-ing semispinalis cervicis, multidus, androtators.61

Positioning Imaging of the cervical mus-cles has been described with the subjectsitting39,63 or prone lying,37,61,62,63 with theneck in a neutral position. Rezasoltani etal63 used an inclinometer to help ensurethat the thoracic and cervical postureswere horizontal during the ultrasoundmeasurements. Locating the vertebrallevels to be imaged has been achieved bypalpation of the cervical spinous process-es between C2 (the rst bony landmarkcaudal to the occiput) and C7 (the mostprominent spinous process), as detailedby Lee et al.39

Transducers Examples of transducersused for the different muscles are listedin TABLE 2. For example, a 7.5-MHz lin-ear transducer was used for imagingsemispinalis capitis61,63 and splenius ca-pitis,62 which are relatively supercialat muscles, while a 5-MHz curvilineartransducer was used for the deep musclegroup, which has a more oval shape.61

Conversely, for imaging cervical multi-dus, a deep oval muscle, Lee et al39 used a10-MHz linear transducer and Kristjans-son37 used a 7.5-MHz linear transducer,possibly determined by availability oftransducers rather than suitability. Mostresearchers have held the transducer inplace manually, but custom-made devicesto hold the transducer have also been de-scribed.39 The devices can enable a moreconsistent technique than manual appli-cation but need to allow the transducer tobe tilted or angled to sharpen the imageif necessary. Devices obviously have costimplications.Imaging Technique Procedures havebeen described for splenius capitis atC3,62 semispinalis capitis at C3,61,63 thedeep muscles as a group at C3,61 and mul-tidus at C437 and C4 to C6.39 In all cases,

the transducer was placed transversely inthe midline over the spinous process atthe level of interest and then moved lat-erally to image the left or right muscles.Identication of the echogenic (bright,reective) laminae is then useful, which-ever muscles are imaged.

The splenius capitis lies deep to thetrapezius and is a broad, at muscle. Thesemispinalis capitis is easily recognizedas a long, strap-like muscle divided into2 sections by an aponeurotic intersection(FIGURE 10). The deep neck muscle grouphas a distinctive teardrop shape, but thefascia between the 3 constituent muscles(semispinalis cervicis, multidus, androtatores) are not always easy to distin-guish in symptomatic or asymptomaticsubjects with RUSI (FIGURE 11). The cervi-cal multidus muscle lies ventral to thesemispinalis cervicis and the fascia be-tween them is more consistently denedusing 7.5- to 10.0-MHz linear transduc-ers than a 5.0-MHz curvilinear trans-ducer (FIGURE 11).

Morphometry of the Posterior CervicalMusclesResearchers have reported data for CSA,linear dimensions, and shape ratios inhealthy populations and some examplesare shown in TABLE 5. The muscles of theneck are relatively small (mean CSA be-tween 1 and 3 cm2) compared with thelumbar muscles. Atrophy of the cervicalmultidus muscle was demonstrated inwomen with chronic whiplash-associ-ated disorder (mean SD multidusCSA at C4: right, 0.96 0.19 cm2; left,

FIGURE 10. Transverse ultrasound image of the leftsemispinalis capitis muscle, a long strap-like muscle,using a 7.5-MHz linear transducer. The cross-sectionalarea and aponeurosis (A) dividing the muscle intomedial and lateral parts are indicated. (Reproducedfrom Rankin et al,61 with permission).


1.06 0.19 cm2) compared with healthyfemales (right, 1.23 0.09 cm2; left, 1.25 0.10 cm2) (P.05).37 Studies of mul-tidus at C4 showed slight differencesin CSA between the groups studied butmarked differences in shape ratio,37,39 as

evident in TABLE 5. These differences forcervical multidus could have been dueto the different postures used for imag-ing, as in 1 study the subjects were ly-ing prone37 and in the other they weresitting,39 which could have affected thetonic activity of the resting muscle. Therewere no differences in measurements ofthe semispinalis capitis muscle made inprone and sitting,63 and the 2 studies ofthe semispinalis capitis were in agree-ment.61,63 The shape ratio value indicatesthe shape well, for example, the 2 atsupercial muscles, splenius capitis andsemispinalis capitis, were approximately7 to 8 times wider than they were thick.The multiplied linear dimensions werecorrelated with CSA in all muscles (r =0.77-0.96).

Reliability of Measurement of ParaspinalMusclesVarious factors inuence the robustness

of measurements and have been discussedelsewhere in a related commentary.79 Con-sistently recognizable bony features canbe useful internal landmarks, such as theechogenic vertebral laminae, when imag-ing the paraspinal muscles.68 To our knowl-edge, 8 studies have reported the reliabilityof using RUSI to measure paraspinal mus-culature. Differences in study design, sta-tistical tests, and reporting method makedirect comparisons somewhat difficult,but those values considered key when in-terpreting reliability have been included inTABLE 6. The majority of researchers mea-sured muscle girth (CSA),59,61,63,68 whileothers measured thickness utilizing theparasagittal view.34,74,76 Intraclass correla-tion coefficient (ICC) values range from0.72 to 0.98.

In addition to the ICCs, the standarderror of measurement (SEM) or 95% lim-its of agreement, both of which are con-sidered measures of response stability,

FIGURE 11. Bilateral transverse ultrasound image ofthe deep posterior cervical muscle group, using a 7.5-MHz linear transducer, showing the teardrop shape,consisting of multidus, rotatores, and semispinalis.The cross-sectional area of cervical multidus isindicated on the right side of the image. (Reproducedfrom Kristjansson37 with permission.)

TABLE 5 Cervical Paraspinal Muscle Morphometry in Healthy Populations*

Abbreviations: AP, anteroposterior; CSA, cross-sectional area; Lat, lateral; L, left; NR, not reported; R, right.* Subject positioning is indicated for each study. Data are mean 1 SD, except for age ranges, with 2 exceptions.

CSA VersusLat Linear

Shape AP Dimension Dimension DimensionsMuscle/Position Level Population Age (y) CSA (cm2) Ratio Lat/AP (Thickness) (cm) (cm) Multiplied (r)

Splenius capitis

Prone lying62 C3 Females, n = 10 19-29 R, 1.90 0.23 R, 8.83 1.05 NR NR 0.77L, 1.76 0.25 L, 8.54 1.08

Semispinalis capitis

Sitting63 C3 Males, n = 18 19-34 R, 1.99 0.37 R, 6.82 0.93 R, 0.58 0.08 R, 3.85 0.39 0.85L, 1.93 0.38 L, 6.58 1.04 L, 0.59 0.08 L, 3.76 0.36

Females, n = 28 19-34 R, 1.57 0.35 R, 7.00 1.07 R, 0.51 0.08 R, 3.55 0.42L, 1.56 0.34 L, 6.86 1.10 L, 0.52 0.07 L, 3.53 0.41

Prone lying61 C3 Males, n = 46 20-72 1.77 0.40 7.20 1.14 0.53 0.08 3.73 0.39 0.86Females, n = 53 18-70 1.34 0.42 7.10 1.34 0.48 0.11 3.27 0.48 0.84

Deep neck muscles

Prone lying61 C3 Males, n = 46 20-72 3.15 0.67 0.57 0.06 2.76 0.36 1.57 0.17 0.96Females, n = 53 18-70 2.60 0.05 0.57 0.10 2.49 0.28 1.40 0.19 0.84

Cervical multidus

Sitting39 C4-C6 Males and 26.8 3.8 C4, 0.92 0.16 C4, 2.40 0.47 C4, 0.72 0.10 C4, 1.70 0.20 NRfemales, n = 17 C5, 0.96 0.16 C5, 2.67 0.52 C5, 0.68 0.08 C5, 1.80 0.25 NR

C6, 1.20 0.29 C6, 2.54 0.63 C6, 0.77 0.09 C6, 1.90 0.38 NRProne lying37 C4 Females n = 10 31.5 11.4 R, 1.23 0.09 R, 1.68 0.19 NR NR NR

L, 1.25 0.10 L, 1.58 0.14 NR NR NR



may be reported (TABLE 6). The purposeof the measurement must also be takeninto consideration. For example, it hasbeen shown that by taking an average of3 measures of the transversus abdominismuscle with RUSI, the SEM is reducedby approximately 50%.67 Reducing theSEM may be helpful in detecting groupdifference, but may be more importantwhen the purpose of the measure is to as-sess change postintervention. To be 95%condent that true change (greater thanmeasurement error) has occurred frompreintervention to postintervention, thechange score must exceed the minimaldetectable change (MDC) for that mea-sure. The MDC95 is SEM 2 1.96,where 1.96 represents the value of the tdistribution for a 95% condence inter-val (CI) and is in the units of the mea-sure. For example, Van et al74 used RUSI

to measure lumbar multidus musclethickness during contraction. The ICCwas reported to be 0.98 and the SEM was0.31 cm. If this measurement were usedto assess change in muscle thickness fol-lowing an intervention period, the MDC95could be calculated. To be 95% condentthat true change occurred, the thicknessmeasured would have had to change byat least the value of the MDC95, which is0.86 cm, based on 0.31 2 1.96 =0.86. In general, the reliability of usingRUSI to measure paraspinal musculaturecan be considered to be fair to excellent(ICC = 0.72-0.98) and acceptable forclinical use, as dened by Portney andWatkins.58

Validity of Measurements of ParaspinalMusclesHides et al25 conducted a study to deter-

mine the validity of RUSI measures oflumbar multidus compared with MRI.Bilateral measurements of CSA weremade at vertebral levels from L2 to S1in healthy females. No signicant differ-ences were demonstrated between RUSIand MRI, despite the inherent differenc-es in position for imaging (prone lying forRUSI and supine lying for MRI), whenresearchers adhered to a strict measure-ment protocol.25

To validate the use of RUSI for mea-suring muscle contraction, changes inmuscle thickness have been compared toEMG activity of various muscles, includ-ing the transversus abdominis49,29 andlumbar multidus muscles.34 The rela-tionship varies between muscles and theexperimental protocol (eg, contractiontype), but, in general, it is considered tobe curvilinear.

TABLE 6Reliability of Rehabilitative Ultrasound

Imaging of the Paraspinal Muscles

Abbreviations: CSA, cross-sectional area; ICC, intraclass correlation coefficient; L, left; NR, not reported; R, right; SEM, standard error of measurement.

Interrater Reliability

Researchers Population and Muscles ICC Response Stability ICC Response Stability

Stokes et al68 10 healthy subjects (5 male). Within session and 95% limits of agreement NR NR

Lumbar multidus CSA at L4 between days, within session, 0.25 to

0.98-1.0 0.5 cm2; between days,

0.62 to 0.67 cm2

Pressler et al59 15 healthy females.

Multidus CSA at S1 Between-days ICC3,1: SEM: R, 0.32 cm2; NR NR

R, 0.80; L, 0.72 L, 0.37 cm2

Kiesel et al34 8 healthy subjects. Lumbar ICC3,1 = 0.85 NR Measurements made by NR

multidus thickness measured both raters on same

on parasagittal images scans. ICC3,1 = 0.95

Van et al74 25 healthy subjects. Lumbar Within-day ICC1,1, 0.98 SEM: rater 1, 0.31 cm; ICC2,3 = 0.98 SEM, 0.31 cm

multidus thickness at L4/5 and 0.97 rater 2, 0.32 cm

Wallwork et al77 Lumbar multidus thickness ICC1,3 = 0.92, NR ICC3,2 = 0.97 NR

at L4/5 both raters

Rankin et al61 Semispinalis capitis CSA Within session and 95% limits of agreement NR NR

between days, 0.99 within session, 0.09

to 0.16 cm2; between

days, 0.16 to 0.16 cm2

Rankin et al61 Deep cervical muscles CSA 0.98-0.99 95% limits of agreement NR NR

within session, 0.27 to

0.28 cm2; between days

0.04 to 0.41 cm2

Rezasoltani et al63 Semispinalis capitis CSA 0.98 NR 0.98 NR

Intrarater Reliability


In the parasagittal view of the lum-bar multidus muscles, Kiesel et al34

studied the relationship between thick-ness change (percent change from rest)and ne-wire EMG activity (percent ofmaximum) during a contralateral pronearm-lifting task with increasing resis-tance, which automatically recruited theipsilateral multidus muscle. This taskproduced contractions from 19% to 43%of maximum effort, with a strong corre-lation (r = 0.79, P.001) between thick-ness change and EMG activity. But, therewas no signicant difference in multi-dus thickness change between the last 2levels of activation, indicating that theEMG signal continued to increase withload but thickness change was nearingits maximum. Muscles are consideredto reach their maximum thickness atrelatively low EMG values (approxi-mately 20% of maximal contraction).29

In isometric contractions this relates tothe point at which tendon stiffness pre-cludes further tendon stretch and themuscle continues to form cross-bridgesand increase electrical activity, but withminimal further change in length and,therefore, thickness. Many functionaldaily activities involve contractions atrelatively low forces, which would fallwithin the linear part of the relationship,where change in EMG reects change inmuscle thickness. With respect to jointstabilization, mathematical models havepredicted that only low-level contrac-tions of the lumbar multidus muscleare required to stiffen the spine.6 Clini-cians have therefore advocated low-levelvoluntary contractions to train the mul-tidus muscle for this role, which can beaided by observing changes in thicknesson RUSI images.24

Vasseljen et al75 used high-speed M-mode ultrasound to identify deformationof the deep bers of the lumbar multid-us muscle with concurrent EMG signal totest the validity of using the ultrasoundto measure the timing of activation. Sub-jects performed rapid arm lifting, whichis known to activate the deep and super-cial lumbar multidus muscle,51 the onset

of which may be delayed in patients withLBP. Visual determination of the muscleonset using ultrasound was comparableto EMG, but with a small systematic de-lay. Although preliminary, these resultssuggest that ultrasound may be used inthe future to measure deep muscle onsetsclinically.

Validity of RUSI against MRI was ex-amined for the cervical multidus musclein 10 healthy subjects at 3 cervical levelsfrom C4 to C6.39 Lee et al39 consideredthat validity was acceptable for musclethickness measurements (R2 = 0.42-0.64), but not for CSA (R2 = 0.11-0.39)and width (R2 = 0.16-0.69). The smallCSA of the muscle (approximately 1 cm2

compared with 7 cm2 for lumbar multi-dus) may amplify errors, thus inuencethe variability of measurements.

CLINICAL STUDIES OF STATICPARAMETERS

The paraspinal muscles have beenstudied using RUSI to assess the ef-fects of acute and chronic LBP, as

well as the effects of interventions, suchas exercise and spinal surgery.

Acute LBPHides et al27 found marked side-to-sideasymmetry of the lumbar multidus mus-cle CSA in 26 patients with rst-episodeacute unilateral LBP. The smaller musclewas found at the symptomatic segment(identied by manual palpation), was onthe side ipsilateral to symptoms, and wasconned predominantly to 1 vertebrallevel. In the 26 subjects with LBP, aver-age (SD) between-side difference was31% 8%, compared with 3% 4% in51 asymptomatic subjects. It was not pos-sible to determine whether the reductionin CSA was pre-existing in these subjects.However, data from a study using a por-cine model have conrmed that the CSAof the lumbar multidus muscle reducesrapidly (as early as 3 days) after injury toan intervertebral disc, is isolated to a sin-gle segment (the level below the injureddisc), and is associated with histochemi-

cal changes in the muscle.28

Kiesel et al33 demonstrated the effect ofpain on lumbar multidus muscle func-tion experimentally in humans. Increasesin multidus thickness during arm-liftingtasks were signicantly reduced by painin response to injection of saline into theerector spinae muscles. This investigativeapplication of RUSI not only contributedto knowledge about the effects of pain onmuscle activation but added to the valid-ity of RUSI as a clinical measurement ofmuscle dysfunction.

Chronic LBPSignicant atrophy of CSA was found byHides et al22 in patients with chronic LBPcompared with healthy controls at thelowest 2 lumbar vertebral levels. Greatestasymmetry was seen at L5 in those withunilateral pain. These results were in agree-ment with previous computed tomographystudies indicating that the pattern of lum-bar multidus muscle atrophy in patientswith chronic LBP was localized to the lowerregion of the spine rather than generalized13

and that asymmetry occurred in those withunilateral pain.1 In an MRI study of patientswith LBP, Barker et al1 also reported thisselective, localized atrophy. Conversely, an-other study using computed tomography tomeasure patients with chronic LBP foundgeneralized atrophy in the lumbar spinebut also relatively greater CSA of multi-dus on the symptomatic side.70 This ndingwas consistent with histological evidence oftype I ber hypertrophy and type II beratrophy in individuals with chronic LBP,17

possibly indicating an adaptive responseto muscle wasting. We speculate that thispseudohypertrophy could also be related tofatty inltration.35

Prelumbar Surgery and PostlumbarSurgeryImaging techniques have proved use-ful for investigating the effects of spi-nal surgery on the lumbar multidusmuscle.32,38,66 In cases of unilateral LBP,researchers using computed tomographyfound that paraspinal muscles were 10%to 30% smaller on the affected side com-


[ CLINICAL COMMENTARY ]pared to the unaffected side and fatty de-generation was also evident.38 Reducedmuscle CSA was seen using RUSI inpatients prior to surgery with atrophybeing more severe in those with greaterLBP.32 Postoperative images showed nofurther decrease in CSA. However, it wasnot possible to conrm that muscle at-rophy had not occurred, as size changescould have been masked by intramus-cular inammation, seen as hypoechoicareas. Long-term follow-up at 1 year in-dicated that multidus muscle atrophywas long lasting.

QUALITATIVE ASSESSMENTAND FEEDBACK

Both static and dynamic param-eters can be assessed qualitativelyusing RUSI. Static assessment gen-

erally involves evaluating the ultrasoundimage focusing on tissue quality. The as-sessment of dynamic parameters includesusing USI to evaluate the ability of themuscle to contract and teaching muscleactivation using the image as a source ofbiofeedback.

Assessment of Static ParametersImpairments of the lumbar muscles insubjects with LBP have been demon-strated in terms of both decreased mus-cle size and density.27,50 Decreased muscledensity can be caused by fatty inltration(increased fat-muscle ber ratio) or ac-tual fatty replacement of bers.35,45 Whilechanges in density have been predomi-nantly reported in computed tomographyand MRI studies, changes in consistencyof the lumbar multidus muscles havebeen observed using USI.27,32 The ultra-sound appearance of healthy muscle isusually dark, due to its excellent perfu-sion and resultant high uid content.The presence of fatty inltration, brouschanges, or scar tissue (noncontractiletissue) leads to a change in its sonograph-ic appearance, as noncontractile tissue ishyperechoic, making muscle appear morewhite (FIGURE 12).27 On computerized to-mographic scans, normal healthy muscle

appears grey and uniform. Consistencychanges will present as dark areas. Incontrast, on specic MRI sequencing,fatty inltration and brous changes ap-pear white. Consistency changes havemost commonly been reported in sub-jects with chronic LBP.30

The fat content of the lumbar multi-dus and longissimus muscles was mea-sured in 25 patients with chronic LBPand 25 matched asymptomatic volun-teers using MR spectroscopy.50 There wasa signicantly higher mean percentage offat content in subjects with chronic LBP(23.6%; 95% CI: 17.5%, 29.7%) than inasymptomatic subjects (14.5%; 95% CI:10.8%, 18.3%). Values for the longissi-mus muscle did not differ between pa-tients and control subjects. Further work

is required to validate the interpretationof muscle density on RUSI and to de-termine reliability. This is likely to be acomplex task because image brightnessis inuenced by the individualized gainsettings used by the operator.

Lumbar multidus muscle atrophy ap-pears to be a common nding in patientswith chronic LBP. In a recent MRI studyof 78 patients with LBP (with and withoutlower extremity pain), changes in multif-idus muscle consistency were graded asmild (fatty or brous tissue replacementless than 10%), moderate (replacementless than 50%), and severe (greater than50%).30 Degeneration of multidus waspresent in 80% of the subjects with LBP,and most commonly occurred at the L4-L5 and L5-SI levels. Sixty-six of the 78patients with LBP (85%) had degener-ated lumbar discs on MRI.

Assessment of Dynamic ParametersClinical assessment of paraspinal muscleperformance involves palpation of thelumbar multidus muscles at each ver-tebral level as the patient preferentiallyactivates the muscle. Muscle thicknesschanges can be seen using real-timeRUSI (FIGURE 13) as the patient performsthe test maneuver and have been dem-onstrated reliably in the lumbar24,26 andcervical muscles.39

FIGURE 13. Biofeedback of lumbar multidus: parasagittal view using split-screen function and 5-MHz curvilineartransducer. The facet joints (F) were used as landmarks for the lower borders of the multidus (M) muscle. Duringcontraction (right panel), the muscle becomes thicker and the angle of the bers becomes steeper, providingfeedback. The left panel shows the muscle at rest.

FIGURE 12. Hyperechoic lumbar multidus muscleat L5 in a patient with chronic low back pain, usinga 5-MHz curvilinear transducer. The muscle tissueappears whiter compared with that in the scans ofnormal subjects in Figures 3, 7, 8, and 9.


The ability of patients with chronicLBP to activate the lumbar multidusmuscle has been found to be reduced, asevidenced by smaller increases in thick-ness on RUSI images during contrac-tion than in asymptomatic controls.77 Arandomized controlled trial of healthysubjects by Van et al74 examined whethervisual biofeedback using RUSI enhancedthe ability to activate the lumbar multi-dus muscle. All subjects received clinicalinstruction on how to activate the mul-tidus muscle isometrically and verbalfeedback on performance (acquisitionphase). The intervention group receivedvisual biofeedback with RUSI in parasag-ittal section.24,26,34 Both subject groupsimproved voluntary contraction (increas-es from resting thickness) in the acqui-sition phase, but the RUSI biofeedbackgroup achieved greater improvements.On reassessment a week later (retentionphase), the RUSI group maintained theimprovements, whereas performance inthe control group decreased.

A clinical randomized controlled tri-al of people with acute LBP used RUSIsuccessfully for feedback of lumbar mul-tidus muscle activation.26 Symmetry ofmultidus CSA was restored in the exer-cise intervention group within 4 weeks.Despite pain relief and the general muscleuse associated with return to normal ac-tivity levels, patients in the control group(conventional treatment) still displayedmultidus atrophy at a 10-week fol-low-up. Long-term results revealed thatsubjects from the specic-exercise groupexperienced fewer recurrences of LBPthan the control group.23 A limitation ofthis work is the lack of comparison withan exercise group focusing on multidusrehabilitation without RUSI feedback.Nevertheless, other investigators havesimilarly advocated the benets of RUSIfor teaching muscle activation.14,20,24,74

The principles of motor learning16 mayexplain why visual feedback is of benet forsubjects with LBP. In the initial stages oflearning a new skill (cognitive stage), timeis spent understanding the demands of thetask, what to do, and what to feel. The clin-

ical observation that people with LBP ndit difficult to contract the lumbar multi-dus muscle may be due to processes suchas reex inhibition,69 which was thought toplay a role in multidus wasting in individ-uals with acute LBP.27 Biofeedback may bebenecial as subjects with LBP have beenshown to have decreased proprioception,57

which affects their ability to provide andprocess internal feedback.

Clinical ImplicationsPrescription of therapeutic exercise forthe patient with LBP is based on knowl-edge of normal function of the paraspinalmuscles, and the presence and nature ofimpairment in terms of size or activation.Impairment of lumbar multidus is of-ten specic to the side and vertebral levelof symptoms22,24,26,27 and this has beenfound in subjects with acute and chronicLBP. Before the introduction of RUSIinto clinical practice, physical therapistscould only palpate for multidus muscleatrophy. This may have previously ledto an underestimation of atrophy. Viavisualization of the paraspinal musclesusing RUSI, impairments can be betterassessed and documented. In addition toobjective measurements of muscle size,changes in muscle consistency can alsobe observed. RUSI can be used to pro-vide baseline measures of impairments,and also to document improvements overtime and with intervention. Therapeuticexercise may need to be as specic asthe impairments that occur in order toaddress them. RUSI can provide visualfeedback to enhance motor learning forcontracting a specic muscle or part of amuscle. From a clinical perspective, theuse of imaging techniques has alreadyprovided a wealth of information in bothresearch and clinical practice.

Evidence that feedback with RUSI en-hances motor learning holds promise forthe future but studies are needed on sub-jects with LBP, and therapeutic exerciseinterventions need to be compared withand without the use of RUSI for biofeed-back, to ultimately determine the benetsof this rehabilitation tool.

DIRECTION OF FUTURERESEARCH

Almost all lines of research onparaspinal muscles produce morequestions or uncover areas of un-

certainty. If RUSI is to become a routineaid to physical therapy practice and a ro-bust research tool, standardized protocolsare needed. Technical studies of the sizeof the transducer and whether linear andcurvilinear arrays produce the same mea-surements are needed to provide guid-ance on appropriate methodology. Thepredictive value of linear measurementsto provide an estimate of CSA needs to beestablished for different muscles in dif-ferent states, such as resting, contracted,wasted, or hypertrophied. The validityof using linear measurements to predictthe CSA of irregularly shaped muscles re-quires attention.

Comprehensive studies of healthypopulations are needed to generate refer-ence databases for assessing the effects ofpathology and interventions. Factors toconsider include age, gender, body type(physical characteristics including heightand body mass), ethnicity, geographicdistribution (due to lifestyle differences),and levels of habitual physical activityfrom sedentary to elite sporting groups.Data for interrelationships between dif-ferent spinal levels would be useful fordetecting abnormality at a specic level.

Substantial work remains to validatethe dynamic techniques for measuringboth magnitude and timing of changes inmuscle for clinical use. Longitudinal epi-demiological studies are needed to deter-mine those at risk of developing LBP orneck conditions, whether wasting occursbefore the onset of injury and/or pain,and to help elucidate the mechanisms ofwasting.

The contribution of noncontractiletissue to CSA, affecting the density (orconsistency) of muscle, needs to be quan-tied to determine true muscle size withpathology, particularly in subjects withchronic pain, and aging. The sonographictechnique of elastography is potentially



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useful for distinguishing the biome-chanical behavior of these tissues.53,79 Itwould be of interest to know if the ratio ofnoncontractile tissue to contractile tissuecan be altered with therapeutic exercise.Elastography may also help distinguishbetween activity of the deep and super-cial parts of muscle to study their differ-ing functions.

The effects of different pathologieson the paraspinal muscles need to beestablished in musculoskeletal and neu-rological disorders. Large randomizedcontrolled trials are needed to demon-strate that RUSI is a reliable outcomemeasure for assessing the effects of in-terventions. We recommend that futurestudies present data consistently and usethe same statistical methods, as outlinedby Whittaker et al79 to enable valid com-parison between studies and to enhanceaccumulation of large reference databas-es as a common resource for evaluationof abnormality.

ACKNOWLEDGEMENTS

We thank the following forproviding images for the gures:Dr Cliff Barnes, Associate Pro-

fessor in charge of Neuroanatomy in theDepartment of Physical Therapy at RegisUniversity, Denver, for help with produc-ing the image of the cadaver dissectionin FIGURE 1; Nick Smith, Peter Worsley,and Martin Warner, School of HealthProfessions and Rehabilitation Sciences,University of Southampton, UK, for theultrasound scan in FIGURE 4. T


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Rehabilitative Ultrasound Imaging of the Posterior Paraspinal Muscles