Rehabilitative Ultrasound Imaging: a

Musculoskeletal Perspective

Presented by: Zinat Ashnagar

Introduction

Ultrasound imaging (USI) has been used for medical purposes since the 1950s.

Ultrasound imaging related to musculoskeletal rehabilitation has been developing rapidly since the 1980s.

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The first report of muscle imaging linked to rehabilitation was in

1968, when Ikai and Fukunaga related the size of the upper arm

muscles to strength.

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It was the work of Dr Archie Young and colleagues at the University of Oxford in the 1980s that sowed the seeds for the use of USI by physical therapists.

A recent (1990s) resurgence in the interest of rehabilitative applications of USI has been seen amongst clinical therapists.

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Detect atrophy of the lumbar multifidus in individuals with acute low back pain (Hides et

al,1994) USI\Hides et al,1994.pdf

Recovery of this muscle was not automatic when pain subsided (Hides, Richardson & Jull, 1996)USI\Hides, Richardson et al,1996.pdf

The biofeedback provided by USI might facilitate the relearning process.

dRehabilitative USI (RUSI)

Current applications of USI in rehabilitation essentially fall into 2 distinct areas of

musculoskeletal imaging:

Diagnostic imaging

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Rehabilitative USI (RUSI)

1. evaluation of muscle structure (morphology) and behavior

2. the use of USI as a biofeedback mechanism

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• the measurement of morphological features (morphometry), such as:

• muscle length

• depth

• diameter

• cross-sectional area

• volume

• pennation angles

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changes in these features and the impact on associated structures (fascia and organs such as the bladder) with contraction

tissue movement and deformation (eg, high-frame-rate USI and elastography)

qualitative evaluation of muscle tissue density.

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• In May 2006, the first international meeting on RUSI was hosted by the US Army-Baylor University Doctoral Program in Physical Therapy in San Antonio, TX.

• USI\USI.SYMPOSIUM.pdf

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• The purpose of the symposium was to develop best practice guidelines for the use of USI for the abdominal, pelvic, and paraspinal muscles, and to develop an international and collaborative research agenda related to the use of USI by physical therapists.

• At that symposium the participants agreed on the use of the term RUSI.

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“RUSI is a procedure used by physical therapists to evaluate muscle and related soft tissue morphology and function during exercise and physical tasks.

RUSI is used to assist in the application of therapeutic interventions aimed at improving neuromuscular function.

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This includes providing feedback to the patient and physical therapist to improve clinical outcomes.

Additionally, RUSI is used in basic, applied, and clinical rehabilitative research to inform clinical practice.

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Basic Physics

• Penetration – Intensity– Frequency– Speed of sound wave

• Attenuation– Reflection– Scattering– Refraction– Absorption

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Mechanism of RUSI

When a sound wave encounters an

interface, the portion that is reflected

back to its source is referred to as

“reflection” and serves as the basis

for image formation.

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At every tissue interface, sound waves are absorbed, reflected, and/or scattered.

When sound energy reflects back to the ultrasound probe, the unit can determine:

1. where along the length of the transducer it arrived,

2. how long it has taken to go out and come back, 1. its amplitude

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the ultrasound unit uses these 3 parameters to assign the echo from a particular structure a pixel (picture element).

The horizontal location of the pixel is determined by the location to which the

echo returns along the length of the probe face.

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vertical placement is determined by the amount of time the sound takes to go out and come back.

The brightness of the pixel depends on the strength of the returning echo;

The stronger the echo, the whiter, and

the weaker the echo, the darker it will appear.

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Illustration of how a B-mode ultrasound image is generated. (A) Sound waves penetrate into the tissues. At each interface, a portion of the sound wave is reflected back to the transducer. (B) The unit can determine where along the face of the transducer the echo returned, the amount of time it was away, and its amplitude. It uses these 3 parameters to determine the vertical (time) and horizontal (transducer) location of a pixel representing the echo from a particular structure, and the amplitude to determine the brightness. (C) This process is repeated until an ultrasound image is generated.

Terminology

Echogenicity: Capacity of a structure in the path of an ultrasound beam to reflect back sound waves.

Hyperechoic: The structure examined in the ultrasound image shows a high reflective pattern and appears brighter than the surrounding tissue.

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Isoechoic: The structure demonstrates the same echogenicity as the surrounding soft tissues.

Hypoechoic: The structure examined in the ultrasound image shows a low reflective pattern, manifesting as an area where the echoes are not as bright as the surrounding tissue.

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Anechoic: The image of the structure shows no internal echoes (e.g., simple fluid).

Longitudinal Scan: is lengthwise and parallel to the long axis of the structure, organ, or body part.

Transverse Scan: is crosswise and at right angles to the long axis of the structure, organ, or body part.

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(A) An ultrasound image of the bladder. Note the hypoechoic nature (black) of the urine. (B) A transverse ultrasound image of the fifth lumbar vertebrae. Note the brightness of the muscle bone (lamina) interface (arrows). (C) An ultrasound image of the muscle and fascia layers of the lateral abdominal wall. Note that the muscle layers are darker (hypoechoic), while the intervening fascia is brighter (hyperechoic). Abbreviations: EO, external oblique; IO, internal oblique; SP, spinous process; TrA, transversus abdominis.

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Transducers

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Linear Array

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Curvilinear Array

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FrequencyThe choice of frequency used for an imaging application will be dependent upon the depth

of the region or structures of interest.

• Higher frequencies (7.5-10.0 MHz) are more valuable for examining superficial structures (superficial muscles, ligament, and tendons).

• Lower frequencies (3.5-5.0 MHz) for deeper structures (deeper muscles, the bladder, and contents of the abdominal/pelvic cavities).

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USI devices generate images based upon several assumptions:

sound travels in straight lines, echoes only originate from objects located in the 2 dimensions of the sound beam

the amplitude of an echo is directly related to the reflecting or scattering properties of the objects it encounters

the speed at which sound travels through all the tissues is a constant 1540 m/s

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Artifacts

Artifacts

Acoustic enhancement

ReverberationReverberation

Acoustic shadowing

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Enhancement

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Shadow

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Edge Shadow

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Reverberation

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Brightness mode & Motion mode USI

There are several options (modes) available to display the electrical signal representing the

ultrasound echo that returns from the tissues.

The most common modes of display employed in rehabilitative settings are “B” (brightness,

brilliance) and “M” (motion, movement) modes.b-mode m-mode

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B-Mode USIB-mode displays the ultrasound echo as a cross-

sectional grey-scale image and is the mode of display most typically associated with USI.

B-mode images provide information gathered from the entire length of the transducer and consist of visible dots or pixels of varying degrees of brightness that represent the location and density of structures encountered by the ultrasound beam.

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A brightness mode (b-mode) image of the lateral abdominal wall. Abbreviations: EO, external oblique; IO, internal oblique; TrA, transversus abdominis.

M-ModeM-mode displays information collected from the midpoint of the transducer as a continuous

image over time.

With time on the x-axis, and the depth of the underlying anatomical structure on the y-axis,

the m-mode image represents changes in thickness, or depth of a structure, over time

and is, therefore, referred to as “time-motion” mode.

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A split-screen image with b-mode on the left and motion mode (m-mode) on the right. The m-mode image represents the information from the dotted line on the b-mode image displayed over time (x-axis). Static structures produce straight interfaces while structures that change in thickness or depth (in this case the TrA) create curved interfaces. The increase in depth of the TrA correlates to a contraction.

High-Frame-Rate USIConventional m-mode ultrasound images are

constructed from data updated approximately 25 to 50 times per second.

Although these frame rates are capable of detecting deformation (thickness) and changes in the depth of a muscle, they are not high enough to provide information related to the normal anticipatory response demonstrated by certain muscles and the loss of this response with dysfunction.

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In fact, to be able to record anticipatory muscle response (defined as a contraction

occurring from 100 milliseconds before and up to 50 milliseconds after activation of a prime mover ) frame rates need to

be on the order of 500 frames per second.

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Although intramuscular EMG is considered the gold standard for evaluating onset of muscle activity, high-frame-rate m-mode

USI is a promising noninvasive alternative, as it allows for the visualization of the onset of deformation of muscle as it

starts to contract.

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ElastographyIt is possible to post process the electrical signal

produced from the echo returning from the tissues to the transducer in such a way as to quantify tissue movement and deformation in response to internal or external mechanical forces.

Elastography is a process of estimating the biomechanical properties (elasticity) of tissues

through imaging techniques.

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Tissue hardness can be determined by applying a known pressure on the tissue under study.

Because pathologic tissues distinctively have different biomechanical properties from normal tissues, elastography can help monitor pathologic conditions.

Therefore, the elastic properties of tissues can be helpful in making a diagnosis of pathology.

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The principles of elastography are as follows:

First, tissue compression produces strain and displacement within the tissue.

Second, the strain is smaller in harder tissue than it is in softer tissue.

Lastly, tissue hardness can be estimated by measuring the tissue strain induced by compression.

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It is important to keep in mind that elastography images do not directly represent tissue elasticity but, rather, tissue displacement and strain.

However, in conditions in which local tissue stress can be calculated (or estimated), strain and stress values can be used to map local tissue stiffness.

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USI versus other imaging methods

Although MRI is considered the gold standard for musculoskeletal imaging,

emerging applications of USI and CT are capable of providing insight into in vivo

features of the musculoskeletal system. Each imaging method has strengths as well

as weaknesses.

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Magnetic Resonance ImagingMRI, unlike USI, has multiplanar and multislice

imaging capabilities.

There are 2 conventional MRI sequences: T1 and T2 weighted.

Images from T1-weighted scans demonstrate excellent anatomical contrast of fat and other soft aqueous tissues (e.g, skeletal muscle).

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T2-weighted scans provide outstanding detail related to the features of inflammation that are suggestive of neopathological conditions.

The drawbacks of MRI remain cost, accessibility, constraints in the number of joints that can be investigated per session, limited real-time imaging capacity, and variable patient tolerance (e.g, metallic implants, pacemaker,

and pregnancy).

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Computerized TomographyCT, like MRI but unlike USI, permits

multislice imaging and can offer better scan resolution and shorter imaging times than MRI.

It is not without the inherent risks associated with exposing a patient to ionizing radiation.

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CT is useful in diagnosing traumatic musculoskeletal injuries, such as

fractures, and has been effectively used to evaluate and quantify cross-sectional

area of paraspinal musculature in patients with low back pain.

While CT produces high-quality images, they are dependent on tissue densities in

order to provide contrast.

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When tissue densities between pathologic and adjacent anatomy are similar, contrast

media may be required for differentiation, rendering CT inadequate

if a patient has a history of contrast reaction.

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Ultrasound Imaging

USI, although less sophisticated in terms of resolution than MRI and CT, has

advantages as a safe, cost-effective, portable, and clinically accessible method

for gathering information about the static characteristics of muscle, as well as muscle

behavior during dynamic events.

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Unlike CT, USI does not expose the patient to ionizing radiation and is well tolerated by patients.

A feature unique to USI is its dynamic capability of scanning in real time, which makes it superior to MRI and CT for evaluating mobile structures such as tendons, nerves, and muscles, and it may become an important tool for directing appropriate physical therapy treatment decisions.

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USI is not without disadvantages and is highly operator dependent.

Perhaps the most promising feature of USI is its accessibility and the feasibility for physical therapists to acquire the skills needed to incorporate its use into clinical practice.

However, evidence for its use in different applications within rehabilitation is needed before widespread routine clinical use can be promoted.

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Ultrasound Imaging & Muscle Function

What is the relationship between the pattern and magnitude of

change in muscle size and muscle function ?

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One aspect of muscle function that has been compared to change in muscle size is muscle electrical activity.

What is the relationship between changes in muscle size (measured with USI) and muscle activity (measured

with EMG)?

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The findings are clearly inconclusive, with correlation statistics ranging anywhere from 0.14 to 0.93.

McMeeken et al., reported a linear relationship between 2 measurements (thickness and EMG signal amplitude) for the TrA (R2 = 0.87).

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Hodges et al., described a nonlinear relationship (the majority of thickness change occurring within the first 22% of EMG signal amplitude) for the external oblique (EO) (r = 0.23), IO (r = 0.93),and TrA

(r = 0.90) muscles.

Brown and McGill found no definitive relationship for the EO (r = 0.22) and

IO (r = 0.14) during contraction.

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There are many factors, in addition to muscle activity, that may influence changes in muscle thickness or size.

the resting state (activity and length) of the muscle,

the extensibility (compliance) structure (parallel versus pennate

muscle fiber orientation) of a musculotendinous unit,

the type of contraction taking place (isometric, concentric, eccentric)

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the presence of external forces that an expanding muscle must compete against

(eg, increases in intra-abdominal pressure or contraction of adjacent muscles)

out-of-plane changes

imaging technique

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Consideration of each of the mentioned factors and their influence on changes in muscle size is critical when attempting to

interpret the findings of a dynamic imaging study.

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An illustration of factors that influence the change in thickness of a muscle. (A) An increase in thickness and decrease in length of a normal muscle (gray, at rest, precontraction; black, active, contracted) during a submaximal concentric contraction. (B) A relatively smaller increase in thickness and decrease in length then seen in a normal muscle, due to increased resting activity (e.g, secondary to pain).

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(C) An increase in the extensibility of the myofascial unit (e.g, postpartum). (D) Competing forces, specifically an increase in resistance from an adjacent muscle contracting (2-headed black arrows), and an increase in intra-abdominal pressure (black upward pointing arrows).

In addition to factors associated with the myofascial unit, it is also important to

consider those associated with interpreting 2-dimensional ultrasound

images and the imaging technique itself, specifically, architectural changes

occurring outside of the plane of motion being imaged.

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An illustration of a multifidus contraction in the transverse plane, resulting in an increase in the cross-sectional area (CSA) of the muscle.

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(B) A transverse ultrasound image of a multifidus contraction, depicting both an increase in thickness and width associated with the overall increase in CSA. (C) A sagittal ultrasound image of a multifidus contraction, depicting only an increase in thickness of the multifidus, as the increase in width cannot be viewed from this imaging plane. Abbreviations: MF, multifidus; SP, spinous process.

Therefore, although USI may be a valid and reliable measure of muscle size

(in healthy populations), it is not surprising that the literature regarding the

relationship between increases in muscle activity (EMG) and thickness change

(USI) is not conclusive, with changes in muscle size and muscle activity not

always demonstrating a direct relationship.

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it is important to consider that, in addition to not establishing a relationship between USI and EMG measures, these studies have been conducted on small numbers of young, healthy participants in nonclinical environments.

Consequently, there is a lack of information regarding this relationship in other populations or during other dynamic maneuvers.

Therefore, the validity or ability to use USI to quantify muscle activity is, at best, context dependent.

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Rehabilitative Ultrasound Imaging of

the Abdominal Muscles

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RUSI is particularly relevant for assessment and rehabilitation of the

abdominal muscles, as it provides one of the only clinical methods to appraise the morphology and behavior of the deepest

abdominal muscle, the Transversus Abdominis (TrA), which is a common

target of rehabilitation in contemporary exercise management of certain types of

low back and pelvic pain.

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Anterior view of the regions of the abdominal wall.

1.The upper region is above the 11th costal cartilage, 2.the middle region is between the 11th costal cartilage and the iliac crest; 3.the lower region is below the level of the iliac crest.

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Ultrasound image of the left lateral abdominal wall, in which normal resting activity is assumed.

In the region between the inferior aspect of the rib cage and the superior aspect of the iliac crest, the OI muscle is the thickest, followed by OE, and then TrA muscles.

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Due to the superior clarity of the muscle boundaries,

the ease of identification of the individual muscles,

and the clarity of changes in muscle thickness during activation,

the middle region of the abdominal wall is most commonly selected for USI of the

lateral abdominal muscles.

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Patient PositionThe lateral abdominal muscles are typically

imaged with the subject relaxed in supine with the hips and knees flexed (hook-lying posture).

One of the advantages of USI is its versatility in assessing these muscles in many postures and during functional tasks (quadruped, sitting, sitting on physioball, reclined in a chair, standing, or walking).

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A picture demonstrating

patient positioning for rehabilitative ultrasound imaging of the abdominal

wall.

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Transducer Selection Ultrasound transducers ranging from 5 to 10

MHz have been used to assess the lateral abdominal muscles .

Although a range of transducer frequencies permits adequate visualization of the lateral abdominal muscles, a higher frequency curvilinear transducer, with its diverging

field of view, is ideal, as it allows for greater visualization of the muscle throughout its length.

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Demonstrates the entire length of the TrA muscle.

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If the goal is to assess a specific region or movement of a region, such as the lateral slide of the anterior aspect of the TrA muscle during an abdominal drawing-in maneuver (ADIM) or functional activity, a higher frequency linear transducer may allow for greater accuracy.

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Thickness Measurement

Measurement of thickness of the lateral abdominal muscles is dependent on the location where the measurement is obtained along the length of the muscle and the point in the respiratory cycle.

Although the lateral abdominal muscles have a relatively uniform thickness in the middle and lower regions, this can vary and the location of the measurement should be noted.

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As activity of the abdominal muscles is modulated with respiration and the thickness of the abdominal muscles changes with activation, it is predictable that the muscles would be thicker during expiration than during inspiration.

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The measure used for analysis will vary depending on the intention of the evaluation in clinical practice or research.

Absolute and relative thickness values may be appropriate for assessment of thickness of adjacent muscle layers.

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Assessment of asymmetry in baseline thickness values may be best represented as a percent difference between the symptomatic and nonsymptomatic side.

Statistical techniques or study designs that address potential confounding variables (e.g, BMI, gender) as covariates are an option.

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Dynamic Measurement

During dynamic tasks, performance measures can be assessed by measuring a change in the thickness of a muscle or a

lateral displacement (slide) of the anterior medial edge of a muscle.

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As the TrA muscle thickens and shortens, a lateral slide of the anterior aspect of the TrA muscle and its fascia can be observed on USI.

The lateral slide has been associated with tensioning of the anterior fascias, resulting in increased tension of the deep muscular corset, and is considered to be an important observation with RUSI of the lateral abdominal muscles.

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Measurement of lateral slide is used as an indication of tightening of the anterior fascia associated with the TrA muscle and an indirect measure assessing the shortening of the TrA muscle during

activation.

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For example, Abdominal Drawing In Maneuver (ADIM) can be visualized as a shortening and thickening of each side of the TrA muscle.

This lateral displacement is readily observed for the TrA muscle during the ADIM.

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Ultrasound imaging of the lateral abdominal wall muscles during the abdominal drawing in maneuver (ADIM). Images include the transversus abdominis (TrA), obliquus internus abdominis (OI), and obliquus externus abdominis (OE) muscles. The white dot represents the anterior reach of the TrA muscle. (A) An ultrasound image of the left lateral abdominal wall at rest. (B) An ultrasound image of the left lateral abdominal wall during the ADIM.

RA muscleUnlike the 1-dimensional measure of the lateral

abdominal muscles, the CSA, thickness, and width of the RA muscle can be calculated using USI.

In addition, the distance between the right and left RA muscle can be measured to assess those with diastasis recti and to track changes in the distance between the recti associated with pregnancy.

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Ultrasound image of the

rectus abdominis (RA) muscle

(cross section).

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Ultrasound imaging of interrecti distance. Both the left and right rectus abdominis (RA) muscles, as well as their intervening fascia, are observable. (A) Note the RA muscles are adjacent in midline resulting in a small interrecti distance. (B) Note the increased in the interrecti distance associated with diastasis recti. The interval between the plus signs represents the interrecti distance. (From Whitakker J. Ultrasound Imaging for Rehabilitation of the Lumbopelvic Region: A Clinical Approach. ©2007, Elsevier)

Tissue Composition

Researchers have found that aging, chronic musculoskeletal dysfunctions,

and/or denervation are associated with a decrease in water content and an

increase in fatty fibrous content within muscles.

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Ultrasound imaging of the lateral abdominal wall demonstrating changes in tissue composition. (A) Resting image of the right lateral abdominal wall at

the point where the lateral aspect of the rectus abdominis (RA) muscle intersects with the obliquus internus abdominis (OI) muscle. Note the ease of delineating the muscle boundaries and their similarity and echogenicity. (B) A comparable image demonstrating a degeneration of the boundaries

and an increase in echogenicity of the RA muscle.

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Reliability of assessment for TrA• Population: 30 nonspecific-LBP aged 18-60• Task: TrA- abdominal drawing-in maneuver, active straight leg raise (20cm)• Measurement: Thickness measurement during 2 sessions 1-3 days apart,• Transducer:2- to 5-MHz curvilinear array

(Koppenhaver et al. 2009)

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Intraexaminer Reliability for TrA

(Koppenhaver et al. 2009)

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Interexaminer Reliability for TrA

(Koppenhaver et al. 2009)

SPINE Volume 31, Number 6, pp E175–E178©2006, Lippincott Williams & Wilkins, Inc.

An MRI Investigation Into the Function of theTransversus Abdominis Muscle During

“Drawing-In” of the Abdominal Wall

Julie Hides, PhD,* Stephen Wilson, PhD,† Warren Stanton, PhD,* Shaun McMahon, PhD,‡ Heidi Keto, BPhty,* Katie McMahon, PhD,§ Martina Bryant, B App Sc,§and Carolyn Richardson, PhD*

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Validity of assessment for TrA

Population: 13 Non-LBP, elite cricketers, mean age 21.3

Task: abdominal drawing-in maneuver (ADIM)

Linear transducer, 7.5 MHz Measurement: MRI (the golden standard)

and ultrasound imaging Interclass correlations: 0.78~0.95

(Hides et al. 2006)

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Validity of assessment for TrA at rest on MRI and RUSI

(Hides et al. 2006)

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Validity of assessment for TrA on ADIM on MRI and RUSI

(Hides et al. 2006)

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Magnetic resonance imaging of the deep musculofascial “corset” of the lumbopelvic region (cross section). Images include the transversus abdominis (TrA), obliquus internus abdominis (OI), obliquus externus abdominis (OE), and the rectus abdominis (RA) muscles. (A) The deep musculofascial “corset” at rest. (B) The deep musculofascial corset during the abdominal drawing-in maneuver, depicting a bilateral concentric activation of the TrA muscle and a decrease in cross-sectional area of the abdominal content (AC).

Measurement of thickness of the TrA, OI & slide of TrA obtained by USI & MRI

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Validity of assessment for TrA

(Hides et al. 2006)

Given the high ICCs and similarity in the mean scores in this study, it could be proposed that the variables measured in this investigation could be adequately assessed using ultrasound imaging.

Ultrasound imaging, despite a limited field of view, may be more practical and just as accurate as MRI. This would be useful where large numbers of subjects are to be investigated or where portability is an issue.

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Is Ultrasound Imaging a Fad?

The existing data suggest that ultrasound imaging has strong potential to contribute to

rehabilitation.

Ultrasound has potential to provide informative measures of muscle and muscle activity, and to

measure parameters that change with rehabilitation, and has no side effects.

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Hodges, 2005

RUSI provides a means by which physical therapists can see what they are feeling with

their hands.

Researchers should address the use of RUSI as a tool to assist physical therapists in clinical

decision making, reliably determining impairments, improving specificity of prescribed therapeutic exercises, and establish its influence

on outcomes.

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Thanks for your

attention

ReferencesWhittaker, Jackie L., Deydre S. Teyhen, James M. Elliott, Katy Cook, Helene M.

Langevin, Haldis H. Dahl, and Maria Stokes. "Rehabilitative ultrasound imaging: understanding the technology and its applications." journal of orthopaedic & sports physical therapy 37, no. 8 (2007): 434-449.

Whittaker, Jackie L., and Maria Stokes. "Ultrasound imaging and muscle function." Journal of Orthopaedic & Sports Physical Therapy 41, no. 8 (2011): 572-580.

Hodges, Paul W. "Ultrasound imaging in rehabilitation: just a fad?." Journal of Orthopaedic & Sports Physical Therapy 35, no. 6 (2005): 333-337.

Hides, J. A., M. J. Stokes, M. J. G. A. Saide, G. A. Jull, and D. H. Cooper. "Evidence of lumbar multifidus muscle wasting ipsilateral to symptoms in patients with acute/subacute low back pain." Spine 19, no. 2 (1994): 165-172.

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Hides, Julie A., Carolyn A. Richardson, and Gwendolen A. Jull. "Multifidus Muscle Recovery Is Not Automatic After Resolution of Acute, First Episode Low Back ‐Pain." Spine 21, no. 23 (1996): 2763-2769.

Teyhen, Deydre S., Norman W. Gill, Jackie L. Whittaker, Sharon M. Henry, Julie A. Hides, and Paul Hodges. "Rehabilitative ultrasound imaging of the abdominal muscles." journal of orthopaedic & sports physical therapy 37, no. 8 (2007): 450-466.

Koppenhaver, Shane L., Jeffrey J. Hebert, Julie M. Fritz, Eric C. Parent, Deydre S. Teyhen, and John S. Magel. "Reliability of rehabilitative ultrasound imaging of the transversus abdominis and lumbar multifidus muscles." Archives of physical medicine and rehabilitation 90, no. 1 (2009): 87-94.

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Hides, Julie, Stephen Wilson, Warren Stanton, Shaun McMahon, Heidi Keto, Katie McMahon, Martina Bryant, and Carolyn Richardson. "An MRI investigation into the function of the transversus abdominis muscle during “drawing-in” of the abdominal wall." Spine 31, no. 6 (2006): E175-E178.

Teyhen, Deydre. "Rehabilitative Ultrasound Imaging Symposium, May 8-10, 2006, San Antonio, Texas." Journal of Orthopaedic & Sports Physical Therapy36, no. 8 (2006): A-1.

Lew, Henry L., Carl PC Chen, Tyng-Guey Wang, and Kelvin TL Chew. "Introduction to musculoskeletal diagnostic ultrasound: examination of the upper limb." American journal of physical medicine & rehabilitation 86, no. 4 (2007): 310-321.

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