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7 Articles in Volume 5, Issue #1
Diagnosing and Managing Interstitial Cystitis
Intractable Pain Centers’ Treatment Approach
Musculo-Skeletal Diagnostic Ultrasound Imaging
Pain Management Pitfalls
Selection Criteria for Intrathecal Opioid Therapy: A Re-examination of the "Science"
‘High Dosage’ Opioid Management
‘Opiophobia’ Past and Present

Musculo-Skeletal Diagnostic Ultrasound Imaging

This evolving, first-line imaging test for soft tissue lesions can provide superior diagnostic accuracy by visualizing internal soft tissue architecture and associated pathologies.

The use of musculo-skeletal diagnostic ultrasound imaging (MDUI) as a first line soft tissue screening test is rapidly gaining in popularity as increasing research evidence demonstrates superior diagnostic accuracy when using this form of imaging.1 The popularity of MDUI is due, in part, to it’s availability, portability, user friendliness and relatively low cost. In comparison to MRI or CT scan, an MDUI unit is inexpensive, has no known side effects or risks directly attributable to the test, such as ionizing radiation or invasiveness, and tests take very little time to perform — as little as five minutes for a shoulder examination performed by an experienced practitioner. The most cited disadvantage of MDUI has been the relatively high operator proficiency required in this form of imaging.2 There is, of course, no substitute for training and experience, but that also applies, in varying degree, to any form of diagnostic imaging.

Figure 1. This longitudinal axis scan shows a gross tearing (dark region) of the gastrocnemius muscle in a high school athlete. The dimensions of the tear exceed the available frame size but are partially captured by D1= width, and D2=length. Diagnostic ultrasound units are now available with extended field of view options, which would have allowed full single scan visualization of this tear. This patient was scanned every 2 weeks to monitor both clinical and anatomical progression (tissue healing). It is interesting to note that full function returned prior to full anatomical healing. This may have implications in terms of assumptions regarding the relationship between structure versus function.

Research Validation

A number of recent studies have concluded that diagnostic ultrasound scanning has very good criterion validity when using either MRI or arthroscopic findings as the “gold standard.”3,4,5 It has, on occasion, demonstrated better overall accuracy than MRI for certain specific target conditions of interest such as rotator cuff tears and bicipital long head lesions.6,7 Newer MDUI technology allows for higher quality resolution and ultimately a more accurate diagnosis. The use of high frequency transducers — optimal for superficial scanning as well as 3D and 4D capability — has enabled DUI practitioners to better separate clinically similar conditions such as tendonitis and tendonosis, as well as partial versus complete rotator cuff tears in the shoulder. Unlike MRI, the actual internal tendon architecture can be visualized with even the most basic ultrasound unit. Fluid collections such as those we expect in joint effusions and inflammed bursae can easily be identified and correlated clinically. This makes MDUI ideal in confirming the presence of inflammatory conditions. The powerful added feature of Doppler capability in an ultrasound unit can provide valuable perfusion information about a specific lesion. Chronic tendonitis and/or tendonosis conditions can be differentially diagnosed from their more acute counterparts based on perfusion characteristics. A “hot” region containing inflammatory exudate and increased blood flow (hyperaemia) from acute injury is easily seen under doppler ultrasound. One of the distinguishing features of tendonosis versus tendonitis is the relative lack of blood perfusion in these lesions and is characteristic of chronic lesions in general.

“Without diagnostic imaging, clinicians must observe and measure both impairment scores and functional status to determine clinical improvement. MDUI adds a third dimension in the global assessment of patient improvement — that of anatomical verification that the problem is improving.”

MDUI Can Confirm Positive Therapeutic Intervention

The presence of muscle strains and frank tearing can also be easily seen with MDUI since the actual muscle pennate structures are visible using this form of imaging (see Figure 1). This enables clinicians to not only identify the existence of pathology, but also to grade the tears through simple machine assisted measurements. It is these serial measurements that forms the basis for “evidence” that the therapeutic intervention is working and the patient is getting better.

Without diagnostic imaging, clinicians must observe and measure both impairment scores and functional status to determine clinical improvement. MDUI adds a third dimension in the global assessment of patient improvement — that of anatomical verification that the problem is improving. For perhaps the first time in recent history, clinicians have a way of taking multiple observational samples of the clinical condition to aid in verifying the stage of healing. This can be done rather quickly and inexpensively, without significant patient inconvenience since DUI units are very portable. This type of imaging can really help clinicians test their assumptions regarding the interplay between disability, impairment, and injury as it pertains to anatomical normalization of tissue.

MDUI can provide added confidence to clinical decisions, especially in return to work or return to play scenarios for workers and athletes, respectively. It can be rather disconcerting to find a patient has returned to work or play prematurely based on your best recommendations, only to find out that re-injury has occurred. The use of DUI can provide confirmation of a healed tendon, muscle or ligament. Diagnostic imaging has been shown to be an invaluable adjunct in making these activity-related decisions that the patient, payor, and legal community expects clinicians to make. Diagnostic scanning of soft tissue structures provides much needed evidence to support clinical examination findings and subsequent treatment interventions, as well as helping to guide important patient decisions.

MDUI Can Evaluate Utility of Traditional Tests

Clinicians tend to have a favorite cluster of special tests they perform on various areas of the body to rule out, or rule in, conditions of interest. Orthopedic textbooks are filled with such tests and they form the basis for many orthopedic clinical examinations today. It is always an interesting exercise to examine the psychometric properties of such tests, that is, their ability to accurately detect, or reject, the presence of a specific condition of interest. Diagnostic tests are evaluated with a different set of rules than are new therapies or interventions. Unlike a new treatment technique or medication, both of which can be clinically tested in a randomized clinical trial with proper controls — such as double blinding and concurrent control groups — new diagnostic tests are evaluated, in most cases, by comparing them to a “gold standard” test.8

When comparing a new test to an established test, it is critical that both tests measure the same attribute or dimension. An example of this is the “lift off test” developed initially to identify subscapularis deficiencies.9 Clinicians routinely have patients suspected of having rotator cuff (RTC) injury simultaneously internally rotate the arm and lift off (back of hand pushing away from low back) to assess the level of strength generated by the patient’s internal rotator (subscapularis) in this end range position. The test scores positive (for the condition of interest) if no or low force is generated and/or if the patient cannot even be put in this position. The test is considered negative (for the condition of interest) if the patient can fully internally rotate while generating internal rotatory forces. The accuracy of this test is gauged by it’s ability to identify subscapularis lesions (positive test in the presence of subscapularis lesion, negative test in the absence of subscapularis lesion) and can be calculated by using a 2 x 2 table or matrix. The various validity indicis for categorical data can then be calculated (i.e. sensitivity, specificity, negative and positive predictive values).

With this type of information one can now evaluate the overall accuracy and clinical utility of each test(s) as it applies to a unique condition of interest. MDUI can serve as the criterion measure for many orthopedic tests and thus allows the clinician an opportunity to select only the “best” orthopedic tests for a given diagnosis. This systematic evaluation of the existing battery of diagnostic tests — with the goal of selecting only those that are most precise and unbiased — is consistent with evidence based and best practice paradigms.10

Figures 2 (left-side) and 3 (right-side) are longitudinal scans (long axis views) of both uninvolved and involved shoulders of the same patient (normal left shoulder, Figure 2; and injured right shoulder, Figure 3; respectively). The right shoulder shows a virtually complete RTC tear with the tear extending almost entirely from cortical to bursal RTC surfaces. The left view is a normal RTC converging in a “crows beak” fashion into the greater tubercle of the humerus.

Normal Sonographic Anatomy

One of the strengths of DUI is the capability it brings to the user in visualizing internal soft tissue architecture including muscle fiber(s), connective tissues such as fibro-adipose septa, fascial bands and aponeurosis, and many pathological conditions that primarily affect these structures. DUI relies on visual interpretation that involves the ability to read grayscale and, for this reason, sonographic anatomy is described in terms of echo-texture or echogenicity. A region in a sonogram is described to be hypo-echoic (darker), hyper-echoic (whiter) and/or anechoic (black). Many pathologies manifest sonographically in terms of their echogenic deviation (footprint) from normal. It is therefore incumbent on the sonographer to be thoroughly familiar with normal sonographic anatomy before abnormal anatomy can be identified. Figure 2 presents an image of a normal rotator cuff tendon in a healthy shoulder and is devoid of injury. The scan shows the conjoint RTC tendon consisting of supraspinatus, infraspinatus, subscapularis and teres minor muscles.

The shoulder is a good example of DUI’s ability to image a joint. DUI has been shown, in many cases, to be as accurate as MRI for this application.6,7 In partial RTC conditions (see Figure 3) we expect to see a focal hypo-echoic area usually in the mid-substance of supraspinatus. The hypoechoic feature is consistent with acute inflammation which will bring more fluid into the injured area, along with a reduction in muscle fiber density. Acute muscle tearing or sprains/strains will swell and cause fluid to accumulate locally, as will an irritated bursa (see Figure 1). Trained sonographers can distinguish between swelling and tearing through a series of transducer manipulations which are beyond the scope of this paper to describe.

The condition of tendonosis presents it’s own “sonographic signature” including areas of hyper-echogenicity from tendon degeneration and subsequent fibrosis. This condition is seen with more chronic RTC disease and, in some cases, will also manifest with cortical irregularity consistent with degenerative disease in general. Cortical signs seen in DUI are useful in other ways, including being pathognomonic for soft tissue pathology.11 Although DUI is not being used to replace conventional radiography, musculo-skeletal sonographers are also familiar with diagnostic ultrasound’s ability to scan the surface of cortical bone, making this a useful adjunct to plain film radiography in detecting bony lesions.12 For instance, cortical irregularity of the greater tuberosity at the supraspinatus insertion can be a useful sign when trying to distinguish between tendon tear and tendonosis; this sign being associated primarily with tendon tearing versus degenerative tendonopathy. Another useful sign of RTC tearing is the “deltoid dip” which occurs as a result of RTC tendon atrophy and subsequent tearing leaving an unsupported “gap” where the loss of tissue occurs. This is similar to a collapsing truss that normally acts to support a structure. When the supporting framework collapses, the supported structure falls through. The same phenomenon occurs with the overlying deltoid muscle in RTC tearing, whereby the deltoid simply collapses into the space where the RTC previously occupied.

“...one can now evaluate the overall accuracy and clinical utility of each test(s) as it applies to a unique condition of interest. MDUI can serve as the criterion measure for many orthopedic tests and thus allowing the clinician an opportunity to select only the “best” orthopedic tests for a given diagnosis.”

These are just a few of the more common pathological RTC manifestations seen during shoulder ultra-sonography. Other clinically relevant conditions that DUI can identify include tissue atrophy-hypertrophy, cysts, masses, calcifications, metal implants or objects, scarring, effusions, fibrosing, stretched fibers, fibro-cartilage tears. The list of potential diagnostic applications grows as DUI technology continues to improve and provide even greater resolution capability.12

“MDUI requires training and experience in the recognition of normal, as well as pathological anatomy, before reliable interpretation can be expected. Once the technique is learned however, the diagnostic information that ultra-sonography contributes to a patient examination, or diagnostic yield, is substantial.”

Conclusion

Diagnostic ultrasound appears to be gaining ground as a primary form of soft tissue imaging for numerous reasons including cost-effectiveness and patient compliance. Certainly in the case of shoulder sonography, the research studies conducted in the last five years have consistently demonstrated high sensitivity/ specificity, and negative/positive predictive values. Naturally these values are not universal and depend on sonographer training, DUI unit used, and population prevalence for the target condition of interest (i.e. RTC tears) at a specific research center. The documented benefits of this form of imaging are several, including low relative cost, patient convenience, availability of test, and superior image resolution especially with advancing technological improvements. Musculo-skeletal DUI requires training and experience in the recognition of normal, as well as pathological anatomy, before reliable interpretation can be expected. Once the technique is learned however, the diagnostic information that ultra-sonography contributes to a patient examination, or diagnostic yield, is substantial.

Last updated on: December 13, 2011
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