Musculo-Skeletal Diagnostic Ultrasound Imaging
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.
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).