The future of imaging for PTs?

By Tiziano Marovino, pT

Picture this: your physical therapy clinic has just received a referral from a local physician's office and the patient is in your exam room. The patient was sent to you for right shoulder problems, which developed as a result of injuries sustained in a work-related upper extremity lifting maneuver.

The diagnosis on the prescription vaguely states "right shoulder pain." You begin the examination and find weakness and range of motion deficits in abduction and external rotation of the glenohumeral joint. Special testing (e.g., impingement signs, lag signs) supports your primary hypothesis of rotator cuff involvement, specifically the supraspinatus.

Simplifying the Referral Process

Until now, a PT who suspected moderate to severe musculotendinous ruptures or tears—based on history, symptoms, clinical testing and/or poor patient treatment response—had no other choice but to direct the patient back to a primary care physician for further follow-up. The primary care provider might then refer the patient to an orthopedic surgeon, who in turn might order a confirmatory MRI or CT arthrogram.

This referral process can be time consuming and expensive, not to mention disruptive to rehabilitation. Furthermore, the therapist needs to know the degree of severity of the problem he has been requested to treat. As a rule, therapists would like to have this information prior to commencing a course of treatment in order to choose the best treatment options available.

In an ideal situation, a therapist could confirm the location and degree of musculotendinous irritation (or tearing) using a noninvasive, accurate and relatively inexpensive form of imaging known as diagnostic ultrasound imaging (DUI). In so doing, this technology could fill an invaluable niche in various rehabilitation and multi-disciplinary settings across the country.

Ultrasonography

Physical therapists will be more familiar with such traditional types of ultrasonographic (US) studies as echocardiography, Doppler studies (to rule out deep vein thrombosis), and routine visceral and pelvic imaging studies performed in an ob/gyn, urology or internal medicine office. More recent applications of ultrasound imaging include needle-guided aspirations/biopsies,¹ breast cancer imaging/screening,² and musculoskeletal imaging.³

It is this last application that will have more relevance for PTs in the future, as we strive to develop both our therapeutic and diagnostic competencies. With the advent of the DPT and direct access–and the societal/professional expectations they carry with them, combined with an increasing emphasis from payers on objectively documenting physical findings–PTs will be under continued pressure to demonstrate well-supported practices consistent with an evidence-based paradigm. DUI could be a useful tool among the numerous types of PT-based interventions that currently exist.

Soft Tissue Scanning (DUI)

A diagnostic musculoskeletal ultrasound device utilizes conventional sound waves emitted by a transducer of varying frequency ranges. We typically use a frequency range between 5 and 15 MHz, with the higher-frequency soundheads providing better resolution but at more superficial depths.

As in therapeutic applications, the lower the frequency, the deeper the tissue penetration. Ultrasonic imaging relies on good signal quality, so generally speaking, a higher frequency transducer is best for scanning muscles and joints.

The DUI scanner itself consists of a soundhead or transducer, which acts to both transmit and receive echoes (soundwaves). The signal is fed into a microprocessor and an image is then constructed based upon the relative strength characteristics of returning echoes. These, in turn are determined by the relative density of the reflecting tissue.

The final image is seen on a computer screen as a series of 256 shades of gray that form a black and white image. The rest is just recognizing anatomical structures. The distinction between normal and diseased tissue comes by way of practice and experience.

This form of imaging has no known adverse effects when conducted within established protocol settings, which allow for safe repeat scans on the same person without concern for damaging radiation. Sound waves not returning to the transducer are transformed into vibrational energy and eventually dissipate inconsequentially as heat.⁴

Diagnostic ultrasound imaging for musculoskeletal purposes has been evolving steadily since the 1970s. Advancing technology has led to the current state-of-the-art DUI units capable of high image resolution capabilities along with three- and four-dimensional image reconstruction properties.

Add in a color Doppler feature and clinicians have the capability to accurately scan for a multitude of commonly seen conditions, including sprains/strains, tears/ruptures, tendonitis/tendinosis, inflammation, fibrosis, embedded foreign objects, edema, hypertrophic and degenerative conditions, masses/cysts and internal joint derangements, to name but a few.

The best part about using DUI is that it is real-time data, which allows for dynamic evaluations. Unlike static imaging that is sensitive to motion artifact, DUI encourages movement during the examination so that all interdependent structures can be identified and evaluated for structural and/or functional deficits. DUI examinations are performed relatively quickly in the hands of an experienced clinician sonographer, and cost a fraction of other comparable imaging tests such as MRI or CT scans.

Diagnostic Accuracy

Diagnostic ultrasound imaging of musculoskeletal structures has demonstrated impressive accuracy over the past few years, more so in studies carried out between the late 1990s and the present day.

DUI has rivaled and even surpassed MRI in imaging of certain areas such as the shoulder,^5-7 where the superficial anatomy of this joint lends itself well to being scanned. Investigations utilizing conventional Bayesian methods of calculating validity, as occurs when researchers compare DUI to a "gold standard" test such as MRI in diagnosing a specific lesion such as a rotator cuff tear in the shoulder, are actually estimating a value or index (sensitivity/specificity, negative/positive predictive values) that represents the interaction between operator and machine.

It is this operator dependency that has drawn the most criticism in the literature as the major drawback against the routine use of DUI.⁷ To date, there are no formal diagnostic musculoskeletal US imaging curricula available for formal study at the certification level, which introduces a standardization problem for novice learners.

Case Study: Rotator Cuff Tear

For the purposes of this article, we will use shoulder pathology to illustrate how diagnostic musculoskeletal ultrasonic imaging can be applied. Not only can we detect the presence or absence of partial/total thickness rotator cuff (RTC) tears, but we can use those findings to validate the accuracy of our (pre-DUI) special test selection.

As therapy progresses, a second scan can readily verify the effectiveness of the healing process, making DUI a very useful and objective outcome measure as well. Repeat scans of the same patient on different occasions serves not only to confirm the healing process, but also to guide our clinical decision making, along with providing visual confirmation to our patients regarding the progress of their condition.

The information gained by using DUI early in the treatment planning can only improve the quality of physical therapy by providing the therapist with a more accurate initial diagnosis. A clinical impression is transformed into a verifiable diagnosis.

Subtle differences in pathology, such as tendonitis versus tendinosis—which typically require different treatment approaches but which are often treated as one and the same—can be distinguished by sonography. Each condition is seen as having very unique sonographic characteristics.

The old saying, "we only diagnose what we recognize" takes on greater significance with a visual feedback tool such as DUI to aid in the diagnostic process. Diagnostic US not only allows us to recognize a wider variety of conditions, it assists us in grading their severity (e.g., strains grade 1-3) for classification, documentation and treatment planning purposes.

Benefits and Efficacy

Needless to say, diagnostic US can be a popular imaging test within the payer community, for several reasons. It is convenient (scans take less than 10 minutes per area), it is relatively inexpensive compared to other soft tissue imaging tests, adverse effects attributable to the test are a non-issue, and no ionizing radiation exists (unlike CT or plain films).

Properly performed scans also have very good overall accuracy rates; tests are real time and dynamic. Clinicians are not relegated to interpreting single slice images, which require a high interpretive component. Dynamic US scanning captures the essential structures of the living organism, whether the target tissue is a muscle or a joint.

The interplay between muscle, tendon, sheath and synovial fluid plays out in streaming video format, allowing the viewer a unique "real time" perspective into soft tissue musculoskeletal dynamics. Figure 1 is a sonogram which shows a full thickness rotator cuff tear (RTC).

There is an abundance of clinical studies published in peer-reviewed journals validating the use of diagnostic ultrasonography as a clinically accurate imaging tool. Some of the more recent studies have examined the use of DUI for such purposes as evaluating tendon architecture,⁸ imaging specific ligaments integral to joint stability,⁹ glenoid labral tears,¹⁰ enthesopathies of the elbow,¹¹ carpal tunnel syndrome and median nerve neuropathy.¹²

The use of DUI is limitless and requires a basic understanding of the unit itself, along with a good foundation in anatomy. As Arthur Jones of Nautilus fame once wrote of exercise technique, "practice makes perfect, but only if you practice perfectly." Understanding soft tissue sonography requires practice and integration of anatomical principles with good positional techniques.

Imaging: Pushing the Limits

The future of physical therapy appears to hold the promise of eventual direct access for most, if not all states. Combined with the advent of the entry-level DPT and the expanded professional responsibilities that might follow, this autonomy could lead to greater expectation pressures from health care partners and from society in general regarding improved PT diagnostic capabilities.

Diagnostic ultrasound imaging could be a natural choice for those more adventurous clinicians intent on "pushing the diagnostic limits" and expanding their diagnostic scope beyond physical examination.

As with any form of diagnostic imaging, the idea is not to supersede the physical exam, but to enhance the quality of the diagnostic process in general. The axiom that still holds true regarding diagnostic testing applies to DUI as well: imaging tests should be used to confirm a diagnosis, not to establish one.

Diagnostic US imaging is rapidly evolving as a first-line soft tissue imaging test. Physical therapists are encouraged to familiarize themselves with this form of imaging. There is a high likelihood that it will become a common part of the diagnostic landscape in the near future.

• References are available online at www.advanceweb.com. Select the ADVANCE for PTs and PTAs publication, and then click "References" on the left-hand tool bar.

Tiziano Marovino is a licensed PT at Preferred Medicine, Spine, Sports and Occupational Therapy Center, Allen Park, MI. His undergraduate degrees are in physical education/pharmacology, recreation management/administration and physical therapy, with graduate studies in clinical kinesiology. He is completing his DPT degree at Creighton University, Omaha, NE. The author can be reached at 313-928-0700, ext. 232 or sonotiz@cs.com