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Ultrasound Imaging of Musculoskeletal Disorders

  1. Disease/Disorder:
    Definition

    Musculoskeletal ultrasound (MSK US) involves the use of high-frequency (up to 17 MHz) sound waves to image soft tissues and bony structures in the body for the purposes of diagnosing pathology or guiding real-time interventional procedures. 

    Epidemiology including risk factors and primary prevention

    During the past decade an increasing number of physiatrists have integrated MSK US into their practices to facilitate the management of patients presenting with a wide variety of musculoskeletal and neurological complaints.  Ultrasound is currently the fastest growing diagnostic and therapeutic (image assist) imaging modality among physiatrists and other clinicians managing patients with musculoskeletal disorders (e.g., rheumatologists, sport medicine physicians, podiatrists).  There are no known risk factors or contraindications to the use of US by a qualified practitioner.

    Patho-anatomy/physiology
    MSK US machines  consist of a "box" containing hardware and sophisticated high-speed computer systems connected to one or more transducers.  Each US transducer contains over 100 thin crystals that are stimulated by electrical voltage, which by the reverse piezoelectric effect, generates ultrasound waves in complex patterns.  These waves travel through the body, where they encounter acoustic interfaces (areas between adjacent tissue layers where tissue density and/or stiffness changes).  At each acoustic interface, some sound is reflected back to the transducer, which then serves as an antenna and by the piezoelectric effect, generates the electric signal needed to process the information and generate a two-dimensional black and white image known as B-mode US.  The ability to detect subtle acoustic interfaces allows modern MSK US machines to resolve structures with a resolution of less than 1 mm.  The combination of submillimeter resolution and real-time imaging has positioned MSK US as a powerful clinical problem-solving tool in physiatric practice.
    Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)
    Current applications include, but are not limited to:
    1. Diagnosis of tendinosis, partial- and full- thickness tendon tears (e.g., rotator cuff, patellar tendon, Achilles tendon).
    2. Diagnosis of nerve entrapments (e.g., carpal tunnel syndrome, ulnar neuropathy at the elbow, tarsal tunnel syndrome).
    3. Evaluation of ligamentous injury and joint instability syndromes such as valgus instability of the elbow or varus instability of the knee.
    4. Evaluation of dynamic complaints such as subluxating/dislocating ulnar nerves, snapping popliteus tendons, snapping hip syndrome, and peroneal tendon subluxation/dislocation.
    5. Diagnosis of acute (e.g., contusion or strain) or chronic muscle injury (myopathy or denervation).
    6. Joint aspiration/injection, peri-tendinous injection, or peri-neural injection, in which US can be used to accurately and efficiently guide the needle to the target region.
    7. Aspiration and injection of various fluid collections  (e.g., Baker's cyst, olecranon bursitis).
    8. Percutaneous lavage and aspiration of calcific rotator cuff tendinosis.
    9. Advanced procedures such as percutaneous tenotomy and precise delivery of biologics and regenerative therapies such as platelet-rich plasma and stem cells.
    Specific secondary or associated conditions and complications

    There are essentially no contraindications to a MSK US examination.  MSK US examinations are unaffected by claustrophobia, impart no radiation to the patient or examiner, and unlike magnetic resonance imaging (MRI) and computed tomography (CT) are relatively unaffected by prostheses and other orthopedic hardware.  Studies have shown that patients with shoulder complaints prefer US over MRI scan. Furthermore, US is an excellent tool to investigate tendon disorders and fluid collections associated with orthopedic implants.

  2. Essentials of Assessment
    History

    ​As a dynamic imaging study, MSK US is best utilized in the context of a patient-specific clinical history and physical examination.  A typical required MSK history includes:

    1. Onset of injury
    2. Location
    3. Pain location, quality, character, aggravating/alleviating factors
    4. Neurological concerns
    Physical examination

    ​Diagnostic US examinations should follow established protocols.  During a US examination, many physical examination manuevers can be performed to assess dynamic aspects of musculoskeletal pathology not visualized on static imaging modalities such as X-rays, CT, or MRI.  Consequently, MSK US examinations are most effective when performed in conjunction with a standard physical examination of the affected region, consisting of:

    1. Inspection
    2. Palpation
    3. Range of motion
    4. Neurological examination
    5. Special (named) tests
    Functional assessment
    ​Perhaps the most important advantage of MSK US is the ability to assess MSK structures in a dynamic or functional state.  Real-time MSK US imaging is the only imaging modality currently available to dynamically evaluate soft-tissue structures, thus facilitating the investigation of dynamic processes such as nerve instability and snapping tendons or bursae. In addition, through "sonopalpation," the physiatrist can place the probe directly over the point of pain or other complaint and correlate pathologic findings with reproduction of symptoms.
    Imaging
    Although the many advantages of MSK US render it an attractive, office-based imaging modality for clinical practice, every physiatrist should be aware of three important limitations of MSK US:
    1. Limited penetration: US beams lose energy as a function of depth. The rate of this energy loss is dependent on frequency. High frequency transducers (> 10 MHz) provide submillimeter resolution, but may penetrate only 2-3 cm into the body.  Lower frequency transducers may penetrate 7-10 cm or more, but with reduced resolution. Thus, depending on the desired resolution, the diagnostic capabilities of MSK US may be reduced when evaluating deep body regions such as the hip or in patients of large body habitus. US does not effectively penetrate normal bone. Consequently, US cannot be used to evaluate bone marrow disorders and provides only a limited view of most joint surfaces. 
    2. Equipment cost: In a way similar to electrodiagnostic equipment, physiatrists must generally purchase or rent MSK US machines in order to effectively integrate MSK US services into their practices.  Although US machine quality continues to improve, there are significant differences among available models.  Cost will generally be determined by resolution and the number of probes purchased. Luckily, there are numerous high-quality machines currently available to meet the needs and budgets of most physiatric practices.
    3. Operator dependence: The clinician must recognize the abnormality and appropriately interpret it. However, similar to electrodiagnostic examinations, MSK US also requires the physiatrist to physically acquire the information.  Acquiring the skill of optimal image acquisition often provides the greatest challenge to most physiatrists who are seeking to integrate MSK US into their practices. 
    Early predictions of outcomes
    US can improve patient outcome by offering more precise diagnostic and treatment locatizations in real time, often without delays or high costs seen with other imaging modalities such as MRI.
    Environmental
    ​A key advantage of MSK US is the ability to study structures right in the office setting as a supplement to the history and physical exam.
    Professional Issues
  3. Rehabilitation Management and Treatments
    Available or current treatment guidelines
    Many of the conditions identified with MSK ultrasound respond most favorably in the initial treatment phase to supervised active rehabilitation. A role of US in society is to hopefully reduce health care costs by reducing the need for expensive MRI studies in many cases.  Also the immediacy of diagnosis reduces anxiety for the patient.​  Proper training  is essential before adding this modality to a musculoskeletal practice. ​
    At different disease stages
    The presence or extent of Doppler flow may also reflect the severity or chronicity of a tendon or ligament disorder.  Although not available in the United States at this time, US contrast agents will likely expand the applications of Doppler US, including the possibility of identifying viable tissue and/or monitoring  tissue healing via precise assessment of vascularity. 
    Coordination of care
    Physiatrists skilled in musculoskeletal medicine and employing ultrasound guided techniques still must remain grounded in coordinating multidisciplinary treatment approaches to care of the patient designed to maximize functional outcomes.
    Patient & family education
    ​Patients and family can be educated on their injury immediately at the time of diagnosis with US, versus waiting days or weeks for other advanced imagining modalities to be completed (example, MRI, CT, etc.)
    Translation into practice: practice "pearls"/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills
    A major concern at this time is that MSK US training is not mandatory in PM&R residencies and fellowships. As a result, there is great diversity among the skill sets of physiatrists currently utilizing MSK US in their practices.  Weekend courses, one-on-one mentorships, on-line learning, and independent practice are just a few methods that clinicians currently use to obtain training.  Residencies and fellowships have begun to incorporate MSK US into curricula. Therefore, it is important to adopt practice guidelines that reflect competence and provide practitioners guidance as to what they need to know in order to feel confident and competent in MSK US.
  4. Cutting edge/emerging and unique concepts and practice
    Cutting edge concepts and practice
    ​The current applications for MSK US in physiatric practice are broad and will continue to expand as technology and experience advance.  In the near future, contrast agents may become available in the United States to allow more precise assessment of vascularity.  Elastography is a technique by which US can be used to determine tissue stiffness, and its role in MSK US is currently being explored. Finally, matrix probes with 2-dimensional crystal arrays will become available at the high frequencies necessary for MSK applications, thus providing real-time 3-dimensional imaging capabilities. These probes will advance both the diagnostic and interventional capabilities of MSK US, as physiatrists will be able to acquire tissue volumes, not slices of information, and will be able to track needles and interventional devices in three planes simultaneously.
  5. Gaps in the evidence-based knowledge
    Gaps in the evidence-based knowledge
    ​The role of MSK US as a clinical problem-solving tool in physiatric practice is already well established. Multiple studies have documented the utility of diagnostic US when performed by competent individuals. For example, a recent a meta-analysis concluded that  MSK US is equally accurate to MRI to evaluate the rotator cuff.  However, further research will continue to define the specific indications for diagnostic MSK US. With respect to interventional procedures, the increased availability of MSK US has resulted in significantly increased utilization. However, image guidance is probably unnecessary for all procedures.  As concerns are raised pertaining to overutilization, research and consensus should seek to define specific circumstances in which US guidance adds value in terms of improved patient safety, increased procedural efficiency, improved efficacy, or reduced cost.
    References

    Bibliography

    DeJesus JO, Parker L, Frangos AJ, Nazarian LN.  Accuracy of MRI, MR arthrography, and ultrasound in the diagnosis of rotator cuff tears: a meta-analysis. Am J Roentgen. 2009;192:1701-7.

    ​Jacobson JA.  Musculoskeletal ultrasound and MRI: which do I choose?  Semin Musculoskelet Radiol. 2005;9:135-9.

    Middleton WD, Payne WT, Teefey SA, Hildebolt CF, Rubin DA, Yamaguchi K. Sonography and MRI of the shoulder: comparison of patient satisfaction. Am J Roentgen. 2004;183:1449-52.

    Nazarian LN.  The top 10 reasons musculoskeletal sonography is an important complementary or alternative technique to MRI.  Am J Roentgen. 2008;190:1621-6.

    Parker L, Nazarian LN, Carrino JA, et al. Musculoskeletal imaging: Medicare use, costs, and potential for cost substitution.  J Am Coll Radiol. 2008;5:182-8.

    Serafini G, Sconfienza LM, Lacelli F, Silvestri E, Aliprandi A, Sardanelli F.  Rotator cuff calcific tendinitis: short-term and 10-year outcomes after two-needle US-guided percutaneous treatment--nonrandomized controlled trial.  Radiology 2009;252:157-64.

    Smith J, Finnoff JT.  Diagnostic and interventional musculoskeletal ultrasound: Part 1. Fundamentals.  PM&R 2009;1:64-75.

    Smith J, Finnoff JT.  Diagnostic and interventional musculoskeletal ultrasound: Part 2. Clinical applications.  PM&R 2009;1:162-7.

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