Combining a review of the literature with insights from their experience, these rheumatologists offer pertinent pointers about the adjunctive potential of musculoskeletal ultrasound in diagnosing common arthritic conditions ranging from rheumatoid arthritis to crystal-induced arthropathies.

Musculoskeletal ultrasound (MSU) is an excellent technique for evaluating soft tissue and cortical involvement in rheumatic diseases. Over the past few years, rheumatology health care professionals have demonstrated an exponentially growing interest in MSU due to its diagnostic potential.1 Indeed, ultrasound provides an adjunctive tool in the assessment of many of the common entities (i.e. shoulder pain, swollen joints) that clinicians encounter in daily practice.

In comparison to other imaging modalities, ultrasound is the only imaging tool clinicians can use at the bedside and they can also use the modality to assist with joint injections. The main advantages of MSU are dynamic real-time scanning, absence of radiation, low cost, exact localization of symptoms and, most importantly, patient acceptance. To aid in diagnosis, the sonographer performing the scan can correlate the clinical findings with the ultrasound images and immediately compare the contralateral side.

With the advancing technology over the years, ultrasound has evolved to a point where it allows exquisite visualizations of anatomy without invasive procedures. Musculoskeletal ultrasound has proven to be valuable in diagnosing common rheumatological conditions including rheumatoid arthritis, crystal-induced arthritis, seronegative spondyloarthropathies and osteoarthritis (see “An Overview Of MSU Benefits In Rheumatology”). In addition, clinicians may view the nerve, cortical bone, muscle, tendons and ligaments.

Here one can see early erosion of the second metacarpophalangeal joint in a patient with rheumatoid arthritis.

When one starts to use ultrasound scanning, it is important to take a standard approach. The technique is an art and having a solid knowledge of anatomy is essential for MSU. Secondly, like learning any other technique, practice is essential. Thirdly, one must learn the limitations of ultrasound. For example, ultrasound has not been useful for imaging internal cortical pathology. Therefore, clinicians should consider ultrasound as a complementary modality to magnetic resonance imaging (MRI) and conventional radiography in daily practice.

Understanding The Fundamentals Of Ultrasound Imaging
Having a strong grasp of pattern recognition is essential when it comes to interpreting MSU images. All tendons, nerves, muscles and bone have a characteristic quality on MSU imaging. Tendons have a fibrillar pattern or appear as densely packed bright white lines on a dark background. The best example is the Achilles tendon. Nerves have a fasicular pattern. For example, with the median nerve, clinicians will note bright whites lines that are not densely packed on a black background. One can compare a MSU image of muscle to a feather with characteristic bright white lines emanating from the septa.

Keep in mind that ultrasound has not been useful for imaging of internal cortical pathology. However, it is an excellent technique for a quick evaluation of cortical surface. Clinicians can easily identify bone by its bright echo-texture and it is usually the deepest or lower image one sees on the screen.

It is imperative to have a grasp of what ultrasound is before one can truly appreciate the technology. Simply, ultrasound waves are mechanical sound waves above the hearing frequency of the human ear. Humans hear frequencies between 20 Hz to 20,000 Hz. Sounds below 20 Hz, which can only be heard by animals, are called infrasound. Ultrasound refers to sounds above 20,000 Hz.

Today, we have diagnostic ultrasound machines capable of hearing up to 18 MHz. The images are generated by a transducer and a synthetic piezoelectric crystal that vibrates under electric currents. The ultrasound pulses travel through tissues and are reflected at interfaces or boundaries in which tissues with different acoustic properties meet. For example, fluid and bone have different acoustic properties, and one can easily distinguish these under ultrasound. Bone will appear bright white (hyperechoic) and fluid black (hypoechoic). The echoes that return traverse the piezoelectric crystal and create electrical potentials to grey-scale imaging. This leads to the grey and black images we see on the ultrasound monitor. To help detect blood flow and direction, we use color Doppler ultrasound. However, when it comes to MSU, we are more interested in power Doppler ultrasound, which aids in detecting low blood flow states in conditions such as synovitis.10

The terminology is equally important. The reflected sound waves are either hypoechoic, hyperechoic and anechoic. Anechoic sound waves are structures without internal reflectors. No echoes are returned with these sound waves so clinicians will see black areas of the image (i.e. cartilage, effusions). Hypoechoic sound waves involve structures with low-level echoes that produce weaker reflections or darker grey areas of the image (i.e. muscle, synovial tissue, peripheral nerves). Hyperechoic sound waves are structures with high level echoes that produce bright grey reflections of the image (i.e. bone, calcifications, tendons, foreign bodies).

Can MSU Help Identify Rheumatoid Arthritis?
Often, rheumatoid arthritis (RA) manifests as bilateral and symmetrical small joint involvement. However, changes may not be temporaneously symmetrical and this can make diagnosis difficult. Furthermore, clinical examination is relatively insensitive when it comes to demonstrating synovitis.9 However, researchers have described using MSU in patients with RA to help detect erosions, synovial proliferation and tenosynovitis. It is important to accurately detect early erosions before changes become evident radiographically. There is increasing evidence that bone erosion occurs early in RA and conventional radiographs fail to detect early erosions.11 Magnetic resonance imaging has been the gold standard in detecting early erosions. However, due to the cost of obtaining a MRI, it is an impractical modality to screen patients, image multiple joints and monitor patient disease activity.

Note the image of the abnormal Achilles tendon, which is less hyperechoic with scattered calcifications and has increased width of .85 cm in comparison to a normal Achilles tendon. The patient was originally diagnosed with osteoarthritis. After evaluating the patient’s heel with ultrasound, the author diagnosed psoriatic arthritis secondary to the enthesitis found.

Moreover, correlating one’s clinical exam with sonographic findings can be useful in diagnostic and therapeutic decisions. In my personal experience, I have had a number of instances in which the patient’s medical management was influenced by sonographic findings.

Seronegative Spondyloarthropathies: Can MSU Aid In The Diagnosis?
The family of seronegative spondyloarthropathies is characterized by a number of overlapping features and inflammation at the insertion of tendons to bone, which is referred to as enthesitis. The group includes ankylosing spondylitis, reactive arthritis, psoriatic, juvenile spondylitis and enteropathic arthropathy. While clinicians can usually detect peripheral enthesitis via the clinical exam, there is a lack of specificity when it comes to generalized pain, swelling and tenderness. Also, the characteristic sign of disease on radiograph (such as sacroiliitis) often occurs as a late manifestation.

Recently, clinicians have recognized MSU as a sensitive technique to assess tendon or ligament involvement. Researchers have reported using power Doppler to detect inflammation and low blood flow within the tendon, which is a sensitive indication for tendinitis. Clinicians have also described enthesitis in psoriatic arthritis. In a study, clinically asymptomatic SpA had abnormal entheses sonographically.12

In comparison, note the normal view of an Achilles tendon where it inserts into the calcaneous.

In clinical practice, it can be challenging to diagnose patients who present with generalized arthralgias and without psoriasis. Out of the lower limbs, the most common sites of entheseal involvement are the knee and heel where the Achilles attaches to the calcaneus. For example, one patient was initially diagnosed with osteoarthritis of the knee. After we used MSU, we were able to diagnose psoriatic arthritis based upon the sonographic findings of his Achilles.

Clarifying Difficult Cases Of Knee Effusions
Osteoarthritis is one of the most common rheumatological conditions clinicians see in the outpatient setting. The most vulnerable and largest joint in the human body is the knee. Without controversy, clinicians have used MRI to aid in identifying intraarticular knee pathology. However, there are also a number of conditions that are extraarticular and practitioners can easily identify these via ultrasound.13,14 For example, using MSU can help you discriminate between a Baker’s cyst and deep venous thrombosis. One may also use MSU to detect a suprapatellar effusion, diagnose tendonitis and bursitis, and evaluate the cartilage all at the bedside.
Most of us have come across cases in which there was a question of a knee effusion. However, we could not make a definite clinical diagnosis because of the patient’s body habitus. Using MSU enables us to easily and quickly answer whether the patient has a knee effusion.

For example, an obese female patient had undergone a dry needle tap by the primary physician and was subsequently referred to me for ultrasound testing. A previous X-ray showed osteoarthritis of the knee with medial joint space narrowing. With the patient supine and the knee slightly bent, I placed the probe over the suprapatellar recess and easily identified an effusion. With MSU guidance, I proceeded to drain the knee of 40cc of yellow clear synovial fluid.

Can MSU Have An Impact In Diagnosing Crystal-Induced Arthropathies?
Crystal-induced arthropathies may also be demonstrated sonographically.14,15 While there are few studies involving MSU and crystal-induced arthropathies, researchers have described changes of the hyaline cartilage and bony surface with both monosodium urate crystals and chondrocalcinosis crystals appearing as hyperechoic echoes.

In gout, the hyperechoic crystals deposit on the top layer of the black cartilage.16 Due to its high water content, cartilage appears as black or hyperechoic under ultrasound. In chronic gout, the cartilage interface or top layer may show the same thickness as the bone. This has been described as the “double contour sign.”
In chondrocalcinosis, the hyaline cartilage is depicted by dashes or dots that reflect hyperechoic foci within the cartilage. I have described this as the “route 66” sign.

The role of ultrasound does not replace the gold standard of synovial fluid analysis in detecting crystal-induced arthropathies. However, in cases of suspected crystal-induced arthritis, MSU can provide accurate guidance in cases in which there is difficult or even minimal fluid collection.17

What About Ultrasound-Guided Injections?
Routinely, injections and therapeutic aspirations are guided based upon one’s clinical examination. However, there is now sufficient data to show the accuracy is not as sensitive as we previously believed.18 When it comes to injecting viscosupplements, intraarticular accuracy is of therapeutic value. Perhaps the most challenging joint to inject is the hip. Most clinical rheumatologists perform fluoroscopic-guided hip injections. Using MSU guidance would enable clinicians to perform hip and other joint injections without exposure to radiation.

Here is a knee effusion in an obese patient who complains of knee pain. A previous X-ray suggested osteoarthritis of the knee with medial joint space narrowing. With MSU, the author was able to easily identify the effusion and subsequently drain the knee of 40 cc of yellow clear synovial fluid.

Does MSU Have Diagnostic Utility For Shoulder Pain? What A Case Study Reveals
As a private rheumatologist, I have found that MSU is not only a useful modality to help with injections but can also be a diagnostic problem solver. One of the most complicated and challenging joints to evaluate is the shoulder. Many of the physical exam shoulder maneuvers for detecting abnormalities are sensitive but are not specific for any one condition.19 The challenge is to differentiate all the possible ailments such as rotator cuff tear, bursitis, acromioclavicular arthritis, synovitis or effusion. To complicate matters, all can coexist in causing shoulder problems. However, using MSU at the bedside in combination with the physical exam can help clinicians arrive at the diagnosis quickly.

A 57-year-old female presents with right shoulder pain. She has a history of diabetes mellitus, hypertension and coronary artery disease. She also has a pacemaker.

The patient was admitted for complaints of right-sided weakness and was found to have a cerebral infarction. She was treated and then sent to the nursing home for rehabilitation. At this point, I saw the patient during a consult.

The patient complained of severe right shoulder pain and was unable to lift her arm above her head. She had been wheelchair bound and had been undergoing physical therapy. This episode of pain began two days after being transferred from her chair to the bed.

In performing the clinical exam, I saw no sign of muscle atrophy or gross swelling. The patient had a good handgrip and the reflex exam was brisk. Her range of motion was limited to 45 percent abduction, the drop arm test was positive and she complained of tenderness with palpation over the bicep tendon.
The differential diagnosis included rotator cuff tear, sub-deltoid, subacromial bursitis, fracture, frozen shoulder and neurologic pathology. A plain radiograph was unremarkable for a fracture and there was a limited study because of the patient’s pain. There was osteoarthritis of the acromioclavicular and glenohumeral joints. One could not completely rule out an effusion.

Magnetic resonance imaging was contraindicated due to the patient’s pacemaker. We proceeded to examine her right shoulder with MSU. We took standard views of the bicep tendon, subscapularis, acromial-clavicular joint, supraspinatus, infraspinatus and deltoid muscle.

An Overview Of MSU Benefits In Rheumatology

- • Correlate clinical examination with MSU images • Guided injections • Real-time dynamic bedside tool • Diagnosing early rheumatoid erosions and overall diagnosis • Sub-clinical inflammatory disease • Monitoring patient under treatment

When scanning the shoulder, one should position the patient’s arm in different positions in order to best visualize the structure in question. I also examine the tendons in two planes whenever possible.
The bicep tendon on transverse scan revealed a large hypoechoic effusion surrounding the long head of the tendon. The supraspinatus was absent and a large anechoic compressible signal was present. The findings were consistent with right shoulder bursitis and a full thickness rotator cuff tear.

Under ultrasound guidance, we drained the right shoulder of 30cc of yellow cloudy synovial fluid. The patient had immediate relief of her shoulder pain. Her range of motion increased to 90 degrees abduction.
In this case, the clinical suspicion was correlated with ultrasound images.
We obtained the diagnosis quickly and bedside ultrasound guidance helped facilitate the aspiration.

Case Study Discussion Points
When it comes to viewing the supraspinatus via MSU, it is best to place the patient’s arm behind his or her back. Normally, the supraspinatus is convex and attaches on the hyperechoic humeral head. One may easily see the overlying deltoid muscle and bursae. In this patient’s case, the supraspinatus was absent and the hypoechoic fluid produces the convex shape normally produced by the rotator cuff.

There are many criteria that describe rotator cuff tears. However, failure to visualize the cuff has a high positive predictive value. Other findings that are helpful in diagnosing rotator cuff include fluid collections and cortical irregularities of the humeral head.

In Conclusion
Musculoskeletal ultrasound has proven to be a contender among the other radiographic modalities. It is an exciting, evolving technique and readily available for the rheumatology health care professional. Indeed, MSU should be part of the armamentarium of the professional who evaluates and treats musculoskeletal conditions. One may consider MSU to be an extension of the physical exam or the stethoscope for the rheumatologist.

Rheumatologists worldwide have adopted ultrasound in their clinical practice. At present, in the United States, MSU has slowly been introduced among rheumatologists. This slow acceptance is due in part to training and the lack of consensus of standard scans between rheumatologists and radiologists.

Much work is needed in regard to standardization and certification. With training and plenty of practice, it is possible to introduce MSU in any practice. Not surprisingly, there have been a number of training courses in MSU. However, most courses are geared to the radiologist. To date in the U.S., the only course in MSU for rheumatologists is the Antonio J. Reginato course at Cooper Hospital in Camden, N.J.