Shoulder Ultrasound (old)

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Ultrasound in assessing and treating the painful shoulder

Introduction

Ultrasound is an excellent screening test to evaluate the painful shoulder. Often, shoulder pain comes from the superficial soft tissues around the shoulder joint, such as the tendons and the subacromial bursa1, which can be readily seen and evaluated during an ultrasound examination.

Ultrasound is a safe technology that is based on sound waves and does not involve x-rays. X-rays and CT scans are good to image the bones of the shoulder and are ideal for conditions such as fractures after trauma or to look for osteoarthritis.

Ultrasound has the advantage of dynamic scanning and real-time sonopalpation: During the examination, the patient’s pain and the images can be directly correlated, which is very useful in establishing the cause of the pain2.

Real-time ultrasound can also be used during ultrasound-guided interventions, such as therapeutic steroid injections, joint aspiration, or aspiration of calcium deposits in the tendons.

MRI (magnetic resonance imaging) is also often used to image the shoulder. It is indicated when an injury to the deeper strictures is suspected, such as a labral tear that cannot be seen with ultrasound. With the new generation of ultrasound machines, the tendons can be seen in more detail and higher resolution than MRI.

Figure 1. Anatomy of the shoulder, demonstrating the supraspinatus tendon, subacromial bursa, and the long head of biceps tendon.
Figure 1.  Anatomy of the shoulder, demonstrating the supraspinatus tendon, subacromial bursa, and the long head of biceps tendon.

The shoulder joint is one of the most mobile joints with a wide degree of motion. To allow this excellent mobility, the bone contact in the shoulder joint is relatively small. Therefore, the soft tissues, including the labrum, tendons, and muscles, play a crucial role in shoulder stability. The four tendons directly covering the shoulder joint are collectively known as the rotator cuff. The tendons of supraspinatus, infraspinatus, teres minor, and the subscapularis muscle constitute this cuff3.  Another important tendon, the long head of the biceps tendon, is located at the front of the shoulder. Overlying the rotator cuff, there is the subacromial bursa. The function of the bursa is to provide a gliding interface during shoulder movement. The rotator cuff tendons and the burse are often affected by overuse, repetitive injuries and can become painful.

Ultrasound is safe, readily available, and less resource-intensive, in particular, compared to MRI. There may be, however, circumstances where a final diagnosis cannot be reached using ultrasound alone.

Common causes of shoulder pain and their appearance on ultrasound

Subacromial bursitis

Shoulder Ultrasound Image showing Subacromial Bursitis
Figure 2. Ultrasound image of subacromial bursitis. Thickened bursa (red), supraspinatus tendon (green), articular cartilage (blue), bone (brown).

Inflammation of the subacromial bursa is one of the most common causes of shoulder pain. The bursa lies between the roof of the shoulder (the acromion) and the rotator cuff tendons. It contains a trace amount of liquid that reduces the friction of the rotator cuff tendons against the surrounding static tissues during shoulder movement. Acute bursitis is usually the result of overuse, including overhead activities or repetitive shoulder movements. Minor trauma, such as jolting the shoulder, can also cause bursitis.  It is more common among the elderly but can also occur in young and middle-aged adults. Diabetes and constrictive bony shapes are predisposing factors for this.

Subacromial bursitis often starts with symptoms of mild shoulder pain on specific movements, such as elevating the arm off to the side or during internal rotation of the shoulder. When bursitis gets more severe, the pain becomes disabling and night pain is also a common problem. On ultrasound, the normal bursa is seen as a very thin strip of fluid overlying the rotator cuff tendons. An inflamed bursa can readily be appreciated as a bursal thickening or accumulation of excessive fluid, called a bursal effusion. In severe bursitis, ultrasound can show increased blood flow in the bursal surface. In chronic bursitis, the fatty tissues around the bursa become thickened, or the bursa can lay down calcium or even form multiple small deposits, called rice bodies4. Ultrasound is also used to perform ultrasound-guided steroid injections into the subacromial bursa.

Supraspinatus tendinosis

Ultrasound Images of the Shoulder showing supraspinatus tendinosis
Figure 3. Ultrasound image of supraspinatus tendinosis. Thickened supraspinatus tendon (green), bursa (red), articular cartilage (blue), bone (brown).

The rotator cuff refers to four tendons surrounding the shoulder joint, which include:

  1. Subscapularis tendon at the front
  2. Supraspinatus at the top (see Figure 1)
  3. Infraspinatus at the back
  4. Teres minor tendons also at the back of the shoulder.

The inflammation of these tendons, called tendinosis, has similar causes to bursitis: overuse, repetitive movements, and acute trauma. Once again, age and diabetes are predisposing factors. The supraspinatus tendon is most often affected.

Modern ultrasound machines are excellent in demonstrating tendons. Tendons are tissues composed of tightly packed collagen fibres arranged in a parallel fashion. On ultrasound, tendons appear as ‘shiny’ bright structures. The internal architecture of the tendons can be seen as multiple fine linear layers of fibres.  An inflamed tendon often has minor microscopic injuries, attracting fluid and causing the tendon to swell. The tendon loses its ‘shiny’ properties and becomes diffusely dark. Ultrasound is also used for guided steroid injections that can support rehabilitation of the shoulder.

Calcific Tendinitis

A specific form of inflammation of the supraspinatus tendon is calcific tendinitis.  Calcium deposition in the tendon results in shoulder pain is often more resilient to physical therapy and can take much longer to improve. The calcific deposits are easily seen as bright spots in the tendon during the ultrasound. Ultrasound is also used to perform a procedure called barbotage5. The calcium deposits are broken down, dispersed, flushed with fluid and aspirated with the help of a needle. This can speed up the reparative phase of tendinitis.

Rotator cuff tears / supraspinatus tendon tear

Ulatrasound Image of the Shoulder showing a Supraspinatus tendon Tear
Figure 4. Ultrasound image of a supraspinatus tendon tear. Full-thickness supraspinatus tendon tears with minimal retraction (red/green), articular cartilage (blue), bone (brown).

The supraspinatus tendon is the most vulnerable to tears among the rotator cuff tendons. Due to its position and use, it often undergoes degeneration (‘tendinosis’). The degenerated tendon is weakened and more prone to developing small tears that often propagate over time. Healthy rotator cuff tendons can also tear in young patients with significant trauma. Symptoms of a chronic supraspinatus tear can be similar to bursitis, but the weakness of active movements can be more pronounced. Modern high-resolution ultrasound is very accurate in detecting tendon tears. It can classify tears as complete/incomplete and partial/full-thickness tears. Ultrasound can also assess the quality of the supraspinatus muscle bulk, which gets weakened in chronic tears. This can guide your doctor and physical therapist to decide on the best treatment plan. Ultrasound is also used to guide steroid injections for pain relief.

Frozen Shoulder

Frozen shoulder or adhesive capsulitis is a painful condition with markedly limited mobility of the shoulder. In primary frozen shoulder, patients develop a symptom without apparent cause. Patients with chronic conditions such as diabetes or thyroid disease are more likely to develop a frozen shoulder.  There is a preceding event in secondary frozen shoulder, such as trauma, fracture, tendon tear, or a recent operation. Patients classically undergo three phases, with severe pain in the first phase, then transition to the markedly limited range of motion, followed by a phase of the resolution of symptoms. While the excruciating pain often gets better after a few months, the stiffness can take over a year to resolve. In the frozen shoulder, the inner soft tissues, the joint capsule, and ligaments become inflamed, finally becoming thickened, contracted, and fibrosed. This soft tissue thickening can sometimes be seen on ultrasound. Still, the primary role of ultrasound in the frozen shoulder is to rule out other rotator cuff abnormalities, such as tears. Ultrasound is also used to guide steroid injections for pain relief, perform hydrodistension of the joint, and loosen the fibrosed joint capsule6.

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References

  1. InformedHealth.org [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. Shoulder pain: Overview. 2020 Feb 13. Available from: https://www.ncbi.nlm.nih.gov/books/NBK554693/
  2. Nazarian LN. The top 10 reasons musculoskeletal sonography is an important complementary or alternative technique to MRI. AJR Am J Roentgenol. 2008;190(6):1621-1626. doi:10.2214/AJR.07.3385
  3. Maruvada S, Madrazo-Ibarra A, Varacallo M. Anatomy, Rotator Cuff. [Updated 2021 May 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441844/
  4. Bacha, R., Manzoor, I. & Gilani, S.A. Sonographic presentation of rice bodies in subacromial-subdeltoid chronic bursitis. Ultrasound J 11, 16 (2019). https://doi.org/10.1186/s13089-019-0130-y
  5. Tafti D, Byerly DW. Ultrasound Guided Barbotage. [Updated 2021 Aug 15]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK572096/
  6. Cho CH, Bae KC, Kim DH. Treatment Strategy for Frozen Shoulder. Clin Orthop Surg. 2019;11(3):249-257. doi:10.4055/cios.2019.11.3.249