Ultrasound assessment of the painful shoulder
Advantages of ultrasound
Ultrasound is an excellent screening test to evaluate the painful shoulder. Often, shoulder pain comes from the soft tissues around the shoulder joint, such as the tendons and the subacromial bursa[1], 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-ray radiation. X-rays and CT scans are good for imaging 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 pain[2].
Real-time ultrasound can also be used during ultrasound-guided interventions, such as therapeutic steroid injections, aspiration of joints or cysts, or aspiration of calcium deposits in the tendons[3].
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 in higher resolution than MRI.
While ultrasound is safe, readily available, and less resource-intensive compared to MRI, there are circumstances where a final diagnosis cannot be reached using ultrasound alone.
The Shoulder Joint
The shoulder joint is one of the most mobile joints with a wide range 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 and movement. The four tendons directly covering the shoulder joint are collectively known as the rotator cuff[4]. The tendons of supraspinatus, infraspinatus, teres minor, and the subscapularis muscle constitute this cuff. 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 and repetitive injuries and can become inflamed and painful.
Common causes of shoulder pain and their appearance on ultrasound
Subacromial bursitis and subacromial pain syndrome
Subacromial pain syndrome is an umbrella term used for pain that originates from below the roof of the shoulder and can spread towards the neck or the arm. Subacromial impingement is another term that is often used to refer to this condition. It can have different causes, including inflammation of the bursa (i.e., subacromial bursitis), inflammation of the tendons, or tendon tears.
Subacromial bursitis is an inflammatory painful shoulder condition caused by repetitive overhead activities and minor trauma such as a fall or a sudden pull of the shoulder. It is one of the most common causes of shoulder pain. The subacromial bursa is a fluid-filled sac that serves to lubricate the tendon surfaces to reduce wear and friction. The bursa lies between the roof of the shoulder (the acromion) and the rotator cuff tendons. After overusing or minor injury, the bursa can become thickened and accumulate fluid as signs of inflammation.
Patients often describe a painful arc while lifting the arm to the side between 60 degrees to 120 degrees and report pain at night when lying on the same side. The presentation can be acute or chronic in onset. Young patients often have an acute onset following a recent traumatic event or significant overexertion (e.g., gym workout or lifting a heavy box). Older patients or patients with repetitive overhead activities often have a gradual onset of symptoms. There are conditions that can predispose to developing bursitis, incl. diabetes and rheumatoid arthritis.
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 thickening of the bursa 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 fibro-fatty tissues around the bursa become thickened, or the bursa can lay down calcium or even form multiple small deposits, called rice bodies. Ultrasound is also used to perform ultrasound-guided steroid injections into the subacromial bursa for pain relief.
Supraspinatus tendinosis
The rotator cuff refers to four tendons surrounding the shoulder joint, which include:
- Subscapularis tendon at the front
- Supraspinatus at the top
- Infraspinatus at the back
- Teres minor tendon, also at the back of the shoulder.
The inflammation of these tendons, called tendinosis, has similar causes to bursitis: overuse, repetitive movements, and mild acute trauma. Once again, age and diabetes are predisposing factors. The supraspinatus tendon is most often affected, and the symptoms can be very similar to subacromial bursitis.
Modern ultrasound machines are excellent in demonstrating superficial 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 reduce pain and support rehabilitation of the shoulder.
Calcific Tendinitis
Calcific Tendinitis is a specific form of inflammation of the rotator cuff tendon where calcium deposition occurs within the tendon. This can result in marked shoulder pain and 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 barbotage[5]. 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
A rotator cuff tear is a tear or gap in one of the rotator cuff tendons, most often the supraspinatus tendon. 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 becomes 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, also called adhesive capsulitis, is a severely painful condition with markedly limited mobility of the shoulder. In primary frozen shoulder, patients develop symptoms without apparent cause. Patients with chronic conditions such as diabetes or thyroid disease are more likely to develop a frozen shoulder. In secondary frozen shoulder, there is a preceding event such as trauma, fracture, tendon tear, or a recent operation. Patients classically undergo three phases, starting with severe pain in the first phase, then transitioning to gradual improvement of pain, but with persistent marked stiffness of the shoulder. In the last phase, there is gradual resolution of symptoms. While the excruciating pain often gets better after a few months, the stiffness can take over a year to resolve[6].
In the frozen shoulder, the inner soft tissues, the joint capsule, and ligaments become inflamed resulting in thickening with contraction and fibrosis. 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 used to guide steroid injections for pain relief, perform hydrodistension of the joint, and loosen the fibrotic joint capsule[7].
Dr M Siebachmeyer
Musculoskeletal radiologist based at St Georges Hospital, London.
References
[1] “Shoulder pain: Overview,” Feb. 2020, Accessed: Oct. 08, 2023. [Online]. Available: https://www.ncbi.nlm.nih.gov/books/NBK554693/
[2] L. N. Nazarian, “The top 10 reasons musculoskeletal sonography is an important complementary or alternative technique to MRI,” AJR Am J Roentgenol, vol. 190, no. 6, pp. 1621–1626, Jun. 2008, doi: 10.2214/AJR.07.3385.
[3] N. Baloch, O. H. Hasan, M. M. Jessar, S. Hattori, and S. Yamada, “‘Sports Ultrasound’, advantages, indications and limitations in upper and lower limbs musculoskeletal disorders. Review article,” International Journal of Surgery, vol. 54, pp. 333–340, Jun. 2018, doi: 10.1016/J.IJSU.2017.11.034.
[4] S. Maruvada, A. Madrazo-Ibarra, and M. Varacallo, “Anatomy, Rotator Cuff,” StatPearls, Mar. 2023, Accessed: Oct. 08, 2023. [Online]. Available: https://www.ncbi.nlm.nih.gov/books/NBK441844/
[5] D. Tafti and D. W. Byerly, “Ultrasound-Guided Barbotage,” StatPearls, May 2023, Accessed: Oct. 08, 2023. [Online]. Available: https://www.ncbi.nlm.nih.gov/books/NBK572096/
[6] V. Pandey and S. Madi, “Clinical Guidelines in the Management of Frozen Shoulder: An Update!,” Indian J Orthop, vol. 55, no. 2, p. 299, Apr. 2021, doi: 10.1007/S43465-021-00351-3.
[7] C. H. Cho, K. C. Bae, and D. H. Kim, “Treatment Strategy for Frozen Shoulder,” Clin Orthop Surg, vol. 11, no. 3, pp. 249–257, Sep. 2019, doi: 10.4055/CIOS.2019.11.3.249.