What Is Shoulder (Subacromial) Bursitis?

Pain and tenderness around the shoulder, especially when raising the arm above the head, may be a sign of shoulder bursitis. Shoulder bursitis occurs when the large bursa near the top of the shoulder becomes inflamed.

A diagnosis of shoulder bursitis is often accompanied by a diagnosis of shoulder impingement syndrome or other shoulder problems. The shoulder’s soft tissue structures (muscles, ligaments, tendons, and bursae) are packed closely together, so their health is interdependent. If one becomes damaged, others are likely to become damaged, too.

The Subacromial Bursa and Bursitis

The purpose of a bursa is to provide a cushion and reduce friction between hard bone tissue and adjacent soft tissue. There are more than 140 bursae in the body,¹Azar FM, Beaty JH, Canale TS, eds. Campbell’s Operative Othopaedics, 13th ed., vol 1, page 482. Philadelphia PA: Elsevier; 2017. and the shoulder’s subacromial bursa is one of the largest.²van Holsbeeck & Strouse. Sonography of the shoulder: evaluation of the subacromial-subdeltoid bursa. AJR Am J Roentgenol. 1993 Mar;160(3):561-4. PubMed PMID: 8430553.

All bursae are a thin, slippery, fluid-filled sacs. Each is composed of:

• A thin outer membrane, called the synovial membrane or synovium
• An inner fluid, called synovial fluid

See What Is a Synovial Joint?

The subacromial bursa is located below a part of the shoulder blade called the acromion (hence the name “subacromial”).

• The acromion is the topmost part of the shoulder blade. It forms the bony top of the outer shoulder.
• The acromion lies above the bones that form the shoulder’s ball-and-socket joint (glenohumeral joint).
• In most people, there is 1 cm to 1.5 cm of space between the acromion and the shoulder’s ball and socket.³Umer M, Qadir I, Azam M. Subacromial impingement syndrome. Orthop Rev (Pavia). 2012 May 09;4(2):e18. This small space is called the subacromial space.
• Sandwiched in the subacromial space are rotator cuff muscles, tendons, and the subacromial bursa.
• The subacromial bursa provides a cushion and reduces friction between the shoulder’s muscles and tendons and the acromion.

When the arm is raised up, particularly up and out to the side, the subacromial space becomes smaller, and soft tissues may be pinched.

Small changes to the bursa can lead to bursitis symptoms
When the subacromial bursa becomes inflamed it is called subacromial bursitis or shoulder bursitis. The inflamed bursa may thicken only a tiny amount.²van Holsbeeck & Strouse. Sonography of the shoulder: evaluation of the subacromial-subdeltoid bursa. AJR Am J Roentgenol. 1993 Mar;160(3):561-4. PubMed PMID: 8430553. (This is in contrast to knee and elbow bursitis, in which bursa swelling is visibly apparent.)

For example, one study found that healthy subacromial bursae were on average 0.74 mm thick, while painfully inflamed subacromial bursa were 1.27 mm thick⁴Tsai YH, Huang TJ, Hsu WH, Huang KC, Li YY, Peng KT, Hsu RW. Detection of subacromial bursa thickening by sonography in shoulder impingement syndrome. Chang Gung Med J. 2007 Mar-Apr;30(2):135-41.—a difference of just 0.53 mm. Because the subacromial space is small, even this small change can cause shoulder pain and tenderness.

Shoulder Impingement Syndrome

Shoulder impingement syndrome is an umbrella term that describes the painful pinching of soft tissue when the arm is raised, and it is considered the most common cause of shoulder pain.⁵Bhattacharyya R, Edwards K, Wallace AW. Does arthroscopic sub-acromial decompression really work for sub-acromial impingement syndrome: a cohort study. BMC Musculoskelet Disord. 2014; 15:324. As cited in Consigliere P, Haddo O, Levy O, Sforza G. Subacromial impingement syndrome: management challenges. Orthop Res Rev. 2018;10:83–91. Published 2018 Oct 23. doi:10.2147/ORR.S157864

Shoulder impingement syndrome can be caused by:

• Shoulder bursitis, in which the bursa is inflamed and swollen,
• Tendonitis, in which a tendon is inflamed and swollen (the biceps tendon, which connects the biceps muscle to the shoulder socket, is commonly affected).
• Acromioclavicular arthritis, a rotator cuff tear, or another shoulder condition that causes the subacromial space to shrink; this shrinking leads to irritation of the bursa and tendons, eventually resulting in bursitis or tendonitis.

  See What Is Acromioclavicular Arthritis (AC Joint Arthritis)?

A diagnosis of shoulder impingement syndrome may be temporary. Medical imaging, such as ultrasound and MRI, may allow for a more precise diagnosis⁶Papadonikolakis A, McKenna M, Warme W, Martin BI, Matsen FA, III; Published Evidence Relevant to the Diagnosis of Impingement Syndrome of the Shoulder. The Journal of Bone & Joint Surgery. 2011 Oct;93(19):1827-1832. (such as bursitis or rotator cuff tear).

Read more about Shoulder Impingement on Sports-health.com

Septic Shoulder Bursitis

If the inflamed bursa is infected, it is called septic bursitis. Septic bursitis in the shoulder is unusual but can be serious.

See Septic Bursitis

People with septic shoulder bursitis will experience the same symptoms described above and may also feel tired, feverish, and sick, and notice warmth and redness at the shoulder. The pain level will also be much higher. Anyone with septic shoulder bursitis should seek medical attention to be treated with antibiotics to prevent the spread of infection into the bloodstream.