What is the Sub-Acromial Bursa?
A bursa is a small fluid-filled sac. It covers the upper surface of the rotator cuff tendons. It lies between the rotator cuff and the under-side of the acromial process of the scapula. Thus it is known as the “Sub-Acromial” Bursa. The two layers of the bursa with a film of fluid between slide against each other as the rotator cuff tendons pass backwards and forwards under the acromion. This in a sense lubricates the tendons to minimise any friction or catching under the acromion during shoulder movements.
What Causes Sub-Acromial Bursitis?
Bursitis is an inflammation of the bursa. Inflammation results in thickening of the bursa and an excess of fluid within it. The excess of bursa tissue and fluid will make it difficult for the bursa to slide freely under the acromion. This will result in shoulder pain especially in positions where the acromion comes in closer proximity to the rotator cuff tendons. The bursa is like the “meat in the sandwich”.
The pain can be a sharp catch with shoulder movement or aching after activity. Sleeping on the shoulder may be painful. It can be a common complaint in sports people. Swimmers, tennis players and throwing athletes are prone to this condition. Occupations requiring repetitive overhead use of the arms can also trigger the condition. Less often a fall on to the shoulder can cause acute inflammation of the bursa.
The size of the sub-acromial space may be relevant. Some patients have a naturally curved acromion. Others may develop a bony spur at the front edge of the acromion over the years. This can then start to irritate the bursa and or rotator cuff tendons. Bursitis is often a significant component of Shoulder Impingement.
Inflammatory diseases such as Rheumatoid arthritis can causes intense inflammation and thickening of the Sub-Acromial Bursa.
Diagnosis of Sub-Acromial Bursitis
The pain symptoms may be characteristic. The nature of causative activities or injuries will raise a suspicion of bursitis. There may be localised tenderness when pressure is applied to the bursa. There will also be positive rotator cuff impingement signs. Special tests may help:
- X-rays will show the shape of the acromion. An acromial bone spur may be apparent.
- Ultrasound will reveal thickening of the bursa and excess fluid in the bursa.
- MRI will demonstrate changes in both the acromial shape and bursal thickening.
- Cortisone Injection in to the bursa. A positive response supports the diagnosis.
Avoidance of aggravating activities is important. Modification of work or sporting activity may help. Sometimes a brief break from sport may be appropriate. Analgesics and anti-inflammatories may help. An Ultrasound guide Cortisone injection in to the bursa may reduce the swelling of the bursa enough to break the irritation cycle. This can have a lasting effect. Even if there is only a temporary improvement it at least helps to support the diagnosis.
Resistant or recurring cases may require a surgical treatment in the form of an Arthroscopic Acromioplasty (Rotator Cuff Decompression) and removal of the thickened portions of the bursa.