Subacromial bursitis develops when the subacromial bursa, a small fluid-filled sac positioned between the acromion and the rotator cuff tendons, becomes inflamed. This irritation typically arises from repetitive overhead motions, direct trauma, or gradual wear and tear, leading to pain and restricted movement in the shoulder.
Primary Mechanical Irritants
The most common mechanical causes involve compression or friction within the subacromial space. Repetitive overhead activities, such as throwing, painting, or swimming, repeatedly narrow this space, pinching the bursa and initiating an inflammatory response. Additionally, a sudden fall onto the shoulder or a strong pull on the arm can directly injure the bursa, causing immediate swelling and pain.
Bone Spurs and Anatomical Variations
Structural abnormalities in the acromion, such as a hooked or curved shape, significantly reduce the available space for the rotator cuff. These anatomical features can create constant friction against the bursa during arm movement. Furthermore, the development of bone spurs on the acromion or the clavicle can physically rub against the bursa, acting as a persistent source of irritation and inflammation.
Associated Conditions and Systemic Factors
Underlying health conditions can predispose an individual to subacromial bursitis by affecting tissue integrity or immune response. Rheumatoid arthritis triggers chronic synovitis that can extend to the bursa, while gout leads to crystal deposition that incites intense inflammatory episodes. Less commonly, infections introduced through trauma or bloodstream can cause septic bursitis, requiring urgent medical intervention.
Age-Related Degeneration
As individuals age, the tendons surrounding the shoulder naturally lose elasticity and blood supply, making them thinner and more prone to fraying. This degeneration increases the likelihood of the tendons rubbing against the bursa during everyday motions. The chronic low-level irritation from this friction gradually thickens the bursa walls, transforming it into a persistent source of pain.
Risk Amplifiers and Lifestyle Contributions
While not direct causes, certain lifestyle factors and occupational hazards can significantly amplify the risk. Poor posture, particularly forward shoulder rounding, can further constrict the subacromial space. Occupations involving repetitive lifting, carrying, or overhead reaching place sustained stress on the bursa, accelerating the onset of inflammation.
