Impingement Syndrome: Causes

Pathogenesis (development of disease)

Lateral elevation of the arm occurs due to traction of the rotator cuff (group of four muscles whose tendons, together with the ligamentum coracohumerale, form a coarse tendon cap that encompasses the shoulder joint), especially the supraspinatus tendon (attachment tendon of the supraspinatus muscle (upper spine muscle); runs just below the acromion). The humeral head (upper end of the humerus bone) slips under the acromion in the process. The rotator cuff and the bursa subacromialis (shoulder bursa) also slide underneath. Normally, there is sufficient space for these displacements. As a result of tightness in this so-called subacromial space, the constant rubbing against the acromion leads to degenerative changes or inflammation of tendons and muscles. The supraspinatus tendon is particularly frequently affected. As part of the rotator cuff, it must withstand the greatest stresses.

The following mechanisms can lead to impingement syndrome:

  • Alteration of biomechanics
    • Loss of function of the rotator cuff or the long biceps tendon
    • Disturbed scapulothoracic rhythm with premature attachment of the humeral head to the acromion (bony prominence of the scapula (shoulder blade))
    • Multidirectional instability (the shoulder is unstable in multiple directions).
    • Overuse – due to throwing/impact sports (e.g., handball, volleyball, tennis) or overhead work (e.g., painter)
  • Volume increase in the subacromial space.
    • Bursitis subacromialis (shoulder bursitis).
    • Changes in the rotator tendons due to calcification (calcification), degeneration.
  • Narrowing of the subacromial space
    • Acromion shape variants
    • Ossification (formation of bone tissue) in the course of the coracoacromial ligament.
    • Osteophytes (bone neoplasms) in osteoarthritis of the acromioclavicular joint (acromioclavicular joint).
    • Prominent tuberculum majus (large humerus) – e.g., after a fracture (bone fracture).

Etiology (causes)

Biographical causes

  • Anatomic variants – variations in the shape of the bones and soft tissues involved that drive degenerative processes.
  • Occupations – occupations that involve a lot of overhead work (e.g. painters).

Behavioral causes

  • High-risk sports such as throwing/impact sports (e.g., handball, volleyball, tennis).

Disease-related causes.

Injuries, poisonings, and other consequences of external causes (S00-T98).

  • Trauma to the shoulder, unspecified