What is the cause of shoulder impingement?
Mechanical wear and tear. True tear of the cuff is actually a problem of older subjects, whereas rotator
cuff disease and impingement tend to affect primarily laborers (whose job requires repetitive and protracted
overhead activity) or young athletes (whose sport also involves repetitive overhead motions, such as throwing, swimming, volleyball, and tennis and other racquetplaying activities). Raising the arm over the shoulder forces the humerus against the edge of the acromion.
Usually, there is enough room between the acromion and rotator cuff to allow the tendons to slide easily
underneath the bone while the arm is being elevated. Recurrent arm-raising, however, eventually creates
impingement (i.e., friction on the subacromial bursa and the distal part of the tendon). With time, this causes irritation and swelling of the bursa (bursitis), further narrowing the space between the acromion and rotator cuff. As a result, impingement on the tendon becomes more severe, which is risky since its blood supply is limited. Hence, the resulting tendinitis and, ultimately, the degenerative damage. Bony spurs of the acromioclavicular (AC) joint (which sits directly above bursa and rotator cuff tendons) may further narrow the subacromial space, and so can abnormal acromial morphology (such as a hooked acromion).
Mechanical wear and tear. True tear of the cuff is actually a problem of older subjects, whereas rotator
cuff disease and impingement tend to affect primarily laborers (whose job requires repetitive and protracted
overhead activity) or young athletes (whose sport also involves repetitive overhead motions, such as throwing, swimming, volleyball, and tennis and other racquetplaying activities). Raising the arm over the shoulder forces the humerus against the edge of the acromion.
Usually, there is enough room between the acromion and rotator cuff to allow the tendons to slide easily
underneath the bone while the arm is being elevated. Recurrent arm-raising, however, eventually creates
impingement (i.e., friction on the subacromial bursa and the distal part of the tendon). With time, this causes irritation and swelling of the bursa (bursitis), further narrowing the space between the acromion and rotator cuff. As a result, impingement on the tendon becomes more severe, which is risky since its blood supply is limited. Hence, the resulting tendinitis and, ultimately, the degenerative damage. Bony spurs of the acromioclavicular (AC) joint (which sits directly above bursa and rotator cuff tendons) may further narrow the subacromial space, and so can abnormal acromial morphology (such as a hooked acromion).