Impingement occurs most commonly in patients under 25 years, typically in active/athletic individuals or in manual professions
Impingement can occur in the older population secondary to degenerative changes or acromioclavicular bony changes
Pathophysiology
Shoulder impingement
Refers to the inflammation and irritation of the rotator cuff tendons as they pass through the subacromial space, resulting in pain, weakness, and reduced range of motion within the shoulder
Intrinsic mechanisms
Muscular weakness - weakness in rotator cuff muscles can lead to the humerus shifting proximally towards the body
Overuse of the shoulder - repetitive microtrauma can result in soft tissue inflammation of the rotator cuff tendons and the subacromial bursa
Degenerative tendinopathy - degenerative changes of the acromion can lead to tearing of the rotator cuff, which allows for proximal migration of the humeral head
Extrinsic mechanisms
Anatomical factors - congenital or acquired anatomical variations in the shape and gradient of the acromion
Scapular musculature - a reduction in function of the scapular muscles may result in a reduction in the size of the subacromial space
Glenohumeral instability - can lead to superior subluxation of the humerus, causing an increased contact between the acromion and subacromial tissues
Rotator cuff tendonitis
Repeated impingement results in inflammation or damage of the rotator cuff tendons
Subacromial bursitis
In more severe cases of rotator cuff tendonitis, there may be calcification of the tendon, and associated subacromial bursitis → subacromial bursa also becomes inflamed
This can then exaggerate the problem, as the now inflamed tendons rub against the acromium, and clavicoaromial joint and ligament