Shoulder impingement – what is this and why does it occur?

Common terms for shoulder impingement syndrome are “subacromial impingement”, “painful arc syndrome”, or “swimmers shoulder”. This is a clinical syndrome where the tendons of the rotator cuff muscles are compressed during shoulder movements, causing the tendons to become irritated and inflamed as they pass through the subacromial space. This results in pain, weakness, and loss of movement and function at the shoulder.

The subacromial space is the gap between the anterior edge of the acromion and the head of the humerus, through which the supraspinatus tendon passes and the subacromial bursa lies.
Impingement should not occur during normal shoulder function, but when impingement does occur the rotator cuff tendon becomes inflamed and swollen (rotator cuff tendonitis) and the bursa can become inflamed (subacromial bursitis). If this condition worsens it can also lead to partial or full thickness rotator cuff tendon tears.
Most common symptoms are pain, and limited range of movement in the shoulder. Pain is often worse with movement overhead, and may occur at night when lying on that shoulder. Pain can be of an insidious nature (gradual onset with no specific trauma) or can be a result of an acute injury. The patient often describes a dull and lingering pain in the lateral or antero/lateral aspect of the shoulder/upper arm, which people often mistake as deltoid pain.

Shoulder impingement syndrome has either structural or mechanical causes (due to poor muscle function/muscle imbalance or posture). This results in further narrowing of this subacromial space hence impinging on the tendon and/or bursa.

Structural narrowing can be due to:

• Anatomical variation in the shape of the acromion in the shoulder;
• Osteoarthritic spurring that occurs on the acromion, or AC joint;
• Thickening/calcification of the coracoacromial ligament.

Mechanical narrowing can be due to:

• Poor posture;
• Poor function of the scapula muscles and stabilisation of the scapula;
• Loss of function or imbalance in the rotator cuff muscles due to injury or reduced strength, which may cause the humeral head to move superiorly in the glenohumeral joint resulting in subacromial impingement.

This clinical syndrome is treatable and not something that will tend to resolve itself on its own. See the team at In Touch Physiotherapy. Early intervention is key to reduce inflammation and pain, and to restore movement and function in the shoulder. Identification of the causes of this “impingement” is important for long term management and resolution of this condition.