Subacromial Impingement (SAI) Syndrome is a common shoulder disorder, thought to account for between 44%-65% of all shoulder complaints. It can affect anyone at any age; and has been reported that approximately 1 in 5 people experience this condition at some point in their lives. It is very common in manual workers and people who partake in regular overhead activities, such as tennis players and swimmers.
The subacromial space is a small area within the shoulder prone to irritation due to its contents and nearby joints. It is bordered by the base of the Acromioclavicular joint, and the top of the Glenohumeral joint (ball and socket joint). The subacromial space provides passageway for the rotator cuff tendons, the tendon of the Long Head of the Biceps, and houses the Subacromial bursa (a protective fluid-filled sac).
The syndrome refers to the inflammation and irritation of the structures which are contained within the space; which is turn reduces the size of the Subacromial space and results in compression of the remaining structures.
There are many different conditions that can cause the syndrome, including:
Rotator cuff tendinopathy
Calcification of the rotator cuff tendons
Rotator cuff tears/ ruptures
Variations in the bony structure of the joint
Symptoms of SAI include:
Progressive pain over the top and front of the shoulder joint
Pain that spreads from the top of the shoulder to the elbow
Pain and therefore restriction with overhead and behind the body movements, affecting daily activities such as brushing your hair or putting on a coat
Loss of shoulder movement above 90 degrees
Weakness into the shoulder and arm
Possible tingling into the hand or fingers
Pain when sleeping on the affected shoulder, which may disrupt your sleep.
Is this the same as Frozen Shoulder?
SAI is very different from Frozen Shoulder (or Adhesive Capsulitis).
Frozen Shoulder is characterised by shoulder pain and stiffness on shoulder movements. It is caused by the thickening and tightening of the capsule surrounding the shoulder joint- although there is no clear reason why this suddenly starts to happen. It’s more likely to occur in people with Diabetes or those who have had to immobilise the shoulder due to surgery (such as mastectomy) or an arm break for example.
Frozen shoulder is also characterised by its longevity, and typically this condition can last from 1 to 3 years.
The main differences include:
All active (you controlling the shoulder) AND passive (someone else doing the movement for you) ranges of motion will be physically restricted with Frozen Shoulder. Whereas SAI will mainly be limited in active Abduction (bringing your arm out to your side) and rotational movements, and passive movements will typically not be affected.
Frozen Shoulder typically has a slow, gradual onset. Whereas SAI can often be accounted for by activity or injury.
Frozen shoulder, like subacromial SAI, can be painful at night; but Frozen shoulder will typically be painful during any times of rest.
Both conditions can be treated using physical therapy. Typically treatment for an SAI will focus on strengthening and stabilising the shoulder joint and surrounding muscles, whereas treatment for Frozen Shoulder will include strong articulations and mobilisations to stretch the joint capsule.
The recovery of both conditions will also rely on patient cooperation with a home exercise plan.