In today’s blog, we are going to review 2 closely related conditions that affect the shoulder joint, (1) a rotator cuff tear and (2) Sub-acromial impingement syndrome. We are going to explore how we can differentiate between the two conditions and how they relate to each other. Beware they can coexist. Let’s start by looking at the anatomy of the shoulder.


The shoulder girdle is comprised of the collar bone (clavicle), shoulder blade (scapula), and arm bone (humerus). These are then held together with ligaments and muscle tissue.


– Glenohumeral ligaments

– Coracoacromial arch

– Coracoclavicular and acromioclavicular ligaments

These ligaments encapsulate the head of the humerus onto the scapula to provide stability to the joint.


There are four main muscle groups in the shoulder we are going to predominantly focus on the rotator cuff.

Stabilizers – Rotator cuff

Comprised of 4 muscles that come together to form a cuff that holds the humeral head in the glenoid fossa throughout the movement. The 4 muscles are:

1. Supraspinatus

2. Infraspinatus

3. Teres minor

4. Subscapularis

Biceps and its tendon – helps to hold the humeral head in the glenoid along with raising the arm and bending the elbow.

Scapulothoracic muscles -These muscles give the shoulder stability and attach the shoulder blade to the spine (axial skeleton) and include the rhomboids, levator scapulae, and trapezius muscles.

Superficial muscles – including the deltoid and pectoral muscles, encompass the shoulder and help to give power to the shoulder

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The subacromial bursae are the largest in the body and sit between the acromion and the humeral head (see above pic). This structure allows for smooth movement of the tendon and separates the rotator cuff from the hard-bony structure of the acromion.

Subacromial impingement

Subacromial impingement (also known as ‘swimmers’ shoulder’) is the pinching of structures in the subacromial space.

The structures that pass through this space include the supraspinatus tendon, the biceps tendon, and the subacromial bursa.

In impingement syndrome one, two, or all these structures are squeezed between the humeral head and the overlying acromion of the scapular (shoulder blade).

The impingement syndrome itself can occur because of 2 reasons, either:

1. The sub-acromial space gets smaller à such as with poor posture or a bone spur growing into the space

2. The structures running through the space get larger à such as when tendons and bursae become inflamed and swollen.

This repetitive encroachment of the subacromial space and the compression of these structures causes damage to the tissue and a resultant inflammatory response (including swelling). This elicits a painful response that is consistently seen when raising the arms above the head or when the arm is forced into an internally rotated position.

Below is the classification system used for subacromial impingement

1. Type I – <25 years old, Reversible, Swelling, Tendonitis, No Tears

2. Type II: 25-40 years old, Permanent Scarring, Tendonitis, No Tears

3. Type III: >40 years old, Small Rotator Cuff Tear

4. Type IV: >40 years old, Large Rotator Cuff Tear

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Rotator cuff tear

A rotator cuff tear is a tear to either or combination of the supraspinatus, infraspinatus, subscapularis, or teres minor muscles. It differs from subacromial impingement syndrome where swelling due to repetitive or traumatic compression of structures causes pain and shoulder dysfunction, instead torn fibers of the muscle directly inhibit muscle function due to loss of structural integrity.

The main causes of rotator cuff tears are:

1. Degenerative changes

2. Repetitive microtraumas

3. Severe traumatic injuries

4. Atraumatic injuries

5. Secondary Dysfunctions

Rotator cuff tears are classified into types due to the combination of muscles damaged.

1. Type A: supraspinatus & superior subscapularis tears

2. Type B: supraspinatus and entire subscapularis tears

3. Type C: supraspinatus, superior subscapularis & infraspinatus tears

4. Type D: supraspinatus & infraspinatus tears

5. Type E: supraspinatus, infraspinatus & teres minor tear

How are these two injuries related?

It is clear that both injuries affect the small rotator cuff muscles in the shoulder, and in many cases (aside from acute trauma) it is a classic case of the chicken and the egg scenario, which one occurred first? Because both injuries affect similar muscles, they have the potential to cause the other.

For instance, was there initially a small rotator cuff tear that created swelling in the tendon thereby increasing its size in the subacromial space and causing impingement syndrome? Or has there been repetitive impingement over a sustained period that has progressively weakened the musculotendinous unit causing a tear in the muscle?

In the case of acute and large rotator cuff tears surgery may be required to repair the tear, however, most other types of tears or impingement will respond well to conservative treatment, so achieving an accurate diagnosis is important.

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The principles of treatment for either a tear or impingement remain the same. We aim to reduce pain in the initial stages by limiting shoulder movement and releasing tight muscles and stiff joints. We then engage in a series of exercises aimed at restoring posture and creating as much room as we can in the subacromial space to unload the impinged or torn tendon and allow it to heal. Once pain and range of movement have been restored, we then follow a progressive strengthening program to maximize strength in the scapular stabilizers and rotator cuff muscles before engaging in a return to sport program.