The rotator cuff is a group of four muscles that play a critical role in stabilizing the head of the humerus within the glenoid fossa of the scapula (glenohumeral joint). Each of the rotator cuff muscles inserts on the humerus and contracts at a slightly different angle to help the head of the humerus stay within the glenoid fossa during movements of the arm.
The supraspinatus is one of four muscles that make up the rotator cuff. The muscle originates in the supraspinous fossa (top of the scapula above the spine of the scapula) and inserts on the greater tuberosity of the humerus (anterior, superior part of the humerus). The location is critical to understanding its function.
It is also important to know that the supraspinatus muscle runs under the acromion process on its way to the humerus. This creates a type of tunnel for the muscle to run through.
When the supraspinatus contracts, the humerus is pulled up and away from the body in a movement called abduction. When there is no inflammation, there is enough space for the supraspinatus to contract while the arm moves through abduction.
Mechanism of an Impingement Syndrome
When the supraspinatus tendon becomes inflamed from overuse, the tissue swells and can become “impinged” between the acromion process, the subacromial bursa, and the head of the humerus as the arm is abducted (Foundations of Athletic Training, 4th Edition, 2009). The further the arm is abducted away from the body, the more the tendon is impinged and the more pain the patient will feel.
The risk factors for an impingement syndrome include:
- Excessive repetitive overhead motions
- Lack of flexibility and strength of supraspinatus
- Weakness of posterior rotator cuff muscles (infraspinatus, teres minor)
- Limited space under acromion process
- Hypermobility (excessive movement) of shoulder joint
- Weakness of scapular muscles (serratus anterior, rhomboids)
Stages of Impingement Syndrome
There are four stages of impingement syndrome that range on a continuum from mild pain and no dysfunction (Stage 1) to a complete supraspinatus tear (Stage 4). The condition gradually worsens over time resulting in increasing weakness and disability.
The important thing to know is that if the syndrome is diagnosed early, the damage of the supraspinatus is reversible. If the syndrome is not treated correctly and the individual continues to exasperate the condition over time, the result can be permanent damage to the supraspinatus muscle and supporting structures.
Diagnosing Impingement Syndrome
The key to diagnosing an impingement syndrome is a thorough medical history specifically looking at the activity of the individual and the onset of pain. This is an overuse injury meaning that the pain would have a gradual onset over time. An acute onset of pain would be more indicative of a strain rather than an impingement.
Second, the type of activity is a key indicator. Activities in which the arm is repetitively abducted more than 90 degrees and then moved forward (freestyle in swimming) are prime causes of injury.
Last, the pain in an impingement increases with activity with pain worsening in the “painful arc” (70 to 120 degrees of abduction). Movement with the humerus below 70 degrees is usually pain free because the supraspinatus muscle is not brought into a position where it can be impinged.
Management of Impingement Syndrome
Once the condition is recognized it can be properly treated. The key treatment for an impingement syndrome is rest and modified activity (activities that keep the humerus below 70 degrees of abduction).
The goal for rehabilitation is to calm down the inflammation while maintaining mobility of the joint. This can be done with rest, ice, anti-inflammatory medication, and modified activity. Once the inflammation has calmed down and movement is pain free, a gradual strengthening program can be undertaken to strengthen scapular and rotator cuff muscles.
An aggressive strengthening program too early can cause further injury to the supraspinatus tendon and worsen the condition. This is one condition in which the patient cannot “push through the pain.” Any activity that causes pain increases the damage to the tendon.
Once the pain is gone and the rotator cuff and scapular muscles have been gradually strengthened, the individual may begin functional activities to acclimate the muscles to return to full activity/sport.
Terry Zeigler - Educating through writing with over twenty-five years of experience as a Kinesiology Professor and Certified Athletic Trainer.
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