By Dr. Andrew Meyers D.O.

Shoulder Impingement: The Likely Culprit of Your Pain

Most of us have heard it, “The shoulder is the most mobile joint in the human body” and in no coincidence, is also one of the most common locations for discomfort experienced by cross-training athletes. But what exactly is causing that pain that just won't go away? Odds are, it is, or at least started with a diagnosis chalked up as impingement syndrome. Unfortunately, this injury is not as clear cut as it seems. 

Shoulder impingement accounts for an estimated 45-65% of all shoulder disorders. It is usually first noticed as an insidious and sharp pain with overhead activities. For some, it waxes and wanes. For others, it's more constant. The discomfort can present over any aspect of the shoulder. Without activity modification or treatment, this acute inflammatory process can become a recurring cycle of annoyance and agony. Over an extended period of time, it may develop into something even more sinister. 

What makes this topic such a heavy discussion, is not its prevalence. Nor is it the varying symptoms as just mentioned. Shoulder impingement is actually a very broad term and several types of impingement can be classified under this umbrella. It is important to understand each because although similar enough to be grouped under one term, they may rely on a different focus of treatments for successful relief. 

Let's start with a brief anatomy review. The shoulder is made of three bones; the humerus, scapula, and clavicle. On the humerus are the boney insertion sites of the rotator cuff; the greater and lesser tuberosities. On the scapula is the glenoid, acromion, and the coracoid. With these structures, are the formation of the glenohumeral joint, acromioclavicular joint, and scapulothoracic joint which involves the posterior ribs. 

Fig. 1 Fig. 2
Fig. 1 and 2, X-ray demonstrating an anteroposterior and scapular Y (lateral) views of the right shoulder

Surrounding these bones are soft tissues consisting of ligaments, tendons, muscles, bursa, and more. Specifically, the rotator cuff is made up of four muscles and their tendinous insertions. These muscles are the supraspinatus, infraspinatus, subscapularis, and teres minor. The main bursa in this focus is the subacromial bursa, which is located on top of the supraspinatus muscle and under the acromion and the lateral edge of the clavicle.

Fig. 3 Fig. 4
Fig. 3, MRI demonstrating coronal slice of right shoulder Fig. 4, illustration demonstrating the positioning of the individual rotator cuff muscle from sagittal (side) view of shoulder

Our first type of impingement syndrome is internal impingement. This is when there is repetitive contact between the greater tuberosity of the humeral head and glenoid border of the scapula, which squeezes the articular side of the supraspinatus and infraspinatus, [Fig. 5]. This occurs during maximum arm abduction and external rotation. This pathology is historically seen in throwing athletes, such as pitchers, but can be simulated in crossfit exercises like kipping pull ups and muscle-ups. The most well-known cause of Internal impingement has been described as tightness in the posterior capsule, specifically the posterior band of the inferior glenohumeral ligament.

Fig. 5
Fig. 5, illustration demonstrating impingement of the articular side of the supraspinatus between the humerus and the glenoid.

The second type of impingement syndrome is external impingement. This results in inflammation, irritation, and degradation of the anatomic structures within the subacromial space, and as such, is frequently referred to as subacromial impingement in practice. The roof of this space is created by the acromioclavicular (AC) joint; the acromion and coracoacromial ligament provide the anterior border, and the humeral head serves as the floor.5 Narrowing of this space places pressure on the bursal side of the rotator cuff. Subacromial (External) impingement can be further broken down into primary and secondary, based on its cause. 

Primary subacromial impingement is based on the structure of your personal anatomy. There are several calculated parameters to determine type, slope, tilt, angle, and index of the shoulder, but most boil down to the acromion shape [Fig. 6]. Depending on the degree of each measurement, there is a higher incidence of impingement due to a mechanically narrow space. 

Fig. 6 Scapula Y view x-ray with illustration demonstrating type 1, 2, and 3 acromion and space narrowing

Secondary subacromial impingement results from a functional disturbance leading to abnormal displacement of the humeral head during rotation. When the humeral head is not correctly centered on the glenoid, it will rise upward, pinching the contents of the subacromial space against the acromion or the coracoid. This disturbance can be attributed to muscular imbalance, scapular position, and mobility. Let's take a closer, but simple look at these factors. 

There have been many studies focusing on the biomechanics of the musculature surrounding the shoulder girdle and its effects on the glenohumeral joint. One well-described example is of a weak rotator cuff and overpowering deltoid. The deltoid pulls an upwardly directed force on the humerus, resulting in compression of the subacromial space. 

The position of the scapula also affects the amount of room in the subacromial space. Theorized by Dr. Janda's “Upper Crossed Syndrome”, scapula position can again be credited to muscle imbalances. This is characterized by tightness of the cervical extensors (levator scapulae, upper trapezius, suboccipitals) and pectoralis muscles with combined weakness in the deep cervical flexors, the middle and lower trapezius, infraspinatus, and serratus anterior. In his model, this creates a forward tilt in the scapula, further narrowing the room for the underlying soft tissues.

Mobility is another key element in our spotlight on secondary subacromial impingement. Most are aware and understand this association to the glenohumeral joint, but this is just the first link in the chain as it relates to range of motion. In all things human biomechanics, we are led back to the spine. Tracing back the shoulder, we have the scapula that overlies the posterior ribs. This connection is known as the scapulothoracic joint. Proper movement of the scapula relies on the orientation of the ribs. As we follow this trail, it leads us directly to the thoracic vertebrae. Thoracic spine mobility, specifically extension of the spine, allows for posterior tilt of the scapula. With decreased spine mobility, or a kyphotic posture, the scapula orientates with the ribs anteriorly, limiting your overhead range of motion, leading to the possibility of impingement, as seen in figure 7. 

Fig. 7
Fig. 7, clinical photograph demonstrating comparison side and back view of shoulder range of motion with straightened posture versus kyphotic alignment

Now that we have discussed internal and subacromial impingement, the question becomes, which do you suffer from? To help guide the diagnosis outside of advanced imaging, we rely on physical exam maneuvers. Two popular provocative (pain means positive) special tests for subacromial impingement are the Neer and Hawkins tests.

The Neer test [Fig. 8] is performed as the individual is sitting upright. The examiner then stabilizes the individual's scapula with one hand while the other hand passively flexes the arm in forward flexion as it is internally rotated. 

Fig. 8
Fig. 8, clinical photograph demonstrating Neer impingement test

The Hawkins test [Fig. 9] is performed by again having the individual sitting upright while the examiner stabilizes the scapula. the patient's shoulder is placed in 90 degrees of flexion with the elbow flexed to 90 degrees. The arm is then internally rotated. 

Fig. 9
Fig. 9, clinical photograph demonstrating Hawkins impingement test

For internal impingement, there are also two popular tests used, the posterior impingement and relocation test. The posterior impingement test [Fig. 10] is conducted with the arm placed into a position of 90° abduction and 15° extension, with maximal external rotation. Pain in the posterosuperior aspect of the shoulder is indicative of a positive test. 

Fig. 10
Fig. 10, clinical photograph demonstrating posterior impingement test

For the relocation test, the setup is similar to the internal impingement test with the elbow flexed and shoulder abducted to 90 degrees along with external rotation to the shoulder. But this time, a posteriorly directed force to the shoulder is then applied. If the patient's pain is reduced, the test is considered to be positive.

Regardless of the type of impingement you suffer from, the first step is the same. Rest and activity modification are required. As stated above, this is an acute process of inflammation. This means your soft tissues need a break, otherwise, they will continue to remain aggravated. To follow and just as important is adjusting your activity. This can be done by ceasing, limiting, or changing the likely mechanism that is instigating the pain. For some, this could mean a lower rep of kipping pull-ups. For others, performing only one overhead weighted exercise a week. Once the acute pain has subsided, then you should focus on further treatment and prevention. 

This is when a physical therapist is an orthopedic surgeon's best friend. They are a wealth of knowledge and skilled at using stretching, strengthening, and manipulation to care for each shoulder impingement syndrome without surgical management.  Large retrospective studies show that approximately 70% of patients with impingement syndromes will respond to conservative management.

Now, I'm sure most of you are wondering how to avoid that doctor's office visit and referral to a physical therapist. I will advise, it is in your best interest to follow up with a medical professional. Not only for the accurate diagnosis but to obtain direct evaluation and confirm the vast techniques and exercises that are taught, are being performed correctly. With that said, here are a couple of examples to hold you over.

For Internal impingement, there are two main stretches to decrease excessive posteroinferior capsular tightness. The first is the sleeper stretch [Fig. 11]. To perform correctly, lie on the side to be stretched, making sure the scapula is retracted. Roll your body backwards to face upwards at about 45 degrees. The arm is then placed at 90-degree abduction and elbow to 90 degrees flexion. Your opposite arm is then used to place the arm into internal rotation for a mild stretch in 30-second increments. Repeat for 3-5 reps. 

Fig. 11
Fig. 11, clinical photograph demonstrating sleeper stretch

The second stretch is the side-lying cross arm stretch [Fig. 12]. The set begins again on your affected side, arm abduction 90 degrees. This time the opposite arm pulls the affected arm across the chest. This should also be a mild stretch held for seconds in 3-5 reps. 

Fig. 12
Fig. 12, clinical photograph demonstrating side-lying cross arm stretch

For subacromial impingement, the treatments for primary and secondary do have heavy overlap. One misconception is that those with primary impingement will only gain relief from surgical intervention. This is not true. As mentioned, start with rest and activity modification to calm the active inflammation.

Then focus should be on strengthening the rotator cuff muscles, balancing the scapula with targeted muscle strengthening (lower trapezius, rhomboids, and serratus anterior) and stretching tight pectorals and cervical extensors. Also, let's not forget increasing thoracic spine mobility. 

It's important to realize, If your body repeatedly battles the fight with impingement syndrome, the wear and tear can take a toll and further damage may occur. This could result as partial or full thickness rotator cuff tears, damage to the labrum, progression to adhesive capsulitis, and more. Needless to say, if you have remained diligent in your own treatment and preventative care yet still suffer, see an orthopedic surgeon. They will confirm the correct diagnosis, can evaluate with advanced imaging, and make the referral to formal physical therapy. They can also offer additional conservative treatment modalities, including but not limited to joint injections from corticosteroids to platelet rich plasma. Unfortunately, the final treatment is surgical intervention, however orthopedic surgeons will work with you to pursue the treatment that is best for your individual needs and lifestyle.

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