Shoulder pain and stiffness are common upper extremity complaints. Estimates are pain felt under the acromion process (called subacromial pain) may encompass somewhere between 44 and 66 percent of all shoulder complaints seen by orthopedists.¹ For many years, shoulder pathology in this region was called subacromial impingement syndrome (SIS), which indicates tissue compression (impingement) as a primary cause.

Interestingly, recent research indicates mechanical impingement may not be the primary cause of pain in some cases. Today, researchers advise renaming this condition subacromial pain syndrome (SAPS) to more broadly include all the various pathological causes for subacromial pain.

SAPS can include a spectrum of pathologies, such as partial thickness rotator cuff tears, rotator cuff tendinosis, calcific tendinitis, and subacromial bursitis, as well as metabolic, inflammatory, and degenerative changes in the tendon. In this column, we explore the multiple causes of subacromial pain, look at a variety of treatment strategies, and explore where massage therapy may play a role in reducing this debilitating condition.

Anatomy and Biomechanics

Our exploration of SAPS begins with a review of key anatomical structures in the region. The scapula plays a primary role in subacromial pain and has two prominent bony projections. The first is the acromion process, which is out to the lateral edge of the shoulder. The second is the coracoid process, which angles off in an anterior direction. The coracoacromial ligament spans between these two bony projections. The expanse, including the acromion process, coracoacromial ligament, and coracoid process, is referred to as the coracoacromial arch (Image 1). Subacromial pain is most commonly thought to arise from tissue irritation under the acromion process but could also occur from irritation under other parts of the coracoacromial arch.

The region under the coracoacromial arch is anatomically unique. There are very few places in the body where soft tissues get pinched between adjacent bones or ligaments. The space underneath the arch is relatively small and susceptible for soft-tissue compression. In addition, dysfunctional scapular mechanics can play a role in these problems. For example, the scapula must move in upward rotation during shoulder abduction movements. If it does not fully rotate upward, the humerus is more likely to pinch soft tissues against the underside of the acromion process. Often, a nerve in the cervical region, the long thoracic nerve, may be responsible for these dysfunctional shoulder mechanics.

The long thoracic nerve is a motor nerve that innervates the serratus anterior muscle. Compression of the long thoracic nerve (near the brachial plexus) may cause weakness of the serratus anterior muscle. Weakness in the serratus anterior leads to inadequate upward scapular rotation during abduction and the resulting subacromial compression. This sequence of events is an example of how nerve compression near the neck can lead to soft-tissue compression in the lateral shoulder.

Another potential cause of subacromial impingement is excessive translation or movement of the glenohumeral head during shoulder motions. For example, the rotator cuff and biceps brachii muscles play prominent roles in keeping the humeral head partially depressed during overhead shoulder motions. These muscles are critical for ensuring the humerus doesn’t migrate in a superior direction and pinch tissues under the coracoacromial arch. Now that we have explored the architecture and mechanics of this region, let’s examine some of the main causes of SAPS.

Tissues involved in subacromial pain: 1. Subacromial bursa; 2. Supraspinatus tendon; 3. Upper margin of the glenohumeral joint capsule;
4. Coracohumeral ligament; and
5. Long head of the biceps brachii tendon. Image from 3D4Medical’s Complete Anatomy application.

Tissues involved in subcoracoid pain:
1. Upper margin of subscapularis tendon; 2. Coracobrachialis bursa; and 3. Upper margin of the glenohumeral joint capsule. Image from 3D4Medical’s Complete Anatomy application.

Description of Pathology

There are two primary models of SAPS: the mechanistic and the biological. We now realize many shoulder complaints are a combination of both. The mechanical has been the dominant model for decades and is a bit more complex, so we’ll take a detailed look at it first.

The mechanical model suggests there is a biomechanical problem leading to the subacromial pain.² As noted earlier, this condition was previously referred to as subacromial impingement syndrome. Subacromial impingement is usually divided into two categories. The first is primary impingement, which results from problematic architecture of the subacromial region. For example, if there is very little space between the acromion process and the upper part of the humeral head, this narrow space would make impingement more likely and be considered a cause for primary impingement. Secondary impingement is a result of biomechanical dysfunction or overuse in the shoulder region but does not necessarily result from decreased subacromial space.

The original description of subacromial impingement was presented by Charles Neer in a paper he wrote in the early 1970s.³ According to his classification, the pathology begins with edema and thickening of the bursa in the first stage. It progresses to fibrosis and other inflammatory changes within the supraspinatus in the second stage. Eventually this can lead to a complete tear of the supraspinatus tendon in the third stage. However, more recent findings have called into question this tissue progression, so Neer’s classification is no longer considered a standard sequence of events.

Most models of mechanical impingement now focus on the subacromial region, thus they’re being labeled as subacromial impingement syndrome. Pain is generally felt more in the lateral aspect of the shoulder and is most aggravated during shoulder abduction movements but may be felt during forward-flexion movements, as well. The tissues most involved in subacromial impingement include the subacromial bursa, supraspinatus tendon, upper margin of the glenohumeral joint capsule, coracohumeral ligament, and long head of the biceps brachii tendon (Image 2).

There is another region of potential impingement that does not get as much attention as the subacromial space. Tissue compression under the coracoid process, or the lower margin of the coracoacromial ligament, is called anterior or subcoracoid impingement. Possible causes of subcoracoid pain include entrapment of the superior border of the subscapularis tendon, bursitis, subscapularis tendon calcification, or ossification and inflammatory enlargement of the glenohumeral ligaments.⁴ Pathology of the bicep tendon may also be a cause (Image 3).

Some research also points toward subcoracoid pain arising from the underside of the subscapularis where it comes in contact with the glenohumeral joint. In some cases, excess friction can irritate the underside of the subscapularis and lead to muscle tears, producing pain that is often mistaken for external impingement.

Clearly there are various factors that lead to soft-tissue compression under the coracoacromial arch. Yet, recent research has shown us that there are some people with decreased space or significant soft-tissue degradation in the subacromial region who have no pain. There are also those with significant pain complaints who don’t appear to have any evidence of impingement damage that can be identified on imaging studies. This has led researchers to look for other potential causes of anterior and lateral shoulder pain.

Our current understanding of tendon pathology helps shed some light on potential alternative explanations for shoulder pain that may not be caused solely by compression damage. Newer theories suggest there may be a more complex interaction between mechanical and biological factors in tendon pathologies around the shoulder.

The number of chronic overuse tendon disorders throughout the body increases as people age.⁵ Histological studies indicate changes occur at the cellular level within these tendons. It looks as if some subacromial pain complaints are a combination of mechanical irritation, along with degenerative and metabolic change in the tendons. But the idea that metabolic and degenerative changes within the tendons are responsible for subacromial shoulder pain has only recently become more accepted within the research literature. It remains likely that numerous shoulder pain complaints involve both mechanical and metabolic/degenerative factors.

Assessment

The best chance for identifying subacromial pain starts with a detailed and thorough client history. Clients usually report pain in the anterior/lateral shoulder region that may radiate to the lateral humerus as well. Subacromial impingement generally produces more lateral shoulder pain, while anterior impingement produces more pain on the front side of the shoulder. It is common to hear reports of night pain, especially when lying on the affected side or sleeping with the arm overhead, as those positions further compress the subacromial structures.

X-rays and MRIs are still used for evaluation, but these methods may not reveal crucial information about functional movements and mechanical stresses. A truly thorough approach needs to include a comprehensive physical examination and analysis of assessment patterns that suggest particular tissue involvement. This pattern analysis helps drive the most appropriate treatment strategies.

For example, suppose a client presents with lateral shoulder pain during active abduction that is decreased but still present near the end range of passive abduction and during resisted abduction. The presence of pain during active and resisted abduction movements strongly indicates contractile tissues such as the supraspinatus. In most cases, we wouldn’t expect to see muscle-oriented pain during passive movements of that same motion. However, the supraspinatus is susceptible to compression under the coracoacromial arch during abduction, so this is one place in the body where pain during a passive movement could indicate muscle-tendon unit involvement. Recognizing these patterns is more helpful than any isolated orthopedic test or a single image from a high-tech diagnostic study.

As mentioned earlier, subacromial pain will tend to be more significant during active, passive, or resisted abduction motions, while subcoracoid impingement is more likely to produce pain during active, passive, or resisted flexion motions. Because subcoracoid impingement frequently involves the subscapularis tendon, it is also common to see pain or discomfort during resisted internal rotation because that engages the subscapularis. There may also be pain felt during either active or passive external rotation of the shoulder where the subscapularis is stretched. Sometimes there is a popping or snapping sensation associated with range of motion evaluations in the shoulder, as well.

There are various special orthopedic tests frequently used to identify impingement problems, such as the Neer impingement sign, empty can test, or Hawkins-Kennedy test, but they don’t always have a high degree of accuracy. They may also lead clinicians into more recipe-oriented thinking about the evaluation process by prioritizing this test without evaluating the other critical pattern and movement assessments. Rather than focus on these special orthopedic tests, I find it far more valuable to explore the results and patterns from the active, passive, and resisted motions in the shoulder.

Treatment

The primary goal of SAPS treatment is to eliminate pain and restore appropriate function. What defines appropriate function varies for each client. For example, it isn’t always necessary to achieve a particular numerical range of motion measurement. It may be enough just to get the person to decrease pain for the essential things they need to do as part of their daily activities.

SAPS treatment generally begins with conservative measures, such as limiting aggravating movements along with moderate exercise. Any rehabilitative exercise is usually performed within a range that does not significantly aggravate the pain. Massage plays a great role at this stage, as it can help reduce irritation and increase overall mobility in the shoulder region. We shouldn’t think of massage as necessarily making more space in the subacromial region. Instead, massage helps restore overall shoulder movement, decreases apprehension in shoulder movements, and gradually contributes to increasing available range of motion. A wide variety of techniques can be used to help enhance a greater sense of movement and pain reduction.

Previously, we emphasized techniques such as deep transverse friction to the distal supraspinatus tendon to address scar tissue during the healing process. Friction techniques may still be beneficial, but we now find great benefit in techniques that are not as focused on a particular tissue. A wide array of methods used to treat the shoulder girdle can help decrease apprehension and restore a sensation of safe, increased movement as the condition subsides. The greater sense of pain-free movement can encourage the person to perform gradually increasing activity levels that will provide graded exposure and conditioning for the soft tissues so they can improve more rapidly.

Surgery may still be considered if conservative treatments are not initially effective. Common surgical approaches include increasing the subacromial space by shaving off the underside of the acromion process in a procedure called acromioplasty. However, recent research suggests treatment outcomes from surgical procedures may be similar to those from conservative treatments, and this has led to a decreased perception of the necessity for surgery.⁶ In many cases, surgery is still effective, and what becomes clear is there is no catchall solution that works for everybody, in every situation.

As we have seen, there are numerous causes of SAPS. It is a common occurrence and a condition your clients are likely to present with. The more knowledgeable you are about pathologies in this region, the more helpful you can be for them. In addition, you may be working as part of a health-care team with other professionals. When you understand the nature of the problem and how others may be approaching it, you are a more valuable contributor.

Notes

1. Christina Garving et al., “Impingement Syndrome of the Shoulder,” Deutsches Arzteblatt International 114, no. 45 (November 2017): 765–76, https://doi.org/10.3238/arztebl.2017.0765.

2. Teemu V. Karjalainen et al., “Subacromial Decompression Surgery for Rotator Cuff Disease,” Cochrane Database of Systematic Reviews 1, no. 1 (January 2019), https://doi.org/10.1002/14651858.CD005619.pub3.

3. Charles S. Neer, “Anterior Acromioplasty for the Chronic Impingement Syndrome in the Shoulder: A Preliminary Report,” Journal of Bone & Joint Surgery 54, no. 1 (January 1972): 41–50, https://doi.org/10.2106/JBJS.8706.cl.

4. Gregory Cunningham and Alexandre Lädermann, “Redefining Anterior Shoulder Impingement: A Literature Review,” International Orthopaedics 42, no. 2 (June 2017): 359–66, https://doi.org/10.1007/s00264-017-3515-1.

5. Teun Teunis et al., “A Systematic Review and Pooled Analysis of the Prevalence of Rotator Cuff Disease with Increasing Age,” Journal of Shoulder and Elbow Surgery 23, no. 12 (December 2014): 1913–21, https://doi.org/10.1016/j.jse.2014.08.001.

6. R. Diercks et al., “Guideline for Diagnosis and Treatment of Subacromial Pain Syndrome,” Acta Orthopaedica 85, no. 4 (March 2014): 1–9, https://doi.org/10.3109/17453674.2014.920991.