The Truth About Shoulder Impingement

The purpose of this blog is to tell you the truth about shoulder impingement!

Looking to improve the strength, range of motion, and resilience of your shoulders to enhance your function and performance? Check out our Shoulder Resilience program!

What Is Shoulder Impingement?

To better understand the research and arguments I’m going to present that challenge the long-held beliefs about shoulder impingement, it’s important for me to define it and briefly describe the relevant shoulder anatomy.

The shoulder consists of three bones: 

• The humerus, or arm bone
• The clavicle, or collarbone
• And the scapula, or shoulder blade

The scapula has two bony landmarks known as the coracoid process and the acromion. The ligament that attaches from the coracoid process to the acromion is called the coracoacromial ligament. The connection between the acromion and the clavicle is referred to as the acromioclavicular joint.

The area between the humeral head and these structures is known as the subacromial (under the acromion) space. Within this space is the supraspinatus tendon (one of the rotator cuff muscles), long head of the biceps brachii tendon, subacromial bursa, and the capsule of the shoulder joint.

When most people discuss shoulder impingement, they are referring to these tissues being compressed in this space.

The History of Shoulder Impingement

The popularization of the shoulder impingement theory can be attributed to Dr. Charles Neer in 1972, who based his beliefs on dissections of cadavers and what he observed during shoulder surgery. In his 1983 paper, he wrote that he believed “…95% of tears of the rotator cuff are caused by impingement…”

Therefore, he proposed and developed a surgery to treat shoulder impingement. The acromioplasty, now more commonly referred to as subacromial decompression (short video), involves removal of the subacromial bursa, cutting of the coracoacromial ligament, and shaving of the acromion. 

The intention of the surgery is to decrease the compression of tissues within the subacromial space, such as the supraspinatus tendon, during various shoulder movements to reduce symptoms. 

Although this sounds reasonable, there was no concrete evidence to substantiate the shoulder impingement theory or the benefit of surgery. However, Neer’s ideas have greatly influenced medical, rehabilitative, and resistance training practices over the past 50 years.

Does Subacromial Decompression Fix Shoulder Impingement?

Considering the rapid adoption and rising incidence of the surgery, with one paper by Judge et al in 2014 finding a 746.4% increase in the surgery from 2000/2001 to 2009/2010, we’d expect subacromial decompression to be overwhelmingly successful. 

There are 5 papers from the past 5 years that will shed light on this topic.

1. A study by Kolk et al in 2017 compared bursectomy (removal of the bursa only) to bursectomy plus acromioplasty. The authors found that the addition of the acromioplasty did not result in a clinically relevant improvement in shoulder function or relief of pain at 12 years’ follow-up compared with bursectomy alone. They also did not find a statistically significant difference in the prevalence of rotator cuff tears after 12 years.

2. Beard et al in 2018 conducted a randomized, placebo-controlled trial “to determine whether decompression compared with placebo (arthroscopy only) improved pain and function, whether decompression differed in outcome to no treatment, and whether placebo differed to no treatment.”

There were three big takeaways from this study:

1. “There were no differences in outcomes between decompression surgery and placebo surgery…”
2. “…surgery might not provide clinically significant benefit over no treatment…”
3. “The mechanism of the treatment effect in the patients who received surgery might be the result of a placebo, postoperative physiotherapy, or other factors.”

3. A 2019 Cochrane review, which is the gold standard for the appraisal of research, concluded that “High-certainty evidence shows that subacromial decompression does not provide clinically important benefits over placebo in pain, function or health-related quality of life.”

Based on the information up to this point, the British Medical Journal created a clinical practice guideline in 2019 that made a strong recommendation against surgery. “The panel concluded that almost all informed patients would choose to avoid surgery because there is no benefit but there are harms and it is burdensome.”

4. A systematic review with meta-analysis by Lähdeoja in 2020 concluded that “Subacromial decompression surgery provided no important benefit compared with placebo surgery or exercise therapy, and probably carries a small risk of serious harms.”

5. Finally, Paavola et al in 2021 conducted a randomized, double blind, placebo surgery controlled trial to assess the long-term efficacy of arthroscopic subacromial decompression (ASD). They also included an exercise group for comparison. The authors concluded that “ASD provided no benefit over diagnostic arthroscopy [placebo] (or exercise therapy) at 5 years for patients with shoulder impingement syndrome.”

They go on to state – “As the current evidence indicates that the impingement theory has become antiquated, we would also recommend to abandon the term shoulder impingement as it refers to this mechanical theory.”

Does That Mean Shoulder Impingement Doesn’t Exist?

Shoulder impingement occurs, but it’s not the bogeyman it’s been made out to be.

A study by Lawrence et al in 2019 examined participants with and without shoulder pain and discovered 3 important findings:

1. Contact between the supraspinatus tendon and coracoacromial arch occurred in 45% of all participants.
2. There was no difference between symptomatic and asymptomatic subjects.
3. Contact was most common at 60 degrees of elevation, which means I might be “impinging” my shoulder all day long while typing, eating, drinking water, and doing most other daily tasks.

For the next 2 papers, it’s helpful to know that the acromiohumeral distance, the distance between the acromion and humeral head, is just one way of measuring and describing the subacromial space.

A systematic review by Park et al in 2020 found no relationship between the acromiohumeral distance and pain in adults with shoulder pain. The authors also found “…no consistent increase in subacromial space with improvement in pain or disability over time.”

A study by Hunter et al in 2021 concluded “Individuals with subacromial impingement syndrome had a larger acromiohumeral distance and greater supraspinatus tendon thickness than controls.” Tendon thickening is actually considered a beneficial adaptation, and I’ll describe what it potentially means toward the end of this blog.

Short Recap

So, up to this point, what information have I presented?

1. Shoulder impingement refers to compression of soft tissue structures, such as the supraspinatus, between the humeral head and the overlying acromion, coracoacromial ligament, and acromioclavicular joint.
2. The shoulder impingement theory was popularized by a surgeon in the 1970’s before he proposed a surgery to treat the issue. 
3. If symptoms were solely caused by compression of these overlying structures, we’d expect their removal to improve symptoms and function. However, research demonstrates that subacromial decompression is no better than placebo surgery.
4. Subacromial decompression also doesn’t seem to change the long-term prevalence of rotator cuff tears. What I haven’t mentioned is that rotator cuff tears are also present in asymptomatic individuals and are more common as we age, like many other imaging findings. In fact, a study by Barreto et al in 2019 concluded that “Most abnormal MRI findings were not different in frequency between symptomatic and asymptomatic shoulders.” People in their study had similar rates of partial tears in both shoulders despite only having symptoms on one side. 
5. Compression of tissues in the subacromial space is common, occurs equally in people with and without symptoms, and happens with normal, day-to-day tasks. 
6. A smaller subacromial space is not correlated with symptoms or disability.

Why Does Any Of This Even Matter?

Not only is the diagnosis of shoulder impingement unhelpful, it can be harmful.

A study by Zadro et al in 2021 found that participants labeled with subacromial impingement expressed “feelings of psychological distress, uncertainty, and that the condition is serious and has a poor prognosis.”

A paper by Cuff and Littlewood in 2018 explored the beliefs, experiences, and perspectives of patients diagnosed with shoulder impingement. 

Here’s what one patient had to say:

• “It is the tendon being caught by this piece of bone and wearing it away.”
• “(How are we going to get this pain to go away?) By removing this piece of bone.”
• “I can’t imagine how any amount of physio is going to shift this piece of bone which is in my shoulder.”

Another patient said:

• “I couldn’t see how physiotherapy would help with a tear… I’d be worried that I was doing even more damage.”

As the authors suggest, the diagnosis can negatively influence expectations, which are extremely important for recovery, and may act as a barrier to rehab.

Are There Bad Exercises?

The so-called dangers of shoulder impingement have also heavily influenced the fitness community, most notably as it relates to exercise selection. The upright row is probably the most well-known example of an exercise being labeled as “bad” because it’s supposedly harmful for your shoulders.

I’m going to provide counterpoints to some of the main arguments against the use of upright rows and other similar exercises.

1. Research by Giphart et al in 2012 and Lawrence et al in 2017, 2018, 2019, and 2020 demonstrates that impingement most often happens at lower angles of arm elevation. Since this commonly occurs in asymptomatic individuals, you’d have to keep your arms by your side at all times if you truly wanted to avoid impingement. 
2. You might suggest that upright rows are only dangerous when performed to 90 degrees or higher based on an article from 2011. However, the same research just mentioned discusses that the rotator cuff becomes positioned in such a way that it can no longer be compressed by 90 degrees of elevation.
3. But it’s actually the internal rotation that matters, right? Well, it’s not so clear. A review of the literature by Lawrence et al in 2020 discusses how internal rotation has been shown to increase or have no effect on the acromiohumeral distance, while external rotation has been shown to increase, decrease, or have no significant effect. This is why it’s important to examine the biomechanical literature instead of relying on skeletal models.
4. Why do doctors and physical therapists perform the Hawkins-Kennedy test, which mimics the upright row, to assess for shoulder impingement then? Honestly, they probably shouldn’t. A systematic review with meta-analysis by Hegedus et al in 2012 informs us that it’s not a valid test. The test just tells us that people with shoulder pain sometimes experience shoulder pain when their arm is positioned in a way they’re unaccustomed to. You could just as easily crank their arm into external rotation. 
5. But what if you’ve had shoulder pain with upright rows before? That’s totally fair, but there’s also people who report feeling better from doing upright rows (see second comment).
6. “You might not have issues with upright rows now, but just wait 20 years.” Imagine replacing upright rows with any other exercise or activity. 
   1. “You might not have issues with squats now, but just wait 20 years.”
   2. “You might not have issues with running now, but just wait 20 years.”
   3. “You might not have issues with playing sports now, but just wait 20 years.”
   4. Would you really be that surprised if someone who squats, runs, plays sports, bench presses, etc. has at least one episode of back, hip, knee, shoulder, or elbow pain? I’d be more surprised if they didn’t because that doesn’t happen. People experience pain with exercise from time to time. It’s normal. We don’t suddenly label every exercise that contributes to your pain at some point in your lifetime as bad. And you can’t compare upright rows, something with zero research to support that they’re harmful, to smoking cigarettes, which has decades of unequivocal research to demonstrate their harm.

I’ve already said this in a previous blog, but I think it’s worth reiterating. You don’t have to do any exercise that you don’t want to do. Your exercise choices don’t personally affect me, and I’m not getting paid by “Big Upright Row.”

But part of my goal here is to reduce the fragility beliefs that have been created, disseminated, and instilled in society. The human body is resilient and adaptable.

Why Does My Shoulder Hurt Then?

When someone asks this question, they’re usually in search of a specific anatomical structure. Unfortunately, despite popular belief, it’s incredibly difficult to pinpoint a specific cause of pain in most instances.

Earlier I mentioned that supraspinatus tendon thickening is a common finding in those with shoulder pain as opposed to a smaller subacromial space. While often perceived as a negative finding, tendon thickening may be considered a positive adaptive response during periods of excessive loading, acutely or chronically.

Therefore, one component of the answer to the question “Why does my shoulder hurt then?” might be that you simply did a little more than your shoulder could currently tolerate. Think about the phrase – too much, too soon.

For example, you might have started a new gym routine or increased the volume, frequency, or intensity of your current program and pushed beyond your shoulder’s current limits of recovery. It happens.

For someone else, perhaps you decided to repaint your house after years of not doing much overhead work.

Either way, you did too much, too soon.

The other component of the answer relates to your overall well-being. As much as we like to focus on load-related factors and emphasize the strength, range of motion, and movement of the shoulder, a person’s general health status can impact the onset or persistence of symptoms, such as sleep habits, physical activity levels, smoking status, nutrition, etc. This is truer for some people than others.

In any case, the goal is to address the possible contributing factors that are within your control, which will be unique for each person. Generally, this includes:

• Modifying aggravating activities
• Gradually reintroducing those aggravating activities that are meaningful to you as your symptoms improve
• Performing exercises with the intention of improving your function
• And trying to optimize certain aspects of your lifestyle to improve your overall health and well-being

What Should We Call Shoulder Impingement Instead?

Different terminologies have been proposed, such as Subacromial Pain Syndrome (SAPS) and Rotator Cuff Related Shoulder Pain (RCRSP).

The more important question is, “What’s the purpose of a diagnosis?”

Hopefully, at least in part, it’s to inform management. 

Do these diagnoses do that?

They do to some extent because, as you now know, surgery isn’t recommended.

However, shoulder impingement, and these other labels attempting to fill its void, have become catch-all diagnoses for any non-traumatic shoulder pain that isn’t related to instability, frozen shoulder, and some other diagnoses that may respond to specific medical management. 

They are an attempt to simplify the complex and multifactorial nature of pain, while also easing our own uncertainty about the exact tissue structure that may be contributing to symptoms.

But as a physical therapist, as long as I know that you’re experiencing non-traumatic shoulder pain unrelated to some of the other diagnoses I just mentioned, how we name your pain doesn’t necessarily influence rehab.

What’s more useful for me is knowing your age, occupation, lifestyle, sleep habits, exercise habits, goals, what makes your symptoms better, what makes your symptoms worse, etc.

You might have the exact same diagnosis as someone else, but your answers to these questions could be vastly different. And those answers are what influence rehab.

This doesn’t mean that the general rehab process needs to be significantly different from what’s already being used – it’s the explanation that changes and matters:

• Exercise is safe and encouraged.
• You’re not damaging your rotator cuff when you lift your arm and experience pain.
• You don’t have to worry about removing a piece of bone to get better. 
• Compression of tissues is normal in the shoulder and elsewhere. We compress nerves, tendons, ligaments, and muscles all day long when we sit, bend, lift, twist, walk, etc.

Final Thoughts About Shoulder Impingement

Occasionally, it’s important to ask ourselves, “How do I know what I know?”

I knew shoulder impingement was a valid and useful diagnosis because it was taught to me by my professors in physical therapy school. And my professors knew it was a valid and useful diagnosis because someone taught it to them. And that goes back at least 50 years.

It’s the same reason surgeons have been performing the subacromial decompression or personal trainers advise against upright rows. 

Bloodletting and leech therapy were used for thousands of years before someone finally questioned their validity and usefulness. 

Certain clinicians have actually been pushing back against the diagnosis of shoulder impingement for over a decade, but it’s hard to change 50 years of medical history that we think we know to be true.

However, enough research has surfaced since that time to question the usefulness of shoulder impingement as a diagnosis. 

Do you have to agree with everything I’ve said in this blog? Of course not. But for the things you disagree with, ask yourself, “How do I know what I know?”