Shoulder Impingement: What You Should Know

This article will highlight the common diagnosis of subacromial impingement, or “shoulder impingement (SI)” and address a brief history of this diagnosis, current research, and how we can improve our diagnosis, prognosis narrative, and exercise to reflect this research.

Defining Shoulder Impingement

To effectively analyze the research and perspectives presented here regarding long-held beliefs about shoulder impingement, we must first define the relevant anatomy.

The shoulder consists of the humerus, clavicle, and scapula. The scapula features the coracoid process and acromion, connected by the coracoacromial ligament. The acromioclavicular joint connects the acromion and clavicle.

Within the subacromial space beneath the acromion lie the supraspinatus tendon, long head of the biceps brachii tendon, subacromial bursa, and shoulder joint capsule. SI refers to the compression of these tissues in this space.

Image adopted from the Providence Center for Orthopedic Specialists

Shoulder pain is a common complaint among lifters and overhead athletes. Whenever there is a “pinching” sensation at the top of the shoulder, it is often attributed to “shoulder impingement.” This diagnosis is common in the rehab space as a catch-all term to describe discomfort at the top of the shoulder secondary to the shoulder complex elevating and compressing the supraspinatus against the inferior aspect of the acromion. This compression is commonly believed to be the source of the above-described “pinching” pain.

The shoulder impingement theory really took off thanks to Dr. Charles Neer in the 1970s. Based on cadaver dissections and shoulder surgeries, he believed around 95% of rotator cuff tears were caused by impingement[8]. This led to the popularization of a surgery called subacromial decompression to relieve compression in the space. The surgery involves removing tissue and shaving the acromion to increase joint space.

While this makes intuitive sense, there wasn't really evidence backing up the impingement theory or surgery benefits at the time. Nonetheless, Neer's ideas influenced medical practice for decades. So with such widespread use of subacromial decompression, you'd expect overwhelmingly good results. But is that actually the case? Let’s take a deeper look.

Shoulder Impingement Can Occur, But Is Not Dangerous

The traditional view of SI makes two assumptions: First, the assumption is that because supraspinatus is underneath the acromion, that it must come in contact with the acromion and become compressed with shoulder elevation. The second assumption is that this compression is painful. So how can we determine if these assumptions are accurate?

Can the supraspinatus become compressed against the inferior aspect of the acromion? Yes, but the research varies. In 2019, Lawrence et al. discovered that 45% of all participants experienced impingement contact, but there was no difference between patients with symptoms vs without symptoms[7]. This is supported by the findings of Park and colleagues in 2020 where they identified that the amount of subacromial space did not have a consistent relationship to pain or disability over time[11].

Despite what many videos online may tell you, upright rows are not an inherently dangerous exercise. While it is true that technique and range of motion (ROM) adjustments can alter symptoms, one specific method is not necessary. Schoenfeld et al suggested in 2011 that it may be safer to only elevate the arms to just below shoulder height (90 degrees); however, the most common position for impingement contact was at 60 degrees of shoulder elevation[7, 13]. This means upright row height may not be the main contributor to symptoms. It also means that one may be “impinging” the shoulder during normal tasks like typing this article, checking one’s watch, or drinking coffee.

The 2019 study by Lawrence also suggests that subacromial contact occurs at lower angles secondary to scapular dyskinesis (decreased upward rotation of the scapula during shoulder elevation[7]). Conversely, a recent systematic review concludes that scapular dyskinesis is a common finding among half of asymptomatic people and is likely not the cause of shoulder pain symptoms[12].

How does this impact Neer’s theories on subacromial impingement and decompression surgery?

A 2018 study randomly assigned people to get decompression surgery, placebo surgery where they just scoped the shoulder, or no treatment[1]. Some key findings were that decompression wasn't better than placebo surgery for outcomes. Surgery also didn't seem to provide much benefit over no treatment. The effects of surgery were possibly due to the placebo effect, post-op physical therapy, or other factors rather than the surgery itself.

A 2019 systematic review, which is considered the best source for research findings, concluded that decompression doesn't provide meaningful benefits over placebo for pain, function, or quality of life[6]. Based on this, guidelines in 2019 strongly recommended against doing the surgery since there's no proven benefit and potential for harm. The recent 2021 study randomly assigned people to get decompression surgery, placebo surgery, or exercise therapy. They found no advantage of decompression over the other two at 5 years for shoulder pain. They suggested abandoning the term "impingement" since research shows that mechanical theory is outdated[10].

What IS Happening?

It is important to understand how we communicate these discrepancies to clients and patients who are experiencing these painful symptoms.

Asserting a specific diagnosis of “shoulder impingement” does a few things:

It applies a mechanical explanation to the source of pain.
It creates the belief that the patient has something wrong with their shoulder’s structure or function.

First, the mechanical explanation of pain is a disservice because the above highlighted research shows that mechanical compression is not a valid explanation for pain prevalence. Pain can occur through a combination of one’s beliefs, perceptions, life-stressors, fear, past experiences, and physical abilities.

Next, the belief that this “impingement” is the cause of their pain, means that one might draw the conclusion that unless they “fix” their shoulder, they will continue to have pain.

This is largely unhelpful because unless there is trauma or significant structural damage, it assumes that something IS wrong with the shoulder. In reality, the only “issue” is often that pain is present. If compression occurs like SI describes, but it isn’t painful and it doesn’t limit one’s abilities, does it even matter that impingement is present? I suspect that most people wouldn’t care.

Further, these compressive forces are not unique to the shoulder. During knee flexion, there is plenty of compressive force at the knee joint, but we do not coin this as impingement also. So why would compression be problematic at the shoulder, but not the knee?

The contact between the supraspinatus and acromion is only problematic if it hurts. The goal of rehab is to decrease painful symptoms, not necessarily decrease compression. If assigning a diagnosis increases the perception of a mechanical problem, it can create an additional barrier to overcome regarding one's ability to decrease their pain.

A 2017 systematic review by Nickel et al. examined the implications of how terminology for the same conditions influence psychological outcomes[9]. They concluded that, “when a more medical or more precise term was used to describe a condition, people tended to have stronger preferences for more invasive management options.” The small number of people who prefer surgery based on these findings may lead to a larger increase in unnecessary surgeries at the population level.

Patients put their trust in clinicians, and are particularly vulnerable to the language used by their healthcare provider [2]. The use of words that may generate fear or anxiety can make it more difficult for people to make informed decisions as an active participant in their own care[3]. This means that symptoms can be influenced by one’s personal thoughts, beliefs, and perspectives.

While these factors may not be the cause of the symptoms present, they can magnify, perpetuate, or worsen them [5]. Because we know that using different terms for the same condition can influence one’s understanding and threat perception of a condition [4], here are three alternative terms for shoulder impingement:

Subacromial Pain Syndrome (SAPS)
Rotator Cuff Related Shoulder Pain (RCRSP)
Acute Superior Shoulder Pain

To review what we’ve gone over so far:

While shoulder impingement may occur, it doesn't seem to be the main source of shoulder pain as it was originally proposed to be.
Contact in the shoulder area happens commonly, even without pain and with normal activities.
A smaller space between the bones also doesn't correlate with symptoms.
Arthroscopic subacromial decompression isn’t superior to placebo surgery or exercise to manage pain.
Most importantly, labeling something as impingement and pursuing surgery can actually do more harm than good.

If Not Shoulder Impingement, Why Does My Shoulder Hurt?

If this article has done nothing else, it should highlight how most non-traumatic pain is not caused by a specific anatomical structure in most instances. For the active or athletic individuals who are likely reading this article it’s important to understand that the source of pain is largely secondary to performing activities at intensities that exceed one’s current abilities (demands > capacity).

If performing an exercise hurts, it is likely that the painful movement’s:

New or hasn’t been trained recently
Volume has increased recently (per session or per week)
Performed heavier or closer to failure than usual
Technique has changed substantially

These factors impact how much recovery is required between training sessions and if changes occur too quickly, it can increase symptom irritability.

Further, your health status outside of training may be contributing as well.

Imagine you’re in a visibly bad mood. You’ve just worked late two days in a row, you’re coming down with a cold, you’re behind on bills, and you’re fighting with your significant other. If someone asks you what’s wrong, is it just one thing, or are all the above factors at play?

The same approach is true for pain. Training programs, sleep habits, nutrition, life stress, and emotional distress can all contribute to symptoms.

If any of the above factors are negatively impacting your life, and they are within your control, it’s advisable to address them. You may:

Modify irritable activities
Reduce ROM, loads, or speed of aggravating movements
Adjust training frequency or volume
Prioritize other aspects of your lifestyle that positively impact your well-being

As a physical therapist, if I know your shoulder pain is non-traumatic and unrelated to another diagnosis, we try to collaborate on all of these factors to influence your plan of care.

The details of your priorities, exercise plans, sleep habits, and life stressors will influence how one person’s rehab for the exact same pain may look different than the next person’s rehab. The overarching principles all remain the same, but how they are delivered can vary significantly.

Conclusion

Not everything supported by evidence is equally valid. Information changes and those changes should impact how treatment and education are provided. Shoulder Impingement was once a valid diagnosis, but emerging evidence questions the usefulness of this term.

If you have been presented with shoulder impingement as a diagnosis in the past, or been taught that this is something that should be avoided, you may benefit from looking at your experience with the new perspective provided in this article.

It is likely that pain is secondary to doing too much, too soon. Rather than needing to stop certain exercises all together, or get surgery to fix your pain, smaller adjustments to the variables within your control may have more benefit.

Citations

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Lawrence RL, Braman JP, Ludewig PM. The Impact of Decreased Scapulothoracic Upward Rotation on Subacromial Proximities. J Orthop Sports Phys Ther. 2019 Mar;49(3):180-191. doi: 10.2519/jospt.2019.8590. Epub 2019 Jan 18. PMID: 30658048; PMCID: PMC7112160.
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Nickel B, Barratt A, Copp T, et alWords do matter: a systematic review on how different terminology for the same condition influences management preferencesBMJ Open 2017;7:e014129. doi: 10.1136/bmjopen-2016-014129
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Park, S. W., Chen, Y. T., Thompson, L., Kjoenoe, A., Juul-Kristensen, B., Cavalheri, V., & McKenna, L. (2020). No relationship between the acromiohumeral distance and pain in adults with subacromial pain syndrome: a systematic review and meta-analysis. Scientific reports, 10(1), 20611. https://doi.org/10.1038/s41598-020-76704-z
Salamh, P. A., Hanney, W. J., Boles, T., Holmes, D., McMillan, A., Wagner, A., & Kolber, M. J. (2023). Is it Time to Normalize Scapular Dyskinesis? The Incidence of Scapular Dyskinesis in Those With and Without Symptoms: a Systematic Review of the Literature. International journal of sports physical therapy, V18(3), 558–576. https://doi.org/10.26603/001c.74388
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