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    Shoulder Impingement: Causes of Subacromial Impingement Syndrome

    14 min
    |
    |
    May 15, 2026
    HealthScienceEducation

    Learn about Subacromial Impingement Syndrome (SIS), a common cause of shoulder pain where the supraspinatus tendon and bursa become pinched in a crowded space.

    Shoulder Impingement: Causes of Subacromial Impingement Syndrome

    Best quote from Shoulder Impingement: Causes of Subacromial Impingement Syndrome

    “

    Subacromial impingement is a 'crowded house' situation where the focus must shift from just strengthening a tendon to integrated shoulder mechanics. You can create more room through better mechanics, stronger stabilizers, and smarter movement patterns rather than relying on surgery.

    ”

    This audio lesson was created by a BeFreed community member

    Input question

    Teaching on assessment, testing, investigation, diagnosis and physiotherapy treatment of shoulder impingement syndrome

    Host voices
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    Knowledge sources
    Shoulder Impingement Syndrome - StatPearls - NCBI Bookshelf
    link
    https://www.ncbi.nlm.nih.gov/sites/books/NBK554518/
    Diagnosing and Managing Impingement Syndrome of the Shoulder - OrthoNet AI
    link
    https://www.orthonet.on.ca/2025/07/diagnosing-and-managing-impingement-syndrome-of-the-shoulder/
    Effect of scapular stabilization exercises on subacromial pain (impingement) syndrome: a systematic review and meta-analysis of randomized controlled trials - PMC
    link
    http://www.ncbi.nlm.nih.gov/pmc/articles/10940535
    Evidence-based approach to the shoulder examination for ...
    link
    https://link.springer.com/article/10.1186/s12891-024-08144-z
    Conservative Impingement Syndrome
    link
    https://www.allinahealth.org/-/media/files/ortho/shoulder/01-conservative-impingement-syndrome.pdf
    Optimal management of shoulder impingement syndrome - PMC
    link
    https://ncbi.nlm.nih.gov/pmc/articles/PMC3945046/

    Frequently Asked Questions

    Subacromial Impingement Syndrome, or SIS, is a progressive orthopedic condition characterized by a "crowded house" effect within the shoulder. It occurs when the tiny subacromial space, typically only 1 to 1.5 centimeters high, narrows and pinches structures like the supraspinatus tendon, the bursa, and the long head of the biceps. This syndrome is a leading cause of shoulder pain, accounting for approximately 44% to 65% of clinical shoulder complaints.

    Shoulder impingement is often caused by a lack of space within the subacromial area, which can be due to an individual's physical anatomy or specific movement patterns. While many associate it with bone spurs, it is actually a dynamic clinical syndrome that overlaps with rotator cuff-related pain. When the space narrows, the internal tendons and bursa are squashed, leading to symptoms that can progress from simple swelling to more serious tissue damage.

    According to the Neer stages of this orthopedic condition, the syndrome is progressive. It typically begins as Stage I, which involves reversible edema or swelling within the shoulder tissues. If the impingement continues without intervention, it can lead to Stage II and beyond, resulting in more permanent changes such as fibrosis, tendinosis, and eventually full-blown rotator cuff tears as the tendons and bursa remain chronically pinched.

    In a crowded subacromial space, several key structures are at risk of being pinched or squashed. These include the supraspinatus tendon, the subacromial bursa, and the long head of the biceps tendon. Because these tissues must all function within a very narrow gap of about 1 to 1.5 centimeters, any reduction in space due to inflammation or structural issues can lead to the cluster of symptoms known as Subacromial Impingement Syndrome.

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    Key Takeaways

    1

    The Subacromial Crowded House

    0:00
    0:30
    1:01
    1:19
    1:45
    2

    Primary Versus Secondary Friction

    2:09
    2:30
    2:45
    3:06
    3:21
    3:47
    3

    The Detective Work of the Physical Exam

    4:07
    4:30
    4:46
    5:04
    5:16
    5:36
    5:41
    6:03
    4

    Imaging When the Story Doesn't Add Up

    6:15
    6:32
    3:21
    7:12
    7:26
    7:41
    7:55
    5

    The Scapular Engine and the Serratus Secret

    8:09
    8:34
    8:49
    9:07
    9:23
    3:21
    9:57
    6

    From Protection to Plyometric Power

    10:17
    10:38
    10:53
    11:10
    3:21
    11:30
    11:44
    7

    The Reality of the Surgical Option

    12:03
    12:20
    12:36
    12:51
    13:08
    9:07
    8

    Building a Resilient Shoulder

    13:36
    13:53
    14:12
    14:29
    14:40

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