What is shoulder impingement and does it really exist?

What is shoulder impingement syndrome?

Shoulder impingement syndrome is when there is reduced clearance between the humeral tuberosities and the coracoacromial arch during elevation, which pinches the intervening soft tissues. The vulnerable soft tissues are the subacromial or subdeltoid bursa, the rotator cuff tendons and the long head of biceps. (CSP guidelines)

Shoulder Impingement




Internal Glenoid Impingement


Anatomy of the shoulder:

Before we discuss the above classifications further, you need to know a bit about the anatomy of the shoulder:








shoulder-jointsGlenohumeral joint:

Scapula (glenoid) and humerus


Shallow glenoid

Large head of humerus

Labrum around glenoid

Closed packed position: full abduction and external rotation

Capsular pattern: External rotation >Abduction>Internal rotation>Flexion

Very mobile and unstable




Sternoclavicular joint:

Sternum to clavicle

Saddle joint

Closed packed position: Arm abducted to 90


Scapulothoracic joint:

Underside of scapula with thorax (ribs)

No true articulation


sternoclavicular-Joint-InjuryAcromioclavicular joint:

Clavicle to scapula (acromion)

Plane synovial

Closed packed position: Arm abducted to 90






Main muscles of the shoulder (excluding the rotator cuff):


Levator Scapulae:levator-scapulae


Latissimus Dorsi:latissimus-dorsi

Serratus anterior:serratus-anterior


Pectoralis Major:pectoralis-Major

Pectoralis Minor:pectoralis-minor

Biceps Brachii:biceps-brachii

Triceps Brachii:triceps-brachii

Teres Major:teres-major-muscle



Muscles of the rotator cuff:



Supraspinous fossa of scapula to greater tubercle of humerus

Assists deltoid in abduction of humerus







Infraspinous fossa of scapula to greater tubercle of humerus

Externally rotates the humerus






teres-minorTeres Minor:

Lateral border of the scapula to Greater tubercle of humerus

Externally rotates the humerus





Subscapular fossa of the scapula to lesser tubercle of humerus

Internally rotates the humerus





glenoid-labrumSoft fibrous tissue rim called the labrum surrounds the socket to help stabilise the Glenohumeral joint. The rim deepens the socket by up to 50% so that the head of the humerus fits better. In addition, it serves as an attachment site for several ligaments.





shoulder-bursaeFluid filled sacs that help to reduce friction. The sub-acromial bursa is the most commonly inflamed of the shoulder bursae.


So now on with the classifications of shoulder impingement:


Primary impingement or external-Subacromial impingement:

shoulder impingement stretches shoulder joint anatomy

This was first proposed by Neer in 1972 and there is even a Neer test used to determine impingement. This type is when an area of the Rotator cuff is torn or irritated and there is chronic bursitis. The impingement is outside of the glenohumeral joint itself and confined to the Subacromial space, hence usage of the word ‘external’ (Tagg et al 2013).

Primary shoulder impingement syndrome typically affects people older than 50 years of age although it can happen in the young but it is less likely.

Pain is often felt in the anterior or front of the shoulder during overhand activities. They can get pain at night when they roll onto that shoulder.


Secondary Impingement:

This is when there is a problem with keeping the humeral head centred in the glenoid fossa during movement of the arm. Generally this is caused by functional instability (neuromuscular control) combined with a laxity in the glenohumeral joint capsule and ligaments.

Secondary impingement generally occurs in the coracoacromial space due to anterior translation of the humeral head as opposed to the Subacromial space that is seen in primary impingement.

Patients are usually younger and pain is commonly felt in the anterior or anterolateral aspect of the shoulder. The symptoms are usually activity specific and involve overhand activities.


Internal Glenoid Impingement, also called posterior-superior glenoid impingement (PSGI):


This is probably the most common cause of posterior shoulder pain.

It is commonly misdiagnosed as rotator cuff tendinopathy. (Jobe, 1995)

PSGI is caused by the impingement of the posterior edge of the supraspinatus and the anterior edge of the infraspinatus against the posterior-superior-glenoid and glenoid labrum.

It is commonly seen in overhead athletes and patients involved in occupational overhead activities.

The mechanism of injury is shoulder extension, abduction and external rotation mechanism. This is the exact mechanism the arm is in when you try and throw a ball overhand. (Arroyo, 1997)


How common is shoulder impingement?


In general 74% of patients in primary care are shoulder impingement and we have seen loads of patients with this at our clinics in Stoke-on-Trent.

What causes shoulder impingement?


Causes of primary shoulder impingement:

Consequence of the aging process

Mechanical compromise of the subacromial space

Degenerative Joint Disease of the acromioclavicular (A/C) joint

Subacromial spurring

Rotator cuff atrophy

Rotator cuff/scapular weakness

Increased thoracic kyphosis

Poor posture


Causes of secondary shoulder impingement:

Rotator cuff weakness

Functional instability

Congenital Capsular laxity

Acquired capsular laxity from trauma (e.g. dislocation)


Causes of Internal Glenoid Impingement:

This is probably the most common cause of posterior shoulder pain.

It is commonly misdiagnosed as rotator cuff tendinopathy. (Jobe, 1995)

PSGI is caused by the impingement of the posterior edge of the supraspinatus and the anterior edge of the infraspinatus against the posterior-superior-glenoid and glenoid labrum.

It is commonly seen in overhead athletes and patients involved in occupational overhead activities.

The mechanism of injury is shoulder extension, abduction and ER mechanism. This is the exact mechanism the arm is in when you try and throw a ball overhand. (Arroyo, 1997)


How do you diagnose it?


Primary shoulder impingement:

Due to the degenerative nature of primary Shoulder impingement syndrome, an X-ray can be useful. Here you can analyse the shape of the acromion process of the scapula (shoulder blade) as this plays a big part in recovery.

acromial types

Type I: Flat acromion low incidence of impingement

Type II: Curved acromion higher incidence of impingement

Type III: Beaked acromion very high incidence of impingement

Type III is usually genetic but it may be a previous Type II that has degenerated into a type III.

95% accuracy with Hawkins-Kennedy, painful arc and infraspinatus muscle test grouped together


However, because impingement is something that happens when you move you can’t really tell with images. Barreto et al  (2019) found that in people with one sided shoulder pain they found abnormal MRI findings in both shoulders. Only full-thickness tears in the Supraspinatus tendon and glenohumeral osteoarthritis were higher (approximately 10%) in the symptomatic shoulder.  Tests such as the Neer test and the Hawkins Kennedy test are commonly used and assessment of pain patterning and assessment of muscle strength to determine any muscle imbalance around the shoulder joint.


Secondary shoulder impingement:

There is insufficient evidence upon which to base selection of physical tests for shoulder impingement (Hanchard et al 2013)

For secondary impingement it is important to look at the history (e.g. previous trauma, hypermobility syndrome etc.)

Testing should examine the passive and active stability of the joint along with questions about the problem and it’s pattern of pain


Internal Glenoid Impingement:

Done through the symptom history and patient presentation:

Posterior shoulder pain in the throwing shoulder

Slow insidious onset with no history of trauma

Pain is primarily associated with the athletic or work activity.


Who tends to get shoulder impingement?

Swimmers:  Brushøj et al (2007) found that 28% of swimmers suffer with impingement, in fact it can even be called swimmer’s shoulder in some circles.

Obviously people who work above head and in sports that involve throwing actions.

swimmers shoulder


The debate about shoulder impingement:

Does shoulder impingement actually exist?

Is it actually normal for your humeral head to translate upwards? Heugel et al (2015) believes just this. They found that in normal healthy individuals their humeral head translated upwards and compressed the sub-acromial space without pain or issue. This implies that this area is designed to be compressed and ‘impinged’.

People often have a surgery call an arthoscopic sub-acromial decompression (ASAD) for shoulder impingement syndrome. The aim of this surgery is to shave the end of the bone of the Acromion process, which is blamed for causing the impingement and eventually Rotator cuff tears in the shoulder. But, Gill et al (2002) found no link between the shape of the Acromion process and Rotator cuff tears, which throws doubt onto the impingement theory.


Another problem that is blamed on shoulder impingement syndrome is Sub-acromial bursitis, again due to the compression onto the bursa. However, Couanis et al (2016) found thickened Sub-acromial bursae on normal health swimmers without any pain or symptoms. This means that the bursa gets compressed and as long as the activity or load is progressed gradually then this is a normal adaptation of the bursa to ‘normal’ impingement in the shoulder.


If it is symptomatic how do you treat shoulder impingement?


So physiotherapy for this will depend on you individual issues causing the problem but a combination of exercises and manual therapy is a good approach according to Steuri et al (2017) and this is what we do at Hawkes Physiotherapy. Exercises focus on strengthening the Rotator cuff and improving muscles imbalances. We even use things such as a Compex Neuromuscular electrical stimulator (NMES) to target certain muscles that are inhibited.

Below is an example exercise that we commonly prescribe some of our patients:




Arthoscopic sub-acromial decompression (ASAD):

asad surgery

This surgery is basically keyhole surgery to decompress the sub-acromial space by removing bone and soft tissue. This is a surprisingly common surgery but its effectiveness is very much in doubt. In fact I have seen many shoulder pain patients in our Stoke-on-Trent clinics that have had this surgery performed with poor success rates. Amazingly, Beard et al (2018) did a randomised surgical trial with a fake ASAD as one of the groups and they found that just going in with the keyhole instruments and not shaving anything off was just as effective as the real ASAD!

Overall summary

Shoulder pain is definite and so is impingement, however it would seem that having impingement is not the only reason to have shoulder pain. You can have impingement and no issues at all. It is more complicated than was originally thought. Like most injuries you need to look at things like doing too much too soon or even things like stress or mood as these may be relevant more than the impingement itself. These are the details that we look into in our Physio sessions in Stoke-on-Trent to get to the root of the problem.

If you need any further information or would like to book an appointment then call Hawkes Physiotherapy on 01782 771861 or 07866 195914.


The content in this blog article is provided for general information purposes only and is not meant to replace a physiotherapy or medical consultation.


  • Arroyo, Julian S., Stuart J. Hershon, and Louis U. Bigliani. “Special considerations in the athletic throwing shoulder.” Orthopedic Clinics 28.1 (1997): 69-78.
  • Barreto, Rodrigo Py Gonçalves, et al. “Bilateral magnetic resonance imaging findings in individuals with unilateral shoulder pain.” Journal of shoulder and elbow surgery 28.9 (2019): 1699-1706.
  • Beard, David J., et al. “Arthroscopic subacromial decompression for subacromial shoulder pain (CSAW): a multicentre, pragmatic, parallel group, placebo-controlled, three-group, randomised surgical trial.” The Lancet 391.10118 (2018): 329-338.
  • Brushøj, C., et al. “Swimmers’ painful shoulder arthroscopic findings and return rate to sports.” Scandinavian journal of medicine & science in sports 17.4 (2007): 373-377.
  • Couanis, G., W. Breidahl, and S. Burnham. “The relationship between subacromial bursa thickness on ultrasound and shoulder pain in open water endurance swimmers over time.” Journal of science and medicine in sport 18.4 (2015): 373-377.
  • Gill, Thomas J., et al. “The relative importance of acromial morphology and age with respect to rotator cuff pathology1.” Journal of shoulder and elbow surgery 11.4 (2002): 327-330.
  • Hanchard, Nigel CA, et al. “Physical tests for shoulder impingements and local lesions of bursa, tendon or labrum that may accompany impingement.” Cochrane Database of Systematic Reviews 4 (2013).
  • Huegel, Julianne, Alexis A. Williams, and Louis J. Soslowsky. “Rotator cuff biology and biomechanics: a review of normal and pathological conditions.” Current rheumatology reports 17.1 (2015): 476.
  • Jobe, Christopher M. “Posterior superior glenoid impingement: expanded spectrum.” Arthroscopy 11.5 (1995): 530-536.
  • Neer II CS. Anterior acromioplasty for the chronic impingement syndrome in the shoulder: a preliminary report. J Bone Joint Surg Am 1972; 54 (1) 41-50
  • Steuri, Ruedi, et al. “Effectiveness of conservative interventions including exercise, manual therapy and medical management in adults with shoulder impingement: a systematic review and meta-analysis of RCTs.” Br J Sports Med 51.18 (2017): 1340-1347.
  • Tagg, Catherine E., Alastair S. Campbell, and Eugene G. McNally. “Shoulder impingement.” Seminars in musculoskeletal radiology. Vol. 17. No. 01. Thieme Medical Publishers, 2013.

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Online Physiotherapy

Put simply this is Physio done via either telephone or video over the internet. Skype and facetime are examples of this.

Contrary to popular belief online physiotherapy can be very effective and it can help the same injuries that face to face physio can help. I have helped many people with injuries such as disc prolapses, tennis elbow, neck pain and much more).