Shoulder Impingement SyndromeAn In-depth Review
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Table of Contents
1 – What is Shoulder Impingement?
2 – History of Shoulder Impingement
3 – The Different Types of Shoulder Impingement
3.1 – Subacromial Impingement
3.2 – Internal Impingement
3.3 – Coracoid Impingement
3.4 – Suprascapular Nerve Entrapment
4 – What are the Shoulder Impingement Treatment Options?
4.1 – Non-Invasive
4.2 – Acupuncture
4.3 – Injections
4.4 – Surgery
5 – The MUJO Shoulder Impingement Treatment
Shoulder impingement is one of the leading causes of shoulder complaints[18, 19, 20]. It is defined to be a form of disabling contact between soft-tissue and/or bony structures in the shoulder complex. Subacromial impingement, internal impingement, coracoid impingement and suprascapular nerve entrapment are the four types of shoulder impingement.
There are many signs and symptoms of impingement. The two main ones are pain and reduced range of motion or strength.
There are multiple theories of causes, which can also be a result of impingement. This has made defining treatment methods difficult. However numerous investigations in both conservative and non-conservative treatment methods suggest that physiotherapy is currently the best go to treatment option, whilst surgery and injections may not provide any additional benefit.
Literature recommends individualised neuromuscular control training or PNF, eccentric training and scapulothoracic strengthening regimens to best tackle shoulder impingement. We have developed our shoulder impingement treatment plan based on combining these recommendations with our powerful, smart MSK shoulder devices.
What is Shoulder Impingement?
The term “Impingement” can be defined to be some form of a disabling contact between the soft-tissues and bony structures within the shoulder complex. This could be contact between the following:
- Soft-tissue sandwiched and compressed between bony structures, like a pinch (Bone – Soft-tissue – Bone).
- Grinding between soft-tissue and bony structures (Soft-tissue – Bone).
- Collision between bony structures (Bone – Bone).
This disabling contact is present during different motions of the upper arm. Various types of impingement have been defined in clinical research and they are as follows:
- Subacromial impingement Syndrome – formerly known as supraspinatus syndrome.
- Internal impingement – Also referred to as the posterosuperior glenoid rim impingement.
- Coracoid impingement.
- Suprascapular nerve impingement.
It is important to note here that this definition of impingement does not include contact with a joint replacement or implant. For purposes of this article, we have not included this type of impingement.
A brief history of shoulder impingement will be described followed by each of the individual types of shoulder impingements defined above.
History of Shoulder Impingement
Shoulder impingement was first reported and described in 1852. It was later termed “supraspinatus syndrome” throughout the mid 1900s[3, 4]. At the time, supraspinatus syndrome was initially thought to occur when the supraspinatus tendon and subacromial bursa, were compressed and sandwiched between the humeral head and the lateral component of the acromion. However, Charles Neer II argued and showed that it was compression on the anterior portion of the acromion in 1972. The term “supraspinatus syndrome” was then dropped and replaced by the term “shoulder impingement syndrome”. This became well-established and the definition still stands today although with a minor refinement in 1990. Shoulder impingement syndrome as described by Neer is what is known as “Subacromial Impingement” today.
The second type of shoulder impingement, “Internal Impingement” was reported and described by Walch in 1992. The third type of impingement, “Coracoid Impingement” was first reported and described by Goldthwait in 1909, before supraspinatus syndrome was defined and studied. Finally, “Suprascapular Nerve Impingement” was initially reported and described by Thomas in 1936.
The timeline of discovery of the different types of impingement and their refinements show that this is a complex disease and one that is difficult to study. This is still the case today as there are differing opinions about causes of impingement and how different clinicians and researchers define the terms.
The different Types of Shoulder Impingement
The four different types of impingement are described in detail here.
This type of impingement is probably the most studied disease in comparison to the other types.
What is Subacromial Impingement?
Currently, it is defined to be the “compression of supraspinatus tendon, subacromial bursa with the anterior third of the acromion, coracoid, coracoacromial ligament and the AC joint”.
Charles Neer further categorised the progression of the disease into three stages[12, 13]. Each stage was found to be present in certain age groups. They are as follows:
- Under 25-: Aching discomfort in supraspinatus tendon and long head of bicep. Histologically, there is edema and haemorrhage of the supraspinatus and a synovial reaction in the subacromial bursa making it larger.
- 25 – 40-: The continued irritation and impingement leads to fibrotic changes in the supraspinatus tendon and subacromial bursa, further reducing the subacromial space. This causes pain during activity.
- Above 40-: Extended history of shoulder pain and continued impingement leads to development of osteophytes and partial or full thickness rotator cuff tears.
When does Subacromial Impingement Occur?
It is thought that some motions are far more likely to result in impingement when a patient suffers from it. Neer claimed that a humeral elevation at 90° with internal rotation results in impingement as it reduces the subacromial space. In this position the scapula has not rotated upward sufficiently[14, 15]. In addition, a general lack of upward rotation and posterior tilt of the scapula along with additional superior translation of the humeral head can reduce subacromial space and result in impingement[14, 15, 16, 17].
Who Usually Suffers from Subacromial Impingement?
44% to 65% of shoulder complaints during physician visits have been reported to be due to shoulder impingement[18, 19, 20]. As this type of impingement is more common in overhead activities [21, 22], it is also believed that those who perform manual labour and those who perform repetitive overhead tasks likely suffer from this condition[11, 22]. This is a common condition for patients of all ages and activity levels .
What are the Causes, Signs and Symptoms of Subacromial Impingement?
The causes, signs and symptoms have been grouped under one heading as there is debate as to whether the proposed causes lead to impingement or whether they are a result of the impingement. From this point on, they will be referred to as associations. The associated phenomenon of this condition have generally been categorised into two types[5, 24]:
There are other associations that fall outside of these two categories and are described later.
The structural category describes impingement to be a result of musculoskeletal damage. The following table lists the structures that are affected and how they change leading to impingement.
Change or Property
Rotator Cuff Tendon
Malunion of Fracture
Nonunion of Fracture
Shorter Lateral Band with Larger Cross-Sectional Area[21, 29]
Shortened with atrophy
The functional category describes impingement to be a result of another underlying ailment or functional change related to the functional anatomy. The following table lists the structures and their functional changes that is associated with impingement.
Imbalance or change[10, 13, 32, 33, 34]
Poor Stabilisation[10, 13, 32]
Scapula or Scapulo-thoracic Gliding Plane (STGP)
Neuromuscular Control[13, 41, 42]
Restriction in Motion
Position (dyskinesia) & kinematics[10, 13, 14, 15, 43, 44, 45, 46, 47, 48]
Postural Adaptions[13, 21, 49, 50, 51, 52, 53, 54]
Central Nervous System
Decreased corticospinal excitability of the infraspinatus
Other functional changes that lead to impingement include glenohumeral instability[11, 21, 61, 62], changes in strength and torque at the shoulder[63, 64, 65, 66]. Other causes that fall outside of these two categories include eccentric overload and pain.
How is Subacromial Impingement Diagnosed?
There are two main motion tests to determine whether a patient suffers from this type of impingement:
However, there have been serious critique of these tests[11, 68, 69, 70], rendering them unable to diagnose the type of impingement accurately. Neither test can differentiate between subacromial impingement and internal impingement. Moreover studies have shown that these tests may also cause subscapularis to compress against the bony structures[68, 71], which is neither defined to be subacromial or internal impingement. Braman concluded that definitive clinical tests do not exist with known anatomical basis.
This type of impingement is also commonly studied but likely less so than subacromial impingement.
What is Internal Impingement?
Internal impingement is defined to be rubbing or pinching of the supraspinatus and infraspinatus tendon on the posterosuperior portion of the glenoid labrum.
When Does Internal Impingement Occur?
This type of impingement is thought to occur during elevation of the arm whilst externally rotating[7, 72]. However this type of impingement has also found to occur during the Neer and Hawkins tests.
Who Usually Suffers from Internal Impingement?
This type of impingement is usually found in overhead sport athletes. This includes but is not exclusive to baseball, cricket, tennis, basketball etc. However, it is believed that normal individuals without the symptoms of a typical patient can also experience this type of impingement.
What are the Causes, Signs and Symptoms of Internal Impingement?
All of the “associations” mentioned for subacromial impingement are also very relevant for internal impingement. This condition was first discovered with the hypothesis that repetitive throwing leads to pathological internal impingement. This is when the motion results in impingement of the rotator cuff tendon between the humeral head and the posterosuperior portion of the glenoid rim[7, 13]. It is believed that this type of impingement leads to rotator cuff tears and fraying of the glenoid labrum[7, 38]. It has also been hypothesised that joint laxity leads to internal impingement[73, 74]. It is believed that anterior laxity of the glenohumeral capsule leads to an anterior migration of the humeral head. This results in internal impingement. Moreover, this type of instability was commonly found in overhead throwing athletes[75, 76] and the main associated condition.
The hypothesis that instability leads to internal impingement has been challenged. Burkhart[78, 79] believed that internal impingement was not due to a pathological cause, rather it is a natural phenomenon to prevent hyper-external rotation of the glenohumeral joint. He believed that a tight posterior capsule resulted in internal rotation deficit. This then leads to a shift in the glenohumeral contact point in the posterior and superior direction. This is said to decrease the ‘cam effect’ and results in a secondary stretching of the anterior glenohumeral capsule leading to an increase in external rotation. The increase in external rotation is what causes SLAP tears. He stated that the rotator cuff and labrum injuries are not due to the abrasion, rather it is due to the increased shear forces due to the twisting mechanism whilst throwing.
One of the main symptoms of internal impingement is pain in the posterior portion of the shoulder. Overhead athletes tend to complain about pain during the late stage of the cocking-phase of throwing and that it can be difficult to warm up. Some patients have also reported to experience anterior shoulder pain.
Some of the signs of internal impingement include the same amount of loss of internal rotation as increase in external rotation. Patients may also show a loss of internal rotation during 90° of abduction.
How is Internal Impingement Diagnosed?
A clinician may perform range of motion tests to check for some of the signs mentioned above. The Jobe relocation test similar to the Neer and Hawkins test is often positive for internal impingement and has a sensitivity of approximately 75%. During this test the patient is laid down facing up. The arm is then abducted to 90° and externally rotated. The clinician then applies an anterior force to the shoulder followed by a posterior force. The test is considered positive if the patient feels posterior pain when the anterior force is applied and relieved of pain when a posterior force is applied.
Coracoid impingement is less common in comparison to subacromial and internal impingements[11, 81].
What is Coracoid Impingement?
This type of impingement is defined to be the collision and compression of the subscapularis tendon between the coracoid process and the lesser tuberosity of the humerus during motion[8, 82]. It has also been referred to as “subcoracoid impingement syndrome”.
When Does Coracoid Impingement Occur?
This type of impingement usually occurs during a combination of flexion, adduction and internal rotation of the humerus after a history of repetition of these motions, overuse and micro-trauma.
Who Usually Suffers from Coracoid Impingement?
There are no reports in the published literature of the incidence and prevalence of this condition as of yet. However, an individual case study may suggest that rock-climbers may be more prone to this type of impingement.
What are the Causes, Signs and Symptoms of Coracoid Impingement?
One of the main causes of coracoid impingement is overuse and micro-trauma of the shoulder. The following table categorises the additional possible causes[82, 85, 86] into three subsets:
Malposition of the coracoid tip
Calcification of the coracoid tip and subscapularis tendon
Humeral head and neck fracture
Malunion of coracoid fracture
Malunion of glenoid fracture
Displaced fractures of scapular neck
Posterior sternoclavicular dislocation
Previous anterior shoulder surgery (Bristow/Trillat procedure)
Posterior glenoid osteotomy
Patients can suffer from tendinosis and pain inside of the shoulder. The continuous contact between the coracoid and the lesser tuberosity causes progressive bone degeneration, inflammation of the subscapularis bursa and damage to the subscapularis tendon. This type of impingement can lead to subscapularis partial or full thickness tear[1, 83].
How is Coracoid Impingement Diagnosed?
The diagnosis of coracoid impingement has not been exclusively studied in-depth and remains a condition that is diagnosed by eliminating other possible conditions. However, there are tests that have the potential to indicate the presence of this type of impingement. The ‘coracoid impingement test’ is similar to the Hawkins test, except that the patient’s arm is placed in adduction, forward flexion and internal rotation to try and induce contact between the lesser tuberosity and the coracoid. The test would be deemed positive if the patient feels pain. Patients usually feel pain during mid-range of elevation in comparison to end-range in those with subacromial impingement syndrome.
Some clinicians may inject a local anaesthetic to determine whether there is relief of pain. If there is relief of pain, it is believed that the patient suffers from this type of impingement. However, the accuracy and validity of this test has been called into question.
Radiology (X-rays and MRI scans) have been used to try to detect and diagnose this type of impingement, however the accuracy and specificity is questionable.
Suprascapular Nerve Impingement
This type of impingement is rarely mentioned as one of the shoulder impingement conditions and was cited to be the fourth type by Rossi, 1998. This could be because this type of impingement is not related to compression of a muscle or tendon between or against bony structures.
What is Suprascapular Nerve Impingement?
As the name suggests this condition is the entrapment of the suprascapular nerve. The entrapment could occur at the suprascapular notch or the spinoglenoid notch. Damage to this nerve could then lead to infraspinatus and supraspinatus paralysis and atrophy[1, 91].
When Does Suprascapular Nerve Impingement Occur?
It is suggested that this type of impingement occurs during extreme motions such as during service of the ball in volleyball. In addition, elongation and irritation of the nerve has been shown to occur at extreme arm positions in a cadaver study.
Who Usually Suffers from Suprascapular Nerve Impingement?
This condition has primarily been found in volleyball players[1, 91, 93, 94] with a reported incidence rate of 20%. There are no incidence and prevalence reports on the general population.
What are the Causes, Signs and Symptoms of Suprascapular Nerve Impingement?
There are a few hypotheses that describe the causes of this condition. Some believe it is a result of trauma[95, 96], hypertrophy of the spinoglenoid ligament[97, 98], strain[99, 100], ganglion cysts[1, 101] and the repetition of volleyball serves lead to gradual degeneration and elongation of the nerve at the notch.
Damage and entrapment of the nerve results in the following signs and symptoms[1, 91, 92]:
Signs & Symptoms
Decreased strength in external rotation
Pain in posterior and lateral part of the dominant arm
Increased range of motion
How is Suprascapular Nerve Impingement Diagnosed?
Motion tests have not been developed to detect this condition and is likely diagnosed by eliminating other possibilities. EMG analysis may be performed to detect denervation and electrical activity in the muscle.
If muscle atrophy has started, a physical examination of the infraspinatus could indicate a positive diagnosis of the condition.
What are the Shoulder Impingement Treatment Options?
There are specific treatments for each of the different types of impingement, however they can all be brought together under the following categories:
This section will describe each of the different treatment types and the overall message that the literature concludes.
Non-Invasive Treatment Options for Shoulder Impingement
There are numerous treatment options, which fall under one or more of the following types:
- Spine manipulation
- Physiotherapy (includes mobilisation with movement).
- Manual Therapy
In any case, conservative or non-invasive treatment options are highly recommended in comparison to others. Moreover, if these are done properly surgery can be avoided.
Spine manipulation or otherwise known as thoracic spine thrust usually involves the bony re-positioning of the vertebrae. The treatment may also include localised massage therapy. This treatment option has its support as it has shown to work and reduce pain. Others have recommended that this treatment is combined with some form of exercise, ideally supervised physiotherapy. Some clinicians may perform cervical spine manipulation instead of and along with thoracic spine manipulation, however Cook argues that there is no difference between the two and that both provide the same benefit.
More high quality research is needed to conclude whether this treatment is truly beneficial. However, there have been no major findings or studies to suggest that this treatment can do harm.
This is by far the most studied type of treatment in literature in comparison to the others. This is probably due to the numerous different treatment methods and protocols. Physiotherapy is believed to be extremely important in the treatment of shoulder impingement and a 12 week rehab program has proven to work in baseball players. The types of physiotherapy can further be broken down into the following categories:
- Strengthening or resistance based exercises
- Neuromuscular control
In addition, each of these categories of treatment methods can either be supervised or self/home-based and can be combined with one another. Both of which have been shown to be as beneficial as each other and shown to complement each other.
Exercise in general has been found to benefit those who suffer from shoulder impingement[108, 111, 112]. One study showed that in just 9 sessions patients showed a 90% improvement in function. In addition, Dutch physios who use evidence based treatment methods use exercises to treat shoulder impingement.
Numerous studies have investigated the efficacy of strengthening and resistance based exercises[114, 115, 116, 117, 118, 119, 120, 121, 122]. Majority of these studies are in support of these types of exercises. However, some research suggests that rotator cuff strengthening exercises are not beneficial because the rotator cuff strength was found to be the same between patients with shoulder impingement and normal individuals.
Eccentric loading exercises on the other hand, have shown to be beneficial and recommended[115, 116]. Similarly, strengthening exercises that revolve around muscle shortening have been shown to work as well. Lin et al. suggested that strengthening the lower-trapezius and the serratus anterior could help restore normal scapular kinematics to prevent and alleviate impingement. Furthermore, Kamkar et al. stated that individualised scapulothoracic strengthening should be part of any exercise program. Moreover, Kromer et al. found that exercises work when they are individualised to the patient.
Stretching of the shoulder girdle was found to be beneficial and should be added to other exercise or treatment methods.
Dong et al. advised that exercise as a treatment method is best when the syndrome is diagnosed early. However, they also state that in severe cases, exercises should be prescribed first as it has similar outcomes to surgery.
Skolimowski et al. went further and recommended that pain should be treated first and then the aim should be to restore function.
Neuromuscular control has proven to be a large topic as a treatment type for shoulder impingement. The main purpose of neuromuscular control is to restore normal muscle activation patterns. It was already shown earlier that patients with shoulder impingement have different muscle activation and recruitment patterns. Moreover, multiple related studies show that neuromuscular control or motor learning works[110, 127, 128, 129, 130, 131]. It can help with pain, increase mobility[131, 132] and stabilise the shoulder. Some have found it to be better than conventional or traditional physio and manual therapy[134, 135, 136]. Dajah et al. recommended the use of massage therapy and both internal and external proprioceptive neuromuscular facilitation (PNF) exercises to decrease pain and increase range of motion.
Manual therapy is defined to be the “Application of an accurately determined and specifically directed manual force to the body, in order to improve mobility in areas that are restricted; in joints, in connective tissues or in skeletal muscles”. In the context of shoulder impingement, the types of manual therapy include massage and mobilisation techniques. Trigger point therapy in particular has been shown to help with pain. Similarly, mobilisation with movement was shown to work.
Many studies recommend combining manual therapy with some form of exercise[140, 141, 142]. There are some who argue that manual therapy may not necessarily be a beneficial treatment option[143, 144].
Taping or also known as kinesiology taping refers to the use of tape to lift the skin away from the soft tissues. The purpose of this technique is to provide support and encourage better kinematics and thus dynamics without restricting the range of motion.
There is some controversy as to whether this type of treatment works or provides any benefit at all. Some studies suggest that it either doesn’t work or provides pain relief for a very short period i.e. 1 week or is very limited in its benefits[145 ,146, 147]. Another few suggest that it can work but only in the short term[148, 149]. Selkowitz et al. found that muscle activity in the upper and lower trapezius had changed, suggesting that taping could have its benefits.
Higher quality studies are required and specific protocols need to be developed to determine whether taping really does provide benefit for shoulder impingement patients.
There are numerous other treatment methods, which are mostly used in combination with one of the above. Some of these include radiotherapy (only works for secondary impingement), HLT patches, hot and cold compress, herbal remedies, and simply an improvement in dietary intake. The latter are aimed to better health at the cellular level and improve blood flow.
This type of treatment has recently been shown to be safe and provide benefit. However, this type of treatment is in its early stages of research. More randomised control trials are needed to conclude with confidence that acupuncture works.
There are a few different types of injections. The most popular is the corticosteroid injection. Other types and protocols include sclerosing polidocanol injections and mesotherapy.
The use of corticosteroid injections for treating shoulder impingement is controversial with many claiming that it either doesn’t work, has no added benefit to conservative treatments, or had the worst outcomes compared to other treatment methods[125, 152, 156, 157, 158, 159]. Some researchers suggest that it has some benefit in those patients who also have supraspinatus tears. Akram et al. also found that this type of injections works in those who do not have rotator cuff tears but do have a curved acromion. Those who do suggest that these injections work also state that it should be used in combination with physiotherapy[125, 160]. In addition, it is best for short-term relief, whereas physiotherapy is better suited for long-term results.
The main surgical option to treat shoulder impingement is subacromial decompression, also known as acromioplasty. The intent behind this treatment is to relieve the pressure in the subacromial space by shaving away the underside of the acromion. Neer hypothesised that subacromial impingement syndrome was due to an abnormal acromion shape and thus impingement was purely due to a mechanical cause. According to his theory, any patient with shoulder impingement syndrome would directly and immediately benefit from acromioplasty. However this is not the case as some have required further surgery or continued to suffer from pain[161, 162].
Some of the most common conclusions from literature are that there is no difference in outcomes between surgery and exercise[163, 164]. An in-depth review of all trials of the surgery published in 2015 concluded that surgery is not more effect than conservative treatment.
Some of those authors who suggest that surgery does work provide some caveats. Khare et al. suggest that it is good for those who failed to recover using conservative treatment, however the patients in their study received both glenohumeral arthroscopy and subacromial decompression. Ketola et al. on the other hand, suggest that if exercise fails to provide benefit then surgery should not be performed. Others state specific criteria on how to choose patients who will benefit from the surgery[168, 169, 170]. A handful of studies suggest that surgery does work without stating whether patients need to be chosen appropriately[171, 172, 173, 174]. One study concluded that surgery showed benefits after a 12 year follow up. Although, these studies showed benefit, they did not conclude that it was a better treatment option in comparison to physiotherapy or exercise.
The MUJO shoulder impingement treatment
The MUJO shoulder impingement treatment plan has been developed with the findings and conclusions of these studies as its foundation, and has been further enhanced based on the experience and observed database outcomes of various clinicians utilising the MUJO system to successfully treat a range of impingement patients to date.
MUJO treatments typically involve individualised neuromuscular control of the glenohumeral joint and the scapulothoracic gliding plane, involving the entire upper quadrant. The treatment plan is designed to find the root cause of the syndrome and to treat it, but also improve posture, scapular stability and address any muscle imbalance.
At the start of your treatment it is important that a full assessment is performed to gain an informed viewpoint on the particular type of impingement that is presenting. Under supervised guidance you will be asked to perform certain movement paths both on and off the device to pin-point any issues at the neuro-muscular level.
In consultation with your physiotherapist or trainer you will decide on a tailored program that fits in with your schedule to address the underlying deficiency with the goal of providing a longer-term solution to your condition.
The specific program will vary depending on your condition but is likely to be a combination of guided neuromuscular control (Internal and External PNF) exercises to help restore normal muscle activation patterns, assisted stretching / eccentric loading exercises and potentially some basic strengthening movements.
Additionally, certain exercises may be prescribed initially (e.g. very small, controlled movements) to help relieve pain (and turn off the pain-restricting messages in the brain) and de-restrict range of motion to allow you to progress on to complete further full range therapeutic movements.
Shoulder impingement is one of the leading causes of shoulder pain. There are currently four different types of shoulder impingements. Subacromial impingement and internal impingement are the most common. Significant number of investigations have studied the various treatment methods. It is clear from these investigations that some form of physiotherapy provides many benefits. Especially for those that incorporate eccentric training, neuromuscular control relearning or PNF and scapulothoracic strengthening, all individualised to the patient in their regimen. We have developed treatment plans that incorporate all of these methods based on our SMART MSK technology. It is designed to be the best shoulder impingement treatment.
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Overhead activity of the shoulder, especially repeated activity, is a risk factor for shoulder impingement syndrome.