Subacromial Pain Syndrome

Introduction

This page addresses the situation known as the following:

• Subacromial impingement syndrome (SIS)
• Subacromial pain syndrome (SAPS)
• Rotator cuff related disorders
• Biomechanical impingement of the shoulder

There has been considerable controversy regarding the diagnosis of nontraumatic shoulder pain involving the structures of the subacromial space. The diagnostic label Subacromial Impingement Syndrome (SIS) presenting as anterograde-lateral shoulder pain with arm elevation was the first introduced by Dr. Charles Neer in 1972 and based on the method of creating the structure of the subacromial space.[1][2][3] SIS has been considered a sign of irritation of the subacromial structures between the coracoacromial arch and the humeral head during elevation arm of the shoulder/head [1] and as revealed by the literature is considered by many to be one of the most common causes of shoulder pain.

What is important to understand is that impingement itself is not diagnostic but merely descriptive of the process:

Compression of the rotator cuff against the acromion and the anterior surface of the coracoacromial ligament.

Neers Classification of Impingement identified four types of shoulder impingement shown below;

Neer Classification of Subacromial Impingement

According to Neer, impingement syndrome is divided into three categories:

Type I: <25 years Reversible Swelling Tendonitis No Tear Treatment.

• Moderate pain during exercise loss of strength and no restriction of movement. Edema and/or bleeding may occur. This stage usually occurs in patients younger than 25 years and is often associated with overuse injury. At this point, relapse may be possible. [4] .

Option II: 25-40 Year Old Permanent Scarring Tendonitis No Tear Subacromial Decompression

• Pain is frequently reported during ADL and especially at night. loss of mobility is associated with this phase. Type II is more advanced and occurs more frequently in patients between 25 and 40 years of age. Pathological changes show fibrosis as well as irreversible vascular changes.[4]

Type III: >40 years Small Rotator Cuff Tear Subacromial Decompression combined with Debridement/Repair

Type IV: >40 years Large Rotator Cuff Tear Sub Acromial Decompression repaired

While the Neers Classification of SIS was the main tool for understanding shoulder disease at the time, SIS was further divided into four subcategories related to External Impingement (Primary or Secondary) and Internal Impingement.

External Impingement

Figure 1. Acromion Shapes

• Primary External Impingement involving congenital or acquired structural changes that mechanically reduce the subacromial space such as; thinning or osteophyte formation of bones that are not stable after a fracture or increased levels of the subacromial soft nerves.[5][6][7][8][10][11][12][14][15] [16]The shape of the acromion system in the scapula or shoulder can play an important role in recovery and healing from primary impingement.
• Secondary External Impingement involving abnormal force balance changes of scapulothoracic kinematics causing functional disturbances in the center of the humeral head resulting in abnormal central rotation movement when the arm is elevated. Usually as a result of weakness a Rotator Cuff Muscles (functional instability) together with the glenohumeral joint capsule and ligaments that must be weak (micro-instability). Impingement usually occurs in the coracoacromial space secondary to the anterior translation of the humeral head as opposed to the Subacromial space seen in primary impingement. It usually occurs in younger individuals with pain in the anterior or posterior region of the shoulder. The symptoms are usually activity specific and involve handedness.[8][9][10][11][17][18][19][8][21]

Internal Impingement

• Internal Glenoid Impingement is probably the most common cause of posterior shoulder pain in an athlete who throws or climbs overhead. It is caused by impinging on the articular surface (intra-articular) of the Rotator Cuff (posterior edge of the supraspinatus and anterior edge of the infraspinatus). the posterior-superior glenoid and glenoid labrum. Especially seen in the upper repetitive activities of this position becomes pathologic when excessive external rotation anterior capsular instability scapular muscle imbalances[20] and/or when there is frequent overload of the rotator cuff muscle [21] [17] [18] [19] [8] [20] These deficiencies result in poor scapulohumeral control.

This definition and description of SIS is based on the concept that acromial irritation causes external abrasion of the bursa rotator cuff or other structures in the subacromial space.[3] Throughout the years the presentation progressed from SIS to ‘impingement related shoulder pain’ with the increasing notion that ‘impingement’ represents a cluster of symptoms and the possible course of pain rather than the diagnostic pathology itself. This remained the dominant theory of injury to structures in the subacromial space 40 years ago and has been the rationale for informing clinical trials of therapeutic surgical techniques and rehabilitation programs[2] but the validity of this model of acromial impingement has been challenged from a theoretical and practical perspective throughout the last decade by suggestions that The use of SIS terminology may contribute to negative expectations regarding conservative exercises and treatments for patients that may compromise outcomes often leading to increased surgical intervention they are.[22][2][3][22]

While there is ongoing controversy surrounding diagnostic labeling with many different terms being used to describe subacromial pain and it’s pathology in the literature it has been suggested that the label of SIS does not adequately describe the mechanism. Many other diagnostic characters have have proposed but shown that the term Subacromial Pain Syndrome (SAPS) best describes pain thought to be caused by structures between the acromion and humeral head that are often associated with some degree of shoulder dysfunction[23] but do not reflect features of many others which causes the shoulder pain outside the subacromial space.

Bottom line:

• Subacromial impingement: Bursal side
• Internal impingement: Articular side
• Intrinsic mechanisms: Within the tendons
• Extrinsic mechanisms: External to the tissues.

Definition/Description

Subacromial Pain Syndrome is defined by Diercks and colleagues [23] as all non-traumatic typically unilateral shoulder problems resulting in localized pain around the acromion that often worsens with or after arm elevation . . . . Basically, it is a general term that includes the pain associated with any wound in a structure or arrangement within the Subacromial Space. As such the SAPS includes all conditions involving subacromial structures such as subacromial bursitis calcific tendonitis rotator cuff tendinopathy rotator cuff tears biceps tendinopathy or resulting tendon cuff degeneration controversy surrounding the etiology.[23] [24]Subacromial pain syndrome is poorly understood despite being a common finding.[25]

Clinically Relevant Anatomy

The Subacromial Space is the space below the acromion (between the acromion and the top of the humeral head). This space is defined by the acromion and coracoid process (which are parts of the scapula) and the coracoacromial ligament that connects the two. [26] .

Figure 2. Subacromial Structures

The Subacromial Space measures 2 to 17 millimeters depending on the position of the arm and has the following anatomical structures: [9][3][27]

• Coracoacromial Arch consisting of Acromion Coracoid Process and Coracoacromial Ligaments[7].
• Humeral Head
• Subacromial Bursa[28]
• Muscles of the Rotator Cuff; Supraspinatus Infraspinatus Teres Younger and Subscapularis
• Tendon of the Long Head of the Biceps Brachii
• Coracoacromial ligament
• G-H Joint Capsule

Shoulder Biomechanics Review

It is important to remember that shoulder movement does not occur in isolation of the GH joint. As the arm is raised, the following events/movements occur in the shoulder flexors:

• Backward roll and inferior glide of the humeral head.
• Posterior posterior rotation: to activate the posterior pelvis during elevation and posterior rotation of the acromion and help maintain the subacromial space.
• Posterior rotation of the scapular: showing the medial border of the scapula toward the thoracic spine and chest wall. As your humerus rotates externally, the scapular follows that into external rotation.
• The end of a horizontal scapular posterior tilt (the inferior angle of the scapula will move against the chest wall).
• Also upward rotation of the scapular: the inferior aspect of the scapula leaves the thoracic spine.

Usually it is the upward rotation of the scapula that causes the acromion to rise; maintaining that acromio-humeral distance and reducing the possibility of impact by objects in the subacromial space. The upward rotation movement is usually performed with the recruitment of the segments of the trapezius muscle (upper / middle / lower). It is also this movement (upward rotation) that allows the glenoid fossa to follow the humeral head to maintain alignment when the arm is elevated.

Scapulohumeral Rhythm: The ratio of GH stimulation to scapulothoracic motion during arm elevation. Overall, the value ratio is 2:1; meaning that for every 1 scapular rotation we see 2 degrees of humeral elevation – for example, a 180-degree range of motion for elevation we would see 60 degrees scapular upward rotation with 120 degrees of humeral abduction. But the ratio isn’t perfect on a full arc with high shoulders.

The importance of rotating the spine during elevation:

During the arm raise, there is generally an external (external) rotation of the lumbar spine. When the timing of the movement is correct, this increased external rotation of the humerus allows to avoid compression of the greater tuberosity against the subacromial structures. If the time frame abnormal (neuromuscular recruitment internal rotation of the humerus or dysfunctional biomechanics of the shoulder complex) the necessary external rotation will not occur and the greater tuberosity will invade the structures and irritate the muscles.

See the Physiopedia page on Shoulder Biomechanics for more information.

Prevalence/Incidence

SAPS is the most common shoulder disorder[29] accounting for 44% to 65% of all shoulder pain complaints [30] with incidence increasing with age.[31] The peak occurs in the sixth decade of life.[32]

Etiology

Controversy remains regarding the etiology of subacromial pain but mechanisms are suggested to include alterations of extrinsic and combined factors including muscle imbalances and anatomical factors that may affect the subacromial space in acromial shape; the slope of the face; anterior acromion; and the extension of the acromion posterior to the humeral head. Osseous changes in the lower acromioclavicular joint or coracoacromial ligament may also affect the subacromial space. [24] .

While it is recognized that many factors are involved in the pathology many issues remain unresolved such as: which subacromial system is first involved by the pathology and what are the mechanisms responsible for pain? [24] .

Contributing Factors

There are intrinsic and extrinsic factors that can contribute to decreased subacromial space during arm raising.

Physical properties: (usually irreversible) .

• Tendon histology (quality of tendon) .
• Age
• Genetics

External features: (subject to change) .

• Muscle extensibility / performance
• Anatomical/osseous
• GH joint kinematics
• Posture/ergonomics

Different types of impingement

Subacromial posterior flexion: Bursal. Pressure due to subacromial (AHD) space reduction. The pain is usually located on the anterior aspect of the shoulder.

Internal Impact: Articular. It is formed by the articular portion of the supra/infraspinatus and the posterosuperior rim of the glenoid. The pain is located outside the joint when it is in the ABER (throw) position.

Subcoracoid impingement: A history of dull pain in the anterior part of the shoulder. It is aggravated due to the shoulder in forward flexion ADDuction and internal (internal) rotation (like the motion of hitting the ball racket).

Impingement Mechanisms

There are 3 main ways that can affect the distance/space of the subacromial space (acromio-humeral distance) .

1. Loss of control of the humeral head (GH instability) .
2. Loss of scapular control (scapular instability) .
3. Change to the actual size of structures in the space (the root subacromial bursae of the RC muscle for example).

Intrinsic Mechanisms: What can most affect the properties of the subacromial space?

Loads on the tissue (shear or compressive forces). Tendon overload due to excessive or repetitive forces on the tendon. This can lead to reactive tendinopathy or tendon dysrepair (causing painful reactions to movement). Keep in mind that changes in muscle mass are normal based on activity number and age.

Clinical Presentation

Figure 3. Painful Arc

Affected patients are usually over 40 years of age and suffer from chronic pain with no known history of trauma.[33] Patients report pain when the arm is raised between 70 ° and 120 ° within the “Painful Arc” (Figure 3) during forced movement above the head and when lying on the bite the side.[17] Symptoms can be acute or chronic. Usually it is a gradual inflammatory condition that is internalized rather than caused by strong external forces. It is therefore often difficult for patients to pinpoint the exact onset of symptoms.

In recent studies there has been more discussion of GIRD (Glenohumeral Internal Rotation Deficit) which can be understood as a loss of internal (internal) rotation range occurring where all rotation is lost (overall assessment where the two shoulders all move together).

GIRD = (side-to-side difference in ER) + (side-to-side difference in IR) .

It has been suggested that a contributing factor to GIRD is thickening of the external GH capsule limiting all internal circulation of the GH joint.

Differential Diagnosis

There are several shoulder conditions that can initially be confused with subacromial pain syndrome [34]. A thorough physical examination should exclude other conditions such as [35]:

• Rotator Cuff Tears (Partial / Full)
• Thoracic Outlet Syndrome (TOS)
• Cervical Spondylosis
• Subluxating Shoulder
• SLAP or labral lesions
• Acromioclavicular Joint Disorders
• Adhesive Capsulitis (Frozen Shoulder)
• Glenohumeral Arthritis
• Paralysis of the Trapezius
• Calcific Tendinopathy
• Subacromial Bursitis
• Arthropathy
• Glenohumeral Instability
• Cervical radicular pain or referred cervical facet pain
• Nerve Palsy

Physical Examination

A detailed history and clinical examination are necessary to diagnose SAPS. No single test is accurate enough to diagnose SAPS or to adequately differentiate between different shoulder pathologies [36][37] but using a combination of specific tests provides a possibility of post-test … Evaluation of the SAPS. [38] [39] [40]

The Dutch Orthopedic Association Guidelines [23] on the diagnosis and treatment of subacromial pain syndrome recommend the inclusion of the following tests (pain trigger tests) to aid in the diagnosis;

• Hawkins-Kennedy Test
• Painful Arc Test
• Infraspinatus (External Rotation) Resistance Test

The combination of the Hawkins-Kennedy Test the Painful Arc and the Infraspinatus Resistance Test has a significantly higher predictive value;[23][42]

• Screening 3 is positive: the probability that the patient has SAPS is (1056) [42].
• Criterion 2 is positive: the probability that the patient has SAPS is (503) [42].
• 1 test is positive: the probability that the patient has SAPS is (090) [42].
• 0 test is positive: the probability that the patient has SAPS is (017) [42].

The following additional tests should also be used to rule out a Rotator Cuff Tear;

• Drop Arm Test: To test the integrity of the Supraspinatus. [43] .

There is also the Neer impingement test, which specifically evaluates subacromial impingement, and the Hawkins-Kennedy test, which evaluates for the presence of coracoid impingement.

Considerations for muscle dysfunction of the scapula (to be considered and assessed carefully when possible):

• Loss of dynamic stability of the scapula
• Pectoralis minor length and flexibility
• Scapular muscle performance and endurance
• Thoracic spine function/mobility
• Range of motion of GH joint (stiff joint capsule or even GH instability) .
• Rotator cuff muscle balance (agonist/antagonist / synergistic muscle activity) performance and muscle endurance.

Other considerations:

• Capsular tightness: A specific assessment of the external capsule that can restrict the area of motion in internal rotation (GIRD).
• Failure to extend external rotators (infraspinatus/teres minor).
• Muscle strength without muscle control or external rotators (infraspinatus/teres minor) endurance.
• Lack of rotational extension (lattissimus dorsi and pectoralis minor for example).
• Contribution of the serratus anterior muscle to the movement of the scapula (upward rotation of the external rotation and extension of the scapula) during elevation.
• Thoracic spine and rib cage movement. Good spinal and rib stimulation will not interfere with any movement of the shoulder or scapular complex during overhead running.

Diagnostic Procedures

Overall considerations

There are physiological factors that can influence narrowing of the subacromial space such as:

• Presence of subacromial bone spur (which may cause thickening or calcification of the coracoacromial ligament) .
• Shape of the acromion (type I (flat) / type II (curved)/ type III (hook)/ type IV (curved acromion)) .
• AC joint arthritis (surrounding tissue damage) .
• Instability of the humeral head (the GH joint) .

Radiographs can be used to identify anatomical changes in the form of calcific deposits or acromioclavicular joint arthritis. Three recommended views are:[44]

• Antero-posterior View with the arm in 30 degrees external rotation useful for evaluation of glenohumeral joint subacromial osteophytes and sclerosis of the greater tuberosity.
• Outlet Y View is useful because it shows the subacromial space and can differentiate the acromial processes.
• Axillary View helps in visualizing the acromion as well as the coracoid and coracoacromial ligament calcifications of the process.

The size of the subacromial space can also be measured. MRI may show complete or partial tears of the rotator cuff ligaments and inflammation into soft tissue. Ultrasound and arthrography are being used when rotator cuff tears are suspected or in complex cases.[4]

There is a good clinico-radiological correlation between subacromial pain syndrome and ultrasound findings.[45] The diagnostic accuracy of ultrasound is considered to be good and comparable to conventional MRI for detecting and quantifying complete (full-thickness) rotator cuff lesions injuries. The sensitivity and specificity of conventional ultrasound and MRI are not significantly different from the detection of partial or full-thickness rotator cuff tears using MR Arthrography technique which is an accurate method of excision of rotator cuff injuries partly from there.

The Dutch Orthopedic Association Guidelines arise that ultrasounds are used the most valuable and cost-effective diagnostic imaging as the first time conservative treatment fails recommended that they can be combined with conventional radiography of the shoulder see osteoarthritis osseous abnormalities and presence/absence of calcium. It is suggested that where reliable ultrasound is unavailable or incomplete, then MRI of the shoulder is indicated and should be used in patients eligible for surgical repair of rotator cuff tears to assess pull about the depth of the and impaired lipid metabolism. Contrast-enhanced MRI examination may be considered if a tendon abnormality or partial rotator cuff injury should be ruled out. Studies of abduction and external rotation (ABER) are ideally part of the MR arhrography protocol. [23] .

Treatment/Management

Treatment depends on the age activity and overall health of the patient. The goal is to reduce pain and restore function. Preventive therapy is the first line of treatment and should be considered for approximately a year until improvement is noted and return to function is observed.[46] Surgery should only be considered if the patient has not responded to definitive nonsurgical treatment. [23] .

Conservative treatments are; decreased relaxation in enhancement activities especially surface activities NSAIDs for reducing pain and inflammation for physical therapy use and subacromial injection. Cortisone is commonly used for its anti-inflammatory and pain reducing properties but this is an argument based on an involved system and should not be used in neuropathic pain.[47]

There is no conclusive evidence that surgical treatment is more effective than conservative treatment and surgery should be considered when conservative treatment fails to reduce pain only on or inactivates it. There are many surgical options depending on the type and severity is available but there is no clear preference for the surgical approach at present.[23][48]

• Surgery A muscle tear, mostly the long head of the supraspinatus muscle, within the biceps tendon or joint capsule. Note: a rotator cuff tear is not an indication for surgery. [34] .
• Bursectomy or removal of the subacromial bursa.
• Subacromial Decompression to increase the subacromial space by removing cartilaginous or bony exposures under the os acromiale or coracoacromial ligament
• Acromioplasty increases the subacromial space by removing a portion of the acromion. Arthroscopic acromioplasty is less invasive and requires less reconstruction than open (Neer) acromioplasty.

Currently no difference in outcome (shoulder functional complications) has been demonstrated between an arthroscopic approach and an open approach to bursectomy that is likely to yield the same clinical outcome as bursectomy with acromioplasty.

[49][50]

Physical Therapy Management

There is strong evidence that nonsurgical supervised treatment reduces shoulder pain and increases function.[28] Non-surgical treatment should therefore be attempted first assuming that there is no tear that requires surgery. (4 proofs) .

Physical therapy management includes:

• RICE treatment in acute phase to reduce pain and inflammation
• Exercises to correct stability and posture (anterior head tilt/kyphosis) .
• Movement exercises (cervical spine / thoracic spine / upper extremity in general / GH joints and spine) .
• Manual treatment of the uterus and / or thoracic spine (also a tracheostomy) .
• Strength and Neuromuscular control exercises
• Stretching exercises including capsular stretching
• Manual therapy techniques for the shoulder
• Taping techniques (kinesiology taping or rigid scapular taping for example) .
• Acupuncture
• Electrical stimulation
• Ultrasound and musculoskeletal ultrasound
• Low-dose laser therapy has a positive effect on all symptoms except muscle strength[51] (Evidence level 1b) .
• Corticosteroid injections for the first 8 weeks
• High-energy extracorporeal shockwave therapy (ESWT) is more effective than low-energy ESWT ESWT is not recommended in the acute phase.[52](Level of Evidence 2a)

If the patient is presented with acute pain they should first be stabilized then strength / neuromuscular re-education exercises should be used to prevent future injury. Although physical therapy alone has proven effective, the addition of manual therapy ensures a further increase in muscle strength.[53] Physical therapy is a mainstay in the treatment of subacromial impingement but the results showed no significant difference between home-based and outpatient physiotherapy. (Proof number 1b) .

Strengthening exercises should include[54]: (Proof number 1a) .

• Rotator cuff strength such as; external circulation of thera-tubing (therabands).
• Lower and middle trapezius strengthening such as; Press up Unilateral scapular rotation
• Bilateral shoulder external rotation.
• Unilateral shoulder depression.
• Strengthening the lower portion of the trapezius muscle is an important part of exercise therapy. Individuals with impingement syndrome exhibit greater upper and lower trapezius activity than asymptomatic individuals.[55] (Level of proof 3b) .

In general, muscles that will require specific attention and neuromuscular redefinition include (but must be assessed individually to achieve a tailored rehabilitation plan):

• Rotator cuff (mainly external rotators – infraspinatus and teres minor) .
• Latissimus dorsi muscle
• Serratus anterior
• All parts of the trapezius muscle (upper/middle/lower) .
• Pectoralis major and minor
• A general and global approach to the development of scapular muscles to promote normal function and timing of upward rotation of the scapular and external rotation during elevation . . . . A recent study has shown that scapular-focused interventions can improve transient shoulder pain and exercise
• The medial location of the humeral head in the glenoid fossa (mainly the rotator cuff muscles).
• It is also wise to check the resistance of the deep neck muscles and the broad thoracic muscles.

Specific exercise protocols that focus on strengthening eccentric exercises for the rotator cuff and concentric/eccentric exercises for the scapula stabilizers are effective in reducing pain and improves shoulder function. [56] (Proof above 1b) .

Soft tissue mobilization to relieve cartilage and other muscle dysfunction has been shown to be effective along with joint mobilization to restore motion in the treatment of SAI.[55] (Level of proof 3b) .

A combination of physical therapy and surgical treatment will provide better clinical outcomes than physical therapy alone.[57] (Level of proof 2b) .

Movement of the rotator cuff with emphasis on strengthening and internal rotation following rotation and abduction. It is important to remember that the role of the rotator cuff in addition to producing torque is to stabilize the glenohumeral joint. So rotator cuff muscle stiffness it provides better stability of the glenohumeral joint and less flexion. The first typical exercise program involves the use of 4 to 8 weights with 10 to 40 repetitions three to five times per week. A recent study investigated the effectiveness of high-intensity aerobic interval training rotator cuff exercise and found that it appeared to be a useful intervention in SAPS[58].

Patients with Stage II impingement may require a standardized exercise program. Isometric stretches are useful in restoring range of motion. Isotonic (fixed-weight) exercise is a better alternative to variable-weight exercise. The shoulder exercises should therefore be performed with fixed weights rather than a variable weight such as rubber bands. Repetition is emphasized and relative lightness is used. Sometimes sport-specific techniques are especially useful for reinforcing throwing in service movements or swimming. In addition, physical therapy techniques such as electrogalvanic stimulation ultrasound therapy and transverse friction massage may be helpful.[59] (Level of proof 2b) .

How is GIRD (GH internal rotation deficit) dealt with:

• Extended sleep (targeting the posterior capsule).
• Cross-body ADDuction is available in elevated positions (also targeting portions of the posterior capsule) with or without posterior glides.
• Infraspinatus/teres minor re-education (addressing imbalances strength neuromuscular control and muscle recruitment & en

Clinical Bottom Line

• Impingement isn’t a diagnosis – it’s a tool.
• The subacromial space is reduced – wonder why this is happening.
  • Bony factors (humeral head, acromion)?
  • Causes of muscle atrophy (rotational failure to extend the coracoacromial ligament tight posterior capsule)?
  • Abnormal regulation of neuromuscular control (GH joint rotator cuff muscles scapular muscles the posterior rotators and their strength recruitment patterns and overall endurance)?
• Control of the GH joint (instabilities).
• Control of the scapula (overall muscle control).
• Consider the role of the whole kinetic chain of the north.
• Locomotion and contribution of the cervical spinal cord pulmonary spinal cord and bronchial tube.
• Non-surgical management of this shoulder classification is quite good you just need to prescribe a minimum number of exercises (quality over quantity!) .
• To challenge the patient’s dysfunction, a minimum of 12 weeks is recommended.
• All imaging is not considered useful unless the patient has not responded as expected or you have a Red Flag presentation.
• Steroid injections should not be considered a first-line intervention unless the pain is severe enough to preclude participation in conditioning or exercise.