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Subacromial Impingement

Subacromial impingement (also known as shoulder impingement syndrome or subacromial pain syndrome) is defined as a clinical syndrome that occurs when the tendons of the rotator cuff muscles, which pass through the subacromial space, become irritated and inflamed. The subacromial space is the area directly beneath the acromion. Subacromial impingement is a common condition seen in sporting populations and in older age. There are two main types of subacromial impingement: internal and external. There is solid evidence that physical therapy is useful in reducing pain and improving function in patients with subacromial impingement.


subacromial impingement

What is the subacromial space?

The subacromial space is the area below the acromion (between the acromion and the top surface of the humeral head). This space is marked by the acromion and the coracoid process (which are parts of the scapula), and the coraco-acromial ligament which connects the two. The subacromial space contains the rotator cuff with the overlying subacromial bursa.

What is the rotator cuff?

The rotator cuff within the subacromial space consists of the tendinous parts of four muscles: supraspinatus, infraspinatus, teres minor and subscapularis. The rotator cuff has three important functions:

  1. Stabilises the humeral head (of the arm bone) in the glenoid socket (shallow groove made by the scapula) during shoulder movements
  2. Controls inward and outward rotation of the shoulder
  3. Fine tunes forward flexion and lateral abduction of the shoulder

What is the subacromial bursa?

A bursa is essentially a fluid-filled sac. The sac is filled with synovial fluid, a viscous fluid found in the cavities of synovial joints. It aims to to reduce friction between the articular cartilage of synovial joints during movement. The subacromial bursa is located below the acromion and communicates with the subdeltoid bursa forming the subacromial-subdeltoid bursa (SSB). The SSB decreases friction and allows free movement of the rotator cuff relative to the coracoacromial arch and the deltoid muscle.

External impingement

  1. Primary External Impingement (PEI): PEI refers to anatomical changes that are observed either at birth (i.e., congenital) or acquired (i.e., occurs after birth). Examples include narrowing of the subacromial space from osteophyte formation (i.e., bone spurs) or malposition after fracture of the shoulder or acromion. The shape of the acromion also plays an important part PEI.
  2. Secondary External Impingement (SEI): SEI refers to an abnormality in the movement of the scapula and mid back (i.e., scapulothoracic kinematics), strength balance loss in the rotator cuff muscles or of the joint capsule and surrounding ligaments, causing functional issues with centring the humerus on the glenoid of the scapula, which leads to abnormal displacement of the shoulder when the arm is elevated, compressing the contents of the subacromial space.

Internal impingement

Internal Impingement (IG) is the most common cause of shoulder pain in the throwing or overhead athlete. IG is caused by impingement of the articular surface (i.e., intra-articular) of the rotator cuff against the posterior-superior-glenoid and glenoid labrum. IG is mainly seen in athletes who do a lot of repetitive overhead activities. With excessive actitivity of this nature, pathological changes in the subacromial space can occur leading to impingement. Examples of these changes include anterior capsular instability, rotator cuff imbalances, weaknesses or injury. These changes cause poor scapulohumeral control.

Incidence and cause of subacromial impingement

Subacromial impingement is the most common disorder of the shoulder, accounting for 44-65% of all shoulder complaints and the incidence increases with age, peaking during the sixth decade of life.

The exact cause of subacromial impingement is somewhat unclear to medical science. It is suggested that the mechanisms include intrinsic, extrinsic and combined factors as mentioned above. Repetitive overhead activity, such as that seen in overhead throwing and lifting, appear to be risk factors for subacromial impingement. There are several structures within the subacromial space, and thus several tissues can be in lesion.

Signs and symptoms of subacromial impingement

Patients describe persistent shoulder pain without any known trauma. Pain is often located superiorly or anteriorly and described as sharp upon movement. Most pain is present on elevating the arm between 70° and 120°, which is referred to as the “Painful Arc”, on forced movement above the head and when lying on the painful side. Symptoms can be acute (>0–4 days), subacute (5–14 days) or chronic (>14 days). Pain often develops gradually and alongside degenerative changes that lead to “impingement”, and thus patients have difficulty remembering the exact onset of symptoms.

Physical therapy of subacromial impingement

There is strong-quality evidence that a gradually progressive physical therapy regime decreases shoulder pain and improves function. Non-operative treatment should be the first line of defence in treating subacromial impingement, assuming there is no tear that requires surgery.

Conservative management includes:

  • P.O.L.I.C.E protocol in the acute phase to reduce pain and swelling
  • Shoulder and scapulothoracic stability and postural correction exercises
  • Shoulder, scapulothoracic and periscapular strengthening, stretching and mobility exercises
  • Manual therapy techniques of the shoulder including soft tissue massage
  • Dry needling therapy
  • Ultrasound therapy
  • Low-level laser therapy, which has positive effects on all symptoms except on muscle strength

A controlled, graded and progressive exercise program with the aim of reducing inflammation and strengthening the surrounding musculature should be the first rehabilitative steps taken in managing subacromial impingement. The following steps should be taken:

Isometric exercises

Isometric exercises (i.e., force through muscle and tendon without changing its length) are often the first exercise given in the acute pain phase, as they have been shown to help reduce self-reported pain. An example of an isometric exercise used for subacromial impingement is a sustained scaption exercise either closed-chain (e.g., theraband) or open-chain (e.g., dumbbell). During this phase, soft tissue massage, ultrasound and dry needling therapy may provide additional benefit.

Slow-heavy concentric and eccentric exercises

Once pain has subsided enough, the patient can progress to slow-heavy resistance training. Concentric (i.e., muscle shortens under load) exercises are often first explored, followed by eccentric (i.e., muscle lengthens under load) exercises. These can include repetitive scaption and external rotation exercises with therabands and weights, and can lead into more functional exercises, such as a push-up progression or sport-specific exercises including handed throws, wall dribbles, and plyometric step and throws.

Tendon energy absorption and release exercises

The final two steps in optimal shoulder impingement rehab aim to strengthen tendons of the rotator cuff by absorbing kinetic energy into the tissue, and then releasing it like a spring. These types of exercises include fast arm throwing, overhead throwing, dynamic pylometric throwing, medicine ball work and sport-specific drills of varying intensity.

Final thoughts

The effectiveness of physical therapy for shoulder impingement is good, particuarly if rehab is applied as soon as possible. However, shoulder rehab can be a challenging task in terms of frequency and intensity of exercises, sometimes taking up to 3 months to fully resolve, and also relies heavily on patient compliance to exercise.

At Sydney Spine & Sports Centre (S3C), our clinicians are highly skilled and trained to identify, treat and rehab shoulder impingement and pain syndrome, using the latest evidence-based guidelines and techniques. If you have shoulder pain, make an appointment with one of our clinician’s today.

More information

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Chris Knee

Chris is an experienced and qualified chiropractor, sports chiropractor, McKenzie Credentialed practitioner, nutritionist and Certified Strength and Conditioning Specialist (CSCS) and is finishing of his Doctor of Physiotherapy at Macquarie University.