Shoulder Sub-Acromial Impingement

What is Shoulder Impingement?

Relevant anatomy

What is shoulder impingement?

Shoulder impingement is an umbrella term used to describe a certain type of shoulder pain resulting from a few conditions. These include:

The article will describe the conditions and answer the most common questions regarding shoulder impingement in our practice.

Relevant anatomy

The shoulder joint (the glenohumeral joint) is a ball and socket type joint. The ball is formed by the humeral head (the upper end of the arm bone), and the socket is formed by the glenoid, the part of the shoulder blade that articulates with the humerus. There is another smaller joint above the shoulder called the acromioclavicular (AC) joint. This is located between the collar bone (clavicle) and part of the shoulder blade (called the acromion).

The space between the two joints (the glenohumeral and AC joints) is called “the sub-acromial space”. It is very important as it accommodates some key structures, namely the subacromial bursa and the rotator cuff tendons. A bursa is a thin fluid-containing sac usually seen adjacent to a bone to provide cushioning effect and protection. The shoulder bursa is one of the largest in our body and is called (the subacromial bursa). The rotator cuff tendons (mainly the supraspinatus tendon) run between the bursa and the ball of the shoulder joint. These tendons are essential for daily shoulder movements.

Any factor that may result in narrowing the sub-acromial space can cause pinching of the bursa and the rotator cuff tendons. This is referred to as shoulder impingement.

What are the symptoms of shoulder impingement?

- The most common symptom of shoulder impingement is pain that can be felt at the front or back of the shoulder. The pain can also go down into the upper arm. The pain is typically worse when lifting your arm (like reaching for a shelf).

- Reduced range of movement due to pain. Therefore, the condition sometimes is referred to as painful arc syndrome. In more severe cases (like if there is significant subacromial bursitis or rotator cuff tear, the pain could severely interfere with activities and sleep.

What are the causes of shoulder impingement?

As we mentioned above, the three main factors that can result in shoulder impingement are:

Rotator Cuff Disease

The rotator cuff tendons consist of 4 tendons (the supraspinatus, infraspinatus, subscapularis and teres minor tendons). They form a complete cuff of tissue surrounding the shoulder joint and play a vital role in shoulder movement and stability. Dr Al-Ani has published an article about the different conditions that can affect the rotator cuff tendons.

Rotator cuff disease can happen due to repetitive overload or a specific injury. It is one of the common conditions we see in our practice. It can result in thickening and inflammation of the rotator cuff tendons (called tendonitis). In more severe or advanced cases, there could be a tear of the rotator cuff tendons. This could involve part of the tendon thickness (a partial thickness tear) or the rotator cuff tendons' full thickness (a full-thickness tear). To find out more, please see our article about rotator cuff pain.

Sub-acromial bursitis

Shoulder/sub-acromial bursitis can be seen in association with rotator cuff disease. In shoulder bursitis, the bursa becomes inflamed and thickened with fluid build-up. As a result, the bursa could be pinched underneath the acromion, particularly when the arm is raised above the head level. This would result in sub-acromial impingement.

Acromioclavicular joint arthritis

The acromioclavicular joint articulates the clavicle (collar bone) and the acromion (part of the shoulder blade). It is a small joint at the top of the shoulder, different from the main ball and socket glenohumeral shoulder joint. The joint itself can undergo problems leading to pain like injuries or arthritis (wear and tear) changes. In addition, AC joint arthritis can result in bone proliferation around the joint; this is referred to as osteophytes. Downward protruding osteophytes can narrow the underlying sub-acromial space causing pressure upon the sub-acromial bursa and rotator cuff tendons. This would then result in sub-acromial shoulder impingement.

What other conditions can mimic shoulder impingement?

In addition to the conditions described above that can lead to shoulder impingement, a few shoulder problems mimic or overlap with sub-acromial impingement. These include:

How to diagnose shoulder impingement

Subacromial impingement is a clinical diagnosis mainly. Imaging is very useful in confirming the diagnosis and ruling out other causes of shoulder pain. Ultrasound is an excellent modality to assess for any inflammation within the shoulder bursa (sub-acromial bursitis) and the rotator cuff tendons for any tear or inflammation. It can also assess the rotator cuff muscles for any changes in size, which is very useful for management. Dynamic assessment can be performed using ultrasound to look at the movement of the tendons and bursa while lifting the arm. Often, the bursa can be seen pinched during shoulder movement, confirming the diagnosis of shoulder impingement. Ultrasound can also accurately pick up focal areas of calcification within the rotator cuff tendon and diagnose other conditions like calcific tendonitis. More importantly, ultrasound can be used if image-guided treatment is required, as it will ensure accurate delivery of the medicine to the site of inflammation.

A shoulder X-Ray can provide helpful information about the shoulder joint and confirm the presence of calcification. It can also assess the AC joint for any bone spurs formation that could be impinging upon the rotator cuff tendons. Usually, the combination of a shoulder ultrasound and X-ray is very useful in the assessment. MRI shoulder examination can be done if there is diagnostic uncertainty.

Shoulder impingement vs frozen shoulder

Both of these conditions can cause significant shoulder pain. Frozen shoulder is a progressive disease that can worsen over time and has three stages. It is also associated with shoulder stiffness and significant movement limitation, particularly when moving your arm to the outside (external rotation). Shoulder bursitis is usually associated with pain when raising the arm above the head level.

How to treat shoulder impingement?

Management of shoulder impingement is usually aimed at addressing the underlying cause, for example, managing any obvious reason for inflammation of the bursal or rotator cuff tendons. In addition, a physiotherapy exercise program is often required along with anti-inflammatory tablets, icing and activity modification to avoid movements that can worsen the condition. Strengthening exercises to rehabilitate the rotator cuff muscles and patient education about posture and daily activities is also important. Finally, surgical treatment can be indicated in cases not responding to the above measures, particularly in the presence of a full-thickness rotator cuff tear or if there is a large bone spur impinging upon the rotator cuff tendons.

Can steroid injection help with shoulder impingement?

If routine treatment options and physiotherapy are not producing adequate results, then an ultrasound-guided sub-acromial bursa steroid injection can be considered. This is indicated, especially if severe pain interferes with the exercise program. The most common injection treatment is an ultrasound-guided sub-acromial bursa steroid injection. The steroid is a powerful anti-inflammatory medication; injecting it under ultrasound guidance will ensure accuracy. Significant evidence is that injecting ultrasound guidance results in better outcomes. To find out more, please see our article about shoulder steroid injections.

Other treatment options for rotator cuff problems include PRP injection (which might be used for partial thickness rotator cuff tears, but the evidence is inconclusive).

Ultrasound-guided barbotage is a different treatment for shoulder calcification (calcific tendonitis).

Summary

Shoulder impingement is an umbrella term that covers a few conditions, all leading to pinching of the shoulder bursa and rotator cuff tendons resulting in shoulder pain when you lift your arm. Imaging, particularly ultrasound, is very useful in establishing the diagnosis and guiding any injection therapy. An ultrasound-guided cortisone injection is a recognised treatment option for shoulder impingement and sub-acromial bursitis. It usually helps control the pain and allows you to undertake effective rehabilitation.