Painful arc refers to shoulder impingement syndrome. It is characterised by shoulder pain when the arm is raised above the shoulder level (for example, when trying to reach for something high on a shelf). Shoulder impingement is an umbrella term and includes a number of different shoulder conditions. These include:
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 a number of 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 very essential for daily shoulder movements.
Any factor that may result in a narrowing of 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 causes of painful arc/shoulder impingement?
Rotator cuff disease
The rotator cuff consists 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 as a result of repetitive overload or a certain specific injury. In this condition, the rotator cuff tendons get pinched (impinged on) underneath the ligaments and bone (Acromion) when the arm is raised, resulting in the pain characteristic of painful arc syndrome. Rotator cuff disease itself has a range of conditions. In the mild form, there is 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 (referred to as a partial thickness tear) or the full thickness of the rotator cuff tendons (referred to as a full-thickness tear). To find out more, please see our article about rotator cuff pain.
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 painful arc syndrome symptoms.
Acromioclavicular (AC) 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 are the symptoms of painful arc syndrome?
The most common symptom of shoulder impingement/painful arc is shoulder pain. This can be felt at the front, side 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 can happen. In more severe cases (like if there is significant subacromial bursitis or rotator cuff tear, the pain could be severe, interfering with activities and sleep.
What is a painful arc test?
This test is usually done by your doctor to confirm the diagnosis of shoulder impingement. You will be asked to lift up your arm to the side slowly in an arc movement. Typically, there is no pain at the initial part of the movement (0-60 o), and then you will notice shoulder pain in the second part (60-120 o). If you continue above that, usually, the movement is pain-free. You may notice the same pain pattern when bringing your arm down following the same arc movement.
What other conditions can mimic painful arc syndrome/shoulder impingement?
There are a few shoulder problems that can mimic or overlap with sub-acromial impingement. These include:
How to diagnose painful arc syndrome/shoulder impingement?
Sub-acromial impingement is a clinical diagnosis mainly. However, 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. 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.
How to treat shoulder impingement?
Management of shoulder impingement is usually aimed at addressing the underlying cause, for example, managing any obvious reason for bursal or rotator cuff tendons inflammation. 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 are also important. 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 a large bone spur impinging upon the rotator cuff tendons.
Can steroid injections help with shoulder impingement?
If routine treatment options and physiotherapy are not producing adequate results, then an ultrasound guided sub-acromial bursa steroid injection (photo below) can be considered. This is indicated, especially if the pain is severe and interfering with the exercise program. A steroid is a powerful anti-inflammatory medication, and injecting it under ultrasound guidance will ensure accuracy. To find out more, please see our article about shoulder steroid injections. Ultrasound-guided barbotage is a different treatment for shoulder calcification (calcific tendonitis).
Shoulder conditions and treatments