What is Supraspinatus tendinitis (painful arc syndrome)

Supraspinatus tendinitis or painful arc syndrome occurs in the shoulder.

The shoulder joint owes its stability to the ‘rotator cuff’ muscles – which are four small muscles located around the shoulder joint which help with movement, but importantly their tendons stabilise the head of the humerus within the joint capsule.

The tendon of one of these muscles – the supraspinatus commonly impinges on the acromion (the bone forming the tip of the shoulder) as it passes between the acromion and the humeral head. The supraspinatus muscles helps abduct (lift up sideways) the arm. Any friction between the tendon and the acromion is normally reduced by the subacromial bursa – a fluid filled sac between the supraspinatus tendon and the acromion.

Sometimes, with wear and tear supraspinatus tendinitis results, which is commonly associated with inflammation of the bursa – subacromial bursitis. There may even be little tears in the tendon fibres – partial tears or sometimes even complete tears.

Tendinitis and partial tears in the supraspinatus tendon causes a ‘painful arc’ since as the person elevates his arm sideways, the tendon begins to impinge under the acromion throught the middle part of the arc, and this is usually relieved as the arm reaches 180 degrees (vertical).

There may be other causes of a painful arc. Arthritis of the acromio-clavicular joint (at the tip of the shoulder) may also cause pain– but that is typically at the end of the arc – when the arm is almost vertical.

Statistics on Supraspinatus tendinitis (painful arc syndrome)

Supraspinatus tendinitis is very common, it the most common inflammatory problem encountered around the shoulder joint. It is typically seen in people aged 25-60.

Risk Factors for Supraspinatus tendinitis (painful arc syndrome)

  • The tendinitis results usually from chronic wear and tear of the supraspinatus tendon as it passes under the acromion – this may be in sports-people and people that do a lot of overhead work though it may occur in any person.
  • Anatomical factors such as the shape of the acromion or a tight subacromial space due to a thickened ligament may be predisposing factors.
  • Tears in the tendon of the supraspinatus or other rotator cuff muscles (commonly occur together) often result from a fall on the shoulder, usually in older people. They can also result from attrition – gradual degeneration with wear and tear, or other inflammatory disorders such as rheumatoid arthritis.

Progression of Supraspinatus tendinitis (painful arc syndrome)

  • The tendinitis results from trauma (e.g. a fall, dog on leash) in around 30% of cases.
  • 5% of cases are bilateral (involving both shoulders).
  • The pain will severely limit shoulder movement and may cause secondary muscular neck pains.

How is Supraspinatus tendinitis (painful arc syndrome) Diagnosed?

  • An x-ray may show calcification in calcific tendinitis.
  • X-rays can be useful in determining the acromial anatomy though they will not help with diagnosing soft tissue problems such as tendon tears or bursitis.

Prognosis of Supraspinatus tendinitis (painful arc syndrome)

  • Around 70% of patients with tendinitis will improve over 5-20 days and mobilize the joint themselves, though treatment with physiotherapy and steroid injections will help. Further tendinitis and even partial or complete tears may occur in the future.
  • Complete tears are treated surgically in young people, though this may be harder in older people or patients with other causes such as rheumatoid arthritis.
  • Chronic trauma and impingement may lead to osteoarthritis of the shoulder in the long term.

How is Supraspinatus tendinitis (painful arc syndrome) Treated?

  • Rest is important during the initial phase of tendinitis to allow the inflammation to settle.
  • Analgesics such as NSAIDs – naprosyn 250mg three times daily with food.
  • Injection of corticosteroid (e.g. triamcinolone acetate 40mg) with local anesthetic into the subacromial bursa or the supraspinatus tendon itself will help (though there may be an increase in discomfort in the first 48 hours).
  • Calcific tendinitis may require aspiration and injection of steroid into the joint or even surgical removal of the calcium crystals.
  • A surgical arthroscopic (inserting a tiny camera into the shoulder joint through a small cut under anesthetic) acromioplasty – i.e. re-shaping the acromion or dividing the coracoacromial ligament is required often to prevent further episodes.
  • At the same time the rotator cuff tendons can be repaired – though this may be difficult if left too late and the tendon retracts.

Supraspinatus tendinitis (painful arc syndrome) References

  1. Collier, J., Longmore M., Brown TD., Oxford Handbook of Clinical Specialties 5th Ed.
  2. Kumar P, Clark M. CLINICAL MEDICINE. WB Saunders 2002;
  3. Murtagh, J. General Practice. Second Ed. McGraw-Hill, 1998.

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