Causes of winging scapula (scapula dysrhythmia)

1. Loss of serratus anterior muscle function
When one talks about winging of the scapula, true winging is due to serratus anterior muscle dysfunction. This is an uncommon condition and may arise from traumatic injury to the nerve supplying the serratus anterior muscle, the long thoracic nerve; or due to damage to the nerve from pressure lesions or a neuritis (inflammation of the nerve).The test for identifying a long thoracic nerve injury is the wall test. The patient is asked to face a wall, standing about two feet from the wall and then push against the wall with flat palms at waist level.
The treatment will depend on the cause and usually an MR scan is helpful to exlcude a mass lesion pressing on the nerve. See the excellent summary by Steven Fromm at http://freespace.virgin.net/steven.fromm/ for much more detail.

2. Loss of trapezius muscle function
The trapezius muscle is a large muscle above your scapula which lifts and rotates your scapula. It is the muscle you use to shrug your shoulders.Isolated loss of trapezius function is extremely rare and may occur after radical neck surgery (for tumours), where the nerve supplying trapezius may be damaged (the spinal accessory nerve).

3. Weakness of all the scapula stabilisers
Muscular dystrophies, most commonly fascioscapulohumeral dystrophy (FSHD), are the main cause of weakness of all the scapula stabilising muscles.

4. Loss of scapular suspensory mechanism
The coracoclavicular ligaments suspend the scapula from the clavicle and the acromioclavicular joint is the only joint linking the scapula to the rest of the body. Therefore dislocation of the acromioclavicular joint or a fracture of the outer third of the clavicle, with rupture of the coracoclavicular ligaments, leads to an abnormal scapula rhythm and apparent scapula winging with overhead manouevers. This is usually not painful and usually only affects overhead workers and athletes.
Another rare cause is the 'scapulothoracic dissociation', described by Rockwood & Matsen in 1990. The scapula is wrenched from the body in violent trauma leading to fracture of the clavicle and soft tissues around the clavicle.

5. Winging of the scapula secondary to instability
This is one of the commonest causes of scapula dysrythmia (and winging). Recurrent dislocations of the shoulder leads to dysfunction of the muscles that move and support the shoulder complex and scapula. The more frequent the dislocations and the less trauma involved in causing the dislocations, the worse the scapula dysryrhmia (winging). An essential part of treating shoulder instability (recurrent dislocations) is treating the scapula dysrythmia. This is done by an experienced physiotherapist in association with a shoulder surgeon.

6. Winging secondary to pain
This is another common cause of econdary winging and dysrhythmia of the scapula. Any painful condition of the shoulder will lead to abnormal movements of the entire shoulder complex. Reduced movement at the glenohumeral joint will lead to more compenatory movement at the scapula.

7. Brachial Plexus injury or disease
Most of the nerves supplying the stabilising muscles of the scapula arise from the Brachial Plexus. The Brachial Plexus is a bundle of nerves running from the neck to the arm. It carries the nerve supply for the muscles of the arm and shoulder. Sometimes a major accident can affect the muscles of the shoulder more than the arm and lead to winging. When there is no trauma, a condition known as Parsonage-Turner syndrome (Brachial Neuritis) can lead to weakness of the scapula muscles.