Winging of the scapula has THREE causes, each with different nerves and different clinical signs
one is caused by the long thoracic nerve and paralysis of serratus anterior - upward and outward movement of the scapula is caused by activation of SA ie pushing against a wall
the second is caused by a lesion to the spinal accessory nerve and trapezius muscle paralysis, this results in winging on elevation of the arm
the third is caused by a dorsal scapular nerve lesion, resulting in rhomboid weakness, and winging on external rotation of the arm
The direction of movement of the scapula during winging is also somehwat characteristic. A good neuromuscular textbook should give you more information
Nerve conduction studies are unreliable and difficult on proximal nerves in the arm. EMG is again difficult to perform in these muscles, although if the lesion is in the brachial plexus for instance other abnormalities (clinical or electrical) may be present. The diagnosis is a clinical one.
I cannot comment on the best physical therapy for the serratus anterior - I will defer to a physical therapist for the best answer
although the diagnosis of long thoracic nerve is very easy,but you cannot do anything for the patient,i think that this is due to the delay arrive of the patient
Thank you very much for the comments. I really appreciate it.