We experienced a rare case of inferior shoulder instability caused by military training.
A 22 year-old man, the Japanese Self-Defense Forces personnel, received repetitive and hard military training in May, 2007. Going on training, pain and apprehension of his left shoulder appeared gradually. He saw a local doctor then consulted us after twelve days from onset.
His left shoulder subluxated to an inferior direction at rest, and reduced upward easily. There was no anterior or posterior instability, or general joint laxity. He had motor weakness of left shoulder girdles and ring, small fingers, and sensory disturbance on the medial side of his left arm. MRI arthrography of his left shoulder revealed abnormalities of superior labrum and anterior capsule. Electromyography of Deltoid and SSP muscles revealed slight abnormal activity, and motor nerve conduction velocity of median and ulnar nerve were normal.
We diagnosed him as having inferior shoulder instability due to brachial plexus palsy, so called “drooping shoulder”, and decided to treat conservatively. Immobilization of the left shoulder was carried out, symptoms improved gradually. After one year, shoulder arthroscopy was performed to check the structural disorder, but no abnormal finding was observed. After two years, his symptoms had almost recovered, but mild instability remained and he could not to serve in the force.
Nerve disorder is differential diagnosis of inferior shoulder instability. We supposed it was main cause of this case, and chose conservative treatment. But it was possible a combination of structural disorder, and diagnostic arthroscopy should have been considered earlier.
