OAKLAND, CA - MAY 26: Derek Jeter #2 of the New York Yankees hits a single that scored Eric Chavez #12 in the third inning against the Oakland Athletics at O.co Coliseum on May 26, 2012 in Oakland, ...

Posterior shoulder dislocation occurs when the top of the upper arm bone, known as the humerus, moves backward out of its socket. This causes pain, muscle spasms, and a limited range of motion. The ...

A muscle spasm — also known as a charley horse, muscle cramp or twitch — is a sudden, involuntary movement in one or more muscles. Common causes include stress, exercise, or dehydration, but nerve ...