Tennis elbow
From Memory Alpha, the free Star Trek reference.
Tennis elbow, the common name for lateral epicondylitis, is a repetitive stress injury to the muscles and tendons on the outside of the elbow.
Guinan sought treatment from Dr. Beverly Crusher for the condition in 2369 as a ruse to counsel Dr. Crusher, who was relieved of duty while investigating the suspicious death of Ferengi scientist Dr. Reyga. (TNG: "Suspicions")
