Cause: chronic overuse in throwing / other overhead motion (eg, tennis serving) generating increased valgus stress

• acute onset of sharp / gradual onset of increasing pain in medial elbow
• ulnar nerve dysfunction (40%): pain, paresthesia of forearm + in 4^th and 5^th digits
• ossification within ulnar collateral ligament (UCL)
• loose bodies
• osteoarthritis of ulnohumeral articulation
• osteochondritis dissecans of capitellum
• excessive medial joint opening on stress radiographs
  MR (coronal plane):
  • laxity / discontinuity of UCL
  • increased signal intensity of UCL + surrounding tissues
  • poor definition of ligament margins

Rx: rest, application of ice, NSAID, exercise, steroid injections; reconstruction of ligament