A child is spinned around by holding his hand by his father. While doing this the child staed crying and does not allow his father to touch his elbow. The diagnosis is:

Pulled elbow or Nursemaid's elbow occurs in children under 4 years old. It is caused by a sudden pull on the extended pronated arm, usually by an adult tugging on a reluctant toddler. The pronated radial head slips paially under the annular ligament and displaces into the radiocapitellar joint. The child suddenly stops using the arm, holding it in a flexed and pronated position. Radiographs show no abnormalities, since positioning for elbow films will often reduce the subluxation. Reduction is achieved by firmly supinating the forearm and flexing the elbow while pressing down on the radial head. Often, a "click" is felt when reduction is achieved. Soon after reduction the child becomes less apprehensive and gradually resumes use of the arm. Ref: Srinivasan R.C., Tolhurst S., Vanderhave K.L. (2010). Chapter 40. Ohopedic Surgery. In G.M. Dohey (Ed), CURRENT Diagnosis & Treatment: Surgery, 13e.