What is likely the diagnosis for a 3-year-old with a pulled arm and acute elbow pain?

The diagnosis of radial head subluxation, also known as "nursemaid's elbow," is highly likely in this case. This condition typically occurs in young children, particularly between the ages of 1 and 4, when excessive pulling or swinging of the arm leads to the radial head slipping out of its normal position in relation to the annular ligament.

In a 3-year-old with acute elbow pain after having their arm pulled, the child may present with reluctance to use the affected arm, holding it close to the body with the elbow slightly flexed. This classic presentation, along with the mechanism of injury, strongly supports the diagnosis of radial head subluxation.

While fractures and dislocation of the elbow are possible concerns in an injured child, the history of a specific pulling event and age group makes these less likely than nursemaid's elbow. Tendonitis is also uncommon in this age group and is typically associated with repetitive use or overuse injuries, which would not align with the sudden presentation of pain after a single incident. Thus, the presentation fits well with radial head subluxation, making it the most appropriate diagnosis.