What is the leading diagnosis for a patient with a history of minor fall and limited internal rotation of the right hip?

The leading diagnosis for a patient with a history of a minor fall and limited internal rotation of the right hip is transient synovitis. This condition commonly occurs in children and is characterized by inflammation of the synovial membrane, which can lead to joint effusion and limited range of motion. The history of a minor fall often correlates with the onset of symptoms, as it can trigger an inflammatory response in susceptible individuals.

In transient synovitis, the pain and limited movement, particularly with internal rotation, are common clinical findings. The child may present with a limp and may prefer to hold the affected leg in a position that minimizes pain. This diagnosis often arises in the setting of viral infections or post-viral inflammatory responses, which can mimic traumatic injuries but can occur without significant trauma.

Other conditions, like septic arthritis or Lyme disease, would typically present with more profound symptoms, such as fever or systemic signs of illness, and would not usually follow a minor fall. Trauma would suggest an injury, but without the typical significant signs of pain or swelling, transient synovitis aligns well with the clinical picture described.