What is the most likely diagnosis for a child with an insect bite leading to cellulitis, fever, and refusal to walk, with turbid synovial fluid analysis showing a neutrophil-predominant leukocytosis?

The clinical presentation described suggests septic arthritis as the most likely diagnosis. There are several key aspects that support this conclusion.

The child has an insect bite, which can act as a portal of entry for bacteria, leading to an infection. The presence of cellulitis indicates that there is a skin infection, which can easily spread to the underlying structures, including the joints. The fever and refusal to walk further emphasize the severity of the condition, particularly in a young child, where such symptoms often indicate significant pain and discomfort.

The analysis of turbid synovial fluid showing a neutrophil-predominant leukocytosis is particularly telling. In septic arthritis, the synovial fluid typically contains a high number of neutrophils due to a bacterial infection, which is consistent with the findings in this scenario. A significant white blood cell count in the synovial fluid—especially if it is greater than 50,000 cells/μL, with a neutrophil predominance—strongly indicates that the joint is infected.

Other possibilities, such as osteomyelitis, could present similarly, but typically would involve bone marrow infection and may not directly cause the joint fluid to be turbid with leukocytosis, as described. Transient syn