Which of the following is a likely diagnosis for a 4-year-old with acute leg pain, refusal to walk, and low-grade fever?

The likelihood of transient synovitis as the diagnosis for a 4-year-old presenting with acute leg pain, refusal to walk, and low-grade fever aligns with the clinical picture often seen in this condition. Transient synovitis is characterized by inflammation of the hip joint, which commonly occurs in young children. The annoyance and pain typically lead to refusal to bear weight and limit mobility, as the child tries to avoid exacerbating the discomfort. Presentation with mild fever further supports this diagnosis, as it is not uncommon in transient synovitis.

In transient synovitis, the hip may be limited in motion and painful on examination, but it usually responds well to rest and anti-inflammatory medications. The condition is often self-limiting, which also reflects the typical course observed in many pediatric patients.

Other conditions, while they might present with some overlapping symptoms, such as fever and leg pain, usually have additional signs or more serious implications that differentiate them from transient synovitis. For example, osteomyelitis would often present with more significant fever and systemic symptoms, as would leukemia. Juvenile idiopathic arthritis typically involves more chronic symptoms and signs affecting multiple joints rather than the acute, unilateral presentation common with transient synovitis.

Thus, considering