A 4-year-old boy presents with a 5-day history of increasing right leg pain with limp. He was treated for an ear infection previously. His hip is flexed and externally rotated with limited ROM due to pain. X-ray is normal and he fell 7 days ago. What is the most likely diagnosis and the next step?

A 4-year-old boy presents with a 5-day history of increasing right leg pain with limp. He was treated for an ear infection previously. His hip is flexed and externally rotated with limited ROM due to pain. X-ray is normal and he fell 7 days ago. What is the most likely diagnosis and the next step?

• A. Fracture; CT scan of right hip
• B. Transient synovitis; measurement of serum inflammatory markers
• C. Septic arthritis; joint aspiration
• D. Osteomyelitis; bone scan

Answer: (A)

The key concept is that persistent hip pain in a child after trauma with a normal X-ray can still be a serious hidden injury—an occult fracture of the femoral neck. In kids, fractures are sometimes not evident on plain films, especially early on, yet the history of a fall with ongoing pain and a hip held in flexion and external rotation points to pathology within the proximal femur or joint rather than a simple soft-tissue issue. Because a nondisplaced fracture may not show up on X-ray, the next step is imaging capable of detecting subtle fractures. A CT scan of the hip is a practical choice in this scenario: it can reveal a fracture line when the X-ray is nondiagnostic and helps guide urgent management. If CT doesn’t show a fracture but suspicion remains high, MRI is the more sensitive test for occult fractures and would be used, bearing in mind that it can require longer imaging time and possible sedation in a young child. Septic arthritis would push toward urgent joint aspiration due to the risk of joint destruction, typically accompanied by fever and systemic symptoms or marked inflammatory marker elevation—features not clearly present here. Transient synovitis is usually more benign, with less severe pain and ROM limitation and often a more rapid course. Osteomyelitis would raise concern for bone infection with systemic signs and different imaging/tollowing workups. So the best next step is imaging to identify an occult fracture, with CT scan of the hip chosen to detect a hidden fracture quickly and guide definitive care.

The key concept is that persistent hip pain in a child after trauma with a normal X-ray can still be a serious hidden injury—an occult fracture of the femoral neck. In kids, fractures are sometimes not evident on plain films, especially early on, yet the history of a fall with ongoing pain and a hip held in flexion and external rotation points to pathology within the proximal femur or joint rather than a simple soft-tissue issue.

Because a nondisplaced fracture may not show up on X-ray, the next step is imaging capable of detecting subtle fractures. A CT scan of the hip is a practical choice in this scenario: it can reveal a fracture line when the X-ray is nondiagnostic and helps guide urgent management. If CT doesn’t show a fracture but suspicion remains high, MRI is the more sensitive test for occult fractures and would be used, bearing in mind that it can require longer imaging time and possible sedation in a young child.

Septic arthritis would push toward urgent joint aspiration due to the risk of joint destruction, typically accompanied by fever and systemic symptoms or marked inflammatory marker elevation—features not clearly present here. Transient synovitis is usually more benign, with less severe pain and ROM limitation and often a more rapid course. Osteomyelitis would raise concern for bone infection with systemic signs and different imaging/tollowing workups.

So the best next step is imaging to identify an occult fracture, with CT scan of the hip chosen to detect a hidden fracture quickly and guide definitive care.