1

A mother and her 6-year-old son present to your urgent care. The mother reports that last week her child had a cough and fever. She is here today because last night before bed she noticed her son limping, and it continued today. There is no history of trauma, and fever has resolved. The child is afebrile and his joints all appear normal except that he is holding his left leg flexed and abducted and he cries when you range that leg. The recent history of a respiratory infection in this child is most suggestive of what cause of his hip limp?

Toxic synovitis (TS), also known as transient synovitis, is most likely given this history. Most commonly, respiratory infections are known to be associated with TS; however, gastrointestinal or urinary infections have been seen also. Recent trauma can also be seen.

2

Although the case in question 1 most likely is TS, list three diagnoses that should be on your differential

• 1.
  

  Septic arthritis (SA)

  
  
• 2.
  

  Osteomyelitis

  
  
• 3.
  

  Legg–Calvé–Perthes (LCP) disease

Others could include bone tumor or fracture.

3

What two imaging studies should routinely be ordered on a child presenting as described above?

Plain radiographs and joint ultrasound. Plain radiographs are more than likely to be normal in TS but may show some joint space widening. They are most effective in ruling out other diagnoses such as a fracture, slipped capital femoral epiphysis (SCFE), or others. Joint ultrasound is excellent in detecting joint effusions, which are common in both TS and SA. If these studies are not available at your urgent care, you should refer the patient to the emergency department.

4

Abnormality in which laboratory marker is common in TS?

Laboratory values are most likely normal in TS. Laboratory values together with imaging will help rule out other more serious causes. Ultimately, TS is a clinical diagnosis.

5

Once TS is diagnosed, what does the treatment include?

Rest and nonsteroidal antiinflammatory drugs (NSAIDs). TS is self-limiting and resolves without treatment usually in 3 to 10 days. Supportive measures, such as rest and NSAIDs (mainly ibuprofen), have been shown to reduce the number of days of symptoms.

6

Three months later the same child returns with a similar history and pain in his hip. What should be done?

TS can recur in up to 15% of children. For this reason, it is still the likeliest cause of the pain. The same imaging and laboratory studies should be performed as previously discussed.

7

If the child in question 1 did have a fever or warmth around the hip joint, what would the most likely cause of his limp and fever be?

SA of the hip would be the most likely cause.

8

A septic joint is a surgical emergency. Along with the imaging previously discussed with TS, what laboratory studies should you order?

Blood work including a white blood cell count (WBC) with differential, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and blood cultures should be sent immediately.

9

Consider the laboratory studies ordered in question 8. If the results are abnormal, which would be most consistent with SA?

In 2011, Singhal and colleagues reviewed 300 cases of hip pain and found that when paired together, pain bearing weight and an elevated CRP (>2.0 mg/dL) gave patients a 74% probability of having SA. Without pain and elevated CRP, the probability of SA was <1%. Elevated CRP showed an odds ratio of 82, making it the best independent prediction variable.

10

What is the most common bacteria to cause SA, in all ages?

Staphylococcus aureus is the likely cause of the infection in all ages. See Table 25.1 for details by age.

11

The child referred to in question 7 should be sent to the ER for what three interventions?

The first intervention is ultrasound or fluoroscopic aspiration of the hip joint for cell count, Gram stain, and culture performed by pediatric orthopedic specialists. Once the joint fluid has been obtained, the second intervention is empiric intravenous antibiotic therapy. Choice of antibiotic should take age and history into account (see Table 25.1 ). Magnetic resonance imaging (MRI) may be performed if the diagnosis is in question and joint aspiration is not available, but both MRI and aspiration would likely require procedural sedation. The third intervention is irrigation in the operating room by pediatric orthopedic specialists.