Prepare for the PANCE with this challenging clinical scenario on right leg pain in a child. Explore the clinical details to make an informed decision.
A 3-year-old boy is brought by his parents to the emergency department for evaluation of right leg pain. The patient had multiple episodes of watery diarrhea and low-grade fevers five days ago, which have fully resolved. However, over the past two days, the patient began complaining of right leg pain, and today he was limping. The patient has no significant past medical history and does not take any medication. Parents deny dysuria or hematuria. He is up-to-date on his vaccinations. Temperature is 37.9°C (100.2°F), blood pressure is 95/58 mmHg, pulse is 135/min, respiratory rate is 20/min, and oxygen saturation is 97% on room air. On physical examination, the patient is in no acute distress and is well-appearing. There is limited range of motion at the right hip secondary to pain, but active and passive movement is possible. There is no obvious erythema or warmth over the hip. All other joints are within normal limits. Laboratory results are shown below. Hip ultrasound shows an effusion.
Which of the following is the best next step in management?
| Laboratory value | Result |
| Hemoglobin | 12.5 g/dL |
| Leukocyte count | 16,100/mm3 |
| Platelet count | 344,000/mm3 |
| C-reactive protein (CRP) | 1mg/dL |
| Erythrocyte sedimentation rate (ESR) | 15 mm/h |
A. Perform hip arthrocentesis
B. Order hip x-ray
C. Order hip magnetic resonance imaging (MRI)
D. Order Borrelia burgorferi enzyme immunoassay (EIA)
E. Obtain urinalysis
Scroll down to find the answer!
The correct answer to today’s PANCE® Question is…
A. Perform hip arthrocentesis
Before we get to the Main Explanation, let’s look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!
Incorrect answer explanations
The incorrect answers to today’s PANCE® Question are…
B. Order hip x-ray
Incorrect: An x-ray of the hip may identify fracture, osteomyelitis, or other causes of pain and swelling, but is not the best next step in management. This patient’s history is concerning for transient synovitis, However, there is elevation of laboratory studies warranting further evaluation of arthrocentesis to rule out septic arthritis.
C. Order hip magnetic resonance imaging (MRI)
Incorrect: An MRI may identify effusions or abnormalities of the bone and soft tissues, but it is not the best next step for this patient. This patient’s history is concerning for transient synovitis, but there is elevation of laboratory studies warranting further evaluation with arthrocentesis to rule out septic arthritis.
D. Order Borrelia burgorferi enzyme immunoassay (EIA)
Incorrect: Lyme arthritis often presents as monoarthritis of the knee with effusion. This patient has an effusion in the hip and a history of recent gastrointestinal illness, making transient synovitis more likely. However, this patient has elevations in laboratory studies, making arthrocentesis the best next step to rule out septic arthritis.
E. Obtain urinalysis
Incorrect: Urinalysis may be indicated if there is concern for reactive arthritis or urinary tract infection causing pelvic discomfort. This patient has an effusion in the hip and no urinary symptoms. This patient’s history is concerning for transient synovitis, but there is elevation of laboratory studies warranting further evaluation with arthrocentesis.
Main Explanation
This pediatric patient presents for assessment of right leg pain and limping and is found to have limited range of motion of the right hip due to pain. He has had a recent viral illness, which, along with the other clinical features, is suggestive of transient synovitis. Hip effusion is seen on ultrasound. Given that the patient has a white blood cell count over 15,500 and a slightly elevated c-reactive protein, he should have an arthrocentesis on this joint to formally rule out septic arthritis.
Septic arthritis refers to a bacterial infection of the synovium and joint space. Transient synovitis (toxic synovitis) is noninfectious synovial inflammation and can present similarly. Differentiating the two is important since the treatment is different. Transient synovitis is a benign and self-limited illness, whereas septic arthritis requires drainage of the joint and antibiotics to prevent permanent bone, joint damage, and multisystem involvement.
If there is enough suspicion, formal diagnosis of septic arthritis or transient synovitis is confirmed via joint aspiration, with evaluation of synovial fluid cell count with differential, gram stain, and culture. In patients with septic arthritis, synovial fluid analysis will typically reveal bacterial growth, cloudy or purulent fluid, as well as a cell count > 50K WBC/mm3. Patients can also have positive blood cultures. In contrast, patients with transient synovitis will have a negative gram stain and culture, clear or yellow fluid, and a cell count of 5K – 15K WBC/mm3.
Major Takeaway
Arthrocentesis should be performed in any patient with a suspected septic joint. Patients with clinical features consistent with transient synovitis who have findings that are concerning for septic arthritis should also have an arthrocentesis to rule out septic arthritis.
Want to learn more about this topic?
Watch this Osmosis video: Septic arthritis and transient synovitis (pediatrics): Clinical sciences
References
John J, Chandran L. Arthritis in children and adolescents [published correction appears in Pediatr Rev. 2012 Mar;33(3):109]. Pediatr Rev. 2011;32(11):470-480. doi:10.1542/pir.32-11-470
Arvikar SL, Steere AC. Diagnosis and treatment of Lyme arthritis. Infect Dis Clin North Am. 2015;29(2):269-280. doi: 10.1016/j.idc.2015.02.004
Horowitz DL, Katzap E, Horowitz S, Barilla-LaBarca ML. Approach to septic arthritis. Am Fam Physician. 2011;84(6):653-660.
Kliegman, RM, St Geme, JW, Blum, NJ, et al, eds. Nelson Textbook of Pediatrics. 21st ed. Elsevier; 2020.
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