Ultrasound Evaluation of Pediatric Orthopaedic Patients

Jody Litrenta, MD; Karim Masrouha, MD; Amy Wasterlain, MD; Pablo Castaneda, MD

Disclosures

J Am Acad Orthop Surg. 2020;28(16):e696-e705. 

In This Article

Joint Effusions

Septic arthritis and transient synovitis are two commonly encountered pediatric hip conditions. It is essential to be able to distinguish between the two conditions because their treatment and prognosis differ. Septic arthritis is typically treated with surgical débridement and antibiotics, and early treatment is necessary to prevent long-term damage to the joint.[29–31] By contrast, transient synovitis is a benign condition and treatment is usually aimed toward alleviating symptoms. Diagnosis can be challenging because both conditions can cause the child to limp, be unable to bear weight, and have joint effusion.[29]

The Kocher criteria is a widely used diagnostic algorithm to predict the likelihood of septic arthritis, based on the presence of fever, inability to bear weight, elevated white blood cell count, and erythrocyte sedimentation rate.[29] Caird et al[32] additionally demonstrated that C-reactive protein is an independent predictor of joint infection. Although both studies used ultrasonography to perform joint aspiration, neither used sonographic features as diagnostic criteria to distinguish the septic joint from transient synovitis.

There is a paucity of data comparing the ultrasonography findings in these conditions, likely because ultrasonography is most valuable as a quick tool to determine the presence or absence of a hip effusion (Figure 11). This is particularly valuable in young children, who may be difficult to examine, to be confident that the hip is the source of the report. A qualitative study which evaluated 50 pediatric hips suggested that ultrasonography can serve a role in diagnosing septic arthritis and that hyperechogenicity and a thickened capsule were the most common findings[33] (Figure 12).

Figure 11.

Figure demonstrating hip effusion, a 10-year-old girl.

Figure 12.

Figure demonstrating septic hip effusion, a 2-year-old girl.

One study retrospectively studied 127 pediatric patients with ultrasonography data who were ultimately diagnosed with septic arthritis or transient arthritis.[30] This study used two senior radiologists to perform the ultrasonography and considered a distended anterior capsule, a hyperechogenic effusion, and capsular thickening >5 mm to be diagnostic of a septic hip. Ultrasonography had an 86% sensitivity, 90% specificity, and 88% positive and negative predictive value to identify septic arthritis of the hip. It was additionally found to be superior to radiographic, clinical, and laboratory parameters collectively (P = 0.005).

Among those with a false-negative result, 50% had an ultrasonography performed within the first 24 hours of presentation. Similarly, Gordon et al[34] found a 5% false-negative rate in a series of 132 children and identified ultrasonography performed within 24 hours of presentation and inadequate technique as the reasons for these incorrect results. The absence of an effusion should therefore be interpreted cautiously in patients with recent onset of symptoms and monitored closely for an evolving clinical examination.

Understanding how to identify a joint effusion that seems consistent with septic arthritis can be beneficial for the orthopaedic surgeon for many reasons. It provides additional data to suggest a need for timely surgical intervention. In addition, positive results may help identify patients who should undergo further imaging studies, such as MRI. The presence of additional infections, such as osteomyelitis, pelvic abscess, and pyomyositis is becoming increasingly common in septic hips.[31] MRI is useful whenever possible to identify these additional infections so that they can be adequately addressed during irrigation and débridement of the hip joint.

However, MRI can be costly, difficult to arrange, and may require sedation. Screening patients most likely to require MRI based on ultrasonography helps stratify patients in whom further imaging will be most helpful. Similarly, this technique can also be extended to identifying fluid collections around postsurgical hardware, where metal artifact can interfere with imaging.

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