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Addition of Long‐Axis Ultrasound Imaging for the Pronator Quadratus Muscle for the Diagnosis of Pediatric Distal Forearm Fracture

To the Editor: We read with great interest the recently published article titled “Point-of-Care Ultrasound Pronator Quadratus Hematoma Sign for Detection of Clinically Non-Angulated Pediatric Distal Forearm Fractures: A Prospective Cohort Study”. We congratulate Snelling et al. for their clinically important work on ultrasound assessment of pediatric distal forearm fracture. In their prospective cohort of children visiting the emergency department, they found that all the patients with cortical breach fracture over the distal forearm presented with a hematoma inside the pronator quadratus (PQ) muscle. Likewise, the thickness of the PQmuscle at the side with cortical breach fracture was at least 2.1 mm more than that at the contralateral side. The authors concluded that the sonographic findings of the intramuscular hematomas and the increase in PQ thickness were promising measurements for pediatric distal forearm fracture. We have some comments regarding the ultrasound examination protocol. In their protocol, only the views aligned with the long axis of the radius and ulna are imaged. However, the aforementioned views are perpendicular to the course of the PQ muscle. If the investigators want to appreciate the continuity of the muscle fibers, it is better to place the transducer bridging the radius and ulna (Figure 1). Furthermore, the attachment of the PQ muscle on the radius and ulna varies in its thickness depending on the reciprocal position between the transducer and bony cortex. Therefore, the long-axis view of the PQ muscle would be superior to the long-axis view of the forearm in standardizing which part of the PQ muscle is scanned in accordance to the underlying bones. This will definitely increase the comparability of muscle thickness between the normal and fractured limbs. Furthermore, the PQ muscle can be divided into the superficial and deep parts. Due to the oblique course, the ulnar attachment of the deep PQ muscle would appear hypoechoic or anechoic due to anisotropy. This would cause difficulty in differentiating the fascia of the deep PQ muscle from the underlying bony cortex, which also looks hypoechoic or anechoic due to the abundant cartilage content in the pediatric population. Dynamic examination in the longaxis view of the PQ muscle by asking the patient to supinate and pronate the forearm will be helpful in identifying the aforementioned structure borders. Lastly, on ultrasound images, an intramuscular hematoma is presented with disruption of adjacent muscle fibers and focal accumulation of blood, which is categorized as Grade III injury on Peetrons classification. However, whether the muscle fibers are disrupted is hardly determined by the short-axis view of the target muscle. Although petechial hemorrhage and focal edema can be