Infantile sternal osteomyelitis: A case of ultrasound tracking of bone displacement and regeneration

Primary sternal osteomyelitis is a rare infection of the bones, but its fundamental characteristics mirror those of long bone osteomyelitis: increased incidence at a younger age, male preponderance, nonspecific presentation, and unreliability of plain radiographs for diagnosis. Also, the spectrum of reported pathogens roughly agrees with that reported for osteomyelitis at other sites.1 Osteomyelitis complicated by abscesses or sequestra typically requires surgical intervention, such as abscess drainage or necrotic bone removal.2 The patient completed 4 weeks of intravenous antibiotic therapy, which was switched to oral cefalexin and then he was discharged. Regular outpatient ultrasonography confirmed the disappearance of the detached sternal segments and new bone formation in the original sternal position (Figure 1d,e). Subsequent CT also confirmed the resolution of the abscess and bone fragments as well as new bone formation in the original sternal location (Figure 1f). Oral antibiotics were continued for 5 months. The patient was evaluated for immunodeficiency at the previous hospital through immunoglobulin level and lymphocyte subset testing. Aside from a low IgG2 level of 61.2 mg/dL, no other apparent abnormalities were detected. Upon re-evaluation at our hospital, the IgG2 level had recovered to 111 mg/dL, and it was not actively considered a contributing factor to susceptibility to infection. Although this case involved both sequestra and abscess formation, we opted for antibiotic therapy without surgical intervention for the reasons mentioned above. A case series of 74 pediatric primary sternal osteomyelitis cases reported that five out of six cases of abscess formation recovered without surgical intervention.1 Our approach was further justified by our ability to closely monitor treatment progress through frequent ultrasonography examinations and our readiness to promptly implement surgical treatment if needed. In this case, the sternal segments detached, subsequently disappeared, and new bone formation was observed in the original sternal location. At birth, the sternum typically has 4–5 ossification centers, from which ossification spreads. By 1 year of age, ossification extends to the lower part of the sternal body, while ossification of the xiphoid process is further delayed, taking over 3 years. Complete bony fusion of the sternal body occurs around age 30.3 These characteristics may explain why multiple segments detached in this case. Detailed reports of sternal segment detachment and subsequent new bone formation in patients with sternal osteomyelitis are rare, making this case a valuable contribution to the literature. We were able to closely and repeatedly monitor the progression of sternal osteomyelitis and surrounding structural changes using ultrasound. One key factor enabling such detailed observation was the sternum's anatomical characteristics as a flat bone located near the surface, which facilitated clear imaging. Additionally, given the patient's age and the early stage of ossification, ultrasound proved particularly useful, as progressive ossification can lead to acoustic shadowing, limiting sonographic visibility in older patients. All the authors meet the ICMJE authorship criteria. Hiroki Shimono drafted the initial manuscript. Akiko Kinumaki supervised writing the case report and critically reviewed the manuscript. Natsuho Adachi, Hiroyuki Tanaka, Yuko Kajiho, and Shoichiro Kanda critically reviewed and revised the manuscript. All the authors have read and approved the final manuscript. The authors declare no conflict of interest. Informed consent was obtained from the parents of the patient to publish the data in this report.