Plastic Bowing Fracture Ulna

8 Year Old Male With Trauma Due To A Fall. Diagnosis? • Xray of the Week

Figure 1. What is the important finding?

Figure 2

A: AP view radiograph of right forearm. Acute transverse fracture of distal radius visualized (green arrow).

B: Lateral radiograph view of right forearm. Angulation of ulna visualized (red arrows).

Discussion:

The above imaging findings occurred in an 8-year-old child with a trauma after a fall. An angulated fracture of the distal midshaft radius is also visualized, but there is also bowing of the ulna that is more appreciated on the lateral radiograph view. Forearm fractures are common in pediatric populations, likely due to the intrinsic elasticity and uniquely thinner cortex as compared to adult bones [1].

Radiographically, bowing fractures may show visible bending on radiographic imaging, however, as in this case if the bending occurs within the same plane of the radiograph, there may be no visible deformities on radiographic imaging [2]. Unlike other fractures, plastic bowing fractures do not produce a characteristic fracture line, but rather can produce subtle angular changes that appear as “bending” of the bone [3]. Additionally, in contrast to other fractures, the subsequent healing process for a bowing fracture does not involve a periosteal reaction [4]. As seen in this patient, bowing fractures can also be associated with a conventional fracture in the paired bone.

The fracture often manifests in children who present with localized symptoms of pain and swelling after falls on an outstretched hand, and in many cases, the child is playing or participating in common childhood activities like climbing monkey bars or jumping. Plastic bowing fractures most commonly occur in the forearm, but may also be found in the clavicle, fibula, and other long bones. The mechanism of injury often entails an angulated force on the bone producing longitudinal compression, that exceeds the intrinsic elasticity of the bone [4] . Most fractures that disrupt the cortical makeup of a bone exceed intrinsic plasticity, which produces classical fractures [4]. However, due to the natural growth patterns of the bone in pediatric populations, the response of the bone to a force exceeding the elastic injury is a response of bowing, which occurs proportionally to the force [4].

Microscopically, there are microfractures occurring along the bowing edge of the bone, but this is often not appreciated on the radiograph [3]. The bowing often appears fluid-like. Intervention is often not required in most cases, unless when angulation is measured to more than 10 degrees or in children older than 10 years [5, 6]. The decision for reduction may be a dilemma for clinicians, as increased angulation and older age of children may be associated with long-term osteoarthritis [7]. Other differentials that may be considered are buckle fractures, physiological bowing, stress fractures, and greenstick fractures. Due to the subtle presentations of these fractures on radiographs, clinicians need to maintain a high index of suspicion for these injuries in susceptible pediatric populations.

References:

1. Kalkwarf HJ, Laor T, Bean JA. Fracture risk in children with a forearm injury is associated with volumetric bone density and cortical area (by peripheral QCT) and areal bone density (by DXA). Osteoporos Int. 2011;22(2):607-616. doi:10.1007/s00198-010-1333-z

2. Sawkar, A.; Swischuk, L; Jadhav, S. Plastic Bending Fractures in Children, Contemporary Diagnostic Radiology: 2011; (34): 1-6. doi:10.1097/01.CDR.0000406379.59531.8d

3. Crowe JE, Swischuk LE. Acute bowing fractures of the forearm in children: a frequently missed injury. AJR Am J Roentgenol. 1977;128(6):981-984. doi:10.2214/ajr.128.6.981

4. Borden S 4th. Roentgen recognition of acute plastic bowing of the forearm in children. Am J Roentgenol Radium Ther Nucl Med. 1975;125(3):524-530. doi:10.2214/ajr.125.3.524

5. Vorlat P, De Boeck H. Bowing fractures of the forearm in children: a long-term followup. Clin Orthop Relat Res. 2003;(413):233-237. doi:10.1097/01.blo.0000072901.36018.25

6. Vervaecke AJ, Nuyts R, Sys J. The importance of adequate diagnosis of pediatric forearm bowing fractures: A case report. Trauma Case Rep. 2021;34:100508. doi:10.1016/j.tcr.2021.100508

7. Dhillon PS, Currall V, Shannon MN. Traumatic plastic deformation of the tibia: case report and literature review. Ann R Coll Surg Engl. 2012;94(1):e30-e32. doi:10.1308/003588412X13171221498947

Usha Trivedi is a medical student at Rutgers New Jersey Medical School with aspirations to become a diagnostic radiologist. She completed her undergraduate education at The College of New Jersey with a major in Biology and a minor in Art History. She is drawn to radiology due its unique blend of technology, art and medicine that is rooted in patient care. Her first exposure to radiology was through clerkships in medical school, where she saw how crucial imaging can be for patient care. She is currently involved as a director for one of her medical school’s student-run clinics and with her medical school’s humanities-themed magazine for her medical school. She aspires to become a radiologist with specific interests in mentorship, education and advocacy. In her spare time, she enjoys hiking, reading, art and board games.

Follow Usha Trivedi on Twitter @UshaTrivedi11.

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Kevin M. Rice, MD is the president of Global Radiology CME

Dr. Rice is a radiologist with Renaissance Imaging Medical Associates and is currently the Vice Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator.

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